hi learners it's m from santa nerds and this video is on unit 14 the ultrasound system unit 14 ultrasound system the ultrasound system is the computer transducer and display of the unit the ultrasound system performs very complex activities and as a sonographer you should really know in general how the machine creates our images so this unit will follow all the way through the system from beam formation to display on how the image is created and then also discuss some details related to each step now the next page will show you a map of the ultrasound system and all of its components that we will discuss in this unit some of these topics will be discussed further in detail in their own units and discussions surrounding modern technologies and more resolution will be discussed in a subsequent unit as well so here is the map of our ultrasound system it starts at the beam former which is home to the master synchronizer and the pulsar that sends out the beam or the pulse goes through the tr switch which goes to the transducer which goes to the patient those echoes then return back to the transducer back to the tr switch which take a brief little detour through the beam former and eventually make it into the receiver from the receiver the signal is then sent to the image processor where it will go through the a to d converter into the scan converter and from the scan converter it has a few options it can either go to a d2a converter or it can go directly to a display or directly to an archive from the d to a converter we also have the option to go directly to the display or to an archive so this map here is everything that we're going to talk about in this lecture and as i had mentioned some of these will be discussed a little bit more in detail in the next few units but for the most part this is really how the machine creates our images so let's get into some of those details section 14.1 beamformer the beamformer is the main force behind creating an ultrasound beam when using a continuous wave transducer or a single element transducer really only the pulsar pulsars needed to create the voltage when we use an array transducer which remember are multiple elements on a transducer then we need multiple components to get the job done and that's what we're going to focus on for this unit is looking at the array transducer and how they create their images so starting with the master synchronizer the master synchronizer makes sure that the pulses do not overlap and it's really a big reason that the ultrasound is capable of even creating images is because of that pulsed ultrasound and that off time that we get when we create pulses if the machine did not wait for those echoes to return from each pulse then the machine wouldn't be able to differentiate the echoes where and when they came from and we would not be able to create our image so the master synchronizer is responsible for the waiting it's going to take into account the depth that the machine is set at what mode we're using and it's going to decide at what time a new pulse can be created so remember that death is directly related to the prp and inversely related to the prf as the sonographer changes the depth the master synchronizer is going to recognize those changes working with the pulsar to make sure that pulses are sent appropriately so again within the beamformer the master synchronizer is timing everything correctly the pulser then responds to what the master synchronizer tells it and creates the voltages to be delivered to the transducer so the pulsar is responsible for creating the voltages that are dispersed to the transducer during transmission the pulser is going to create the voltages delivered to the transducer thus controlling the amount of power that the patient is exposed to so if we increase the voltage it means that we're exposing the patient to more power which may increase the patient's risk of bio effects however more power usually means that we have an improved image so let's go ahead and take a closer look at these concepts when a system puts out a voltage the stronger the voltage the stronger the ultrasound power when you start with stronger power the echoes that return are also stronger in this example here we are talking about the output power if we start with a low voltage we are going to send out weak ultrasound power weak ultrasound power is going to result in weak echoes and when weak echoes come back the machine codes them as a dark image so weak lower voltages are going to produce weaker echoes usually creating a darker image compare that to a high voltage coming out of the pulsar means we're going to have a very strong or intense or high amplitude wave those types of waves tend to create stronger echoes and when those echoes come back the machine codes them as brighter so weak echoes are usually dark strong echoes are usually bright and we can kind of predetermine what we're going to get out of the body based on the output power from the pulsar so if we're sending low voltages we're going to get weak out goes back if we send high voltages we're going to get strong echoes back so essentially what we're seeing with low voltages are darker images with high voltages we're seeing brighter images but remember with those brighter images we're exposing the patient to more power which can increase our risk for bio effects so the power emitted by the ultrasound transducer is monitored by the machine by mechanical and thermal indices and we'll talk about this a little bit more when we talk more about bio effects in a later unit but remember as we increase that power we increase the risk of causing bio effects either through heating up the tissue or creating little bubbles that can destroy tissue the output power is adjustable by the sonographer and this is why you need to understand that if you increase your output power you are putting your patient at higher risk typically on most machines the output power can be adjusted from about 0 volts to 100 volts when the power is increased all the echoes returning from the body are stronger keyword all so when the power's increased all echoes returning from the body are stronger when the power is decreased all echoes returning from the body are weaker so as a sonographer you really need to balance how you're going to optimize your picture while reducing the patient's exposure to excessive ultrasound energy it's also important to note that the power itself cannot make an image uniformly bright however it does improve the signal to noise ratio so noise is unwanted echoes that can obscure the signal which are our anatomical echoes in an image and noise will always be in our images regardless of the power put out by the machine and the transducer when the voltages are low and the transducer sends out weak waves the noise might overpower our weak signals but when we increase the power the signals that are coming back are stronger and therefore they stick out more which improves the signal to noise ratio as the signal is stronger than that kind of persistent background noise as we can see in this top example here we're going to have background noise regardless we can see it in both images but if we're sending out a weak signal we're going to get back a weak signal we just can't see that as well throughout the noise when we send out a very powerful voltage we're going to get back stronger echoes and those signals are going to really stand out in comparison to that background noise we can see on the bottom here the noise and the signals are all kind of blending together in this picture not super defined where over on this other picture we really see clear borders we're clear seeing clear edges the signal the anatomical information is much more prevalent in this image so remember with increased output power what we are going to see is an increase in the strength of the ultrasound wave which increases the brightness of our image it improves our snr or signal to noise ratio it's also going to improve our penetration depth because less attenuation is going to occur but it increases risks of bio effects so so far off to this point we're still in the beam former the master synchronizer has told the pulsar to do its thing the pulsar has released its voltage now the rest of the beam is responsible for the phasing of the voltages for electronic focusing and electronic steering so essentially the other function of the beam farmer is to distribute those voltages to the elements how those voltages get dispersed to the elements are really going to depend on the mode of ultrasound or modes of ultrasound that we're using what type of transducer we are using what is the goal where do we have our focuses located are we trying to get some appetization reduce those grading lobes so the beam former is going to kind of calculate all this stuff out and deliver those voltages appropriately to the crystals so in our modern ultrasound systems we are using digital beamformers to calculate the phasing patterns to achieve desired focal depth beam steer appetization pulse patterns that are going to create rb mode images or add in doppler on top of it color or pulse wave doppler and all of this is going to happen during a transmission this is all to get ready to make an ultrasound beam the beam former is also an integral part during reception because during reception the beam former is going to adjust for dynamic receive focusing and dynamic aperture remember both of those include choosing how many elements the machine wants to listen with so it can focus the ultrasound beam as it comes back into the transducer working with the beamformer then is something called a tr switch or a transmit receive switch the t stands for transmit are standing for receive so the tr switch is responsible for diverting voltages in the correct direction when the machine is in transmit mode the strong voltages really need to be sent to the transducer if they were to somehow kind of get misdirected into the machine components it could actually really fry our system so the tr switch has the responsibility to make sure that those really strong voltages are going to the transducer during transmission when the machine needs to switch into receive mode it is the tr switch that will tell the machine we are receiving now and will help to direct the voltages coming back from the transducer to the receiver via the beam former so after the voltages have been told to go to the transducer that's exactly what they do they're going to head to the transducer next now we've already spent a lot of units talking about the transducer and its role in image acquisition now remember that as the voltages leave the transducer they are going to interact with the patient and those echoes are going to return that echoes out of returning are a very very low amplitude echo and then the transducer will change those sound waves in to voltages and the voltages are proportional to the amplitude of the echo waves so the echoes that are returning are very weak so are the voltages that are going to head back into the machine those voltages then kind of go by the tr switch because now it's in receive mode it's going to go into the beamformer briefly and then head to the receiver so now we're at section 14.4 receiver the receiver as the name does suggest is going to get all of those echo voltages the receiver is also known as the signal processor so when the echoes return from the transducer again they go through a few manipulations in the beam former but it's the receiver that's going to do most of the manipulation of the voltages it is in the receiver that a lot of the concepts of physics occurs and so as a sonographer you really should know how you can change things to change what happens in the receiver as we make changes to the machine settings the receiver is going to be responsible for applying those to the voltages and once that manipulation has occurred those voltages then are sent to the machine's signal processor where i'll get ready for the display in the receiver there are five key steps that occur you need to know these and you need to know them in order so the first one is amplification then compensation compression demodulation and then rejection so all five functions occur with every pulse that is sent back preparing the scan line for the display again these five steps occur in this order so take note of the order that they're listed in hint here they are in alphabetical order as we learn about these five key steps organize that most of them have some sort of automatic step plus a step that the stenographer can change so let's go ahead and look at each of these a little bit more in detail now our first step in the receiver is amplification and some literature actually has pre-amplification outside of the receiver as more part of the beam former but regardless of where amplification occurs the first thing that must happen is pre-amplification now remember i said that those voltages coming back from the transducer are super super weak they're really too small for a whole lot to happen so pre-amplification must occur which means that we're going to make the amplitude larger we're going to increase the size of the wave so now we have something to work with pre-amplification is not controlled by stenographer the machine just has to do it so it can manipulate the signal further amplification itself then which is sometimes called second amplification is adjustable by the stenographer there's typically a knob on your machine that when we turn it we'll change the gain applied to the image so if the sonographer increases the gain in the image all the echoes are going to be amplified or become brighter and all means all that means noise and signal so remember when we talked about power when we increased the power it was all the echoes that were increased which improved the signal-to-noise ratio increasing your gain does not improve the snr that is because increasing gain also increases your noise so increasing your gain does not improve your snr but when we increase the gain it does not pose any risk to the patient because we are not subjecting them to more ultrasound energy we're just changing how the machine is displaying it so in these three images here the top image has a very overly gained image everything is super super bright including the noise so remember that gain identically affects all the echoes it's going to increase the brightness of all of them the middle picture has a very nice setting to it things that we expect to be anechoic are anechoic things that have low level grays are the correct level of gray this is what we are aiming for we can also decrease our gain which is kind of the opposite of amplification but we can make the entire picture darker by turning the knob to decrease the gain during pre-amplification and amplification we are changing the intensity that the machine is displaying those echoes at so when we have a change in numbers like we do with amplification we are seeing a change in decibels so amplification is measured in decibels so remember that both power and amplification or gain are adjustable by the stenographer and both can make the whole image brighter but increasing the power increases risk for bio effects increasing gain has no effect on the bio effects so we as sonographers need to follow the principle called alara alara stands for as low as reasonably achievable you should know this as low as reasonably achievable means that we are going to use the least amount of power possible so we don't increase our patient's risk of bio effects but we still optimize our images appropriately what this typically comes down to is increasing your gain first if your image is too dark and decreasing your power if your image is too bright now most of our modern systems really don't allow us to change the power very easily often it's kind of buried in some different menus or under some different knobs and really it's not going to let you change it to an unsafe or dangerous level one of the biggest ways that we can pay attention to what power we are using is using the correct preset presets are usually programmed into an ultrasound system that kind of gives us a good starting point so for example we're not going to use a very strong powerful ultrasound beam on a first trimester ultrasound compared to the power that we would need to ultrasound an adult abdominal exam the preset is going to be one of the more effective ways that you are going to make sure that you are not over exposing your patient to excessive ultrasound energy so in theory again if our image is too bright we need to reduce our output power first if your image is too dark then you need to increase your gain first and again we don't really have a whole lot of options for that power modern systems aren't going to give us a lot of leeway with it so this is mostly theory for your boards versus actual practice in the field more often than not we're really just adjusting our gain up and down because the power has already been set at an optimal strength the last part of this idea though is that if your image is too bright or too dark in one area then we're going to use compensation which is our next section because remember both power and gain adjust all the echoes in the image where compensation is going to allow us to change parts of the picture so after amplification our second function of the receiver is compensation and compensation is special because it can make an image uniformly bright remember that as sound travels through the body it is going to attenuate and with attenuation we get weaker echoes weaker echoes mean darker images so compensation is going to allow the machine and the stenographer to account for attenuation and just like amplification compensation is going to occur in two steps the first compensation is an automatic feature of the machine the machine knows and we do too that attenuation occurs and that typically our far field is going to be a little bit darker so the machine automatically compensates for that a little bit in the far field what's left over then is for second compensation which is performed by the stenographer the sonographer can control where they want compensation to occur so second compensation is adjustable by the sonographer this is really where some of the art of sonography comes in an uncompensated image is going to not be uniformly bright you're going to have maybe a really bright near field with a really dark far field or maybe it's the other way around you have a really dark near field with a really bright far field depending on what structures you're imaging if attenuation hasn't occurred in the way that we would expect so as a sonographer you're really going to use your knowledge of attenuation to either decrease the brightness of the echoes in the near field or increase the brightness of the echoes in the far field to really make it even throughout if we look at these pictures we can see here that we've got super bright near field mid grays in the middle field and then we get quite a bit of darkening in the far field jumping to the bottom picture we've got the opposite problem a dark near field middle gray is in the middle field and then very bright echoes in the far field so by using compensation our goal is to get to this middle picture where everything is very even throughout the image and again that is accomplished through compensation now i said that compensation is adjustable by the sonographer and the sonographer is going to achieve that through using the tgcs now tgc stands for time gain compensation and they are usually represented by sliders on the machine console or somewhat newer units have touchscreen sliders so here on this unit we can see the physical sliders as you move these around you are going to adjust different levels of compensation in the image for example this one has eight tgc sliders so if you're imaging to a depth of eight centimeters each slider is responsible for one centimeter of the image if you're imaging down to 16 centimeters each slider is then responsible for two centimeters of the image when you slide these sliders to the left you are decreasing the gain at that level making the image darker at that level and when you slide them to the right you are going to make that area of the image brighter so a lot of machines do have these physical sliders on them but some newer machines have sliders that look like this where you can touch screen adjust them so regardless of which way you have your tgc format sliders or touch screen the goal is really to use them in a gentle curve or a slope to compensate for that attenuation you really want to avoid zigzagging or moving just one slider over because this is going to create stripes in your picture and that's not really going to improve the quality of the picture in our newer equipment we're really seeing much better penetration of the sound beam even into our larger habitus patients so we're not seen as prominent attenuation in our images however in some of the older machines you had to set your tgc's to compensate for that attenuation in the far field so what ended up happening was a very similar slope as you can see in the image here in the near field or the top sliders we are using little to no compensation in the midfield then we are gradually increasing our compensation and then maxing it out in the far field because that's where our weakest echoes are we wanted to make them as bright as we could to make a really even picture throughout so again we want to use very gradual slopes or curves to make our images uniformly bright from top to bottom now when we use a slope in our tgc settings we are actually creating a very particular pattern that has parts to it so the tgc slope does have these five key attributes your sliders at top are your near gain and when you start to compensate this is called the delay from there we're going to have our slope and when you have reached maximum compensation that is our knee and then our last one is our far gain so remember that the near gain is going to correspond with our top sliders induce a slope going through the middle ones and then typically you're going to have your far ones a little bit further over just some last thoughts on the tgcs then tgcs can also be known as dgcs which stand for depth gain compensation or they can also be called swept gain and then tgcs are a special type of amplification so they also are in the decibel unit you have a little clip here on the bottom of adjusting the sliders is oddly one of those very satisfying things that you're kind of doing as a sonographer it's almost kind of like a grounding position where you get them all lined up in the middle but notice how going through you can make that gradual slope or you can make a gradual curve but never ever ever zigzag those sliders around that is not appropriate use of your tgc's the third function of the receiver is compression now the information that the transducer is getting back is a lot of information all those little echoes and voltages are sent to the receiver for processing and the information that comes back is way more than the receiver can handle so it needs to compress that information into a usable range so first compression which is not controlled by the sonographer first compression is the automatic reduction of information coming in so during this reduction nothing has changed about the value of the information it's just recalibrated for the receiver to be able to process it when we look at compression that the sonographer can change that is going to be compression in which we reduce the number of grays that are available for the display so if we're going something from this 256 shades of gray we're going to compress it we can compress this down into fewer choices blacks are still black whites are still white but you just have fewer choices in between so let's take a little bit closer look at really what it means to compress so we've got a hypothetical example here that if you had a machine that's capable of sorting candy and one machine might be able to tell the difference between a chocolate bar chocolate caramel chocolate nougat caramel chocolate new caramel and peanuts and it can also tell the difference between fruity candies you know the ones that are chewy or crunchy the ones that are sour and sweet sucker non-sucker whatever this machine that's super detailed is kind of like your transducer it's really good at parsing out all the detailed information about the echoes returning from your body so let's put our candy in our sorting machine it goes in and it can tell the difference between everything it has sorted everything out this is very real life because there are truly different types of candies out in the world now we've got to put our candies through the receiver so the next candy sorting machine really can't sort things out as well it might be able to tell plain chocolate from chocolate with stuff in it and maybe it can really only tell things with sticks versus things without sticks so let's put this candy through our receiver candy sorting machine and what we end up getting is a sorting that shows us plain chocolate versus chocolate with stuff in it candies without sticks and candies with sticks now it doesn't all of a sudden mistake a lollipop for a piece of chocolate it just can't sort out those fine details as much so i reduce the options of sorting that's essentially what the receiver needs to do it can't take all that real information from the transducer it needs to compress it into the information that it can handle without cross-contaminating the sorting that has occurred so essentially if the transducer sends back thousands of voltages that could be represented into thousands of difference of grays the receiver isn't going to be able to do that the receiver is going to want to take those thousands of voltages and kind of parse them down into something that could be maybe represented as hundreds of grays it's still going to keep the very large signals large and the small signal is small but we're just going to reduce those options in between just like the other two functions that we've talked about already we do have a first and second compression so remember that first compression is the machine just being able to handle the information coming back from the transducer so that's the first compression the second compression is controlled by the stenographer and again this is usually done with a knob or button on your machine it can either be labeled compression or it might be labeled dynamic range so by changing the dynamic range or the compression you're basically telling the machine to reduce the number of grays that you want displayed when we tell the machine we want a low dynamic range we are saying that we want fewer choices and when that occurs we tend to make the pictures a little bit more black and white where if we increase the dynamic range then we are telling the machine that we want more grays displayed and we see more variants in the grays that are visible so in this image here we can see this is a touch screen off of an iu22 and we have all these knobs sitting in front of the touch screen these are called soft keys and depending on what function you are in the functions of these knobs are going to change so for example right now the machine is in 2d mode and this knob here aligns with the compress so by turning this knob we can change the compression of the machine earlier i had mentioned about the power kind of being buried into things this might be where you have to find like hit the next button here and you might finally find power being associated with one of these knobs so it's just a matter of finding where your knobs are and it's a big part of the whole novology piece of becoming a sonographer on this example we're looking at a ge machine again kind of put into your soft keys uh ge labels there's dynamic range and that's going to align up with this knob that's down here want to point out here's that power output it's at 100 push this knob activate your power output and then you can change the power output so a lot of the newer machines rely on touch screens that have multiple functions within the touch screen you just have to be on the right mode or the right function to be able to get to these features so here's an example of changing your compression as a sonographer the top image has a lot of gray in it note though that we still have whites and we still have blacks but we just have a lot of options of gray in between compare that to the bottom image where we have a lot more of a black and white appearance to it again we still have blacks we still have whites but we've really reduced the amount of grays that were seen it really just kind of takes on a darker appearance a more contrasty appearance more black and white so remember that compression and dynamic range mean the same thing we are going to discuss these a little bit more in detail in another unit but for now you just need to know that they change the amount of choices first compression is not adjustable by the stenographer second compression is and lastly that the units for compression is also in decibels now the fourth function of the receiver is demodulation and this is also known as detection so for a wave to modulate it means that it changes amplitudes so demodulation aims to even out the amplitude changes demodulation is the only function in the receiver that is an automatic process and never controlled by the sonographer demodulation just has to happen so when it leaves the receiver it can be processed more easily by the scan converter and the display so there are two steps to demodulation the first one is rectification where it kind of flips negative amplitudes into positive and then the last one is smoothing where it averages out the amplitudes into one and smoothing is also known as enveloping so this is our original signal that's coming in from the transducer it's gone through amplification it's gone through compensation it's gone through compression now it's at its demodulation function this is the original signal the first thing that it's going to do is rectify the signal meaning it's going to take anything below the baseline these negative amplitude shifts and it's going to flip them all to positive so note how we now have everything above the baseline so that's rectification flipping everything up to positive smoothing then it's going to take the average of the voltages and kind of make it into one so we had stronger voltages in this one so it's going to average to a stronger voltage after smoothing our enveloping this one had a little bit weaker voltages once it's averaged we get a weaker average voltage so rectification flips everything up into a positive smoothing or enveloping then averages them all together to make kind of one lump of voltage the last function of the receiver then is rejection so after demodulation the amplitudes of the signal are all above the baseline rejection then is the process by which the machine will decide what echoes it wants to get rid of because they are considered too weak the goal of first rejection is just to get rid of all that extra noise that's in the image so first rejection is not controlled by the sonographer it's going to happen automatically second rejection is controlled by the sonographer rejection in this case is also known as threshold or suppression and again there's typically a knob on the machine that you can use to increase or decrease the rejection so here again we have an example of a touch screen with the soft keys underneath it here compression and rejection are on the same knob notice rejection is not highlighted so the scenographer would need to push this button in that would highlight rejection and then allow them to adjust it and here's a graphical representation of what's really occurring during rejection so remember after demodulation all of our voltages have been flipped above the baseline and they've all been kind of averaged out well rejection is going to say we don't want anything under this level so maybe the first rejection on the machine puts it out and we don't want voltages that occur anywhere underneath this red line that's really going to eliminate our weakest voltages which usually represent noise found in the picture now as the sonographer is looking at their image they might decide that they want to increase the rejection which would mean increasing the level at which we don't want things at so by increasing the rejection we are now saying we don't want this level of echoes and we don't want this level of echoes in our image we only want this really strong one and the second strong one here so by increasing the rejection you're telling the machine to really get rid of all the low level echoes that are below that threshold and we can see that in the image here this one might actually represent being just getting rid of this first little echo here increasing the rejection a little bit might say to get rid of these echoes we can see that we're getting less noise less speckle in our vessel here increase the rejection even more we start to get rid of even more of the echoes and then lastly if we increase our rejection enough we can really get rid of a lot of those low-level echoes really making the picture nice and crisp and eliminating those low level echoes that kind of distract from what we really want in the image so just as a quick receiver review then remember we have those five steps amplification compensation compression demodulation and then rejection they must occur in that order they are in alphabetical order most of them have some sort of first step which is going to be automatically done by the machine knowing that we do need to account for the physics of ultrasound almost all of them are then adjustable by you as a sonographer except for demodulation they all have knobs or sliders or some sort of machine tool that is going to help you to adjust them lastly then make sure you know what basically they're doing amplification makes the echoes brighter or darker compensation evens out the image compression changes the amount of grays that we can display and then rejection gets rid of those low level echoes all right so we have finished our work in the receiver the signal now needs to head off to the a d converter so section 14.5 a d converter the signals leaving the receiver are still in analog form so to process the signals in a digital memory the data must be converted from analog to digital so this is going to be done in the analog to digital converter which is the adc or the a to d converter also known as the digitizer so when converting the analog waveform to digital it is converted into a number that the digital memory can process further to understand what's happening though from the analog world to the digital world we kind of need to talk a little bit more about analog versus digital values so when we think about analog we know that analog numbers have infinite possibilities so if you think about a ramp think about standing on that ramp you can be anywhere on that ramp and have a different value of your location it'll have a very defined number but just moving just the tiniest little bit will redefine where you are on that ramp analog numbers have infinite possibilities are very real life digital numbers then we can think about are more like steps when you're standing on a staircase you can either be on the first step the second step the third step but you can't be on step one point three five four seven you can't be on step two and a half you can only be on step one two or three so digital numbers then are very finite they have very discrete values there is really nothing in between another way that we can think about this is an analog clock versus a digital clock analog clocks are the clocks that we see in our classrooms they have the numbers all the way around you can see the minute hand the hour hand and the second hand usually going around so those are analog clocks because they can really show you any moment it is very real life being represented so if we're at and we're waiting for it to turn to 2 o'clock we can see every moment being represented on that analog clock in between 1 59 to 2 o'clock however if we're looking at a digital clock it is going to be 159 until it's two there's no 159 point one second 159.11111 second it's going to go 159 and then two o'clock when it changes so again we're seeing infinite possibilities with the analog clock very discrete numbers with digital so to get ready for the digital scan converter the adc has to change those real-life voltages those real-life values into discrete digital values and these values are usually represented in binary to the memory so here we have voltages coming in from the receiver these are analog remember like anywhere on this curve does technically represent a new voltage we just kind of have the average of all those voltages that were sent in so this is analog real life in the analog to digital converter it has to assign a numerical discrete value to these analog waves so we're getting 0 0 8 0 0 6 0 2 0 12 0 0 four and zero these numbers are typically going to be assigned then to a level of gray stronger waves typically have bright white echoes where no information is going to be black or anechoic so the analog to digital converter has assigned a very discrete numerical value to it typically it comes in as a binary number because we are working with computers at this point so eight in binary is this six in binary is this we'll actually go over binary numbers in a little bit here but the idea is is that we have taken analog infinite possibilities and have made them into very discrete numbers that information then is mapped to the scan converter and the machine will assign certain levels of black or gray or whatever in between to the values that have been created in the analog to digital converter right after the analog digital converter is something called the summer and the summer is responsible then for combining all the information into one scan line for the scan converter so if this is one scan line the summer has put it all together letting the scan converter know that this is one scan line so it can map it correctly to its memory so next up we have the scan converter in section 14.6 once digitized the scan line information is sent to the scan converter now there is not an image created yet at this point the machine is still acquiring every single scan line for the final display so the scan converter really provides another place in which information can be processed but now we are manipulating digital information versus analog information so we have a spot where we can do pre-processing functions and processing functions around the scan converter and then we also have the scan converter sending information to the display or to the archive or we might have to go through one more step the d to a converter to finally get to the display or archive so there are a few concepts of the image processor that i just want to cover before we get into the details on these so important things to remember at this step is that the scan converter is also known as memory so if you think about your computer memory the scan converter it's the same idea it's getting the information and storing it in memory pre-processing functions are going to occur in the working memory so while the machine is still live and scanning the working memory is going to continuously be written over in the pre-processing part so if we change our gain if we change our tgc's those are all pre-processing functions and need to be reflected in the working memory so we can see those changes on our screen once we freeze the image we are now in the post-processing function and that is going to be changing the information as it was stored from the memory so remember scan converter is also known as memory once scan converter saves that data stores it in its memory we have switched to a post processing functions and then lastly the da converter is only necessary when the display or technically the archive is also analog our modern systems do not have analog monitors anymore they are more digital monitors so they can accept the information straight from a digital scan converter where some older systems did have analog monitors and they could not accept that information from the digital scan converter so we had to change things back so we'll cover all of these a little bit more in detail over the next few minutes here these are four important things to kind of keep in mind while we cover those details now i had mentioned that our current modern scan converters are digital early iterations of ultrasound machines had what we called analog scan converters and the cool thing about analog scan converters is that they have excellent spatial resolution they could take a lot more information from the receiver and process it for the display as a quick overview of what analog scan converters were basically they could take the information from the receiver and process it so the converter itself was in kind of this vacuum tube that was shaped like a funnel at one end the narrow side was something that we call a little electron gun that would get the information shoot out electrons through the vacuum tube towards the other end which had a matrix or like the silicone wafer sitting at the end and as those electrons hit the different parts of the wafer it would fill these little wafers in with electrons because they had what we call electron buckets and by writing to this little wafer with these electrons it kind of told the machine where the bright echo should be and where the dark echo should be and then from there the display could get the information from the wafer matrix and display it the whole science behind analog scan converters is well beyond the scope that we need to know but just know that we originally did have these analog scan converters and although they had that excellent spatial resolution there were actually a lot of problems with them as well they were very unstable and the image component itself would start to deteriorate over time so we needed something better and that's where we come in with the digital scan converter now the digital scan converters are going to use computer technology to convert the image information into numbers and this is called digitizing so remember we have that a to d converter where it took the analog information made it digital through digitizing so the information that is stored in the memory really looks like a giant checkerboard and in each square it's going to be assigned a string of zeros and ones and those zeros and ones are going to represent a digital number and then the number for the square is processed into a level of gray which is then displayed on the monitor so the digital scan converter offered a lot of improvements over the analog scan converter they're much faster very accurate and very durable but the detail that we can see especially the spatial and contrast resolution are limited by two factors one the number of pixels in the scan converter and two the number of bits assigned to each pixel the scan converter memory looks like a checkerboard and each square of that checkerboard is a pixel so the word pixel is derived from picture and element that's where we get pixel from and each pixel can hold information so for our purposes these pixels are going to hold the information about our ultrasound image now we saw this image earlier and so if this was just one scan line represented in our matrix or checkerboard of our memory each pixel would be signed a number like we are seeing along the side here so this pixel got assigned to zero so when the display goes to read the memory it'll know to put an anechoic pixel on the display when it gets to this box it'll know to put a light gray shade in when it gets to this box it knows to put a little bit darker gray shade in so the pixels in the scan converter the pixels in the memory are assigned a digital number by the analog to digital converter what's important to note about each of these pixels in the memory is that each one can only display one gray at a time we can't split this box into two and say make part of it an 8 and part of it a 3. it doesn't work you can only display one gray per pixel now this is important when we talk about detail in our image so pixel density is going to improve the spatial resolution of an image when we have more pixels per inch we can display more detail so if we have a scan converter or a memory that only has 10 pixels per inch that's not going to be able to display very good detail compared to a scan converter that has 40 pixels per inch and we can see that in our examples here so if all three of these were just representing an inch of our scan converter in the first one we only had 10 pixels per inch and a circle need to be made within that inch look at what we're getting we're getting roughly the shape of a circle but we're seeing very jagged pixelated edges and that is because the spatial resolution the pixel density is not very high in this example look at what we get though when we have 40 pixels per inch now the scan converter can assign very discrete numbers along the edges here we get more definition of our circle we appear to get a smoother line so this really improves the spatial resolution of our image and this really highlights again we can't add more than one gray like we could make this circle very nice if we could split these pixels in half make half red half blue but we can't do that it's all or nothing it's red or blue it can't be both and that is why with our 40 ppi we really get a smoother appearing edge because we have much more detail with those extra pixels in there so when we consider high pixel density in the scan converter we have high pixels per inch so we're looking at like that 40 pixels per inch or more we've got a lot of pixels in there that means the pixels are very small and because of that we can get improved detail in our images so the amount of pixels is one of the first things that's going to determine how much spatial resolution we are going to be able to get on our display the second component of the scan converter is how many bits of memory are assigned to the scan converter or assigned to the memory bit is also a special word made from binary and digit and the bit is the smallest amount of memory that can be assigned to a pixel in a scan converter so remember we have all those little tiny little squares in our checkerboard and they're only allowed to be one color so if we are only assigning one bit of memory then the only thing that one pixel can be is either on or off black or white so that means that it is by stable the bit is either on or it is off and in a digital world it means that it is either assigned a zero or a one and that's kind of what we're seeing in these examples here they can be yellow or they can be blue they can be red or they can be blue they can't be a green to kind of fill this in in a different way with one bit of memory you can either have your pixel off or you can have your pixel on off is assigned a zero on is assigned a one now when we assign more bits per pixel we can start to display more shades of gray and that is because the amount of greys that can be displayed are related to the binary number created from turning bits on or off so again in this example we have one bit assigned to this pixel so the bit can either be off or the bit can be on and we can see that with one bit we can display two shades of gray black and white so one bit of memory can display two shades of gray two to the first power is two this is going to be a key pattern in determining how many shades of grey can be displayed per bit so we are going to take a brief detour into what it means to have a binary number and how we figure out binary numbers so we can better understand how many shades of grades can be displayed by the bits assigned to the memory there is a more detailed video in the workbook and you can do some activities with converting decimal numbers to binary binary to decimal after watching that video i am going to go over the basics of binary so we can keep the conversation going about how we figure out how many shades of gray can be displayed so to understand binary though we are going to first take a look at the numbers that we do know our decimal numbers so numbers like 15 45 324 are numbers based on ten digits zero to nine so zero one two three four five six seven eight nine that's ten digits if we look at the number fifteen we know that that is one ten and five ones if we look at the number 45 we know that's four tens and five ones 324 is three hundreds two tens and four ones and so we can see in this chart here that if we expand out all of our places we can say that there's three one hundreds that means three hundred two tens means twenty four ones means four and if we add three hundred plus twenty plus four we get three hundred and twenty four now the other thing that i want to point out that's going to be helpful for understanding binary is that each of our placeholders is based on 10 raised to a power so 10 to the 0 power is 1. 10 to the first power is 10 ten to the second power is one hundred ten to the third is one thousand ten to the fourth is ten thousand and so on so by raising ten to a power we get a new placeholder so keep that in mind now as we talk about binary so our numbers before are decimal numbers and decimal deci stands for 10 decimal numbers tell us we had 10 digits to work with binary numbers are only based on two digits 0 and 1. and we can convert decimal numbers into binary numbers if we learn what the placeholders are so for ultrasound physics you really need to know basically what 2 to the 0 is through 2 to the 8th so just like we had ten to the zero was one two to zero is one but now we have two to the first is two two to the second is fours two to the third is eight two to the fourth is sixteens and so on all the way up to two to the eighth is the 256 placeholder column and remember with our decimal numbers for each placeholder we raised 10 to a power and then we had 10 options that we could express that placeholder with 0 to 9. with binary we raise 2 to each power to create its placeholders but then we can only represent each placeholder with two digits a zero or a one so really once you know what your placeholders are in binary you can either have that number available or you don't it's a zero not available one available so for example if we put in 0 0 0 1 0 0 1 1 1 that's actually 39 in decimal and that is because we are adding 0 256 0 128 0 64's 132 0 16 0 8 1 4 1 2 and 1 1. so if we add 32 plus 4 plus 2 plus 1 we get the decimal number 39 so here we have another example of a binary number again if we just place those into our placeholder columns all we need to do is add up the numbers anytime there is a one in that placeholder so we have one 128 one 64's and eight and we add those together and we get 200 we don't have an on number or a value in the rest of our placeholders so we're not going to add those numbers in so by knowing how binary numbers work we can see then how the bits are assigned either a zero or a one and then by adding bits together we can make more shades of gray and when there's a finite amount of combinations of the bits that means there's a finite amount of grays that can be displayed per the bits available so by turning a bit on or off the pattern it makes with the other bits are going to make new numbers therefore making a new shade of gray so the number of shades of gray a system can make can be calculated by taking the number 2 and raising it to the number of bits so here we have one bit two to the first is two we can have black or we can have white if we apply two bits of memory for each pixel we now can display four shades of gray because two squared is four so we can have both bits assigned to zero which would be a black we could have one bit assigned zero one bit assigned one that might make a dark gray we could have one bit signed one the other bit assigned zero that might make a lighter gray or we can have both bits assigned one which would make a white when we add three bits of memory in now we can display eight shades of gray because two to the third is eight remember it's two times two times two so two to the third is eight so all three bits can be zeros which would be black or off the first bit can be a one then we have the other two bits at zero or off dark gray we have zero one zero a little bit lighter gray one one zero a little bit lighter 0 0 1 you can see that we are going through all the different combinations of either on or off through the bits to make those different grays so 0 0 0 is 0 in binary 1 0 0 is 1 in binary 0 1 0 is 2 in binary 1 1 0 is 3 in binary and you can see then for whatever number that binary is making it's going to get mapped to a certain gray and then that certain gray shade will be expressed by the pixel usually when all the pixels are off that is your black when all the pixels are on that's going to be your white and then you're going to have variances in between so if we keep going with our pattern if we have four bits then the machine can display 16 shades of gray because 2 to the fourth is 16 or 2 times 2 times 2 times 2 equals 16. and so we can see here all the different patterns that we can get by either turning a bit on or off and then all the combinations that we can make by turning them on and off and making different patterns and so by making those different patterns we are assigning different binary numbers by assigning different binary numbers we are getting different shades of gray so a 4-bit machine can display 16 shades of gray so do you need to be able to do binary for your boards probably not but it's good to understand the concepts of why we're getting there we can't display more than black and white if we only have one bit of memory and that is because we only have on or off that's buy stable so number of bits matters and it matters for how many gray shades you can display so you have a couple choices recognize that you can raise two to the number of bits in the memory so two to the third to the fourth to the fifth if you know how to calculate that out you can do that to understand how many number of grays can be displayed or you can memorize this chart most of our modern systems then do display 256 shades of gray because 2 to the eighth is 256 meaning every single pixel in the scan converter has eight bits of memory assigned to it and there are 256 different combinations that those eight bits can be either on or off zeros or ones to display one gray in the pixel and mentioned at the beginning of talking about scan converters that the facial and the contrast resolution is determined by pixels and bits and that is because the number of grades that can be displayed is going to determine a system's contrast resolution if there are more grays we are going to have better contrast resolution so remember one bit can only be black and white two bits can display four shades of gray four bits can displayed 16 shades of gray and eight bits can display 256 bits of gray so we are seeing much more contrast resolution in this image compared to this one which is very contrasty and we're losing a lot of the detail so for your boards i would say that one of the more important pieces of all this is to remember that 8 bits is what most systems are and that that displays 256 shades of gray interestingly though most humans can only really see about 30 shades of grey so we're really not even able to appreciate most of those grays that are being displayed but that is how most machines are set up i did mention in the overview of the scan converter that pre-processing and post-processing are functions of the image processor that occur kind of on either side of the scan converter pre-processing occurs when the scanning is still live so if you're scanning and changing parameters or if you're changing how the machine is scanning and you can immediately see it reflected in the image on your display you are in pre-processing mode you are still writing to the memory rewriting because you are gathering new information acquiring new data and preparing it post-processing is then going to occur when the image is frozen so up until the image is frozen the information regarding the scan lines is just again continually written over and over again once you freeze the image the machine stops acquiring information and the scan converter switches into read mode during read mode the information is what it is it really can't be changed unless you're performing post processing functions we're going to talk a lot more about image processing in the next unit so we are going to put some of this discussion on hold until then the last part of the image processor that may or may not be present depending on the system is a d to a converter so when the information comes back from the transducer remember we had very weak voltages and typically it would go through amplification in the receiver and all the other processes but it was still really susceptible to being contaminated by outside electrical interference so changing the signal from analog to digital reduced the susceptibility making it really more stable as it was processed through the scan converter the problem is though that if you had an analog display connected to your digital scan converter the analog display couldn't read the information so after the scan converter it had to be converted back to analog so it would be correctly displayed on the monitor so in general the process from transducer analog information to the display depends on what type of display you're working with so if you have a digital display you're going to get analog information from the receiver it's going to go to the a to d converter digital information goes into the digital memory and from there a digital display can take that information and use it however if you are using an analog display then after the digital memory it's got to go through the digital to analog converter and from there the analog display will use that information section 14.7 display so now that we've mentioned the display let's talk a little bit more about what it means to have the display and how it affects the image creation so original units used basically really old televisions with cathode ray tubes to create the image and if you have some older study material for the fpi you might see a section in there on cathode ray tubes however that has been removed from the spi at this point so we don't need to cover what a cathode ray tube is but if you are curious it is basically those really old tvs the big monitors they were heavy uh kind of have that like bulgy glass looking front to it so much older versions of what we have currently now most of our modern systems are going to use some sort of flat screen computer monitor which is going to allow for more lines on the display faster refresh rates and really blacker blacks so it's going to use lcd or oled technologies to display the images that we are creating from the system but of course we always have to learn about what early ultrasound systems were so we can kind of see where we've gotten to and way back when ultrasound system started the displays were considered by stable and now we've heard this term before we talked about it when we were talking about pixels the bistable meaning it could be on or off black or white and that's the same idea with those old ultrasound system displays if they were by stable they could only display black and white pictures no grays just black or white so here's an example of a black and white picture that was displayed the large b in the middle here is the bladder this is the uterus here and then the rest of this is just bowel but because you can only do black or white there isn't a whole lot of detail in this image compare that now to our current day monitors that can display 256 shades of gray we've got a nice black anechoic bladder we have the uterus we can see the endometrial lining in here we can see different shades of gray representing the bowel there's just a lot more detail in our images now because we have more options we're no longer limited by what the monitor technology is speaking of monitor technology though almost every single monitor your tv your computer monitors your ultrasound screen monitors are all going to have their own controls to adjust different settings remember that whatever you change on your monitor on your machine is only true for your monitor and for your machine none of those changes are going to be reflected in your pictures because they are not connected to the image data information themselves it is just what's on your machine so if you have a cell phone and you like to change it into night mode so like 10 o'clock it kind of changes colors into like not as much blue light if you're looking at your phone at 10 o'clock at night your phone's gonna be in night mode but not everybody puts night mode on their phone so somebody else's phone at 10 o'clock at night might look very normal your personal preference for your own screens display is where it ends none of those changes end up in your pictures but that being said you still have to have your monitor controls set appropriately to visualize the pictures appropriately so two things that you can change on your monitor are contrast and brightness contrast is going to again determine how many grades are displayed on your monitor or brightness is going to determine how light or brilliant the grays in the image are going to look so i just have an example here again if you've ever looked at your computer or look at your tv screen you usually can change a few things around on your brightness and your contrast on your image but again remember anything you change for your monitor is not displayed on your images if you change the brightness of your monitor to be really really low but then use a whole bunch of gain to counteract that in your images everybody else is going to see overly gained images just because you can see a nice picture on your monitor does not necessarily mean it's going to be true for everyone and in fact that happens quite often there's been many times i think my pictures look great while i'm scanning on my ultrasound system and then i get back to the tech area look at them on the computer and they're like super dark or super bright and that's just the difference of monitors and how they look and how they're displaying the ultrasound data another concept that we need to know too about the scan converter and the display is that during scanning when the transducer is gathering information it kind of gathers information a little bit more in a vertical mode vertical mode is our scan line so scan lines are what are sent to the receiver that's how the scan converter is going to get them in those vertical scan lines now when the scan converter maps those scan lines onto the big checkerboard into the pixels it is doing so so the display can come back through and read things horizontally so again our scan lines kind of are a little bit more in a vertical orientation this information is going to come back to the scan converter and it's going to assign different numbers different grays to each of the squares but when the display goes to read from the scan converter it's going to read side to side instead of in that vertical orientation so that's a big reason why we have to have the scan converter so that the display can translate that information in a way that it can use it once an image makes it onto our display then we can actually interact with that image in a few different ways we can measure things and we can annotate and we can put arrows and all sorts of things so to measure what ends up happening is that the display is going to include range marker dots and those dots are going to align with pixels in the scan converter and the scan converter knows what depth these pixels came from and how they got mapped into the matrix so when we pull up our calipers and place them on the monitor that's going to align with a range marker dot the machine is going to recognize where it's at in comparison to that range marker dot and then be able to give us a depth or if we put two calipers on then we can do a linear measurement modern monitors are also capable of displaying colors so now we can see colored doppler information when we use that tool most of our modern systems use lcd screens and those lcd screens have over 700 000 elements on the screen that are capable of not only those 256 grays but colors on top of it so systems that are able to display color are technically 24-bit systems because they have eight bits of memory assigned to each primary color of light red blue and green so those eight bits for those three colors means that we are at a 24 bit system and with that 24 bit system using the red blue and green we can display over 17 million colors per pixel on the display section 14.8 storage so the last step of the process is to store the images taken for an exam storage can either be digital or analog so a digital analog converter might still be necessary even if the monitor is digital now the main types of output storage are going to include the internal hard drive on the machine itself a usb drive a dvd or a cd using paper or packs typically after you finish an exam you're going to end the exam and that exam is saved directly into the internal hard drive of the machine now the internal hard drive of the machine are limited the machine will self-delete exams after a certain amount of weeks or a certain amount of storage has been taken up usually there's enough on there for at least a few days worth of exams depending on how many cine clips and all that that you're taking after you're on the image and it's saved into the hard drive on the machine most hospital and clinic systems are going to send those images directly over to pax we're going to talk about packs a little bit more in detail here in a second pax is a large server in which all those images are going to be stored on our other options do include a usb which can be plugged in directly to the machine you can export your pictures onto the usb or you can export pictures onto a dvd now most computers these days don't have dvd drives so usb is becoming a little bit more popular the other thing you need to be careful about with usb or dvd is how you export your images again we're going to talk about pax and dicom images dicom images are very specific to the pacs server and most computers cannot view those images so make sure that you are exporting your images in jpeg format so that they can be opened up on your basic personal computer now the other big thing that we often see in the ultrasound world are baby pictures those are typically printed out with a thermal printer that's connected to the machine and those are usually used as keepsakes for the newly expected parents so these three storage systems are pretty straightforward we're very familiar with these so let's take a little bit closer look at what it means to use the pax system so pax is an acronym pac stands for picture archiving and communication system and pax is a place where images and other medical information go to be digitized and then stored typically on a really large computer network and having a packed system is super helpful has a lot of advantages you can have instant access to old images the images are not going to get ruined over time and you can see those images from remote sites you don't have to be at the pac system to be able to see them so here we are at our machine we end the exam the exam gets saved on the hard drive temporarily until it falls off or has to be deleted but those images are definitely going to go to the pac system once they're in the pac system the radiologists can access them the cardiologist can access them they can create a report based on the images that got sent to pax you as a sonographer can go back to another computer and review your images and really the nice part about this is we're not making films of these that need to be stored somewhere they're not going to get lost they're not going to fade over time they're stored digitally in a computer system takes up very little space very little consequences to using it really only positives to using the pac system the pac system however likes to use a certain type of formatted image and that is going to be a dicom image dicom is also an acronym and it stands for digital imaging and computers in medicine so dicom images have to follow certain rules because these images are going to be used on multiple systems so it's the digital imaging part of it it's going to be coded in a way that it can be used on any computer that is used basically in medicine when an image is saved in a dicom format it should work on all devices that accept dicom and allows for better communication between systems and so this is where i was saying you want to be careful about exporting in a dicom format versus exporting in a personal computer format most people's personal computers cannot view dicom images and that is the end we made it all the way from beamformer to storage we now know how our machines handle all that data transform it into something we can see and something that we can review later in our pack system so make sure that you are going through your activities there are quite a few of them because we did cover a lot of steps in this unit and then make sure to go through your nerd check questions to see how well you recall all the information