hi learners it's m from sono nerds and this video is on unit 20 doppler application unit 20 doppler application so now that we have a basic understanding of the physics and instrumentation behind doppler ultrasound this unit is going to focus on more of the clinical application of doppler we will briefly look at what we can see in a waveform how to identify color flow and direction in a vessel and most importantly how to identify artifacts created by doppler settings and then how to fix them section 20.1 spectral tracing the spectral tracing is the graph that appears on the bottom or side during duplex and triplex imaging the resulting graph will show echoes that are returning from the sample volume or gate the echoes are the reflections from blood cells that have traveled through the gate and returned a frequency that is either more or less than what was emitted through the fast fourier transform and calculating velocity the machine can now display diagnostic information for the sonographer and clinician to analyze recall that when the pulse wave doppler has activated a scan line the gate and angle correct will appear on the screen the scan line and therefore the gate are mobile so this means that you can place the gate anywhere you would like this is a huge advantage of pulse wave doppler small gates record fewer blood cell reflections thus creating a thinner spectral tracing where large gates record many blood cell reflections and can make the spectral tracing fill in more due to more varying velocities in this example the gate is well placed it's in the center of the flow and the gate is also small the resulting spectral tracing shows similar velocities of blood flowing through the gate creating a clean thin waveform notice that the angle correct is placed parallel with the flow telling the machine how the blood is flowing in relation to the scan line is the sonographer's job if you place the angle correct incorrectly then you are providing the machine with incorrect information and velocities will be incorrectly calculated so taking a look at this example again we have the scan line we can see the gate here and the angle correct that angle correct and the gate are placed in the center of the vessel where blood flow is expected to be the fastest we also have a relatively small gait and because of that what we are seeing are the reflections of the red blood cells that are moving through that gate all of which are traveling relatively at the same speed because again it's parabolic flow so we are getting a relatively thin clean waveform the top image is showing us a gate that has been placed near the edge of a vessel the spectral tracing is now showing more variance in the velocities of red blood cells thus there are more specks in the tracing near the baseline this may mimic turbulent flow but what it is really showing are how the red blood cells are flowing slower at the edge compared to the ones that are flowing towards the center a wide gate like the bottom image will also show a similar waveform so on this top image here we can see the gate has been placed near the edge of the vessel where we expect slower red blood cells to be moving they're going to be moving faster and faster as they get towards the center and we can see that in our spectral tracing the reflections that are near the baseline are representing those slow moving red blood cells where the ones that are higher in the spectral tracing are the faster moving ones when your gate is too close to the edge you're going to get more variance in the velocities and the machine is going to show that to you in your spectral tracing in this bottom example we can see that the gate has been opened very wide so not only are we getting those fast central reflections but now we're getting edge slow reflections we're actually getting some interference even from the vessel wall and we can see that in our waveform again slower reflections towards the baseline fast reflections up higher and you can see this little white thump that is in each beat that is actually the vessel wall moving through the gate the spectral waveform has a lot of information that it can tell us we can get even more information when we use machine tools to measure different aspects of the spectral tracing deep analysis of the spectral waveform is more specific to cardiac and vascular technologies and not necessary for physics but let's take a look at some of the basics as we will need to know these terms for discussing artifacts later one of the things that we can see in the spectral waveform is the baseline the baseline is the zero point on the scale and it's going to demarcate the switch between positive and negative velocities the baseline can be moved up and down with a knob on your machine in this image we have the baseline labeled as number one it is this kind of gold orange bar that comes across and as we follow it all the way to our velocity scale we will see that it matches up with the zero point above it is negative 40 below it is positive 40. so it is the divide between the negative and positive velocities the y-axis is the vertical portion of the graph this is where the velocity information is displayed remember y-axis velocity information this example uses centimeters per second but some machines will use meters per second notice how this example has negative velocities displayed above the baseline and positive velocity is below this can be inverted with a button to follow industry standards for displaying velocity information the scale of velocity is also adjustable by changing the prf of the doppler scan line so we have two ways in which we can adjust the doppler scale one is an inversion where we can flip positives and negatives and the second is to adjust the prf which adjusts the scale we'll get into more of that later so in our example here number two is pointing out the y-axis or the velocity scale these are velocities in centimeters per second number three is the x-axis the x-axis is the horizontal portion of the graph on the x-axis we display time so as doppler information is being recorded the waveform will kind of scroll or refresh over time and this is the blood flow over time through the gate now how fast the time goes by can also be adjusted through a knob called sweep speed so in this example we're showing the x-axis as number three indicating that it is all of this horizontal portion going across the bottom of the spectral tracing you'll notice these little tick marks on the bottom these do represent time hash marks mention that you can change how fast the time goes by with a knob called sweep speed if you increase your sweep speed you will see less waveforms because it is representing less time where if you decrease your sweep speed you will see more waveforms because it is slowly refreshing or building the x-axis the fourth thing that we can see is the peak systolic velocity the peak systolic velocity or psv is going to be the fastest velocity recorded on a pulsatile waveform like we see here the psv is going to correspond with the ventricular contraction of the heart so when determining the scale for velocities it's always good practice to make sure that all of your psv can be seen and is just below that maximum velocity this will make it easier to measure in this particular waveform we can see a fifth important piece of the waveform called the end diastolic velocity the end diastolic velocity or edv is the speed at which the blood cells are flowing during ventricular relaxation it is typically measured right before the ventricle contracts again when we compare the psv and edv together it actually tells us a lot about the organ that is receiving the blood if it has low resistance or high resistance will tell us are the arterials contracted or relaxed and it will tell us more about how that organ receives its blood now for example the waveforms that you are seeing in this image are of the carotid artery and the carotid artery is bringing blood to the brain and the brain always needs blood flow so we consider this a low resistive waveform it always needs forward moving flow you'll see an example later in the lecture in which i show you a triphasic waveform and that is taken from the leg the limbs don't always need blood they just need enough to keep oxygen going to the cells to keep everything alive and keeping the metabolic processes going again waveform analysis is going to be much more pertinent to the person studying vascular and cardiac applications but the high and low resistance does tie back into our hemodynamic studies the last thing that i want to point out that we can see in the spectral waveform is something called the spectral window the spectral window is the area under the peak systolic velocity so in laminar flow the spectral window is what we call open there are going to be no reflectors in the window the very thin line in the spectral tracing represents those blood cells that are all flowing at similar velocities and so they all accelerate at the same time and they all decelerate at the same time creating that window however in turbulent flow the spectral window does start to fill in and that's because red blood cells are flowing in multiple directions and speeds so the spectral window can falsely be filled in if we use incorrect doppler settings or be truly filled in and be diagnostic in the setting of turbulent flow and again the spectral tracing can tell us more about the type of vessel that we are in depending on what we are seeing these three examples were taken from our hemodynamics lecture in which we talked about pulsatile or arterial flow in the top image more venous or phasic flow in the middle image and then steady flow on the bottom next i want to get into a little bit more of the doppler controls things that you can change on your machine to adjust the pulse wave spectral tracing knowing how these affect the spectral tracing will also help you with your clinical knowledge first up we have baseline now the baseline we talked about as that orange horizontal line that represents the zero mark and this is actually adjustable and we can move it up or we can move it down now this is just going to change how much of the scale can be displayed on either side of the baseline you want to move the baseline so that the side in which velocities are being displayed on can be displayed appropriately in this first example we have the baseline relatively high in the spectral tracing window and that is because we have more velocity information occurring underneath the baseline so the sonographer has opted to change the baseline position to allow for more display of that below the baseline flow same is true if you have more flow above the baseline then you can move the baseline to the bottom of the spectral tracing window now this gives us more room to view the waveform on the upper side again this is going to follow industry standard and what type of waveform you are displaying on your spectral tracing next up we have gain now the spectral tracing has its own gain just like 2d head gain spectral tracing has gain you may have noticed in some of the examples that we've seen so far that there are different varying whites that are being displayed on the spectral tracing and that's because echoes from closer blood cells are going to come back a little bit stronger so they're displayed as a little bit brighter weaker echoes are going to be displayed a little less bright so if your waveform is too bright or too dark the gain can be adjusted but remember gain will change all of the echoes returning so just like our 2d if we increase the gain all echoes noise and signal are going to be increased if we decrease the gain noise and echoes are going to become darker so it's really important that we change the gain appropriately to accurately measure both the psv and the ed values that we're looking to measure again too much gain can cause us to over measure velocities because we've made everything too bright or too little gain can cause us to under measure velocities the best practice for setting your gain in your pulse wave spectral tracing is to bring the gain up until you start to get kind of little specks in the background and then you're going to bring it down like one notch one click to where the background is back to anechoic or almost anechoic so here's an example of where the spectral gain is way too high the spectral window is completely filled in and if we were to measure this we get a psv which is going to be over measured at 101 centimeters per second by having the spectral gain this high we are falsely indicating that there might be turbulent flow or some sort of pathology occurring so we want to make sure that we are setting our gain appropriately and this is an example of appropriate gain the background of the spectral tracing area is completely black and echoic we have a nice spectral window that is open and when we measure this we get a peak systolic velocity at 94 centimeters per second and that is relatively accurate if we were to keep turning down the gain though we're going to cross into an area where the gain is too low the spectral window is still open but now it's actually kind of hard to see the spectral tracing itself and if we were to measure what we can see we are now under measuring the peak systolic velocity at 73 centimeters per second so again too high you're going to over measure overestimate your velocities too low you're going to underestimate your velocities so as a stenographer you really need to work on setting that spectral gain to the point where you don't have specs but it isn't too light either now the next stapler control and probably one of the most important doppler controls that we have is called the prf or the scale remember that the y-axis showed us velocity and i told you earlier that we could adjust how that velocity is displayed well we do that through prf and scale now before we get into that conversation i want you to remember that the frequency shift is measured and velocity is calculated so when we adjust our prf it is going to adjust how the frequency is measured and then how the velocity is calculated and i'm going to show you a little bit of math regarding all of this the math is more involved than what you will need for your boards but it actually loops in a lot of the formulas and concepts that we've talked about in the past and kind of brings us full circle as to why this all works the way that it does so when you place the gate at a certain depth this is going to cause the machine to have a maximum pulse repetition period and pulse repetition frequency so remember we have a maximum depth in our image that affected our prp and prf when you put a gate in that also is going to affect the prp and prf of the doppler portion and wherever that gate is is going to be the limiting factor on what prp and prf can be now the other limiting factor is that we know sound can only travel so fast through any medium and for soft tissue it's at 1540 meters per second so when we are using doppler the prf is limited by where that gate is and the propagation speed so let's go through an example using some of the math but talking about the over arching concepts so you pull up your gate and you move it to where you want it to be and it happens to be 10 centimeters into the body so remember just like our 2d imaging has a max depth and that indicates the prp and the prf that the machine is going through this one scan line that we're using for doppler is also going to have its own prp and prf and it's based on where we place that gate so we can use the same formulas prp is going to be equal to 13 microseconds multiplied by the depth in centimeters so 13 times 10 gives us a prp of 130 microseconds so it takes 130 microseconds for one doppler pulse to reach the gate get its information and head back knowing that prf is the reciprocal of prp or knowing that we can take 77 000 and divide it by the depth we can calculate a prf to be 7 700 hertz so that means that that doppler pulse can go down to the gate and back 7 700 times per second so one of the big takeaways so far is that wherever your doppler gate is is going to affect your prf now the next bit of information that we can get from these numbers is what is the max doppler shift the machine can record with a gate at 10 centimeters well it happens to be 3850 hertz which is the same as 3.85 kilohertz and that number is calculated by dividing prf by 2. so remember that the machine knows what frequency it's sending into the body it's going to know what frequencies it's getting back from the blood cells it's going to take that doppler shift take all the other information and plop it into the velocity formula that we learned in the last unit velocity then is calculated and then displayed on our screen so right now we are trying to figure out what is the maximum that velocity scale on the side of the spectral tracing what's the maximum velocity that the machine will be able to record so remember we needed to know what our operating frequency is we need to know what our doppler angle is it's 60 degrees for this example and then we need to know what the doppler shift is well right now we're just trying to figure out what's the maximum velocity that the machine can even figure out so we're going to use our max doppler shift if we place our max doppler shift our operating frequency our 60 degree doppler angle all into the velocity formula we can calculate that this setup is going to display a max velocity of about 120 centimeters per second it's actually like 119 but we'll say 120 for ease of things so now when we increase our scale or increase our prf the maximum we can get to is being able to display 120 centimeters per second on either side of the baseline so the green highlighted area tells us this is 100 of all the velocities that can be calculated need to follow somewhere between 0 and positive 120 or 0 and negative 120 so the big concept you need to take from that then is by maxing the pulse repetition frequency we increase our scale to display the maximum velocities possible so if we are using the fastest pulse repetition frequency possible we are going to have a max velocity that can be calculated so if you increase your prf you are increasing your scale and the prf is limited by the depth and can only go so high and that's going to be really important later we can only go so high with our scale so in the meantime though what happens if our doppler tracing is only around the 30 centimeter mark well they're going to get a really small spectral tracing and that's because the velocities reported are really only a small percentage of what the machine could display up to 120. so if you see a very very small waveform what you want to do is decrease your prf and when you decrease your prf you're going to tell the machine to make the waveform bigger to let it take up a larger percentage of the measurable velocity so really what's happening when we decrease the prf we are telling the machine to add in some more time to the prp so remember before we were at 130 microseconds for our prp our prf was 7 700. that's the fastest the prf can ever be if we decrease our prf and make it say 5 000 hertz that means we're going to go from 7 700 pulses per second down to 5 000 pulses per second and the only way to do this is to add in some dead time to the prp so as the machine sends the pulse out takes 130 seconds and that's going to add in some dead time if you've decreased the prf if you've decreased the scale it's going to add in that dead time so for example let's just say it adds in another 65 microseconds of dead time so that makes the total prp 195 microseconds this is going to change the prf to about 5133 hertz now this makes the max doppler shift that's measurable 2567 hertz with the max velocity recordable to about 45 centimeters so now we decrease our prf that's going to decrease our velocity scale and then our waveform takes up more of it so i know that was a lot of math and kind of a lot of principles coming back from the past but there are some main key facts about changing prf and scale the first one prf and scale are synonyms so if somebody says increase your scale when talking about the velocity scale you're increasing your prf if they say decrease your scale you're decreasing the prf a lot of people use them interchangeably you need to know that prf and scale when talking about doppler are synonyms next increasing your prf is going to increase the velocity scale so if we are increasing our prf we are saying to the machine i want to display higher velocities i want to increase the velocities capable of being calculated when you increase your prf you're going to make your waveform look smaller in relationship to the scale so remember when we started we had that 30 centimeter waveform on a 120 centimeter velocity scale it looked really small when you decrease your prf you are decreasing the velocity scale so we went from 120 we decreased the prf we decreased the scale and we saw it come down to 45 centimeters per second so when you decrease your prf that's going to make your waveform look bigger in relation to the scale so again going back to our examples we had 30 centimeters per second it looks a lot bigger when it's only being measured out of a scale of 45 centimeters per second lastly then remember that prf and scale are finite they have a maximum that they can be increased to and this is going to be important later when we talk about aliasing so on your machine there will be a knob or a button or slider that's going to increase or decrease the scale aka the prf so adjust your scale appropriately so the spectral tracing fits nicely into the window let's take a look at some examples now in this example the prf is set to high remember that prf and scale are synonyms so looking at the side here we can see that the scale or the velocity max that we are asking the machine to calculate up to is 500 centimeters per second or 5 meters per second and we can see that our waveform is very very tiny it's only taking up a small percentage of the available 500 centimeters per second so again the prf is set too high which means that the scale is very high it could record up to 500 centimeters per second but we don't need that for what we're seeing so we want to decrease our scale or decrease our prf so now we've decreased it and look what has happened to our scale we are now displaying up to 120 centimeters per second that allows that very same waveform that we saw in the last picture this is the exact same spot same waveform it allows it to be bigger it's going to be much more accurate to measure we can nicely see now the characteristics of the waveform and this is much more appropriate for what velocities are being recorded in the area now we can go a step further and decrease the prf even more now we've decreased the prf the scale is showing us up to 40 centimeters per second our waveform got even bigger and actually got to the point where it's not even being displayed correctly so there is a balance between too big and too small so remember that prf and scale are synonyms if your waveform is too small decrease your prf if your waveform is too big increase your prf so you can fit it all in the spectral tracing area the next spectral tracing control that i want to talk about then is the wall filter now the wall filter is going to be another knob on the machine that can be adjusted to get rid of some of those slower velocities it's very similar to 2d reject that gets rid of kind of those low level echoes that are coming back the wall filter is going to reject or get rid of those slow velocities now the velocities do still exist in real life but the machine is no longer going to display them in the spectral tracing the wall filter is also known as the high pass filter so when your wall filter is turned down or off more slow velocities are going to be displayed in the spectral tracing and that's what we're seeing up on top here we have our baseline and we can see a lot of kind of junk or those slow velocities around the baseline and you can actually see right here this tiny little bar right here this is indicating what the wall filter is so it's very minimal very little now when we increase the wall filter we're asking the machine to get rid of all of those low velocities and so that will be reflected in the spectral tracing and it might even look like your waveform is kind of floating so here this is the same area same setting except we have now increased that wall filter so now this wall filter is saying don't display anything that falls into these centimeters per second these velocities and so now you can see we've really cleaned up the baseline we've gotten rid of some of those low slow echoes we've gotten rid of some of the artifact really kind of cleaning up the spectral tracing but you need to be very very careful that you don't adjust the wall filter so high that you start to get rid of important information like your end diastolic value or those small velocity changes that you actually really want to record i mentioned earlier that i would show you a triphasic waveform and this is a triphasic waveform we have part of the waveform going up part of it going down and part of it going up again this is all within the cardiac cycle our peak systolic velocity a little bit of bounce back and then a final closure of the valve and so our edv is kind of still right in here but because this is headed to a leg it doesn't always need that forward flow we just need enough oxygen and blood heading to the limbs to keep them healthy in this top picture here we can look at what the wall filter is set at very minimal we are seeing a true triphasic flow above below above now in the bottom picture i've increased the wall filter and look what happened it got rid of all of those little echoes near the baseline but it also got rid of our third piece of our triphasic waveform and so now we've actually made this waveform look pathological or getting pathological because now it's considered biphasic from what we're seeing so you do not want to increase your wall filter or really any of your settings to possibly falsely indicate some sort of pathology occurring so be very conscious of how your settings are changing what you're seeing what you're expecting from the area that you're interrogating section 20.2 optimizing spectral tracing so when we discuss the controls that can be used for spectral tracing i showed you a lot of examples of things that were too high versus too low and just right using those controls can really change the analysis that can come from the spectral tracing that you are creating so really with pulse wave doppler we're looking for those just right settings to create the diagnostic image one of the biggest challenges we are going to face is how to correct for certain artifacts especially aliasing artifacts occur when ultrasound displays don't match what is truly occurring in the body be it anatomy or velocity displays so aliasing is an artifact that causes high velocities to be displayed incorrectly when using pulse wave doppler now one of the main disadvantages of pulse wave doppler is that it is not able to accurately detect and display high velocities because it is more likely to alias and this really has to do with what the prp and the prf are and that's all inherent to pulsed ultrasound because of that max depth and needed to send pulses out can't overlap pulses so remember when we were talking about prf and the velocity scale that there was a maximum doppler shift that could be detected based on the depth of the gate and if there's a maximum doppler shift this also means that there's a maximum velocity that the machine can calculate accurately if the velocity or the doppler shift exceeds the maximum as determined by the settings then the waveform is going to alias or appear like it's wrapping around so in this image we have an example of aliasing occurring this is the baseline this is the peak systolic heading up and then looking like it basically just got cut off so this is the point where that max velocity has been met what's going to happen though is that this information basically wraps around and then it is displayed incorrectly so if we were to follow this all the way up gets cut off wraps around and we can see that false peak velocity actually being displayed right here in reality this is probably something more like 70 80 centimeters per second but if we were to measure right here we're only getting like 10 15 centimeters per second this is aliasing and this is an artifact aliasing officially occurs when the doppler shift exceeds something called the nyquist limit and the nyquist limit will then also limit the velocities that can be displayed and the nyquist limit determines the velocity that is at the top or the bottom of our graph and is calculated so here it is nyquist limit in kilohertz is equal to the prf in kilohertz divided by two so anything that affects the prf will affect the nyquist limit they are directly related so if the prf increases then the nyquist limit increases if the prf decreases the nyquist limit will decrease so remember back to when we were talking about increase and decreasing the prf we said that that was really inherent to what the propagation speed is and the depth of the gate so anything that changes prf is going to affect the nyquist limit now i want to bring us back to the example i used earlier i said that our gate was placed at 10 centimeters into the body that gave us a prp of 130 microseconds giving us a prf of 7700 hertz the next line that i said was that the maximum doppler shift that can be recorded is half of the prf so in that line i basically told you what the nyquist limit is i gave you the formula for it then but we weren't quite ready to hear that term yet now that we are officially talking about aliasing remember that nyquist limit is half the prf if the doppler shift exceeds the nyquist limit then there will be aliasing now all the information in this word problem tells us the information that we need to know to figure out the nyquist limit we're told what the depth is of the gate which allows us to figure out the prf divide the prf by 2 and you come up with the nyquist limit or the max doppler shift so let's look at two more examples using this math in this example i have the depth of the gate set to 2 centimeters which means that our prp is 26 microseconds 2 times 13 and our prf is 38.5 kilohertz so 77 000 divided by 2 gives us 38 500 hertz convert that into kilohertz we get 38.5 kilohertz the nyquist limit then is 19.25 kilohertz 38.5 divided by two this depth of gate is very shallow two centimeters allows for a very very very quick plus repetition period allowing us to send thirty eight thousand five hundred doppler pulses per second that means that we can really sample what the reflectors are sending back often so we can get those true velocities displayed on the spectral tracing here's another example we've now moved the depth of the gate down to four centimeters so we're deeper in the body which increases our prp to 52 microseconds that decreases our plus repetition frequency to 19.25 kilohertz so we went from 38 500 pulses per second down to 19 250 pulses per second by moving the gate depth deeper so now this is going to reduce our nyquist limit to 9.625 kilohertz because we took the prf and divided it by two so now the machine might get information back a little bit too late to display it correctly in our spectral tracing which is the aliasing now i mentioned the word sampling and i kind of want to show you an example of what i mean so here we have the alphabet going by right we're almost to the end here we're going to wait for it to start over now with your eyes wide open watching this go by we are kind of working like continuous wave now we are getting every letter of the alphabet as it goes by we can record that we know exactly what's happening now in pulse wave remember we get a sample and then we have to wait for all the echoes returned pulse is sent out we wait for those echoes to return and it keeps going in that process so let's sample and wait so pulse sent out and then we wait paul sent out and then we wait paul sent out and then we wait now for the most part we've noticed that the letters have kept progressing in the order that we expect them to we can say yep we've got these letters we can display those they still go in alphabetical order when you decrease your prf you are increasing that waiting time you're increasing the time in between your samples so let's check in so p and now we're going to wait and now we have a decreased prf and increased prp and now we're at b okay sampled now we wait and the longer that we wait the chances are when we come back in for a sample we're going to be completely off from where we were on the alphabet so last letter we saw was c now we're at v we missed everything in between and so when the machine sends that pulse out and has to wait it is limiting itself on what the max doppler shift is what the max velocity is all right so the last letter that we saw was v again we're going to sample and now we're at r all right well now we're waiting and this is going to be similar to a low prf we are missing a lot of that information and so our alphabet right now went c v r like that doesn't make sense and that's what aliasing is it can't make sense of those velocities because they're coming back at a weird time and then they're getting displayed in a weird place on our velocity scale just for the fun of it oh we're back at us so we missed a whole alphabet so if we were graphing this we would say rr was our alphabet and that doesn't make sense and that's what aliasing really is so let's keep moving forward looking at some of the math and looking at what the machine is actually trying to calculate now we just talked about how to get to the nyquist limit that had to do with where the gate was the prp and the prf that predicted the nyquist limit the nyquist limit is basically the max doppler shift that can be calculated and so if we consider the nyquist limit to the be the max doppler shift we can plug in information into our velocity formula and then figure out what the max velocity that the machine will be able to report is so if we say that we are using a three megahertz transducer because we need our operating frequency and we're dopplering at a 60 degree doppler angle because we need the cosine of theta we can plug in our propagation speed multiplied by the nyquist limit or the max doppler shift all divided by 2 multiplied by the operating frequency multiplied by the cosine of theta which is 0.5 in this example polish calculator do the math and what we find out is that when we have a depth of four centimeter gate using a three megahertz transducer with a 60 degree doppler angle we can accurately show max velocities up to 495 centimeters per second so if the velocity of a blood cell coming by is 350 we got it we can map that onto our spectral tracing if a velocity of 550 comes by though it's going to alias we can't map that correctly and so that's going to look a little bit more something like this it's going to wrap around past the nyquist limit and then be mapped onto the other side of the graph so again essentially what is happening if we are not sampling the velocities quickly enough we can't tell exactly where to put them and the machine's like well i don't know just it kind of showed up right here wraps around puts it where it thinks it should be but it's not accurate because it is being displayed in the incorrect portion of our spectral tracing so essentially in the end aliasing is going to occur when the doppler shifts exceed the nyquist limit and we can use those doppler shifts on the nyquist limit to predict what the maximum velocity is so when we graph the doppler shift or graph the velocities what we end up seeing is a wrapping around of the information because we have not sampled it quickly enough to understand exactly where to put it there is too much time in between the pulse being sent velocities going by and new information coming back for the machine to accurately graph where that information should be so from this we know then that the nyquist limit really does determine what the max velocities are via the max doppler shift and as a sonographer then we need to know what can affect the nyquist limit so we can keep our waveforms from aliasing whenever possible so if we look back at all those formulas that talk about prf and doppler shift and velocity and nyquist limit we start to see some relationships kind of some domino effects happening through the formulas so for example if our gate depth increases that means our prp is going to increase and our prf decreases this is going to cause the nyquist limit then to also decrease so in the end what we get from that is that increasing the gate depth is going to increase the likelihood of aliasing the deeper your gait is you're more likely to alias here's another one if prf decreases then the nyquist limit is also going to decrease and that means that the max doppler shift decreases and this causes the max velocity to decrease and so we know that when we decrease the prf we are more likely to alias and we saw that in some of the examples earlier looking at waveforms we had the 500 centimeters per second velocity scale decrease the prf decrease the scale remember those are the same thing brought it down to the 40 centimeters per second and we saw aliasing so when we decrease the prf we're more likely to alias lastly another big correlation through all of this is that if we increase the transducer frequency that's going to increase the doppler shift expressed so by increasing the transducer frequency were more likely to cause aliasing this is why we want to use low frequency transducers when we are performing doppler applications they are less likely to alias therefore we'll get more diagnostic information out of them so now if we know what is more likely to cause aliasing we can do the opposite to correct it now for the spi there are going to be five ways that you need to know how to eliminate aliasing five ways that you should know are to increase the scale which we also know now is the same as increasing prf two to decrease the depth of the sample bring it more shallow three use a lower frequency four move the baseline or five switch to continuous wave doppler so let's take a quick look at these five solutions to aliasing so number one increase the scale now we've already saw the math we saw the relationships in the formula when pulse wave doppler is activated the doppler shift that returns might be higher than the nyquist limit and the current prf allow so if you can increase the prf this increases the scale and allows for accurate graphing of the velocities that are being sampled remember when you increase the scale you increase the prf which increases the nyquist limit you're basically changing the speed limit you went out to the highway and said all right everybody can go 50 miles per hour that's our new limit and anything under 50 miles per hour is going to be graphed accurately and so here's an example of doing just that we have our speed limit quote unquote at 40 centimeters per second this is the nyquist limit this was based off of the prf and the settings that we have this waveform is aliasing it is getting cut off wrapping around and showing back up so one of the easiest and first things you should try is increasing your prf increasing the speed limit increasing the nyquist limit so now we've increased our prf and now our speed limit is at 120 centimeters per second waveform fits just fine in there we have corrected the aliasing the big problem though comes in when you've maxed out that prf you've maxed out your velocity scale and you still have aliasing if that's where you get you need to try another technique and sometimes you can put the techniques together to get the desired effect so number two decrease the sample depth when the sample gate is used in a particular window it might be placed actually pretty deep within the body and the deeper the gate is this is going to decrease our prf and then that is going to decrease the nyquist limit so if the stenographer is experiencing aliasing in one window with a very deep gate they can try a different window that will allow them to move the sample gate to a shallower position by moving that gate more shallow the prf will increase which increases the nyquist limit moving the sample gate won't always be your go-to option sometimes the window is what it is and your flow is where it is so this won't always be an option but it is something to keep in mind when it works these formulas again just show us how the depth affects prf therefore affecting nyquist limit remember if we decrease our depth that is going to increase our prf and when we increase our prf we will see an increase in the nyquist limit the higher the prf the higher the nyquist limit the less likely we are to alias number three use a lower frequency transducer frequency is directly related to the doppler shift high frequency transducers have larger doppler shifts the larger the doppler shift the more likely it is to alias it's going to go past that max doppler shift determined by the prf so sonographer should try switching to a lower frequency transducer to decrease the doppler's shift thus staying below the nyquist limit now remember that the nyquist limit is 100 based on the depth of the gate and the prf that has nothing to do with frequency when you change to a lower frequency transducer you are reducing the doppler shift that is being calculated based on the velocities now when you do switch to that lower frequency transducer you are going to have some trade-off your resolution is going to be a little bit lower but you are going to eliminate the aliasing by doing this and of course i have an example for you showing the difference between a high frequency and low frequency transducer to skip over a lot of the math we have the gate depth set at three centimeters that's going to give us a nyquist limit of 12.8 kilohertz now using that nyquist limit of 12.8 kilohertz and our doppler shift formula we can plug in our 12 megahertz operating frequency the 150 centimeters per second with the zero degree doppler angle and what we calculate in the end is a doppler shift of 23.4 kilohertz when using a 12 megahertz transducer this is more than the nyquist limit therefore we are going to see aliasing so 12 megahertz is a relatively high frequency high frequency transducers create greater doppler shifts greater doppler shifts more likely to exceed the nyquist limit therefore alias taking a look then at transducer 2 we've switched to a 4 megahertz transducer everything else is the same plug your numbers into the doppler shift equation and what we calculate this time is a doppler shift of 7.8 kilohertz this is less than the nyquist limit so we will not see any aliasing now the big thing that i want to point out here everything stayed the same except for the transducer frequency so again high frequency transducers produce high doppler shift values the higher that doppler shift is the more likely it is going to exceed the nyquist limit number four move your baseline remember that baseline can go up and down it's the zero point for a way or towards the transducer by adjusting the baseline you create a larger window on either side of it which might be enough to eliminate the aliasing the trick though is that your waveform cannot alias past that zero point past the baseline so in our example up on top here this is our baseline and our waveform it's aliasing right here wrapping around and being displayed underneath but this is the part that matters a lot it does not cross back over the baseline so we can simply just bring this baseline down and we've eliminated the aliasing works out great the problem is when you have so much aliasing that you've met the nyquist limit or the maximum velocity wraps around wraps around past the baseline and is back up into the upper part of the spectral tracing this is not going to be corrected by simply moving your baseline you have to try the other techniques and lastly number five switch to continuous wave doppler because aliasing can only occur with pulse wave doppler so if all else fails and aliasing is still occurring with pulse wave doppler continuous doppler is an option so if you as a sonographer have the option to switch you should take it now the disadvantages is that you can no longer choose where that sample is coming from exactly but you should be able to get better diagnostic information based on the velocities the continuous wave doppler can record now many general and vascular sonographers don't have the ability just to switch over to continuous wave doppler but a lot of cardiac stenographers do and also do so quite often i do want to point out that this should not be confused with something called high prf or hprf hprf uses a combination of pulse wave and continuous wave to be able to achieve higher velocities in the cardiac setting hprf is not something that will be covered on your boards but for those of you in the cardiac setting it is something to keep in mind that that is an option for you to switch to kind of the combo pulse wave and continuous wave knowing that that can still aliase as well and that you might ultimately still have to switch into continuous wave doppler so here's an example in the heart the sonographer has the gate placed in the mitral valve and we are using pulse wave to evaluate flow through the mitral valve and we are getting aliasing so in cardiac imaging we typically have the peak systolic velocity going away from the baseline as well so the waveform is coming down reaching the nyquist limit wrapping around and then we're seeing those peak velocities kind of somewhere near the baseline again here so aliasing is occurring aliasing can occur up and around or it can occur down and around but either way aliasing is occurring with pulse wave doppler the stenographer then switches to continuous wave and here we see beautiful peaks that can be measured and looking at the scale here we're looking like we're getting into about the 500 centimeters per second range very well over the 120 that was given with the pulse wave so those are the five things that you should do if you are using pulse wave doppler and experiencing aliasing be very comfortable with those methods now remember that aliasing is an artifact we have a couple of other artifacts that might appear in our spectral tracing one of them being clutter now clutter is an artifact sometimes we call it thump artifact and that's going to come from small movements in the body like the heart beating or or the vessel wells pulsating kind of expanding and relaxing with the motion of the blood these little movements are going to be displayed then as low level doppler ships and this is where the wall filter can be important it's adjustable and we can tailor it to what we are seeing but remember it's important that we don't adjust the wall filter to the point that it affects the real diagnostic information we don't want to get rid of any sort of phasicity in a vein we don't want to get rid of slow moving reflectors if they're important to the information so in this example we can see that clutter near the baseline so remember spectral tracing clutter near the baseline we've increased the wall filter and now we've gotten rid of a lot of that extra information it cleans up the waveform a little bit more bringing the attention to the true spectral tracing another type of artifact that you might see is something called crosstalk now crosstalk is kind of a special type of mirror image artifact it artificially shows the spectral tracing on both sides of the baseline so if we were looking at this we might think well there's flow away and towards the transducer but this is not real this is artifact and really only one of the directions is real this is typically going to happen when your pulse wave gain is way too high and the vessel is sitting about at the focus of your beam with a near 90 degree doppler angle to the vessel so usually what you'll see in the crosstalk is one side might be a little bit brighter than the other side if you decrease your pulse wave gain you might be able to decrease this kind of noise or the artifact enough to which it doesn't distract from the true spectral tracing the other thing then that you would want to try is to get away from that 90 degrees to get out of the focus of the beam and to try a different window to eliminate the crosstalk remember then to to use the rest of your spectral tools to optimize the images make sure your gain is appropriate make sure your velocity scale is appropriate make sure your wall filter is appropriate at the end of the unit i do have some quick reference guides that might help make optimizing decisions a little bit easier a little bit quicker regarding pulse wave continuous wave and color doppler so speaking of color doppler let's go ahead and switch over to it section 20.3 color doppler display so now color doppler is a type of pulse wave doppler so we will still see a lot of overlap in the terminology and issues that can arise so first let's look at what color doppler can tell us and then how we can improve it now remember you do not need to know anatomy for your physics boards you're going to be tested on your ability to recognize how the display how the machine information reflects what is happening in the body is the blood flowing towards or away the transducer is it going from left to right right to left knowing what the vessel is or what normal flow is won't be helpful for the spi you need to be able to analyze the display and understand what the physics is telling us so let's start with activating our color when you activate the color application on the machine a color box will appear for sector transducers including the curve linear the color box is going to resemble the shape of the sector so on top here we have a phased array transducer being used in the cardiac setting looking at what looks like probably the aortic arch so this is the 2d picture the color box has the same shape as the 2d but this is where the color is being displayed notice there's no color outside of the color box this is an example of a curved linear transducer image 2d on the back color box is activated takes on the same shape and that is where the color is located this is a kidney showing the renal veins and arteries once you activate that color box you have the option as a sonographer to adjust the size and the location of the box a couple things to keep in mind a wider color box is going to use more scan lines which is going to decrease your frame rate but you get more color information so you need to balance do i want a whole lot of color in my picture or do i want a better frame rate also keep in mind that the deeper the color box goes that's going to increase your pulse repetition period when you increase your pulse repetition period you decrease your prf and this is going to cause aliasing in our color picture so make sure that your box is appropriately sized for the area that you want color on and when possible don't bring it all the way to the bottom of your picture keep it a little bit more in the middle for linear transducers when you activate the color option the same idea happens the color box will come up and it takes on the same shape as the scanning window so we get a rectangular box with our linear transducer the problem is though is that when you have a rectangular box and a horizontal vessel like we do in this example the scan lines that are creating the color box are 90 degrees to the blood vessel so we are not going to get flow within this vessel because we are at 90 degrees so it is very easy to use a 90 degree doppler angle when you're using the linear transducer that is why we say to steer the box when you steer the box or angle your vessel you are creating a doppler angle you should have at least some angle so better color doppler information can be obtained so in these images now the lines that are creating the color information have been steered electronically they are going down at an angle which is coming in at an angle to the blood vessel thus giving us better doppler information we have induced an angle remember though that you can angle and still not get doppler information in this example we have our lines coming down at this angle but now we've crisscrossed over the vessel angle and we're still at that 90 degrees so whatever you do whenever you are using color doppler avoid 90 degrees always try to induce an angle whenever you can now there is a knob that it will steer the box in different directions on the machine again steering the box with the vessel will bring that doppler angle a little bit closer to zero and that's going to provide the best color fill for the area remember that when we're talking about the angle of the scan lines with the reflectors is important we learned that 90 degrees is also known as normal incidence and it's going to be the same idea with color doppler as well so you do not want to bring up your color box add a normal incidence to your blood vessel or to the area that you're trying to interrogate with color normal incidence was awesome for our 2d imaging it is not awesome for diagnostic doppler imaging once you activate the color doppler and you're looking at the image you should be able to recognize where the color map is and then apply that knowledge to your picture remember that whatever color is on top indicates that flow is moving towards the transducer and whatever color is on the bottom indicates flow moving away from the transducer in this example we can see a little bit of a blue vessel back here blue has been coated as towards so this vessel is flowing from left to right towards the transducer red has been coded as a way so the blood is flowing right to left away from the transducer in your workbook you will see a few pictures that i've included with color doppler on and visible color maps remember if no map is present then you cannot tell a direction of flow do not try to guess what vessel that is and then try to guess what normal flow should be you cannot tell unless your color map is visible remember too that that color map can be inverted with the touch of a button if you prefer blue towards and right away you would invert this picture and everything would flip there is no fast red is always on top blue is always on bottom it depends on the sonographer and what they want displayed so let's take a look at this picture what are we seeing the color map tells us that red is towards and blue is away so all of these vessels that are coated as red are moving towards the transducer the vessels that are coated as blue are away from the transducer this image is of an umbilical cord with the color doppler on here's an example of color being used on the heart and we can see actually lots of colors going back and forth through the heart valves as a sonographer you should be able to watch these colors and match them up to our color map so when we see the reds and the yellows we know that the blood is flowing towards the transducer and when we are seeing those blues and bright blues we're seeing blood that's flowing away from the transducer for the way that echo is done this is actually the apex or the tip of the heart up here so these are the ventricles down here and the atria on this side so again when we are seeing red we are seeing blood flowing into the ventricle when we are seeing blue we're actually seeing flow out of the ventricle and away from the transducer so again you do not need to know this anatomy all you need to know is that this jet of blood is red towards the transducer this jet of blood is blue away from the transducer and here's another example this is a scrotum with the color doppler on we are going to see bits of color sometimes veins are blue sometimes they are red it all depends on how they are flowing in direction to the transducer so this vessel this vessel this one and this one and this one are all flowing towards the transducer all the blue ones are flowing away and again we know that because of our color map one last example then to look at here we have blue going towards red going away we can see then that this has been coated red so this is flow away from the transducer it is producing a negative doppler shift but you should also be able to tell which direction this blood is flowing is it flowing from right to left or is it flowing left to right so let's take a look at that so this is another skill that you will need as a sonographer taking the spi remember you don't need to know anatomy so even if you know this is a carotid artery and you know that blood should be flowing from the heart which is typically on this side to the brain which is typically on this side that doesn't matter you do not want to make any assumptions of what vessel you are looking at solely look at what the display is telling you here we are seeing red is away so we know that the blood flow is moving away from the transducer if we just look at kind of how everything is angled how the vessel is angled we can kind of assume then that it is flowing this direction away from the transducer and might easily be able to say it's flowing right to left but i've got a few steps that we can go through to confirm that so the very first thing you want to do is just recognize what's left on your screen and what's right on your screen when we talk about 2d imaging and certain modalities this is technically patient's right this is technically patient's left or this is head feet it all depends though on what modality you're scanning in so that is not the point of the spi this is just do you understand direction and how the blood is flowing so we are going to use our true left and our true right left of the screen right of the screen how is that blood flowing don't go sonographer left right go true left true right next i want you to find where the acute angles are on the color box remember the acute angles are the ones that are less than 90 degrees so this is obtuse obtuse so we've got our acute angles here and here they are going to be opposite of each other on the color box next you're going to take a look at the color that's in your vessel and compare it to the map is it on the upside or is it on the downside looking at this we can see red red and it's down now i want you to place your finger on one of the acute angles and move it so you move your finger down to the other acute angle so we place our finger here we go trace down to the other acute angle we have now moved our finger from more right to more left so we can say that this flow is from the right to the left now the difference here if you tried to put your finger in this one to trace because red was down red's on the bottom you'd go this way and you would not hit the other acute angle so you're going the wrong way so remember you want to connect the dots and if you are moving down to the other acute angle you can see that this is right to left now don't worry we've got tons of examples coming up so here's another one so first off let's just again remind us screen left screen right nothing fancier than that then we want to find our acute angles so remember those are the smaller angles one's less than 90 degrees then we're going to determine is the color matching with the up or the top color map or is it matching with the bottom down color map on this one we can see that it is red and red is going to equal up so now we want to place our finger in the acute angle that is going to allow us to trace up so we trace from the bottom acute angle up to the left acute angle and that tells us then that we have moved more from the right to the left so this flow is right to left as well now you have more examples in your workbook but we'll work through them here here's the next one we now have a blue blood vessel remember that this is left and this is right find your acute angles blue tells us we want to move up because it's on top so we're moving up towards the transducer so we're going to start in this bottom acute angle so we can trace our finger up to the other acute angle we have moved right to left here is another example again left and right find your cute angles and match your color red bottoms we're going to do bottom down so we want to find our acute angle and trace down to the other acute angle this also then is a right to left flow here is another example now the other acute angle has been kind of cut off in this one but we can see it here and remember it's always opposite so acute angle here and acute angle here left of the screen right of the screen colors are matching red down so we're going to go down with the red down from this acute angle to the other acute angle this flow is left to right now looking at these as well you might just be able to kind of work through it that the transducer is up here flow is going away from the transducer and the way that it's angled shows us that a way makes sense here's an example again where that might be helpful the transducer again is up here but now we have a straight color box so this actually makes it a little bit harder to find those acute angles but notice that our vessel is angled so we're not too upset about the straight color box because we have that angled vessel so if we were just to draw a line through the vessel our acute angles now are on this side and this side so you might have to get a little bit more creative on recognizing those acute angles but same idea we're red downs we want to move from down from one acute angle to the other acute angle and we can see too that this blood flow is left to right now if we switch back to looking at some blood flow using phased arrays or curve linear arrays we are going to see something a little bit different whenever you have a vessel traveling horizontally across the screen you're actually going to notice that both colors are typically displayed and that's because the blood is flowing towards the transducer for part of it and then away for the other part remember the scan lines are coming down this direction and then these ones are going down this direction so with this vessel coming across at some point there needs to be a change in how the colors are displayed not all the scan lines are oriented the same way to the flow so when you see a picture like this and you have a sector image and you see the blood vessel coming across the screen one of the best things that you can remember is that flow is always going to be from the top color to the bottom color so in this image we have flow going through the red which is the top color to the bottom so this flow is left to right and you can also think through this one as well just like we kind of talked about the other ones if we are moving towards the transducer and we kind of follow this line up going towards the transducer you have to go this way so that kind of already indicates the left to right and then flowing away from the transducer you kind of have to follow the curve down this way which continues the left to right flow pattern and here's another example of a curved linear with a vessel that's traveling horizontally across it exhibiting two colors so remember again it is the flow on top into the flow on the bottom so we will see flow coming from this way taking a turn and going away from the transducer so this one is flowing from right to left remember that our color maps are able to not only tell us is flow moving away or towards the transducer but it also assigns an average velocity from the color area so when colors match up with the colors that are very close to the baseline to that black bar they're going to represent slower moving blood when colors match up with the colors that are closer to the edge of the map those are going to represent faster moving blood no color or black is going to mean that no detectable velocity or doppler shift is present and that is seen at the 90 degree doppler angle so let's take a look at that last picture that we were using as our example and take a look at what we can see in there again here is that no doppler shift we can see a black bar in between the red and the blue this is 90 degrees to this scan line creating the color from this area so it is being assigned black because it cannot detect a doppler shift there the blue here and the red here match up very closely with the red and the blue that is near the baseline so these are both slow moving velocities red being the slow towards and blue being the slow away now as we look at different parts of the vessel we see a different color notice here this is still blue but now we're into a little bit brighter blue that brighter blue matches up with the edge of the color map so it's still away but because it's closer to the edge down here it indicates a faster velocity same idea with the yellow yellow still indicates towards the transducer but a fast velocity so here we have that fast away and here we have an example of the fast towards now the circle area here is representing an area of aliasing notice how it goes from light blue directly into yellow so we'll talk a little bit more about this later but you know that aliasing means we're having issues displaying the correct velocity because of the nyquist limit so let's take a look at some of the color doppler controls again these are going to help us to be able to create pretty diagnostic color images a lot of these concepts are going to overlap with some of the pulse wave controls so we're not going to cover them in as much detail if they are similar so there is a baseline on the color map remember that baseline is represented by the black bar and the black bar can be changed just like the baseline on pulse wave but i say that with a little hesitation in that it's very rarely done there is a knob that will allow you to change the color baseline and what you'll see is that baseline will move further up into the map allowing for more blues on the bottom or lower in the map allowing for more reds or whatever happens to be the top color more often than not you'll find it smack dab in the middle no matter what you're looking at however if you have color aliasing changing your bass line on your color map can help with that so i want to point it out that it is an option but it is a very rarely used option and just like 2d and pulse wave color has its own gain as well so there will be a separate knob for color gain and this is going to increase or decrease the amount of color seen within the color box and just like all the other gains you can over gain your color causing the color to become very flashy kind of bleed out kind of look like confetti all over the place or you can under gain it and make it look like there's almost no flow occurring again there's going to be a knob or a slider just for color gain so here's an example of too much gain we have a couple vessels in the area we can see those here but we can't see the borders of them we've got all this going on this is not vessel up here this is actually over the sternocleidomastoid muscle so this is all just junky color confetti this is not diagnostic is way over gained as far as color goes now if we start turning the color again down we can start to see where the vessels truly are running but here we still have some color bleeding out of the vessel we don't want this we want wall-to-wall fill and that's where we want it to stop so here's an example then of good wall-to-wall fill if we are looking at this vessel that's mostly red here if we wanted better fill in this vessel we'd have to change some things around but the focus is in this red one here so the gain is just right fills wall to wall we can clearly see the borders of the vessel as we continue turning the gain down then you'll notice that the flow becomes a little bit more spotty now we're missing areas of flow and this too can be a problem we often use color to show that an area is open so if we start to show areas which we call a color filling defect then we might start to think that there's something blocking the flow of blood in that area so we want to make sure that we again just hit that just right setting that allows for walled wall fill no more no less lastly then too we can turn our gain all the way down to the point where we're not even recognizing color phil like we are in this image here this is mimicking a very severe pathology we expect blood flow to be in here and if there is none then it's a question of are the settings correct or is there truly pathology occurring we also have the option to change the prf and scale on our color doppler again it's also associated with the doppler shifts this time though we are presenting average velocities because we are working with color since color doppler is a subset of pulse wave doppler it is also going to be very dependent on the prf of the scan lines getting the color doppler info the prf for color works very similarly to how it did for spectral and the prf scale can be adjusted up and down with a max color prf dependent on the depth of the color box so when your color scale or prf is increased you're going to be able to display higher velocity averages but it's going to make the system less sensitive to slow velocities so again you have to be very careful maybe you don't want that aliasing that mixing of colors but you have to be very careful if you increase that too much you're going to start to lose sensitivity to the slower flows on the opposite side of that then when we decrease the color scale or the prf we are going to start being able to display lower velocity averages but as we decrease that pair of we're more likely to see aliasing so in this example here the prf is way too high we can see the average velocities being displayed on the side here we might just be catching some artifact here this might be true flow but in general we do not have an average velocity of 77 centimeters per second flowing through this area therefore the machine is not sensitive enough to the flow that is going through here and it is not displaying color so prf is too high this is similar to our waveforms being way too small in spectral so now if we decrease our prf we are going to see color starting to fill in so like we're about half of what we were 38.5 this is just right we're not seeing any aliasing we're staying true reds with a little bit of yellow while the wall fill it looks beautiful if we keep decreasing our prf that is when aliasing is going to occur now this is the same blood vessel same velocity information going through here but now the machine is wrapping those colors around to the point that we're getting that aliasing so we're getting very mixed color signals in this area and again very similar to pulse wave color also has a wall filter the filter can be a little bit more helpful when we are using it in the color setting and that is because we talked about not wanting our color to expand beyond where true blood flow is so by using that wall filter we can get rid of some of those slow velocities that are outside of the vessel or that our artifact and kind of clean up the image but again too much while filter can completely hide flow that should be present so here's an example of no wall filter very little wall filter being used we have just a little bit coming out this actually isn't horrible but this is the example that i have so we've got just a little bit of color coming out with our very little wall filter increase the wall filter a little bit more and what you'll notice is now we have lost all the color information right along the walls so you can see actually just like a hair of black that goes through here and that is because those slow velocities have been eliminated from the color map increasing your wall filter is going to get rid of those slow velocities it's not going to be displayed with a color section 20.4 optimizing color images let's take a look at how to optimize color images because artifacts can appear with color doppler as well i mentioned it earlier we can have aliasing with color doppler so you need to be able to recognize it and know how to fix it so aliasing in color looks like a mix of colors you're going to notice that it'll go from the fastest velocity color on one side wrap around to the fastest color velocity on the other side of the color map so in this example we've got yellow which matches up with the highest velocity here traveling right into the bright blue which is the fastest velocity on this side so the hallmark sign of aliasing in color is moving from the fastest velocities on either side of the color map into one another so this is aliasing this blue vessel does not exhibit any aliasing but it does show us some faster areas dark blue slower light blue a little bit faster but not to the point that it's wrapping around and becoming yellows or reds and just like pulse wave aliasing is going to be corrected in a lot of the same ways except there isn't a continuous wave option so your options for fixing aliasing in your color doppler picture are to increase the prf which is probably going to be your most common fix you can try decreasing the frequency of your transducer decreasing the depth of the color box or change the baseline which i mentioned earlier probably isn't going to be your most common go-to but you can try it and see if it works i do want to point out that in this picture we are seeing both aliasing and true flow reversal and that is going to be something that you're going to want to pay attention to when you are analyzing images not only for your physics boards but just in general when you're imaging with color doppler so here we have that true aliasing because again we're going from the bright colors into the other bright colors we're going from yellows to blues this is true aliasing this area here is not aliasing we're going from a dark red to a black to a blue so when you see that black line in between the two colors that actually indicates flow reversal or a change in direction versus aliasing another artifact that you might come across with color doppler then is something called ghosting and ghosting artifacts are going to be kind of the clutter of color doppler so color escapes the blood vessel well and then kind of distracts from where the true color doppler is and where the vessel is actually flowing color wall filters can be helpful to reduce ghosting however minimizing movement of the patient of your transducer and changing some gain in prf settings might also help as well so in this example here we can see a blood vessel traveling through this area we're not really wall-to-wall here we're kind of all over the place we got these little speckly bubblies things coming out of the vessel so we're really seeing kind of that ghosting color fill just out past the wall and into the soft tissue and that brings us to my quick doppler guides i want to quickly go over these with you these are in your workbook so i will let you read through them a little bit closer but i just kind of want to point out some key things that you will find in the quick doppler guides on the first page we have our what type of doppler do i want to use you kind of need to think about what is the goal of doppler in this area do i want to know what direction am i looking for color fill do i want to see very slow flow do i want to see very high flow what is the goal of what i'm looking at so you have your options between pulse wave continuous wave color doppler and power doppler you also really need to know the difference between pulse wave transducers and continuous wave transducers their differences are the big reason why pulse wave is good for one thing and continuous wave is good for another you should know the advantages and disadvantages of both when going to choose which doppler you want to use on the next page then i have how to correct pulse wave doppler spectral tracings again these are just kind of a quick overview things that you can think about trying to correct what you are seeing for example we have too much noise in the background that's going to be reducing your pulse wave gain have aliasing i've got those five things listed that we talked about what to do with crosstalk what to do if your waveform appears to be kind of floating above the baseline so that just quickly goes over some quick things that you can do to correct spectral tracings and then on the last page i do have some ideas for you to help you correct color doppler displays again if we're not seeing color and we recognize bad angle you got to change your angle that's going to help a lot with your color flow if we know we're at a good angle but still aren't seeing color well maybe need to increase your color gain decrease your color prf scale decrease the wall filter and for some of these maybe it's true this might be real pathology that you're seeing and you're not going to be able to correct yourself out of it one thing that we didn't touch on real closely was something and the idea of poor frame rate with color on i did mention earlier that the wider your boxes the more pulses that are needed to create the color information more pulses means lower frame rate so if you need a better frame rate a narrow box is going to be better for that there's also something called persistence that we learned about way back when we were talking about different ultrasound machine features and persistence remember kind of piles on time of color on top of itself and so it averages three frames together and it averages three frames together but it has to wait for all those frames to be created so if you decrease persistence then you are decreasing the waiting for all those frames to be created so they can be averaged together so that's another option for you as well so take a look through that i think it'll be helpful just as a new scanner especially what can i do to fix what i'm seeing and that my friends brings us to the end of unit 20. we have made it through units 18 19 and 20 all of which cover the doppler imaging concepts that makes up about 31 of your spi so these three chapters are going to be huge to understand and know well there's lots of little key tricks lots of little formulas lots of relationships that you need to be comfortable with in regards to doppler as far as this unit goes really focus on how to correct for aliasing both in pulse wave and color focus on the differences between pulse wave and continuous wave why do we want to use one over the other what are the disadvantages of both and then really look at the definitions of the controls that we have and what they're going to do and how they can help you make better diagnostic pictures again you have activities in the workbook that you can work through kind of thinking all of these pieces out and then you have your nerd check questions at the end to double check your understanding of the information presented