Understanding Digital Imaging Technologies

So we are going to be talking about digital imaging and ways to talk about it that are as simple as possible. So as I'm going through the slides, feel free to make notes about ways that I've simplified it. I may not have all the simplification answers yet, so please chime in and let me know. I'm also going to be moving pretty quickly through these objectives. So we're going to define digital imaging to include both computed radiography and digital radiography. That's what those abbreviations mean. CR means computed radiography. DR means digital radiography. And so you'll notice digital imaging is the big umbrella and then beneath that umbrella we have CR and DR. We will discuss computed radiography or CR to include how the CR cassette is constructed with the imaging plate inside of it, what's going on in that photostimulable phosphor plate that sometimes abbreviated the PSP, right? We'll talk about how photo stabilization works, what this technology is, we'll talk about laser beams and how laser beams are made. And then we'll talk about how to erase the digital image, right? Then we'll talk about DR. And we'll talk about two distinctions. So there's a further umbrella underneath DR, we have indirect digital radiography and direct digital radiography. So we'll talk about the differences in those technologies. We'll list steps for how digital conversion works. We'll talk about charge couple devices, which are kind of the weird outlier. Then we're going to talk about image quality and storage and display. If you're going to fall asleep, don't fall asleep until the absolute end with storage and display, because that's the one that is kind of a given, and you'll all have some familiarity with PACs and using computer monitors, right? The image impact, the stuff, the image quality part to this is heavy-hitting material. It's the most abstract material in the presentation, so if we need to take a break or something at the end, we can. I want to make sure that we all pay attention for that part. So digital imaging is just any way of getting a picture that can be manipulated and viewed on a computer. Pretty straightforward. You do it every day with your cell phone. That's what we're talking about, your cell phone picture. In fact, your cell phone camera is a form of, I believe, direct digital imaging, right? So when we get to discussions of direct digital imaging, we can use our cell phones as an example, right? For the purposes of x-ray, this first really came into use in the 1970s with CT. As soon as CT scanners showed up in the department, we had to think about the ways that computers look at pictures, right? It really kind of started to develop into a full-blown part of our work sometime in the early 1990s, right? But it was there as early as 1970. Well, let's talk about what we're talking about when we talk about digital, right? I think it's helpful to think about this awesome digital watch here, right? I remember this watch when it came out. The commercials went like this. Look closely. The hands on this watch are about to disappear, right? It was amazing. It blew everyone's mind. Everyone wants a watch with no hands on it, right? So that was the promise of digital, right? That it could parcel time out in discrete packages. And what I mean by that is that every minute is a minute, right? There's none of this second hand wandering around on things, right? It's a minute is a minute is a minute. Nothing more, nothing less. That's what digital does. It's either on or it's off, right? Versus analog is something that continuously changes, right? Probably the best way to think about digital versus analog, if the watch analogy is not working for you, is maybe like a band like Daft Punk, right, that makes electronic music, right? Versus a band like... Led Zeppelin, right? That they would plug their guitars into their amps and they were making analog music. There was nothing digitized in Led Zeppelin's music. They just plugged their guitars into their amps and whatever was coming out of their guitars was what people were hearing, right? That's an analog process. Versus with Daft Punk, they plug their computers into their amplifiers, right? And they crunch some numbers and the sounds come out, right? So CR versus DR. We all are all pretty familiar with the distinctions between these things because it creates major hurdles for your everyday life in the x-ray tech department, right? Everything we do, it matters if we're using a CR system or a DR system. It affects workflow and everything else, right, the way that we communicate with the patient. CR uses these storage phosphor plates that are inside CR cassettes and a CR reading station and a viewing station before we send the images to PACS, right? So I always think about the viewing station as being kind of the centralized location for where we work with CR images, right? Versus DR may require a room upgrade and a lot of times you take the picture and it just pops up on your computer screen Right, there was no additional reading or anything like that So let's talk first about computed radiography and the way that it works It actually works a lot like film right and that's going to be significant that as this technology rolled out A lot of technologists made the mistake, myself included, of thinking about CR exactly like film and they're really very different even though in terms of workflow they work similarly. The first similarity between CR and film is that they both have a cassette and inside that cassette if it's a film screen cassette it has intensifying screens and a piece of film right that has to be kept in the dark. With CR it has this photo stimulable phosphor plate this white plate that's made out of barium halide or fluorohalide and it's responsible for capturing the x-rays as they exit the patient. Alright so we put the cassette behind the patient, the tube in front of the patient, the x-rays go through the patient and they hit this phosphor plate. So the cassette again is something typically fairly durable made out of plastic and lightweight. A lot of times it has an aluminum backing and that's there just to kind of catch up, catch any x-rays that are exiting the cassette, right, that may have continue on. They do not have intensifying screens, but what they do have is an anti-static material inside of them. Because the photostimulant phosphor plate inside of there is going to be drawn out of the cassette, the reader is going to pull it out of the cassette, and if as it pulled that PSP plate out of the cassette there was static, The static would create an image, it would create an artifact. So we do not want any static as the PSP plate is pulled out of the cassette. One way to think about that, well, might be like when you're trying to pump gas in the wintertime and it's dry outside. Have you ever gotten shocked by a gas thing? In Utah it was a serious issue, like people could get caught on fire because it was so dry there in the winter. You could get blown up by a gas pump. So they would always encourage you to touch your car or touch something before you touch the gas pump. Static is not a good thing. This imaging plate though is where we should probably spend most of our focusing. So we're going to look at pretty much layer by layer how it's constructed. And the layers are important. And so each one of these layers is significant. But the active layer, the part that is the most important for us, is this part that's called the phosphor layer. Without that it would not be able to receive x-rays. Everything else exists in support of the phosphor layer and sometimes it's also called the active layer. So there's a protective layer on the outside and it's just clear plastic right and immediately beneath that protective layer is the phosphor layer active layer sometimes called the PSP right and it It has a photostimulable phosphor that we'll talk a little bit in more detail in just a moment but it is responsible for trapping electrons during exposure. So the x-ray photons produce ionization inside the PSP and that crystal traps the electrons that are produced from the ionization. That's what the crystal is responsible for. It is typically made out of some form of barium fluorohalide. Now that's a big family of chemicals, right? But if you just remember barium fluorohalide, you're good, right? It's also helpful to know that it is photostimulable. What that means is that it is, it gives off light in response to stimulization. So if you stimulate this crystal, it will give off light. The barium fluorohalide glows basically in the dark. It will glow in the dark and the color it will glow is blue, right? Blue violet. So that's important, right? It seems like kind of a trivial thing, but what I'm saying is if you were in the blacklight room, right, checking out everyone's wizard posters or whatever you do in the blacklight. room. This stuff is going to be blue. If you took the CR cassette into the black, we know what black lights do, right? Right. If you take it into the black light, it's going to glow blue, right? Other things might glow different colors like orange or yellow or whatever, right? This one glows blue. Then there's a reflective layer beneath that glowing layer because we want it to glow in a certain direction. In fact, we want it to glow in the direction that we're reading it, right? So it will... allow that blue glow to be emitted in a certain direction, the direction in which the reading is occurring. Sometimes it's black to reduce the amount of light that might be escaping or the kind of light contamination there. Then there's a conductive layer, and this is there to, again, absorb static. Static is the enemy. We've established that with the CR cassettes. Finally, there may be a color layer. It's not labeled here on this one, but it would be basically at the same level as the light reflective layer. And that's just an additional technological innovation that helps with the light that's being emitted by the crystals. Support layers is just a semi-rigid material. If you were to hold the PSP plate, it feels kind of floppy, almost like this catalog or something. And whatever rigidity it has is because of a... kind of a thick plastic inside of it, right? Otherwise the crystals would just kind of go everywhere. And then it has a backing layer and that's just to protect the cassette further. You'll notice one thing I didn't point out though is that there's a barcode labeling thing on it. So we'll talk more about that here in just a moment. So that barcode, sometimes you can see it through the window in the cassette. Sometimes it's there at the end of the cassette. Do techs at your facilities use the barcode for labeling of their cassettes? Right. Back in the day, a film, you had to label your cassettes manually. You would actually take the cassette, you'd have the patient's blocker or like a little patient armband. So you literally had to inspect the patient's armband to pull a plastic thing off of it that you would then use to expose the film, to label the film, and then you would develop the film. Right. That was how you labeled the patient's information. Now we use a barcode to basically scan and tag the PSP plate with the patient's information so that we don't accidentally develop Mrs. Smith's x-rays on Mr. John Doe's account. Does that make sense? And that's generally done by technologists. And so anytime I say the word technologist, if we're talking about digital imaging, we can just think about, okay, that I just introduced the possibility for user error. Are there times when the technologist incorrectly enters information? Yeah, there are, if we're frank. And you probably have seen instances of that, given the amount of time that you've been out in the clinic. So that's why it's important to check the information and double-check the information that you're tagging to the cassette, because you are really kind of where the buck stops in terms of catching errors with the labeling of information on. the images. Some of these cassettes kinda had an innovation like Kodak in particularly you could write on it and there were stickers to orient you know which side of the cassette is up and which side is down that's just proprietary in general I have not seen those being used in departments for the most part people just use the barcode and just go on with their life so This is why we assumed that CR radiography was basically the same thing as film. The workflow was exactly the same. When it says conventional radiography, it means film, right? Film screen radiography. You basically would set up the patient. You'd put the cassette either on the tabletop or in the bucky, and then you have to go and develop the thing, right? So the workflow felt essentially the same. Really the only thing changed was like now there's a barcode and we used to have to flash the film prior to running it, right? So that's the only thing that felt a little bit different is now we have to scan it with a laser for the barcode, right? We use basically the same technology to take the pictures and everything. But there is this huge difference in the way that this technology works in terms of what it's doing. We can think about it kind of the same and in some ways we continue to do that. One example of ways that we continue to think about it the same is speed. When we talk about speed of digital systems, that's a concept that we've imported from film. But this basically breaks down piece by piece. piece what's happening inside of the PSP plate when we make an exposure. The x-rays that are exiting the patient, right, are going to interact with electrons in the barium fluorohalide, right, and those electrons are going to be trapped in what we call a phosphor center, right. So it's almost like, if you want to think about it this way, it's like packing bubbles, right. Whenever you pop a packing bubble, that bubble's popped, right. So the x-rays are popping the little packing bubbles inside of the PSP plate. And from all the packing bubbles that are being popped, we're making a picture. We're going to somehow unpop the packing bubbles in order to read them out. So that's the way I think about these crystals. It's like popping the little packing bubbles. Some people love it, some people hate it. My son hates when we pop packing bubbles. I love it. I'm in the loving it camp. Most cats hate it. So, all right, this trapped signal, the little popped bubbles in the packing thing, can remain that way for a long, long, long, long time, right? It's hard to unpop the bubbles, right? So it's never really completely lost. The more times that we use the PSP plate, the more times we pop the bubbles in it, the less responsive it becomes. But in general, these things have a pretty significant shelf life on them. And one of the things that's interesting... is that they're actually more sensitive to radiation than film. And when I say more sensitive, that's kind of crazy, right? Because the second you pull film out of a cassette and expose it to light, it's toast. That's how sensitive it is to radiation. These things are actually more sensitive to film, more sensitive to radiation than film, right? So we'll talk about how we actually get a picture out of that if that's the case. But the important thing here is that... They are trapped in this thing. They're never completely erased, not completely, and we have some residual ones that are left on the thing that will interfere with repeat exposures. So one thing about that is that before I've read this PSP plate out, it has what I would call a latent image on it, and that's actually a concept that comes from film, that there's a picture on this thing, but I can't see it. That's what latent image means. I captured something but it's not apparent to my eyes, right? If I just pull the PSP plate out of the CR, it's just white. There's no information there. So I have to figure out a way to develop it or read it. And that's what we're doing when we use a CR processor. So we place the cassette into the reader in some way specific to the way it's been things, the way it's been manufactured. It pulls that PSP plate out of the cassette and then it's going to scan it with a laser, right? And in essence, when it scans it with a laser, it's going to allow it to release the light that's trapped inside of it, right? So in the process of unpopping the bubbles and putting the bubbles back in the packing material, they release light. Energy is neither created nor destroyed. So when these crystals reconstitute themselves, when they get their electrons back, they're so happy about that that they give off light, right? And specifically, I said the light was what color? Blue. Blue, violet, or blue. And that's important because our laser is red, right? So the blue, I don't know, I always think about like Obi-Wan Kenobi versus Darth Vader. Obi-Wan's got the blue lightsaber, Darth Vader's got the red one, so you know if the guy with the red lightsaber wins, that's a bad, you know, thing for the good guys, right? So the laser is red, right? And it is a helium neon laser, right? So the way you make a red laser is you get helium and neon. And then you have an anode in the cathode, right? And now we just pass light through it. It's going to output a laser, very intensified light, right? So that's what laser stands for, light amplification stimulated emission of radiation, right? No one remembers that. We just call it lasers. It's not spelled with a Z, though, right? That was the cool way to spell it in the 80s. So it's going to create a light that's amplified by narrowing the beam. And the technology, the reason I included this on the slide is because it is using an anode and a cathode. It's using the exact same technology that's there inside of our x-ray tubes to accelerate the light and focus it. And the color it's producing, in this case, is red. We can make other colored lasers, as we all know, right at this point in history. We've all tried to blind people in traffic with pinpoint lasers, right? I mean, we all do it, right? No. That's who it was. Right. So, um, yeah, I wouldn't go too much into, like, how the lasers work with atoms and stuff. They are doing... Some crazy stuff with atoms though, but I'd probably just leave it at that and don't spell it laser with a Z You're good to go. All right. I'm really sad the day that they got rid of the last like laser tag place in Memphis That was a bad day for me So The CR laser Why do we care about a laser? Well, the first thing I want to point out is that this illustrations a piece of crap Why do I not like this illustration here? What's wrong with it? Here's a hint. It should have been freaking red. Like whoever drew this was on crack, right? It's important that the laser is red, right? I want to underscore that yet again. The helium neon laser is red. But what it uses is this crazy beam deflector, and I've seen one once. It looks like some crazy dark crystal stuff. Like it is this crazy crystal that has all these facets on it, like more facets than a diamond, and it spins around. And as it's spinning, it's deflecting the laser back and forth across the PSP plate. Almost like someone eating corn, right? It's going back and forth across the corn, right? At least the way that Mickey Mouse eats corn. And it's scanning every single corner of the PSP plate, right? So don't worry too much about how all the optics work. Just know it's got this crazy spinning diamond that forces the red laser across the PSP plate. Right? Essentially that causes two scanning directions, right? It has a direction in which the cassette is passing underneath the laser, right? So that's one scan direction, and then it has a separate scan direction that's the laser going across the cassette. And that's basically, they're basically perpendicular to each other. I've seen where they ask questions at that level of detail on this material. That's why I'm telling it to you. There's nothing in this presentation that I have not seen them expect us to know. If you're like, oh my goodness, it's 1 o'clock, 12 o'clock, I don't even know what time it is, on a summer afternoon, and I'm not going to remember any of this, that's okay because we are going to have a whole trimester of this in the spring. Yes. All right. So the reader scans the plate with the red light and a zigzag or raster pattern, right? That's the fancy name for zigzag. It gives energy to the trapped electrons. It empowers them, right, to unpop that packing material, right? And in the process, it gives off light, right? Red laser, blue light. So they did do that illustration correct in terms of the blue light. So here's more information about the translation or the scanning directions of the laser across the thing. So this process is sometimes called translation. There's a slow scan direction. That's the direction in which the plate is moving underneath the laser, right? Then there's a fast scan direction. That's the perpendicular direction that the laser is scanning, whipping across. the PSP plate, right? We then pick up the blue light that's given off by the PSP plate with what's called a photomultiplier. And one way to think about a photomultiplier is it is a crystal that works like a trumpet, right? It amplifies light through a trumpet shape. It's really weird looking too. It's even the weirdest, it's the weirdest crystal of them all. Like if I was out on a crystal quest with my wizard friends, that would be the one we would be after, the phonomultiplying crystal that looks like a trumpet. If you ever get a chance, if they're ever working on the CR reader, go check it out. So it's going to amplify the light and send it to a digitizer, the ADC, the analog to digital converter. So that's what we're doing when we digitize the signal. So, quiz. When the light is picked up by the photomultiplier, what kind of information is that? Analog. It's Led Zeppelin information. It's just analog signal, right? When it gets to the ADC, that's when it turns into digital. That's when it gets turned into ones and zeros, ons and offs, things like that. Up until that point, it is still an analog signal, right? So this light guide directs it through the trumpet shaped photo multiplier thing to the analog to digital converter, right? And it goes pixel by pixel across the plate, takes whatever was... It's given to it and applies that to a matrix. Takes the information, stores it in a matrix. Takes the information, stores it in a matrix with a number value for what was read. If not that much blue light was given off, it might get a zero. If more blue light was given off, it might get a series of ones, right? So that assigns a value to what we call pixels, picture elements, right? which are these little storage containers inside of the matrix. Now one way to think about this is it'd be like a really crazy sock drawer, right? Where this cabinet, this chest of drawers has a drawer for every single sock in your possession, right? Like you got really obsessed with losing socks in the washer and dryer machine, right? And you know where each sock's supposed to go. So as you pull the socks out of the washer or dryer, you place it in its specific drawer. If you didn't find the sock, And you know you can't find its pair or whatever, it doesn't go in the drawer. So that's the way I think about matrixes, is with socks, going in sock drawers. So all of those matrix, all those pixels assign brightness levels or counts, the amounts of information that was given off by the PSP plate. So As you can imagine, and I'm sure the first thing that popped into your mind, just like with me, was like, okay, well, if you got this crazy sock drawer with the socks going in it, it matters what size the sock drawers are, right? I'm not going to go too far down the sock drawer thing, but the important thing here is that what we're talking about in the number of sock drawers is spatial resolution, right? Now, let's say that Ms. Tabor has a chest of drawers, right, and it's 8x8. She can fit eight socks across the top and eight socks down the length of this thing, right? I have a chest of drawers that's the exact same physical size, right? But it has a hundred by a hundred drawers on it, right? Who can fit more socks? Me, right? Even though the physical size of these two matrices was the same, I was able to store more socks, right? And that's important because of my sock collection. No, the important thing is that that helps us understand spatial resolution, right? This is the amount of detail present on the image, and it is largely a function of matrix size. The reason I'm stressing it is, say I've got a PSP plate that looks this big. Like when I pull it out of the cassette, this is how big it is. 8 by 10 or whatever. What does not change is its physical size. But on the computer side, I can change the matrix size all day long. I could read this onto a 4 by 4 matrix and then I would just have four big dots on this. That's all I would have for information. Or I could read it on a 1600 by 1600 matrix and I'd have a lot more information stored. Alright, so matrix size is a function of the computer and it largely determines the spatial resolution. The larger the matrix size, the higher the spatial resolution. So this is also slightly related to the PSP plate as well, right? So the thinner the layer of that phosphor, the higher the resolution as well, right? And that has to do with what we're reading out from it. How much blue light is emitted when it's stimulated by the laser? Is it a lot of blue light or a little bit, right? Is the blue light true to what was received or is there some noise there, right? I'm not going to labor on this point a whole lot. We will come back to it, but it's important. One thing that's significant here, though, is that compared to film, CR, spatial resolution, is crap, right? That's what those numbers mean right there. You can just write crap. crap by cr resolution on your slide film is good spatial resolution right why am i saying it's good well it has 10 line pairs per millimeter every single little crystal of the film can receive information from the x-rays and there's trillions of x-rays like gazillion billion of x-rays right tons And it is able to record each and every one of them very very tiny. It has the tiniest sock drawers of them all, right? The CR spatial resolution is about two and a half line pairs per millimeter. It's not that Great, right? This results in less spatial resolution. Where CR wins out over film is in the dynamic range, right? It's range of readability, right? The number of recorded densities, right? So I said earlier, if you took the film out of the cassette, it would be burned black, right? By light like that. The CR, I said, was... even more sensitive right so how do we get a picture from the computer the computer is even more sensitive than sensitive right it out fought the PSP plate so what I'm saying is as long as you're giving a signal the computer is getting it and turning it into ones and zeros right And that's why they've taken over our reality and everything that you see is actually just a virtual representation and none of this is real, right? No, but that is part of what we're talking about when we talk about dynamic range. That it has a tremendous ability to receive information, right? It is much, much, much higher. So even though the spatial resolution is crap, the contrast resolution is pure gold, right? So that's where it wins in the day, right? We're able to see more differences in tissue density. So here's an example. I can only see so much stuff, right, on an x-ray of someone's knee, right? Spatially, there's only so much I can see. On a film system, whatever I take a picture of, that's what I've got. So if I took the picture, it's a little difficult to see the differences between these two images right now. But if I took the picture on the left, and, you know, it looks like the fibula is a little bit burned out, the head of the fibula is a little bit burned out, there's not much soft tissue detail on that image, that's what I got. End of the story, right? That's what I got. Versus if I took the picture on the right, and I can see a little bit more of the fibular head, there is more soft tissue detail. That's what I got. End of story. That was the dynamic range of film. In fact, if I overexposed it, it would just be completely blackened out. There would not be anything there, right? With a digital system, I could produce either one of these images and any combination of images between, right? In fact, I could apply a technique that's about 200 times the technique that I could use on film and still get a picture. That's what I mean by dynamic range. Film, you got one picture, period. Digital, you've got... Thousands of pictures that you can make. Alright, here's a confusing concept. See our speed, right? When we used film systems, we talked about the speed of the film, right? It was important. If it was a high-speed film, it was very sensitive to x-rays, so it picked up x-rays quickly. Therefore high speed. You did not have to use as high of a mass on a high speed film, right? What you lost was spatial resolution. So it was faster speed, less spatial resolution. Conversely, we would have what we called orthopedic film, which was a slow speed film. We would intentionally use the slower speed film for orthopedic work and extremity work because we needed better spatial resolution. So we had to use a higher technique because it was a slower speed film, but it gave us better spatial resolution. We've kind of imported that same way of talking about things to computed radiography. We can still talk about speed. And in fact, you're already kind of familiar with it because every time you've written down an S number from Fuji, From that CR reader in the lab, you've written down a speed number. What that number told you was the speed at which you took the picture, right? So if we think, put on your thinking caps for just a sec and stay with me. I don't want to get too bogged down, but this is important. What does it mean about your mass or your technique when the S number is high? It was a low technique. Therefore, it was like you shot. on a high speed film. It was a low technique, so it was like you shot it on a high speed film, right? But what does it mean if the S number is low in terms of technique? Yeah, the technique was kind of hot. So if it's low, it's like you shot it on a low-speed film. You used a technique that someone might have used on a low-speed or orthopedic film, right? So what does that mean about the hot or the low S-number image in terms of spatial resolution? Does it have better spatial resolution or less? Is it like the orthopedic work or not? Yeah, it has a higher spatial resolution, right? So it's not just high S number good, low S number bad. It's actually a question that you have control over. What am I trying to see? When I take this patient's picture, maybe I want the S number to be a little low. Maybe I want the technique to be a little bit hot. I will have better spatial resolution, right? Or maybe if I'm doing this one and it's a pediatric... patient or a female patient, what have you, maybe I don't need that much spatial resolution for the study. Maybe I can reduce the dose and treat this as though I were taking this on a high-speed film and use a lower technique, right? Now, I know I just went kind of flipping all through all sorts of technique stuff. Re-listen to the PowerPoint slide if you need to. But the significant thing here is that speed, as we're talking about it, is a reflection of the amount of light that's being given off by the PSP plate. If it was exposed to a lot of radiation, it's going to result in what we would call low speed, right? So we're saying it is largely expressed, best expressed, as what we would call an exposure indicator, right? So speed is something we've imported from film. It is still helpful. The concept still exists. But probably the... better way to talk about it in my opinion is an exposure indicator. Speed is like the technique side of it thinking about it as a tech in terms of high resolution low resolution the actual thing that the computer is doing is indicating how much exposure was received. Now the final thing that we need to do is erase this sucker and so what we do is we expose it to very strong light and if you are watching as the CR reader in the the lab is Finishing up, you can actually see the fluorescent light being emitted from the reader. It's a very, very strong fluorescent light, generally just like a white light. And so it completely erases the PSP plate and allows it to be X-rayed again. Now one thing just to say real quickly before we get into DR is if you, given the sensitivity of CR systems and how sensitive I said it is to natural background radiation, if you don't know. when the last time a CR cassette was used, I recommend erasing it prior to going up on a portable run with it, right? If you don't know, go ahead and erase it and you can start over. All right, I'm switching gears now to talk about DR and I'm going to move pretty quickly here. Basically, what we have is a flat panel detector, if I can talk. Think about it as being like the camera on your cell phone, right? It is a flat panel detector. It has a photoconductor, something that can conduct... light through it, right? And that's what that means, photoconductor. It lets the light pass through it, right? And the one that we use is called amorphous selenium, and it's abbreviated with the A out in the front, selenium. All that amorphous means is it can change. As light passes through it, it changes, right? That's what amorphous means in this context. We might also use things like amorphous silicone and charged couple devices. So... Anytime we're dealing with amorphous selenium, we are dealing with direct capture detectors, and I've said this is the one that is like your cell phone camera, right? It is a direct capture camera, right? So what it does is it has a thin film transistor array, right? A TFT, a thin film transistor array. That means that there's all these little circuits that are now storing the information that's received. So with the PSP plate, I said it was a crystal that's capturing the electrons. For direct capture, it is a thin film transistor. It's actually little circuits that are capturing the information. Right? That's why we call it direct. We do not have to read this out. The minute that the information is received, the transistors capture it and it can start to produce an image. It does not have to be read out. Right? But this amorphous selenium holds a little charge on its surface. When the x-rays hit the amorphous selenium, it bounces the charge back and forth to the transistors, and they read that out as a picture, right? To go through the process one more time, x-ray photons exiting the patient, right, strike the amorphous selenium. They are converted into an electrical signal by electrons being bounced around, and that's detected by the TFT array. So the thin film transistor is really the active part here, and it's present in both the direct systems and the indirect systems, right? All that matters is what we're doing with the x-rays. Are they being bounced around by electrons or not? So... It's on a substrate. That substrate is generally made, and this is going to be extra confusing, out of silicone, right? I've said it's amorphous selenium, and it's sitting on silicone. So think about the motherboard inside your computer, that's a silicone plate, right? That green stuff that's coating it is silicone. We call, you know, that area outside San Francisco, Silicon Valley, right? Why? Because they're doing computer junk there. Right, lots and lots of computer junk. So, it is just used as a thing that can support the components, the transistors in this case, as well as insulate for conduction of electrical signals. So, there's these little tiny transistors and they are basically what is capturing the pixel information. Right, the surface of each transistor is what's capturing. the pixel. So the smaller I make those TFTs, the smaller the pixels get. Here's an example of what we're talking about. So the x-ray strike the absorber, that amorphous selenium, it transfers information to this array of the TFT. This is a blow-up of a single TFT. So it has little sensitivities, further sensitivities. within the TFT. All right. A million plus pixels can be read and converted to a composite digital image in less than a second. That's what's happening every time you snap a picture with your cell phone. That's what's happening every time you take an x-ray with a digital imaging system. It's very quickly reading it out. It's not using a laser or anything like that. You just take the picture, the TFT captures it, and you can move on with your life. All of that though is still stored in data columns and rows, which is what we call a matrix. It's still going in the sock drawer, and the size of that matrix depends on, or the spatial resolution depends on the size of that matrix. Alright, let's talk about indirect conversion or indirect DR, right? This is a two-step process. So the X-ray photons strike a scintillator that produces light. Then that light is captured, right? So in this case we are going to use amorphous silicon. So this indirect conversion involves an additional step and so there's an additional kind of area for interference or noise. So in general these systems are are not considered as quite as efficient as direct capture. But the same process is being happened in terms of readout. It's still being trained on a TFT array, and that TFT array is what's feeding the information into the matrix that's producing the picture. So in this case, just to stress it, we've got incident X-ray photons. They hit the cesium iodide scintillator, which then passes that through the amorphous silicone, right, to be read out by the TFT, right? So that, I may have misspoke earlier. The thing that's actually producing the light is cesium iodide, CS lowercase i, right? Cesium iodide is what's producing the light. So X-rays strike the cesium iodide. It produces light. The light's passed through amorphous silicone to the TFT array. So we're using amorphous silicone inside the detector in this case in order to basically conduct the light towards the TFT array. The reason we like cesium iodide is because it has these little light tunnels in it. Like here's a very, very small picture of what the cesium iodide crystals look like. They have these little tubes to them. So as they produce light... producing it in a single direction toward the amorphous silicon right towards the TFT array they're also very very small right so they allow us to pick up on very very small things like x-rays right So the two points of this is they allow for rapid detection of the x-rays and they also reduce a quality that we call turbidity, right? Which means that kind of light noise, right? Anytime I think about turbidity, I think about, I mean, have you ever been camping outside of a city and the light, the sky towards the area of the city looks kind of purple, right? That's what they call light pollution from the city. That's exactly what we're talking about with this. The cesium iodide crystals are basically reducing the amount of light pollution by just channeling it in the direction that the light needs to go. It's not going every which way. The final thing that we can talk about with Direct is charge coupled devices. These basically use fiber optics. They pass the information down fiber optics to where they're received and stored on the matrix. So we'll talk about them real briefly. They're generally low cost, although they are kind of coming back on the market. We might also talk about CMOS, and these are complementary metal oxide systems. Largely, these have gone away. I've only seen one in my lifetime. This is the part where I've asked you to really pay attention, right, as we talk about detective quantum efficiency, right? And I know we're close to the end. This is talking about how efficiently the X-ray input signal is converted to useful output information. One way to think about it is the fuel efficiency of your car. How well is the gasoline converted to you getting down the road? When we talk about DQE, we're talking about fuel efficiency. We look at a number of things when we think about DQE because things can affect... just how much the information was useful, right? So things like noise affect the DQE, right? The way that we talk about the effect of noise on the detective quantum efficiency is the signal-to-noise ratio, the SNR, right? So signal is the useful information, noise is the not useful information. We want a high SNR, a high signal-to-low noise ratio, right? The more signal you have, the less noise there is, therefore the higher quality of the image. This also has some bearing on contrast, because if we have noisy systems, that reduces our contrast resolution. As we're thinking about DQE, these systems that have a high DQE, we also want to maintain that they have a wide dynamic range. that allows for a wide range of capture. So we don't necessarily want them to be noisy systems. So we have to figure out a way to have both a high DQE while at the same time being able to image small low contrast objects. The easiest way to have a high DQE would be to have a gigantic detection surface. But the problem with the gigantic detection surface is there goes your spatial resolution. Right? So how do we make sure that we're receiving all the information that's being transmitted while at the same time receiving it on a very, very tiny surface? So what we're talking about is really the state of the art, right? How far can we push this technology? When we talk about detective quantum efficiency, we're talking about a whole lot of parts, right? The signal-to-noise ratio, the spatial resolution. the contrast resolution. But rather than get down into the weeds, I just want to emphasize that right now, a high DQE is what's preferable, and we can define it as the ability to image both small, low contrast objects. So high DQE means high spatial resolution and high contrast resolution. Let me slightly rephrase that, I'm sorry. I'm sorry. High spatial resolution, and this is going to sound weird, but a high, low contrast resolution. A high, low contrast resolution. The ability to differentiate low contrast objects, right? The reason I'm making that distinction is because another way of talking about spatial resolution is just to talk about... high contrast resolution, right? Spatial resolution is measured by objects having high contrast, right? So high spatial resolution and then a high, low contrast resolution, the ability to differentiate objects. that have low contrast differences. So... This technology, the improvements that we've had in both indirect and direct capture DR, have made the DQE of these systems higher than CR. That's why Congress and others have said, get rid of your CR systems. Everyone needs to adopt DR, right? Because this is an easy thing to quantify, and politicians aren't that bright, so they like things that are easy to quantify, right? We'll leave it at that. So, going back to the spatial resolution question. The physical characteristics of the detector influence spatial resolution. How big that TFT array is affects spatial resolution, right? In general, we are up against the limit. Because as the pixel size decreases, right, the amount of signal that we can pick up decreases. So, as pixel size decreases... the DQE is decreasing. So this is not necessarily a bad thing, though, for a number of reasons, primarily because there's going to be... Well, let me put it like this. It's the limit, right? How much can we decrease it without completely losing the signal, right? Because as we decrease it, the signal-to-noise ratio is dropping, right? So, these physical components, as the pixel size decreases, do we have a better spatial resolution? Yes. But are we also affecting our signal-to-noise ratio? Yes. All right? So that is the bind, that we're up against the limits of what the technology is capable of doing. Also, if we try to process the signal over and over and over again, we can introduce additional noise into the signal. We can do processing algorithms to improve the image, to get rid of noise. We know what shape noise is, right? So we can process it out, but eventually it starts to affect, in general, image sharpness. So we're back to that question of pixel size versus matrix size. There's a lot on this. That's what I want to point out to you. And that's why I keep talking about this over and over and over again. A lot connects on this question of the sock drawers, right? And I've said that if I have a chest of drawers, it's the same size, right? But there's more drawers in one chest than the other. Who can store more socks? The answer was the drawer. The chest of drawers with the most drawers, right? But we start losing socks if we make the drawers too small, right? What happens if we make the drawers smaller than the socks? That's kind of the rub, if you will. That's what I'm talking about with DQE. The amount of resolution in an image is determined by the size of the pixel, right, and the spacing between them. The fancy term for that is the pixel pitch. So more and more smaller and smaller pixels produce greater spatial resolution. The way to have more and more smaller and smaller pixels is to have a larger matrix right, so they're inversely related as Pixel size decreases your matrix size is increasing I Will be saying that a lot right the larger the matrix the larger potentially the size of the image Stored right and the greater the amount of storage space needed All right, the more information is being stored All right, this is probably one of the nerdiest things that we're going to talk about today. So if you didn't think it was nerdy enough, we're going to completely nerd out now with the Nyquist frequency, right? This is basically just saying that if you're trying to detect something, right, you need twice the signal for whatever you're trying to detect. You need twice the signal. Think about it like someone, like you're not quite sure what someone's saying. It's really windy outside and you're not quite sure what someone's saying. So you ask them, hey, what did you say? The Nyquist frequency, this theorem is saying you're more likely to accurately hear what they say if you ask them to say it twice, right? Think about it like that. It's a windy day outside. It's noisy outside. Hey, what did you say? Right? So if we want good information, not only do we have to have small pixels, we need two times the number of pixels of what we're trying to see. Two times the number of pixels of what we're trying to see. That's going to be the best way to reduce noise while improving spatial resolution. Okay, exposure, latitude, and dynamic range. We've kind of visited this already, but we will give it one last kind of go. Exposure, latitude is just how broad from overexposure to underexposure can we still get a good picture. The exposure, latitude of digital imaging systems is huge, right? Thousands of times the exposure, latitude of film, right? The dynamic range is the receptors ability to respond to different exposure levels. So they're closely related concepts. The one is talking about how much of the signal can still give me a picture and the other one is talking about how much of it can respond. So they're basically saying almost the same thing. A lot of times we use exposure indicators to determine the exposure acceptability. That's what I'm asking you all to do on your digital. So in a few minutes people are going to be heading into the lab and I'm asking you to write down S numbers as a way to tell me whether or not it was an appropriate technique. So if the image appears modeled, we have less than 50% of the desired amount. So we need to increase the signal by at least twice. That's from the Nyquist theorem. So we can no longer look at the picture on the monitor and determine if it's under or overexposed. We have to rely on an exposure indicator to tell us that, right? And there's a lot of different ways that they can be calculated, which leads to confusion. If you understand it properly, it's a good tool. If you don't understand it, it is actually going to work against you. So there's been calls for us to have a universal exposure indicator, and that's what we're talking about when we talk about the deviation index. It's basically a simplification of the existing exposure indicators that allows you to determine, just kind of thumbs up or thumbs down, was it a good picture. All right, let's talk real quickly about monitors. They also have matrices and pixels, right? Inside the monitor, there's a matrix and a pixel. So when you're looking at the surface of your phone, your readout display, that's a monitor. It has a matrix of pixels. that are reading out information to you. In general what we do is use our LCD monitors, right? And all that means is it just has a polarizer that twists the light to be either emitted or not emitted. That also affects spatial resolution, right? So depending on the size of my monitor, I can have better or worse spatial resolution. The main place that we see a problem with this is the CR readout station. where I'm looking at the monitor there to determine if it's a good picture or a bad picture versus what the radiologists are seeing. Their monitor is much nicer than our monitor. So if there's problems with it, they're more likely to see it. One way to think about it is like we're looking at the R on the 10x10, and they're looking at it at the 100x100, right? If there's a problem, they're much more likely to see it. We've talked quite a bit about contrast resolution. But what I'm talking about here is the low contrast resolution. It's the difference between the maximum and minimum luminance of now the monitor, right? So it does impact things at the monitor side. And we have all sorts of specifications for how that's supposed to be applied. The reality is, is though... We can only see about 30 shades of gray. The monitor can display close to 256 different shades of gray. That's the minimum. All right, the final piece of this is informatics, which just means how information is dealt with. Most of this you all have seen before, but the HISS is the Clinical Information System. This is everything that relates to billing primarily or patient information. So what insurance the patient has, it's in the HISS, right? It's what the... people at the front desk need to know. That information, like the patient's name, is communicated via an HL7 connection from the front desk computers to our imaging computers, right? So if you ever have a technologist that has to manually enter information somewhere in the process, chances are they do not have an HL7 connection, right, at that computer. There's a radiology information system, and this is largely, for us in Baptist, used to check patients in and out of the... ER and places like that. We could say, yeah, the exam's been done, and it stores it along with other information. There's DICOM, which is that universally adopted standard for transmitting information that's medical imaging information, and it's tagged with a unique identifier. That's what we're talking about when we talk about accession numbers. And the final thing I think the slide may have gotten clipped would be PACS, that picture archive and communication system, which is where the images are stored in a giant server. Thank you so much.

So we're going to define digital imaging to include both computed radiography and digital radiography. That's what those abbreviations mean. CR means computed radiography.

DR means digital radiography. And so you'll notice digital imaging is the big umbrella and then beneath that umbrella we have CR and DR. We will discuss computed radiography or CR to include how the CR cassette is constructed with the imaging plate inside of it, what's going on in that photostimulable phosphor plate that sometimes abbreviated the PSP, right? We'll talk about how photo stabilization works, what this technology is, we'll talk about laser beams and how laser beams are made. And then we'll talk about how to erase the digital image, right?

Then we'll talk about DR. And we'll talk about two distinctions. So there's a further umbrella underneath DR, we have indirect digital radiography and direct digital radiography. So we'll talk about the differences in those technologies.

We'll list steps for how digital conversion works. We'll talk about charge couple devices, which are kind of the weird outlier. Then we're going to talk about image quality and storage and display. If you're going to fall asleep, don't fall asleep until the absolute end with storage and display, because that's the one that is kind of a given, and you'll all have some familiarity with PACs and using computer monitors, right? The image impact, the stuff, the image quality part to this is heavy-hitting material.

It's the most abstract material in the presentation, so if we need to take a break or something at the end, we can. I want to make sure that we all pay attention for that part. So digital imaging is just any way of getting a picture that can be manipulated and viewed on a computer. Pretty straightforward. You do it every day with your cell phone.

That's what we're talking about, your cell phone picture. In fact, your cell phone camera is a form of, I believe, direct digital imaging, right? So when we get to discussions of direct digital imaging, we can use our cell phones as an example, right?

For the purposes of x-ray, this first really came into use in the 1970s with CT. As soon as CT scanners showed up in the department, we had to think about the ways that computers look at pictures, right? It really kind of started to develop into a full-blown part of our work sometime in the early 1990s, right?

But it was there as early as 1970. Well, let's talk about what we're talking about when we talk about digital, right? I think it's helpful to think about this awesome digital watch here, right? I remember this watch when it came out. The commercials went like this.

Look closely. The hands on this watch are about to disappear, right? It was amazing. It blew everyone's mind.

Everyone wants a watch with no hands on it, right? So that was the promise of digital, right? That it could parcel time out in discrete packages.

And what I mean by that is that every minute is a minute, right? There's none of this second hand wandering around on things, right? It's a minute is a minute is a minute. Nothing more, nothing less. That's what digital does.

It's either on or it's off, right? Versus analog is something that continuously changes, right? Probably the best way to think about digital versus analog, if the watch analogy is not working for you, is maybe like a band like Daft Punk, right, that makes electronic music, right? Versus a band like...

Led Zeppelin, right? That they would plug their guitars into their amps and they were making analog music. There was nothing digitized in Led Zeppelin's music.

They just plugged their guitars into their amps and whatever was coming out of their guitars was what people were hearing, right? That's an analog process. Versus with Daft Punk, they plug their computers into their amplifiers, right? And they crunch some numbers and the sounds come out, right?

So CR versus DR. We all are all pretty familiar with the distinctions between these things because it creates major hurdles for your everyday life in the x-ray tech department, right? Everything we do, it matters if we're using a CR system or a DR system. It affects workflow and everything else, right, the way that we communicate with the patient.

CR uses these storage phosphor plates that are inside CR cassettes and a CR reading station and a viewing station before we send the images to PACS, right? So I always think about the viewing station as being kind of the centralized location for where we work with CR images, right? Versus DR may require a room upgrade and a lot of times you take the picture and it just pops up on your computer screen Right, there was no additional reading or anything like that So let's talk first about computed radiography and the way that it works It actually works a lot like film right and that's going to be significant that as this technology rolled out A lot of technologists made the mistake, myself included, of thinking about CR exactly like film and they're really very different even though in terms of workflow they work similarly.

The first similarity between CR and film is that they both have a cassette and inside that cassette if it's a film screen cassette it has intensifying screens and a piece of film right that has to be kept in the dark. With CR it has this photo stimulable phosphor plate this white plate that's made out of barium halide or fluorohalide and it's responsible for capturing the x-rays as they exit the patient. Alright so we put the cassette behind the patient, the tube in front of the patient, the x-rays go through the patient and they hit this phosphor plate. So the cassette again is something typically fairly durable made out of plastic and lightweight. A lot of times it has an aluminum backing and that's there just to kind of catch up, catch any x-rays that are exiting the cassette, right, that may have continue on.

They do not have intensifying screens, but what they do have is an anti-static material inside of them. Because the photostimulant phosphor plate inside of there is going to be drawn out of the cassette, the reader is going to pull it out of the cassette, and if as it pulled that PSP plate out of the cassette there was static, The static would create an image, it would create an artifact. So we do not want any static as the PSP plate is pulled out of the cassette.

One way to think about that, well, might be like when you're trying to pump gas in the wintertime and it's dry outside. Have you ever gotten shocked by a gas thing? In Utah it was a serious issue, like people could get caught on fire because it was so dry there in the winter.

You could get blown up by a gas pump. So they would always encourage you to touch your car or touch something before you touch the gas pump. Static is not a good thing. This imaging plate though is where we should probably spend most of our focusing.

So we're going to look at pretty much layer by layer how it's constructed. And the layers are important. And so each one of these layers is significant.

But the active layer, the part that is the most important for us, is this part that's called the phosphor layer. Without that it would not be able to receive x-rays. Everything else exists in support of the phosphor layer and sometimes it's also called the active layer. So there's a protective layer on the outside and it's just clear plastic right and immediately beneath that protective layer is the phosphor layer active layer sometimes called the PSP right and it It has a photostimulable phosphor that we'll talk a little bit in more detail in just a moment but it is responsible for trapping electrons during exposure. So the x-ray photons produce ionization inside the PSP and that crystal traps the electrons that are produced from the ionization.

That's what the crystal is responsible for. It is typically made out of some form of barium fluorohalide. Now that's a big family of chemicals, right?

But if you just remember barium fluorohalide, you're good, right? It's also helpful to know that it is photostimulable. What that means is that it is, it gives off light in response to stimulization. So if you stimulate this crystal, it will give off light.

The barium fluorohalide glows basically in the dark. It will glow in the dark and the color it will glow is blue, right? Blue violet. So that's important, right? It seems like kind of a trivial thing, but what I'm saying is if you were in the blacklight room, right, checking out everyone's wizard posters or whatever you do in the blacklight.

room. This stuff is going to be blue. If you took the CR cassette into the black, we know what black lights do, right? Right. If you take it into the black light, it's going to glow blue, right?

Other things might glow different colors like orange or yellow or whatever, right? This one glows blue. Then there's a reflective layer beneath that glowing layer because we want it to glow in a certain direction.

In fact, we want it to glow in the direction that we're reading it, right? So it will... allow that blue glow to be emitted in a certain direction, the direction in which the reading is occurring. Sometimes it's black to reduce the amount of light that might be escaping or the kind of light contamination there.

Then there's a conductive layer, and this is there to, again, absorb static. Static is the enemy. We've established that with the CR cassettes.

Finally, there may be a color layer. It's not labeled here on this one, but it would be basically at the same level as the light reflective layer. And that's just an additional technological innovation that helps with the light that's being emitted by the crystals. Support layers is just a semi-rigid material.

If you were to hold the PSP plate, it feels kind of floppy, almost like this catalog or something. And whatever rigidity it has is because of a... kind of a thick plastic inside of it, right? Otherwise the crystals would just kind of go everywhere. And then it has a backing layer and that's just to protect the cassette further.

You'll notice one thing I didn't point out though is that there's a barcode labeling thing on it. So we'll talk more about that here in just a moment. So that barcode, sometimes you can see it through the window in the cassette. Sometimes it's there at the end of the cassette.

Do techs at your facilities use the barcode for labeling of their cassettes? Right. Back in the day, a film, you had to label your cassettes manually.

You would actually take the cassette, you'd have the patient's blocker or like a little patient armband. So you literally had to inspect the patient's armband to pull a plastic thing off of it that you would then use to expose the film, to label the film, and then you would develop the film. Right.

That was how you labeled the patient's information. Now we use a barcode to basically scan and tag the PSP plate with the patient's information so that we don't accidentally develop Mrs. Smith's x-rays on Mr. John Doe's account. Does that make sense?

And that's generally done by technologists. And so anytime I say the word technologist, if we're talking about digital imaging, we can just think about, okay, that I just introduced the possibility for user error. Are there times when the technologist incorrectly enters information?

Yeah, there are, if we're frank. And you probably have seen instances of that, given the amount of time that you've been out in the clinic. So that's why it's important to check the information and double-check the information that you're tagging to the cassette, because you are really kind of where the buck stops in terms of catching errors with the labeling of information on. the images.

Some of these cassettes kinda had an innovation like Kodak in particularly you could write on it and there were stickers to orient you know which side of the cassette is up and which side is down that's just proprietary in general I have not seen those being used in departments for the most part people just use the barcode and just go on with their life so This is why we assumed that CR radiography was basically the same thing as film. The workflow was exactly the same. When it says conventional radiography, it means film, right?

Film screen radiography. You basically would set up the patient. You'd put the cassette either on the tabletop or in the bucky, and then you have to go and develop the thing, right? So the workflow felt essentially the same. Really the only thing changed was like now there's a barcode and we used to have to flash the film prior to running it, right?

So that's the only thing that felt a little bit different is now we have to scan it with a laser for the barcode, right? We use basically the same technology to take the pictures and everything. But there is this huge difference in the way that this technology works in terms of what it's doing.

We can think about it kind of the same and in some ways we continue to do that. One example of ways that we continue to think about it the same is speed. When we talk about speed of digital systems, that's a concept that we've imported from film.

But this basically breaks down piece by piece. piece what's happening inside of the PSP plate when we make an exposure. The x-rays that are exiting the patient, right, are going to interact with electrons in the barium fluorohalide, right, and those electrons are going to be trapped in what we call a phosphor center, right.

So it's almost like, if you want to think about it this way, it's like packing bubbles, right. Whenever you pop a packing bubble, that bubble's popped, right. So the x-rays are popping the little packing bubbles inside of the PSP plate. And from all the packing bubbles that are being popped, we're making a picture.

We're going to somehow unpop the packing bubbles in order to read them out. So that's the way I think about these crystals. It's like popping the little packing bubbles.

Some people love it, some people hate it. My son hates when we pop packing bubbles. I love it.

I'm in the loving it camp. Most cats hate it. So, all right, this trapped signal, the little popped bubbles in the packing thing, can remain that way for a long, long, long, long time, right?

It's hard to unpop the bubbles, right? So it's never really completely lost. The more times that we use the PSP plate, the more times we pop the bubbles in it, the less responsive it becomes. But in general, these things have a pretty significant shelf life on them.

And one of the things that's interesting... is that they're actually more sensitive to radiation than film. And when I say more sensitive, that's kind of crazy, right? Because the second you pull film out of a cassette and expose it to light, it's toast. That's how sensitive it is to radiation.

These things are actually more sensitive to film, more sensitive to radiation than film, right? So we'll talk about how we actually get a picture out of that if that's the case. But the important thing here is that...

They are trapped in this thing. They're never completely erased, not completely, and we have some residual ones that are left on the thing that will interfere with repeat exposures. So one thing about that is that before I've read this PSP plate out, it has what I would call a latent image on it, and that's actually a concept that comes from film, that there's a picture on this thing, but I can't see it.

That's what latent image means. I captured something but it's not apparent to my eyes, right? If I just pull the PSP plate out of the CR, it's just white.

There's no information there. So I have to figure out a way to develop it or read it. And that's what we're doing when we use a CR processor.

So we place the cassette into the reader in some way specific to the way it's been things, the way it's been manufactured. It pulls that PSP plate out of the cassette and then it's going to scan it with a laser, right? And in essence, when it scans it with a laser, it's going to allow it to release the light that's trapped inside of it, right? So in the process of unpopping the bubbles and putting the bubbles back in the packing material, they release light. Energy is neither created nor destroyed.

So when these crystals reconstitute themselves, when they get their electrons back, they're so happy about that that they give off light, right? And specifically, I said the light was what color? Blue.

Blue, violet, or blue. And that's important because our laser is red, right? So the blue, I don't know, I always think about like Obi-Wan Kenobi versus Darth Vader. Obi-Wan's got the blue lightsaber, Darth Vader's got the red one, so you know if the guy with the red lightsaber wins, that's a bad, you know, thing for the good guys, right? So the laser is red, right?

And it is a helium neon laser, right? So the way you make a red laser is you get helium and neon. And then you have an anode in the cathode, right? And now we just pass light through it. It's going to output a laser, very intensified light, right?

So that's what laser stands for, light amplification stimulated emission of radiation, right? No one remembers that. We just call it lasers.

It's not spelled with a Z, though, right? That was the cool way to spell it in the 80s. So it's going to create a light that's amplified by narrowing the beam. And the technology, the reason I included this on the slide is because it is using an anode and a cathode.

It's using the exact same technology that's there inside of our x-ray tubes to accelerate the light and focus it. And the color it's producing, in this case, is red. We can make other colored lasers, as we all know, right at this point in history. We've all tried to blind people in traffic with pinpoint lasers, right? I mean, we all do it, right?

No. That's who it was. Right.

So, um, yeah, I wouldn't go too much into, like, how the lasers work with atoms and stuff. They are doing... Some crazy stuff with atoms though, but I'd probably just leave it at that and don't spell it laser with a Z You're good to go. All right.

I'm really sad the day that they got rid of the last like laser tag place in Memphis That was a bad day for me So The CR laser Why do we care about a laser? Well, the first thing I want to point out is that this illustrations a piece of crap Why do I not like this illustration here? What's wrong with it?

Here's a hint. It should have been freaking red. Like whoever drew this was on crack, right?

It's important that the laser is red, right? I want to underscore that yet again. The helium neon laser is red.

But what it uses is this crazy beam deflector, and I've seen one once. It looks like some crazy dark crystal stuff. Like it is this crazy crystal that has all these facets on it, like more facets than a diamond, and it spins around.

And as it's spinning, it's deflecting the laser back and forth across the PSP plate. Almost like someone eating corn, right? It's going back and forth across the corn, right? At least the way that Mickey Mouse eats corn. And it's scanning every single corner of the PSP plate, right?

So don't worry too much about how all the optics work. Just know it's got this crazy spinning diamond that forces the red laser across the PSP plate. Right? Essentially that causes two scanning directions, right? It has a direction in which the cassette is passing underneath the laser, right?

So that's one scan direction, and then it has a separate scan direction that's the laser going across the cassette. And that's basically, they're basically perpendicular to each other. I've seen where they ask questions at that level of detail on this material. That's why I'm telling it to you. There's nothing in this presentation that I have not seen them expect us to know.

If you're like, oh my goodness, it's 1 o'clock, 12 o'clock, I don't even know what time it is, on a summer afternoon, and I'm not going to remember any of this, that's okay because we are going to have a whole trimester of this in the spring. Yes. All right. So the reader scans the plate with the red light and a zigzag or raster pattern, right? That's the fancy name for zigzag.

It gives energy to the trapped electrons. It empowers them, right, to unpop that packing material, right? And in the process, it gives off light, right? Red laser, blue light. So they did do that illustration correct in terms of the blue light.

So here's more information about the translation or the scanning directions of the laser across the thing. So this process is sometimes called translation. There's a slow scan direction. That's the direction in which the plate is moving underneath the laser, right? Then there's a fast scan direction.

That's the perpendicular direction that the laser is scanning, whipping across. the PSP plate, right? We then pick up the blue light that's given off by the PSP plate with what's called a photomultiplier.

And one way to think about a photomultiplier is it is a crystal that works like a trumpet, right? It amplifies light through a trumpet shape. It's really weird looking too. It's even the weirdest, it's the weirdest crystal of them all. Like if I was out on a crystal quest with my wizard friends, that would be the one we would be after, the phonomultiplying crystal that looks like a trumpet.

If you ever get a chance, if they're ever working on the CR reader, go check it out. So it's going to amplify the light and send it to a digitizer, the ADC, the analog to digital converter. So that's what we're doing when we digitize the signal. So, quiz. When the light is picked up by the photomultiplier, what kind of information is that?

Analog. It's Led Zeppelin information. It's just analog signal, right? When it gets to the ADC, that's when it turns into digital. That's when it gets turned into ones and zeros, ons and offs, things like that.

Up until that point, it is still an analog signal, right? So this light guide directs it through the trumpet shaped photo multiplier thing to the analog to digital converter, right? And it goes pixel by pixel across the plate, takes whatever was...

It's given to it and applies that to a matrix. Takes the information, stores it in a matrix. Takes the information, stores it in a matrix with a number value for what was read. If not that much blue light was given off, it might get a zero.

If more blue light was given off, it might get a series of ones, right? So that assigns a value to what we call pixels, picture elements, right? which are these little storage containers inside of the matrix. Now one way to think about this is it'd be like a really crazy sock drawer, right?

Where this cabinet, this chest of drawers has a drawer for every single sock in your possession, right? Like you got really obsessed with losing socks in the washer and dryer machine, right? And you know where each sock's supposed to go. So as you pull the socks out of the washer or dryer, you place it in its specific drawer.

If you didn't find the sock, And you know you can't find its pair or whatever, it doesn't go in the drawer. So that's the way I think about matrixes, is with socks, going in sock drawers. So all of those matrix, all those pixels assign brightness levels or counts, the amounts of information that was given off by the PSP plate. So As you can imagine, and I'm sure the first thing that popped into your mind, just like with me, was like, okay, well, if you got this crazy sock drawer with the socks going in it, it matters what size the sock drawers are, right? I'm not going to go too far down the sock drawer thing, but the important thing here is that what we're talking about in the number of sock drawers is spatial resolution, right?

Now, let's say that Ms. Tabor has a chest of drawers, right, and it's 8x8. She can fit eight socks across the top and eight socks down the length of this thing, right? I have a chest of drawers that's the exact same physical size, right?

But it has a hundred by a hundred drawers on it, right? Who can fit more socks? Me, right?

Even though the physical size of these two matrices was the same, I was able to store more socks, right? And that's important because of my sock collection. No, the important thing is that that helps us understand spatial resolution, right?

This is the amount of detail present on the image, and it is largely a function of matrix size. The reason I'm stressing it is, say I've got a PSP plate that looks this big. Like when I pull it out of the cassette, this is how big it is. 8 by 10 or whatever.

What does not change is its physical size. But on the computer side, I can change the matrix size all day long. I could read this onto a 4 by 4 matrix and then I would just have four big dots on this.

That's all I would have for information. Or I could read it on a 1600 by 1600 matrix and I'd have a lot more information stored. Alright, so matrix size is a function of the computer and it largely determines the spatial resolution. The larger the matrix size, the higher the spatial resolution. So this is also slightly related to the PSP plate as well, right?

So the thinner the layer of that phosphor, the higher the resolution as well, right? And that has to do with what we're reading out from it. How much blue light is emitted when it's stimulated by the laser?

Is it a lot of blue light or a little bit, right? Is the blue light true to what was received or is there some noise there, right? I'm not going to labor on this point a whole lot.

We will come back to it, but it's important. One thing that's significant here, though, is that compared to film, CR, spatial resolution, is crap, right? That's what those numbers mean right there.

You can just write crap. crap by cr resolution on your slide film is good spatial resolution right why am i saying it's good well it has 10 line pairs per millimeter every single little crystal of the film can receive information from the x-rays and there's trillions of x-rays like gazillion billion of x-rays right tons And it is able to record each and every one of them very very tiny. It has the tiniest sock drawers of them all, right? The CR spatial resolution is about two and a half line pairs per millimeter.

It's not that Great, right? This results in less spatial resolution. Where CR wins out over film is in the dynamic range, right?

It's range of readability, right? The number of recorded densities, right? So I said earlier, if you took the film out of the cassette, it would be burned black, right? By light like that.

The CR, I said, was... even more sensitive right so how do we get a picture from the computer the computer is even more sensitive than sensitive right it out fought the PSP plate so what I'm saying is as long as you're giving a signal the computer is getting it and turning it into ones and zeros right And that's why they've taken over our reality and everything that you see is actually just a virtual representation and none of this is real, right? No, but that is part of what we're talking about when we talk about dynamic range. That it has a tremendous ability to receive information, right?

It is much, much, much higher. So even though the spatial resolution is crap, the contrast resolution is pure gold, right? So that's where it wins in the day, right?

We're able to see more differences in tissue density. So here's an example. I can only see so much stuff, right, on an x-ray of someone's knee, right? Spatially, there's only so much I can see.

On a film system, whatever I take a picture of, that's what I've got. So if I took the picture, it's a little difficult to see the differences between these two images right now. But if I took the picture on the left, and, you know, it looks like the fibula is a little bit burned out, the head of the fibula is a little bit burned out, there's not much soft tissue detail on that image, that's what I got.

End of the story, right? That's what I got. Versus if I took the picture on the right, and I can see a little bit more of the fibular head, there is more soft tissue detail.

That's what I got. End of story. That was the dynamic range of film.

In fact, if I overexposed it, it would just be completely blackened out. There would not be anything there, right? With a digital system, I could produce either one of these images and any combination of images between, right? In fact, I could apply a technique that's about 200 times the technique that I could use on film and still get a picture.

That's what I mean by dynamic range. Film, you got one picture, period. Digital, you've got... Thousands of pictures that you can make. Alright, here's a confusing concept.

See our speed, right? When we used film systems, we talked about the speed of the film, right? It was important.

If it was a high-speed film, it was very sensitive to x-rays, so it picked up x-rays quickly. Therefore high speed. You did not have to use as high of a mass on a high speed film, right? What you lost was spatial resolution.

So it was faster speed, less spatial resolution. Conversely, we would have what we called orthopedic film, which was a slow speed film. We would intentionally use the slower speed film for orthopedic work and extremity work because we needed better spatial resolution.

So we had to use a higher technique because it was a slower speed film, but it gave us better spatial resolution. We've kind of imported that same way of talking about things to computed radiography. We can still talk about speed. And in fact, you're already kind of familiar with it because every time you've written down an S number from Fuji, From that CR reader in the lab, you've written down a speed number.

What that number told you was the speed at which you took the picture, right? So if we think, put on your thinking caps for just a sec and stay with me. I don't want to get too bogged down, but this is important. What does it mean about your mass or your technique when the S number is high? It was a low technique.

Therefore, it was like you shot. on a high speed film. It was a low technique, so it was like you shot it on a high speed film, right? But what does it mean if the S number is low in terms of technique? Yeah, the technique was kind of hot.

So if it's low, it's like you shot it on a low-speed film. You used a technique that someone might have used on a low-speed or orthopedic film, right? So what does that mean about the hot or the low S-number image in terms of spatial resolution? Does it have better spatial resolution or less?

Is it like the orthopedic work or not? Yeah, it has a higher spatial resolution, right? So it's not just high S number good, low S number bad. It's actually a question that you have control over. What am I trying to see?

When I take this patient's picture, maybe I want the S number to be a little low. Maybe I want the technique to be a little bit hot. I will have better spatial resolution, right? Or maybe if I'm doing this one and it's a pediatric...

patient or a female patient, what have you, maybe I don't need that much spatial resolution for the study. Maybe I can reduce the dose and treat this as though I were taking this on a high-speed film and use a lower technique, right? Now, I know I just went kind of flipping all through all sorts of technique stuff.

Re-listen to the PowerPoint slide if you need to. But the significant thing here is that speed, as we're talking about it, is a reflection of the amount of light that's being given off by the PSP plate. If it was exposed to a lot of radiation, it's going to result in what we would call low speed, right? So we're saying it is largely expressed, best expressed, as what we would call an exposure indicator, right?

So speed is something we've imported from film. It is still helpful. The concept still exists.

But probably the... better way to talk about it in my opinion is an exposure indicator. Speed is like the technique side of it thinking about it as a tech in terms of high resolution low resolution the actual thing that the computer is doing is indicating how much exposure was received.

Now the final thing that we need to do is erase this sucker and so what we do is we expose it to very strong light and if you are watching as the CR reader in the the lab is Finishing up, you can actually see the fluorescent light being emitted from the reader. It's a very, very strong fluorescent light, generally just like a white light. And so it completely erases the PSP plate and allows it to be X-rayed again. Now one thing just to say real quickly before we get into DR is if you, given the sensitivity of CR systems and how sensitive I said it is to natural background radiation, if you don't know. when the last time a CR cassette was used, I recommend erasing it prior to going up on a portable run with it, right?

If you don't know, go ahead and erase it and you can start over. All right, I'm switching gears now to talk about DR and I'm going to move pretty quickly here. Basically, what we have is a flat panel detector, if I can talk. Think about it as being like the camera on your cell phone, right?

It is a flat panel detector. It has a photoconductor, something that can conduct... light through it, right?

And that's what that means, photoconductor. It lets the light pass through it, right? And the one that we use is called amorphous selenium, and it's abbreviated with the A out in the front, selenium. All that amorphous means is it can change.

As light passes through it, it changes, right? That's what amorphous means in this context. We might also use things like amorphous silicone and charged couple devices.

So... Anytime we're dealing with amorphous selenium, we are dealing with direct capture detectors, and I've said this is the one that is like your cell phone camera, right? It is a direct capture camera, right?

So what it does is it has a thin film transistor array, right? A TFT, a thin film transistor array. That means that there's all these little circuits that are now storing the information that's received.

So with the PSP plate, I said it was a crystal that's capturing the electrons. For direct capture, it is a thin film transistor. It's actually little circuits that are capturing the information.

Right? That's why we call it direct. We do not have to read this out. The minute that the information is received, the transistors capture it and it can start to produce an image. It does not have to be read out.

Right? But this amorphous selenium holds a little charge on its surface. When the x-rays hit the amorphous selenium, it bounces the charge back and forth to the transistors, and they read that out as a picture, right? To go through the process one more time, x-ray photons exiting the patient, right, strike the amorphous selenium.

They are converted into an electrical signal by electrons being bounced around, and that's detected by the TFT array. So the thin film transistor is really the active part here, and it's present in both the direct systems and the indirect systems, right? All that matters is what we're doing with the x-rays.

Are they being bounced around by electrons or not? So... It's on a substrate. That substrate is generally made, and this is going to be extra confusing, out of silicone, right? I've said it's amorphous selenium, and it's sitting on silicone.

So think about the motherboard inside your computer, that's a silicone plate, right? That green stuff that's coating it is silicone. We call, you know, that area outside San Francisco, Silicon Valley, right? Why?

Because they're doing computer junk there. Right, lots and lots of computer junk. So, it is just used as a thing that can support the components, the transistors in this case, as well as insulate for conduction of electrical signals. So, there's these little tiny transistors and they are basically what is capturing the pixel information. Right, the surface of each transistor is what's capturing.

the pixel. So the smaller I make those TFTs, the smaller the pixels get. Here's an example of what we're talking about.

So the x-ray strike the absorber, that amorphous selenium, it transfers information to this array of the TFT. This is a blow-up of a single TFT. So it has little sensitivities, further sensitivities. within the TFT. All right.

A million plus pixels can be read and converted to a composite digital image in less than a second. That's what's happening every time you snap a picture with your cell phone. That's what's happening every time you take an x-ray with a digital imaging system.

It's very quickly reading it out. It's not using a laser or anything like that. You just take the picture, the TFT captures it, and you can move on with your life.

All of that though is still stored in data columns and rows, which is what we call a matrix. It's still going in the sock drawer, and the size of that matrix depends on, or the spatial resolution depends on the size of that matrix. Alright, let's talk about indirect conversion or indirect DR, right?

This is a two-step process. So the X-ray photons strike a scintillator that produces light. Then that light is captured, right? So in this case we are going to use amorphous silicon.

So this indirect conversion involves an additional step and so there's an additional kind of area for interference or noise. So in general these systems are are not considered as quite as efficient as direct capture. But the same process is being happened in terms of readout. It's still being trained on a TFT array, and that TFT array is what's feeding the information into the matrix that's producing the picture.

So in this case, just to stress it, we've got incident X-ray photons. They hit the cesium iodide scintillator, which then passes that through the amorphous silicone, right, to be read out by the TFT, right? So that, I may have misspoke earlier. The thing that's actually producing the light is cesium iodide, CS lowercase i, right? Cesium iodide is what's producing the light.

So X-rays strike the cesium iodide. It produces light. The light's passed through amorphous silicone to the TFT array. So we're using amorphous silicone inside the detector in this case in order to basically conduct the light towards the TFT array.

The reason we like cesium iodide is because it has these little light tunnels in it. Like here's a very, very small picture of what the cesium iodide crystals look like. They have these little tubes to them.

So as they produce light... producing it in a single direction toward the amorphous silicon right towards the TFT array they're also very very small right so they allow us to pick up on very very small things like x-rays right So the two points of this is they allow for rapid detection of the x-rays and they also reduce a quality that we call turbidity, right? Which means that kind of light noise, right?

Anytime I think about turbidity, I think about, I mean, have you ever been camping outside of a city and the light, the sky towards the area of the city looks kind of purple, right? That's what they call light pollution from the city. That's exactly what we're talking about with this.

The cesium iodide crystals are basically reducing the amount of light pollution by just channeling it in the direction that the light needs to go. It's not going every which way. The final thing that we can talk about with Direct is charge coupled devices.

These basically use fiber optics. They pass the information down fiber optics to where they're received and stored on the matrix. So we'll talk about them real briefly. They're generally low cost, although they are kind of coming back on the market. We might also talk about CMOS, and these are complementary metal oxide systems.

Largely, these have gone away. I've only seen one in my lifetime. This is the part where I've asked you to really pay attention, right, as we talk about detective quantum efficiency, right?

And I know we're close to the end. This is talking about how efficiently the X-ray input signal is converted to useful output information. One way to think about it is the fuel efficiency of your car.

How well is the gasoline converted to you getting down the road? When we talk about DQE, we're talking about fuel efficiency. We look at a number of things when we think about DQE because things can affect...

just how much the information was useful, right? So things like noise affect the DQE, right? The way that we talk about the effect of noise on the detective quantum efficiency is the signal-to-noise ratio, the SNR, right? So signal is the useful information, noise is the not useful information. We want a high SNR, a high signal-to-low noise ratio, right?

The more signal you have, the less noise there is, therefore the higher quality of the image. This also has some bearing on contrast, because if we have noisy systems, that reduces our contrast resolution. As we're thinking about DQE, these systems that have a high DQE, we also want to maintain that they have a wide dynamic range. that allows for a wide range of capture.

So we don't necessarily want them to be noisy systems. So we have to figure out a way to have both a high DQE while at the same time being able to image small low contrast objects. The easiest way to have a high DQE would be to have a gigantic detection surface. But the problem with the gigantic detection surface is there goes your spatial resolution. Right?

So how do we make sure that we're receiving all the information that's being transmitted while at the same time receiving it on a very, very tiny surface? So what we're talking about is really the state of the art, right? How far can we push this technology? When we talk about detective quantum efficiency, we're talking about a whole lot of parts, right? The signal-to-noise ratio, the spatial resolution.

the contrast resolution. But rather than get down into the weeds, I just want to emphasize that right now, a high DQE is what's preferable, and we can define it as the ability to image both small, low contrast objects. So high DQE means high spatial resolution and high contrast resolution. Let me slightly rephrase that, I'm sorry.

I'm sorry. High spatial resolution, and this is going to sound weird, but a high, low contrast resolution. A high, low contrast resolution.

The ability to differentiate low contrast objects, right? The reason I'm making that distinction is because another way of talking about spatial resolution is just to talk about... high contrast resolution, right? Spatial resolution is measured by objects having high contrast, right?

So high spatial resolution and then a high, low contrast resolution, the ability to differentiate objects. that have low contrast differences. So...

This technology, the improvements that we've had in both indirect and direct capture DR, have made the DQE of these systems higher than CR. That's why Congress and others have said, get rid of your CR systems. Everyone needs to adopt DR, right? Because this is an easy thing to quantify, and politicians aren't that bright, so they like things that are easy to quantify, right? We'll leave it at that.

So, going back to the spatial resolution question. The physical characteristics of the detector influence spatial resolution. How big that TFT array is affects spatial resolution, right? In general, we are up against the limit.

Because as the pixel size decreases, right, the amount of signal that we can pick up decreases. So, as pixel size decreases... the DQE is decreasing. So this is not necessarily a bad thing, though, for a number of reasons, primarily because there's going to be... Well, let me put it like this.

It's the limit, right? How much can we decrease it without completely losing the signal, right? Because as we decrease it, the signal-to-noise ratio is dropping, right?

So, these physical components, as the pixel size decreases, do we have a better spatial resolution? Yes. But are we also affecting our signal-to-noise ratio?

Yes. All right? So that is the bind, that we're up against the limits of what the technology is capable of doing. Also, if we try to process the signal over and over and over again, we can introduce additional noise into the signal. We can do processing algorithms to improve the image, to get rid of noise.

We know what shape noise is, right? So we can process it out, but eventually it starts to affect, in general, image sharpness. So we're back to that question of pixel size versus matrix size. There's a lot on this.

That's what I want to point out to you. And that's why I keep talking about this over and over and over again. A lot connects on this question of the sock drawers, right?

And I've said that if I have a chest of drawers, it's the same size, right? But there's more drawers in one chest than the other. Who can store more socks? The answer was the drawer.

The chest of drawers with the most drawers, right? But we start losing socks if we make the drawers too small, right? What happens if we make the drawers smaller than the socks? That's kind of the rub, if you will.

That's what I'm talking about with DQE. The amount of resolution in an image is determined by the size of the pixel, right, and the spacing between them. The fancy term for that is the pixel pitch.

So more and more smaller and smaller pixels produce greater spatial resolution. The way to have more and more smaller and smaller pixels is to have a larger matrix right, so they're inversely related as Pixel size decreases your matrix size is increasing I Will be saying that a lot right the larger the matrix the larger potentially the size of the image Stored right and the greater the amount of storage space needed All right, the more information is being stored All right, this is probably one of the nerdiest things that we're going to talk about today. So if you didn't think it was nerdy enough, we're going to completely nerd out now with the Nyquist frequency, right? This is basically just saying that if you're trying to detect something, right, you need twice the signal for whatever you're trying to detect.

You need twice the signal. Think about it like someone, like you're not quite sure what someone's saying. It's really windy outside and you're not quite sure what someone's saying. So you ask them, hey, what did you say? The Nyquist frequency, this theorem is saying you're more likely to accurately hear what they say if you ask them to say it twice, right?

Think about it like that. It's a windy day outside. It's noisy outside. Hey, what did you say?

Right? So if we want good information, not only do we have to have small pixels, we need two times the number of pixels of what we're trying to see. Two times the number of pixels of what we're trying to see. That's going to be the best way to reduce noise while improving spatial resolution.

Okay, exposure, latitude, and dynamic range. We've kind of visited this already, but we will give it one last kind of go. Exposure, latitude is just how broad from overexposure to underexposure can we still get a good picture.

The exposure, latitude of digital imaging systems is huge, right? Thousands of times the exposure, latitude of film, right? The dynamic range is the receptors ability to respond to different exposure levels.

So they're closely related concepts. The one is talking about how much of the signal can still give me a picture and the other one is talking about how much of it can respond. So they're basically saying almost the same thing. A lot of times we use exposure indicators to determine the exposure acceptability.

That's what I'm asking you all to do on your digital. So in a few minutes people are going to be heading into the lab and I'm asking you to write down S numbers as a way to tell me whether or not it was an appropriate technique. So if the image appears modeled, we have less than 50% of the desired amount.

So we need to increase the signal by at least twice. That's from the Nyquist theorem. So we can no longer look at the picture on the monitor and determine if it's under or overexposed. We have to rely on an exposure indicator to tell us that, right? And there's a lot of different ways that they can be calculated, which leads to confusion.

If you understand it properly, it's a good tool. If you don't understand it, it is actually going to work against you. So there's been calls for us to have a universal exposure indicator, and that's what we're talking about when we talk about the deviation index. It's basically a simplification of the existing exposure indicators that allows you to determine, just kind of thumbs up or thumbs down, was it a good picture.

All right, let's talk real quickly about monitors. They also have matrices and pixels, right? Inside the monitor, there's a matrix and a pixel. So when you're looking at the surface of your phone, your readout display, that's a monitor. It has a matrix of pixels.

that are reading out information to you. In general what we do is use our LCD monitors, right? And all that means is it just has a polarizer that twists the light to be either emitted or not emitted.

That also affects spatial resolution, right? So depending on the size of my monitor, I can have better or worse spatial resolution. The main place that we see a problem with this is the CR readout station. where I'm looking at the monitor there to determine if it's a good picture or a bad picture versus what the radiologists are seeing. Their monitor is much nicer than our monitor.

So if there's problems with it, they're more likely to see it. One way to think about it is like we're looking at the R on the 10x10, and they're looking at it at the 100x100, right? If there's a problem, they're much more likely to see it.

We've talked quite a bit about contrast resolution. But what I'm talking about here is the low contrast resolution. It's the difference between the maximum and minimum luminance of now the monitor, right? So it does impact things at the monitor side. And we have all sorts of specifications for how that's supposed to be applied.

The reality is, is though... We can only see about 30 shades of gray. The monitor can display close to 256 different shades of gray.

That's the minimum. All right, the final piece of this is informatics, which just means how information is dealt with. Most of this you all have seen before, but the HISS is the Clinical Information System.

This is everything that relates to billing primarily or patient information. So what insurance the patient has, it's in the HISS, right? It's what the...

people at the front desk need to know. That information, like the patient's name, is communicated via an HL7 connection from the front desk computers to our imaging computers, right? So if you ever have a technologist that has to manually enter information somewhere in the process, chances are they do not have an HL7 connection, right, at that computer. There's a radiology information system, and this is largely, for us in Baptist, used to check patients in and out of the... ER and places like that.

We could say, yeah, the exam's been done, and it stores it along with other information. There's DICOM, which is that universally adopted standard for transmitting information that's medical imaging information, and it's tagged with a unique identifier. That's what we're talking about when we talk about accession numbers.

And the final thing I think the slide may have gotten clipped would be PACS, that picture archive and communication system, which is where the images are stored in a giant server. Thank you so much.

Transcript for:Understanding Digital Imaging Technologies

Transcript for:
Understanding Digital Imaging Technologies