hi Learners it's M from son nerds and this video is on unit 19 Doppler physics and instrumentation unit 19 Doppler physics and instrumentation so outside of ultrasound most of us have experienced a Doppler shift if youve ever heard an emergency vehicle with their siren active you may have noticed that the pitch of the siren has changed in regards to the vehicle's location and you now learning about Doppler as it applies to ultrasound doesn't need to alarm you we're going to break this down into sections unit 19 is going to be a little bit more of the math and the physics behind Doppler and then unit 20 will be more of the clinical application of Doppler in unit 19 we're going to cover the Doppler effect Doppler shift the Doppler equation continuous wave Doppler pulse wave Doppler color Doppler and the instrumentation now the pitch getting higher as the vehicle comes towards you and then sounding lower as it drives away is called the Doppler effect section 19.1 Doppler effect the Doppler effect is the change in frequency and wavelength that is caused by the motion of one of three things either the Sound Source receiver or the reflector so let's use a siren on a moving vehicle as our example say we have a fir Tru and the firetruck siren produces a sound with a frequency of 800 HZ if the truck is stationary you are going to perceive the siren sound to also be 800 htz you are receiving those wavelengths you're receiving that frequency as it is coming out of the siren in the stationary position note that the wavelengths are equal and true to the 800 Hertz if the truck is moving towards you that siren is still producing a frequency of 800 htz but as the truck moves towards you the particles are going to begin to oscillate faster creating shorter wavelengths which increases the frequency that you hear so you perceive the siren sound to be 820 Herz so again frequency of the siren has not changed but the fact that it's moving towards you changes how the particles are interacting with one another thus increasing the frequency that you can here looking at our video here notice how the sound waves are being compressed faster which are going to cause shorter wavelengths and remember short wavelengths equal higher frequency as the truck drives past us remember the siren is still at 800 Hertz it has not changed but what we perceive will change so as the truck is moving away from us the particles are going to be oscillating slower behind it that's going to create longer wavelengths which decreases the frequency that we hear so now we might perceive the sound to be at 780 Hertz so again those sound WS are being stretched out a little bit more that causes longer wavelengths and long wavelengths go with lower frequency so in this example the Doppler effect is the physical phenomenon that the sound pitch changed as the Sound Source moved due to the frequency and wavelength changes being perceived by the receiver so in short a sound Source or reflector moving towards the receiver causes short wavelengths which is a higher frequency and higher frequencies sound as higher pitches when the sound SCE or reflector is moving away from the receiver it's going to cause longer wavelengths which cause lower frequencies and are perceived as lower pitches the change in frequency due to motion is the Doppler shift section 19.2 Doppler shift again the change in frequency due to motion is the Doppler shift and the Doppler shift can be calculated by taking the received frequency and subtract in the transmitted frequency so here we have our first equation this is a very basic equation and this is essentially what the machine is using it is going to know what frequency it is sending out so that's frequency T frequency transmitted and then it's going to know what frequency it received that's frequency R so frequency received minus frequency transmitted gives us our Doppler shift so let's use our fir truck again now the transmitted frequency of the siren is 800 Herz and when we're stationary the received frequency is 800 HZ there is no motion therefore there's no Doppler shift so 800 htz is the received minus 800 HZ the transmitted equals 0 Hertz again there's no change because there is no motion we are not experiencing a Doppler shift recall though when the truck was moving towards we were hearing higher pitches because of shorter wavelengths and higher frequencies so now we are receiving a frequency of 820 Hertz so 820 Herz frequency received minus the 800 Herz frequency transmitted equals 20 Hertz 20 htz is the Doppler shift and when the fir Tru is driving away from you as a receiver you're we receiving a lower frequency 780 HZ so 780 HZ the frequency received minus the 800 HZ frequency transmitted equals a -20 HZ -20 Herz is the Doppler shift so I hope you notice that when the received frequency was greater than the transmitted we got a positive Doppler shift and when the received frequency was less than the transmitted we got a negative Doppler shift so again positive Doppler shifts are going to occur when the object is moving towards the receiver and that makes the received frequency greater than the transmitted negative Doppler shifts are going to occur when the object is moving away from the receiver and the received frequency is less than what was transmitted a doler shift can be detected by our machines when it evaluates the frequency of The Echoes being returned off of the moving reflectors which happen to be our red blood cells so when the red blood cells are moving towards the transducer location they will reflect back higher frequencies than what the transducer is producing and when the red blood cells are moving away from the transducer location they will reflect back lower frequencies than what the transducer is producing the red blood cells that are moving towards the transducer produce a positive shift where the red blood cells moving away from the transducer produce a negative Doppler shift so let's take a look at an example of how a Doppler shift might look using ultrasound values remember the Doppler shift is calculated so it's Doppler shift is going to be equal to the frequency received minus the frequency transmitted so let's say we're using a 5 mahz transducer remember this is the same as 5 million Hertz the transducer is going to transmit a frequency of 5 million Hertz into the body that sound wave is going to strike a red BL blood cell and that red blood cell is going to send an echo at a certain frequency back to the transducer in our example we can see that the red blood cells are moving towards the transducer location so these red blood cells are reflecting back a greater frequency to the transducer in this example I've selected 5, 3,000 Hertz so to plug that into our equation then we'll have the received frequency of 5,300 Herz minus the transmitted frequency of 5 million Herz and what we get is a Doppler shift of 3,000 Hertz now remember the red blood cells are traveling towards the transducer their received frequency is greater so we are seeing a positive Doppler shift of 3,000 Herz let's take a look then of how it might look when the red blood cells are moving away from the transducer again we still have our 5 MHz transducer transmitting a 5 million Hertz sound beam as that sound beam interacts with the red blood cells they are going to send an echo back less than the transmitted because they are moving away from the transducer so in this example I selected 4,997 th000 Hertz plugging those numbers into our equation we have the received frequency of 4,997 Herz minus our transmitted frequency of 5 million Hertz and that gives us a Doppler shift of 3,000 Hertz so again we are seeing the reflector moving away from the receiver so we are going to see a negative shift and in this example we get a negative shift of 3,000 Hertz now the machine is going to receive these reflected frequencies along with a lot of other frequencies when dler instrumentation is being used used the machine is going to use the demodulator to demodulate or identify those very small frequency shifts and extract them from the high ultrasound frequencies for further processing now before we move on to the actual Doppler equation I do want to cover some very key facts that you need to know about Doppler shifts and the relationship to Ultrasound first the Doppler shift is a shift in frequencies this is not a change in amplitude intensity or speed it is the frequency that the red blood cells are returning back to the transducer since Doppler shift is a frequency the unit for Doppler shift is going to be Hertz sometimes you will also see it in kilohertz in ultrasound the Doppler shifts we can detect range between 20 Herz to 20,000 Hertz they also will range from -20 HZ to - 20,000 HZ depending on the direction of the reflector since ultrasound Doppler shifts range between 20 HZ to 20 khz this makes the Doppler shift audible so if you have your volume on and you should when you're performing Doppler ultrasound the sound that you can hear is actually the Doppler shift and lastly the Doppler shift is what is detected and calculated by the machine using a relatively complex formula but the Doppler shift is not what we are interested said it's not the diagnostic part of Performing Doppler ultrasound what we really want are the velocities so by rearranging the formula and Performing calculations the machine will display the velocity of the blood in the area being interrogated section 19.3 Doppler equation now we've already seen this Doppler shift equation it is a very basic equation again subtracting the transmitted frequency from the received frequency the machine is actually very good at this equation because it knows what frequency it is sent out and it understands what frequency it is receiving back but the machine being able to recognize Doppler shift is not very helpful for the diagnostic value from performing Doppler ultrasound so the machine takes the Doppler shift value and then can calculate the velocity of the blood moving through the sampled area so that makes the velocity of the blood much more important to sonographers the problem is though is that this equation does not account for velocity of blood so we need to know the Doppler equation so we can rearrange it to solve for velocity so in its very expanded form here is the Doppler equation we have the frequency of the Doppler shift is going to be equal to 2 multili by the transmitted or operating frequency multiplied by the velocity of the blood multipli cosine of thet all divided by propagation speed in a little bit more of a shortened form I have the abbreviations for all of our variables along with the units that are needed for this formula and then even shorter without the units you absolutely need to know the Doppler equation you have to know that it's the frequency of the Doppler shift is going to be equal to 2 multiplied by the operating frequency multiplied by velocity multipli by the cosine of theta all divided by propagation speed so I do encourage you to start with a little bit more shortened form so you know what the components of the Doppler equation are and how they are related you're never going to be asked to do the actual math or do calculations with the Doppler formula but you will need to know how to rearrange this to solve for velocity and you'll need to know the relationships that exist within the formula I will be showing you some examples of the math so you can see how those relationships change when we change other variables so it's going to be very important to also understand the units that are used in the formula as well every variable in the formula is important to understand what it means to the formula so let's go step by step through each variable and talk a little bit more about what it means and its implication on the Doppler equation formula now the whole purpose of this equation is to allow us to calculate the Doppler shift and we're going to need to know all the variables to be able to do this for remember the machine is already able to determine the Doppler shift based on received and transmitted frequencies as determined by the Dem modulator so we'll see later how already knowing the Doppler shift is going to be calculated into velocity measurements but for now remember again that Doppler shift is calculated based on these variables and it is the change in frequencies because of moving objects the two in the equation is a constant and that is always going to be their you must have that two in there and that two represents the fact that there will be a Doppler shift when the transmitted beam strikes the red blood cell and then another Doppler shift when the red blood cell reflects the sound the operating frequency is also known as the transmitted frequency and that's the sound that is produced by the ultrasound transducer so if you working with a 5 megahertz transducer that is the operating frequency now you really need to pay attention to units in this example we have the operating frequency needing to be expressed in kilohertz so again if we're using that five megaherz transducer and we want to plug numbers into our formula we're actually using a 5,000 kohtz transducer and that is calculated by converting 5 mahz to 5,000 khz this is another variable that the machine knows and is determined by the machine as well now I've already mentioned that for the Doppler equation velocity needs to be a known variable however that's really not the case in ultrasound remember the machine knows the Doppler shift it doesn't know the velocity so later we are going to see how to rearrange this formula to solve for velocity but in the meantime let's look a little bit closer at what velocity actually is velocity is the speed and direction of a moving object the key part here is that its speed and a Direction Where speed is just distance divided by time so again if you think of driving on the highway miles hour kilm per hour that is your speed you have to add a direction into that to create a velocity so in ultrasound we often look at speed in the units of cm/s or possibly meters per second and to translate this into a velocity we need to know a direction and so for ultrasound directions are as simple as towards the transducer which is that positive shift or away from the transducer which is the negative shift however velocity is calculated by knowing the angle of flow in relation to the sound beam so that direction comes from knowing how the sound beam and the flow are related to one another so again very important velocity is speed and direction where speed is distance divided by time at the end of velocity I mentioned that we have to know a direction and the direction is calculated by knowing the angle of flow in relation to the sound beam so this is really where the cosine of theta is going to apply so to accurately calculate the Doppler shift and velocity that angle flow to the scan line must be known so we can kind of think of the cosine of theta as a modifier for the velocity it is going going to tell us if flow is away or towards the transducer which is negative or positive this is also important to know because if the sound beam is anything other than parallel only a fraction of the Doppler shift will be reported or a falsely elevated velocity will be reported so I know that was probably a lot to take in right now let's look at some examples of what that angle means and then what cosine of the angle means so when you see that symbol it's the kind of a capital O with a line through the middle of it that is the Greek letter Theta and when you see that symbol that usually represents that an angle is present in ultrasound the angle is going to be between the direction of flow and the direction of the sound beam so in our example here we have the transducer producing a sound beam and it is entering into the body in this direction remember it comes straight from the sound beam sound doesn't bend sound doesn't turn sound travels straight so our direction of beam is this way as it interacts with a blood vessel or flowing blood that is also going to have a Direction so in this example we can see that the direction of flow is heading off at an angle following this line and the angle that is created between the flow Direction and the direction of the beam is Theta and we want to know this value this is going to be very important for determining what the Doppler shift is so remember that angles are measured in degrees and when we think about ultrasound and what value Theta can have it really can have a value anywhere from 0° to 180° that is basically half a circle that the transducer can be in relation to the direction of flow when the beam is parallel to the flow we will see that the Theta or dler angle is going to be equal to 0° or 180° and you can kind of think of 180° as like a 0° it's on the other side of the line when flow is towards the transducer we are seeing that 0 Dee angle and when flow is away from the transducer but parallel we'll see the 180° transducer trans producers that are in either of these positions are going to provide the most accurate and the greatest Doppler shifts they are also going to provide the most accurate but lowest velocity information so when we change Theta to other degrees we are actually changing the accuracy of the measured velocity and the Doppler shift so for example if we are at 30° or 150° the information is going to be a little less accurate as we start to angle more say up to 45° or 135 it's even less accurate the threshold for ultrasound in regards to inaccuracy is going to be 60° I'll show you why in a minute here but 60° or 120° is the absolute threshold we should never exceed angulation more than 60° to the direction of flow as a sonographer you will be responsible for this angulation keeping a 60° or less angle to the direction of blood flow now the absolute worst place that you can be in relationship to the direction of blood flow is at a 90° angle no Doppler shift or velocity can be detected when we are perpendicular to the flow of blood or Theta equal 90° the machine can't tell if blood is Flowing towards or away from the transducer and therefore we are not going to get any information from this angle so again 0 to 180 are the best ones that means that we're parallel with the blood flow we are either moving towards the transducer or away from the transducer but parallel it is okay to add angulation in but we never want to be angled more than 60° to the direction of blood flow never never use 90° never be perpendicular to the direction of flow and here is why so remember these are all angles of theta but the equation calls for the cosine of theta so once we know what Theta is then the cosine of theta can be applied now cosine is a trigonometry function and it's going to give us a ratio we don't really need to get into the math of it but you should know these values so remember remember when we were talking about the absolute best angulation on the direction of flow we said it could be zero or 180 those are both parallel with the direction of flow and note that less than 90 our values are positive over 90° our values are negative so you can kind of think of these ones as just inverses of this side so 0° to 180° those are going to come up with a cosine value of 1 or negative 1 those are going to be the most accurate velocities or Doppler shifts that we can detect now as we start to angle our transducer beam in relationship to blood flow we start to see a different value for cosine at 30° we're at 0.87 at 150° which is basically a -30° we see a NE 0.87 this is where we're going to get our directions from a positive shift or a negative shift towards the transducer away from the transducer that is why we need these large angulations to show a negative Doppler shift but remember this is really just 60° in the other way this is just 45° with blood moving away this is just really 30° with blood moving away so these are not truly over the 60 they are just kind of the inverse of what we're seeing on this side so again as we angle more notice how cosine of theta begins to decrease the further we get away from one the less accurate we are going to be notice then that we get down to zero as a value of cosine of theta when Theta is 90° or perpendicular to the blood flow so spend some time with these charts definitely know the cosine of 0/0 or 180 definitely know the cosine of 60 and -60 or 120 and the cosine value of 90° because these three values are going to be very important to understanding why cosine of theta matters when figuring out velocity and Doppler shift so let's take a look through some scenarios just kind of discuss these numbers a little bit more in relationship to theeta so when we see a positive cosine OFA value then we are recognizing a positive Doppler shift when we see a negative cosine of theta value then we are recognizing that there is a negative Doppler shift this is how the machine knows is it towards or away when the cosine of theta value is 1 or Nega 1 we are getting the most accurate velocity we are not modifying the true velocity because one multiplied by anything is itself so we are not modifying that true velocity so whenever you can use a 0 Dee angle that is going to be the best possible most accurate velocity or Doppler shift now when cosine of theta is anything other than one or negative 1 we're really only reporting on a portion of the Doppler shift being measured so the closer to one cosine of theta is the more accurate the information will be however in ultrasound it's really hard to get a 0 de angle on the blood flow especially when we're looking at limbs so we've decided by ultrasound standards that the maximum we are willing to go to is 60° with Theta and when we take the cosine of 60° we get 0.5 0.5 means that we are really reporting only half of the doppers shift value but we are okay with that we know that this is a reproducible number and lastly when Theta is 90° the cosine of theta is going to have the value of zero and this is very important that we never use 90° that's because when we take that value of cosine Theta we end up basically with 0 divided by the propagation speed if we were to plug that zero into the equation then 0 / by anything is still zero so no do shift can be detected we won't be able to calculate a velocity so never Doppler at 90° to the blood flow lastly then we have our variable on the denominator side of the equation and that is C and C we have learned before represents propagation speed propagation speed determined by the medium medium and ultrasound is soft tissue so we are going to default to the propagation speed of 1540 m/s but as you can see in this formula it is requiring a propagation speed being represented in cm/s so we would need to take our 1540 m/s and convert that to 154,000 cm/ Second as our propagation speed in soft tissue now remember that this is a constant in ultrasound it's a constant with soft tissue so this is the value that you would most likely use from the ultrasound perspective but remember in the back of your mind that c is propagation speed and if we were trying to figure out the Doppler shift in regards to a siren then we would want the propagation speed of sound in air so C is propagation speed because we are dealing with ultrasound and Doppler of blood vessels we will use our constant soft tissue propagation speed so now as with all of our equations that we've been learning throughout physics we really do need to understand what the relationships are and the formulas really allow us to see that very clearly we just talked about propagation speed being a constant so we really don't need to focus on how the propagation speed in soft tissue is related to the frequency of the doler shift because that's going to be a constant what we do need to focus on are how the operating frequency or transmitted frequency velocity and the cosine of theta are going to change the Doppler shift well the good news is from this formula we can see that all three of those are in the numerator position so if any one of those increase we are going to see an increase then in the Doppler shift because they are directly related now these relationships are going to be very important because you're going to be asked about how variables are related to another how they will change one one changes on your quizzes on your tests on your boards you're never going to be given values of variables and then expected to complete a calculation based on the Doppler equation however you might be asked a question kind of like this the Doppler shift with a 4 MHz transducer is 3,000 Herz if the sonographer switches to an 8 mahz transducer what happens to the Doppler shift this question is asking do you understand how the operating frequency and the Doppler shift are related to one another and knowing that frequency of the transducer is directly related to the Doppler shift because you know your formula and know how relationships are represented you should be able to say that the Doppler shift will either double increase by a factor of two or is now 6,000 Hertz and that's just going to depend on the options that you're given there's very little math that is occurring in this question it is truly asking do you understand how these variables are related to one another so I do want to show you some examples of calcul in the Doppler shift using our big formula and through looking at that math we're just going to take a look again at how those variables are related to one another so if you have your workbook out you might want to pause now and just see if you can work through some of the examples see if you can do the math before we get to it but it is not necessary we're going to go through each one briefly here so our first question says calculate the Doppler shift based on this information we're given a transducer that is operating at 4 mahz the velocity of blood is 100 cm/ second and the Doppler angle is 60° we're going to need to take some of this information convert it plug the numbers into our equation and then definitely using a calculator because this is not expected of you to do this math come up with our answer so remember our Doppler shift is going to be equal to two got to remember this two that two will always be there multiplied by the operating frequency now the equation that I gave you requires Kilz so we got to convert 4 mahz into 4,000 khz we're going to multiply that by the velocity of blood which was given to us in our correct unit and then we need to multiply that by the cosine of theta remember Theta is the Doppler angle so we need to take the cosine of 60 and that was one of the values I need you to remember what's the cosine of 60 it is 0.5 and then we plug in our constant propagation speed because we are working in soft tissue so 154,000 cm/ second if you pull out your calculator and plug in 2 * 4,000 * 100 * 0.5 and then divide all that by 154,000 what you'll get is 2.6 and so we are calculating the Doppler shift as being 2.6 khz now 2.6 khz is the same as 2,600 Herz that falls into our range that 20 HZ to 20,000 Hertz that dopper shifts typically are seen in it is a positive value so what we have calculated is a positive Doppler shift of 2.6 khz so I'm going to leave that initial equation down in the corner here for our examples and what I've done is change a few of those numerator variables so we can see what happens to Doppler shift as we change those variables so in example two here I have now doubled the frequency compared to example one what do you think will happen well if we double the frequency we would expect a doubling of the Doppler shift because they are directly related and that's exactly what happened again just plugging our numbers in we get an answer of 5.2 khz 2.6 * 2 is 5.2 so we have seen a double in the Doppler shift you don't even have to do all of this again if you know 8 MHz is twice of 4 MHz then you should be able to multiply 2.6 by 2 to get 5.2 number three says now we've tripled the velocity compared to example one what will happen so we were at 100 cm/s we've tripled the 300 cm/s if velocity increases by a factor of three then we expect the Doppler shift to increase by a factor of three again you can plug your numbers in or you can just take 2.6 multiply it by 3 and we get 7.8 khz the Doppler shift has increased by a factor of three our next example now we've changed the angle to 0° what's going to happen to the Doppler shift now this one's a slightly little trickier because what we need to do is figure out the cosine of 0 compared to the cosine of 60 and if you remember I told you need to know this cosine of theta when Theta is zero the cosine of theta value is 1 so we plug in our value of one do the math and we get 5.2 if you recognize that going from 0.5 to 1 is the doubling then again you don't need to plug in all the numbers again it's just going to be a doubling of the Doppler shift because again any of these variables on top whatever they increase by our Doppler shift is going to increase by so here's another example now we've changed the doler angle to 180° so we have to figure out what the coine of 180° is and plug it into our equation cosine of 180 is NE 1 so now we can put in that negative 1 and because we have a negative value in our cosine we end up with a negative Doppler shift so that is how again Doppler shift is going to be recognized as away or towards the transducer and that is how we're going to get a true velocity of being away or towards is cosine positive or is cosine a negative value this next one I changed the velocity of blood to 50 cm/s so this was half of what example ones was so how is the Doppler shift going to change when we decrease the velocity of blood to half of what it was knowing the relationships again you should be able to say that the Doppler shift will be half of what it was but we can always plug in our numbers and we can verify that 1.3 is half of 2.6 and with our last example I went and changed the Doppler angle to 90° now this one isn't going to be as good to show us relationships but it will show us what happens when we are dopping at a 90° angle remember the cosine of 90° is zero so if we plug this in we put zero in our cosine of theta value spot put this in your calculator 2 * 4,000 * 100 * 0 makes this whole top part the value of zero so we basically have 0 / 154,000 and that's going to equal 0 so there is no Toler shift when we are at 90° now in all of these examples I was able to give you the velocity of blood but that's not what the machine knows the machine knows the Doppler shift and wants to calculate the velocity of blood so let's take a look at what we need to do section 19.4 velocity of blood so we learned the Doppler equation to help us bridge to being able to calculate the velocity of blood the machine already knows what the Doppler shift is so it's really velocity of BL blood that needs to be calculated by rearranging the Doppler equation we can now solve for the variable that the machine does not know the values and the rules for each variable are going to be the same so here we have our velocity equation based on the Doppler equation we will now see that velocity is going to be equal to propagation speed multiplied by the Doppler shift that is divided by 2 multiplied by the transmitted frequency multiplied by the cosine of theta so you need to know the velocity formula as well or know how to rearrange the Doppler equation to get to the velocity equation now again you are not going to be given numbers for your variables and then expected to do this calculation you are going to be expected to know how variables affect one another what are the relationships so so the velocity equation makes the relationships maybe a little bit trickier but we know that the value for C especially in ultrasound isn't going to change that's still our 1540 m/s or for this formula 154,000 cm/s so if we look at the equation a little bit closer what we'll end up seeing is that Doppler shift and velocity are directly related the Doppler shift is on the numerator side of things if it increases velocity will increase if dopper shift decreases velocity will decrease and we already learned that from the Doppler equation relationships so now we need to focus a little bit more on what happens when we change our operating frequency and our cosine of theta so if we decrease our operating frequency we will see an increase in velocity and that is because these are inversely related if we were to increase the operating frequency we'd see a decrease in velocities so the same is going to be true then for the value of the cosine of theta if we decrease the value of cosine of theta then we should see an increase in the velocities that are reported now again you're not going to be asked to do the complex math but you should know your relationships so if we say the Doppler shift doubles what happens to the velocity well they are directly related you should know that velocity will double what happens to Velocity when the Doppler angle changes from 0 to 60° well that is a decrease in the value of cosine it's going from 1 to 0.5 so again we would see an increase in the velocity reported you need to know the formulas to understand the relationships and be able to talk about how those variables change when we learned about the Doppler equation we talked about that the cosine of theta is kind of a modifier on the velocity and the Doppler shift so when we were calculating for Doppler shift as the cosine value became further away from one or less than one we were reporting a fraction of the Doppler shift but now when we are looking at velocities as we get further away from 1 or netive 1 and closer to zero we actually start increasing the velocity that's reported so knowing that our cosine of theta the angle that we are dopping at changes the reported velocity we want to strive to be parallel to the beam when possible and that is because the most accurate velocity is measured when the sound beam is parallel with flow for the abdomen and for the heart we are actually capable of finding windows that allow us to be parallel with flow but it's actually very difficult to be parallel with the blood flow when we are looking at limbs or the neck it's really nearly impossible to be at 0 or 180° to the flow therefore we find that it is acceptable to be at 60° or less when performing Doppler remember 60° can be 60° which is basically 120° so 60° or less when performing Doppler is acceptable now we know that when we are using 60° as our Doppler angle we are creating a cosine value of 0.5 which means that our velocity is actually going to be twice what it really is but we are okay with this the ultrasound values that are used for diagnosing based off of velocities take into account that we can't always be at that 0 degrees and we know that there are limitations to the equipment and to the windows that we are using the important part about using that 60° is that the sonographer one does not go over it but two accurately tells the machine what angle they are using and this is going to be done through a piece of Doppler instrumentation called the angle correct knowing then that 60° is our absolute threshold for the Doppler angle any angle above 60° is too inaccurate for Diagnostic Ultrasound with 90° being the absolute worst and remember that the cosine of theta also determined if the blood was flowing away or towards the transducer and we need to know that because Direction is important to the value of velocity otherwise it would just be a speed if we didn't have a Direction so when the velocity is reported on our Doppler tracings it will be displayed as either above or below a baseline so if we take a look at this spectral tracing this is the graph that shows us the Doppler information that is coming back from the machine what the machine has calculated and this is going to show velocities along the Y AIS we can see here that the units are in cm/ second and then above the Baseline which is zero so above the Baseline are positive Doppler shifts and below the Baseline in this instance are negative Doppler shifts so we can see that the spectral chasing is showing Doppler shifts that are mostly positive with a little short section of a negative Doppler shift in relationship to blood flow and the transducer from this graph then the sonographer can use tools on the machine to measure the absolute highest velocity very accurately they can measure the velocity right before the peak they can measure how much is going below the Baseline with our 60° insation angle or less we consider these velocities to be sufficiently accurate so next up I have the answers to the practice that you'll find in your workbook the questions are asking you to identify which transducers would provide highest and lowest doers shifts uh highest and lowest velocities and questions like that so if it makes sense to you please feel free to skip to the next section otherwise hang around and we'll go over each question now this is the diagram that you will see in your workbook and it will ask you different questions about the transducer position and its accuracy to do shift or to velocities so the first question asks us what transducers are going to produce the most accurate velocities now when we are looking at Accurate velocities we want our sound beam to be as parallel as possible so the most accurate velocities are going to be from transducer a and transducer B A will have a very accurate positive velocity or B will have a very accurate negative velocity they are parallel with the direction of flow the next question asks what are going to be producing acceptably accurate velocities so we already know that A and B are the most accurate so those would be ideal but we know that we can also have angulation to the direction of flow and still be acceptably accurate so C and D are both going to provide accurate flow when considering ultrasound limitations remember we do not want to increase the angle more than 60° next we've have of which transducers are going to produce negative Doppler shifts so these are going to be any transducers in which the direction of flow is heading away from them so that is going to be transducer b d and g next we have which transducers are going to display positive Doppler shifts and these are going to be the transducers in which the blood is Flowing to them so that'll be a c and e next up we have which trans producer will not provide any Doppler shift and that is only f f is at the 90° or perpendicular to the direction of flow therefore a Doppler shift will not be detected now which transducer is going to provide the greatest Doppler shift that'll actually be transducers a and b remember that they are parallel with the direction of flow therefore their cosine of theta value is going to be 1 so we are reporting the highest possible Doppler shift when we are parallel with flow and the cosine of theta value is one the next question asks us then which are going to provide the smallest Doppler shift and that's actually going to be transducer e and G now e and G are not providing diagnostic information but because their angulations are much higher that means the value of cosine of theta is going to decrease and when the cosine of theta decreases we will see a Doppler shift decrease as well because they are directly related now do not confuse greatest Doppler shift and smallest Doppler shift with greatest velocity and lowest velocity because here's why next question asks us where are the highest velocities going to be reported this is going to be transducers e and G because now remember velocity and the cosine of theta are inversely related so when the cosine of theta decreases as it will with E and G the velocity that those transducers will report is going to increase they are inversely related the lowest velocities then are going to be found in transducers a and b the value of cosine of theta has gone up to one so cosine has increased therefore velocity is going to decrease A and B are going to show the lowest velocities but they happen to also be the truest or most accurate velocities as well the last question then is which transducer will provide no velocity information and that is f again we are 90° to the the blood flow and we cannot calculate a velocity when we are 90° section 19.5 Doppler instrumentation now that we've learned about the math and the actual physics behind the Doppler equation let's take a look at how we can provide that Doppler information using our ultrasound machine so modern machines allow for bidirectional Doppler detection remember that's that negative or positive above or below the Baseline so this means that they can recognize and display blood flow that is either moving towards or away from the transducer and the reason that modern machines can do this is because they can use something called phase quadrature now this is a mathematical application and phase quadrature or quadrature detection is going to analyze the Doppler signal to determine the direction of flow as it's related to the transducer now in ultrasound spectral Doppler signals can be attained through either continuous wave Doppler or through pulsed wave Doppler these are both going to produce a graph showing velocities of the red blood cells as they pass through the ultrasound beam now color flow is another type of Doppler that also uses pulse wave ultrasound this is where colors are placed over an image to indicate Direction and average velocities section 19.6 continuous wave Doppler now recall that continuous wave ultrasound being cannot produce an anatomical image they can however produce Doppler shifts which can be graph then into a spectral wave form continuous wave Doppler is most commonly used in cardiac applications and also during physiological vascular testing in the transducer unit we did talk about continuous wave transducers but to review a dedicated continuous wave transducer has to have at least two crystals one to transmit 100% of the time and one to receive 100% of the time the transducer is on 100% of the time meaning it has a duty factor of 100% it is constantly sending and constantly receiving the way that continuous wave transducers are created makes them very sensitive and that is because they don't have a backing material in them without that backing material they have a very high Q factor and a very narrow bandwidth and remember this is all true of dedicated continuous wave transducers now in the cardiac setting phas array transducers are capable of creating images and then using two crystals to perform continuous wave Doppler tests now remember that continuous wave transducers always need two crystals to operate again one to transmit 100% of the time and one to receive 100% of the time in this example the sonographer is using a phased array transducer that is how they are able to create the anatomical image but they have turned on the continuous wave function and now two of the crystals from the face Ray are dedicated to create the continuous wave Doppler so when I continuous wave transducer is being used sound is emitted from one of the crystals and the other Crystal's listening path is going to overlap the transmitted beam and this is going to create a very large area from which the transducer can receive Echoes from and this area is going to be called the sample volume now because there is no Imaging to guide a dedicated continuous wave transducer the sonographer really must rely on anatomical knowledge and Vascular analysis to interrogate the correct area now once you find the area that you are interested in dopping the machine will produce a graph that represents the velocities that are detected from from the sample volume so many sonographers are also going to use speakers on their machine to evaluate the flow through the sample volume because remember those Doppler shifts are audible there are a few advantages and disadvantages to using a continuous wave transducer these do have a little bit more clinical implication and we're going to discuss it a little bit further in unit 20 but just as a preview the advantages of using continuous wave means that we can detect very very very high velocities because the transducer is constantly emitting sound and constantly receiving it makes it so that the truest highest velocities are able to be detected and that is because there is no aliasing again we'll Define Aline and do a very deep dive in it in unit 20 now the disadvantages of the continuous wave probe is that range ambiguity and that refers to the idea that we really don't know where we're getting Doppler information back from remember it's not producing an image we are going off of what we can hear what we can see in our graph and our anatomical knowledge the other issue too then is that there's no TGC for continuous wave dopplers if the area that you're interrogating is very far away from the transducer then your red blood cells are not providing a lot of amplitude to be displayed brighter on the screen so we can't account for attenuation of the sound beam as it travels into the body which can therefore change how our display looks as well section 19.7 pulse wave Doppler so recall that pulse wave ultrasound can create an image and only needs one Crystal to do so so the same is true for pulse wave Doppler only one crystal is needed to create a Doppler spectral tracing and since all of our modern transducers that can produce images can also produce pulse wave Doppler it's very common that we're going to use these multiple modes Doppler 2D and color in conjunction with one another during an exam so when the machine is creating an anatomical image or the 2D image and a doler tracing or color doppers being used we call that duplex Imaging so again that's the 2D plus a Doppler function color or Spectrum when a machine is creating a 2D image and using both color and spectral tracing we call that Triplex Imaging now it's very very uncommon that you will ever just do a 2D image with Doppler tracing we want that color information to help us guide where we place our gate from the pulse wave scan line and just like the continuous wave transducers we did all already cover pulse wave transducers but remember that they do need at least one Crystal to operate they are on only a small fraction of the time meaning that they're usually listening for echo's returning they have lower sensitivity because they have backing material and that backing material is going to cause them to have a low Q factor and a wide bandwidth now when we are using our ultrasound machine to obtain pulse wave Doppler you will typically need to find the anatomy that you want to get the pulse wave information from you're also going to turn on color the color does help to guide us where we want want to place our pulse wave instrumentation next then you will activate the pulse wave Doppler usually through a knob or button and what will appear is a scan line over the 2D image remember that the array transducer only needs to dedicate one Crystal to the pulse wave Doppler application the scan line that appears represents the One crystals scan line so you know exactly where you are getting Doppler information from in the middle of that scan line are going to be two parallel lines and they kind of have a gap in between them this is called your sample gate or sample volume now you can change the size of the gate you can make it bigger or smaller and then you're going to place that gate exactly where you want your Doppler information to come back from now in the gate if there is not a third line that means that the machine is assuming a Doppler angle of 0° and this is usually going to be the case when we are Imaging the heart or when you are not concerned about measuring accurate velocities however any time that you need to measure an accurate velocity and cannot get that 0° you have to have your angle correct on and that is what this third line is called This is called the angle correct now the angle correct allows us to tell the machine what angle to use for the cosine of theta value when calculating velocity so there's two very important things about this angle correct line there will be a knob on your machine that you can turn and it will rotate the angle correct you want to rotate the angle correct and steer your beam so that your angle correct is parallel with the vessel it'll be located through the fastest part of the flow parallel with how the flow is going the second most important part then is that it is telling the machine what this angle is this is Theta this is the angle that we don't want to exceed 60° on on your machine you will typically have a display somewhere that tells you what the Doppler angle is so in this case it is 60° so again this is the angle correct the angle correct will be placed parallel with the flow of blood that means it's typically parallel to the walls of the vessel the angle then is between the flow Direction and the scan line This angle must be less than 60 typically what happens is that you'll place your angle correct so that it is parallel or through the middle of the direction of flow and then you can steer your scan line to become a little bit more of acute or you can make it a little bit more up and down and then that is going to change the angle in between your angle correct that's designating direction of flow and the scan line so there are multiple ways to make sure that we stay at that 60° or less so the really cool part about pulse wve Doppler is that the sample gate does allow us to choose exactly where we want to get that blood flow from so if I had like a really fast jet up here I could move the gate to this area and see what the velocities are here so pulse wave Doppler allows me to choose exactly where I want to get information from and that is known as range resolution so that's a lot different from continuous wave where we can't choose the depth we can't choose where we're getting information from or pulse wave Doppler can now here are some examples of the sample volume and this or the sample gate being placed within a vessel along with the angle correct taking a look at this top one here we can see the scan line coming through the screen the two parallel lines the space that's between them that's the sample gate or sample volume and then you can see a third line through here that is the angle correct now the angle correct first off is not being placed parallel with the flow so that's already a big no no we're not going to get diagnostic information secondly you probably can't see it super well but it is at 84° so that is way too much of a difference in beam angle versus flow angle we need that to be under 60 so this is a very very poorly placed angle correct and way too large of a Doppler angle in this example we are now below 60 so we've got 16° for our Doppler angle again that's the angle between the angle correct and the scan line but again our angle correct is not accurately placed to show how the blood is Flowing so this again is not an accurate way to measure velocity we have to tell the machine how the blood flow is flowing and it will recognize then what the angle of theta is in this example we are finally at a correct diag ostic placement of the angle correct and the scan line so again we can see the angle correct here is now parallel with the flow so we are telling the machine this is how the blood is flowing and then the machine can calculate what is the angle between the scan line and the direction of blood flow it is telling me that we are at 60 Dees that is acceptable and quite often preferable especially for necks and limbs so this creates a diagnostic image and diagnostic values for our velocities now this example is in the heart and we are looking at our scan line coming down and our two parallel lines that's the sample gate now in this example we don't have that third line really being visible cutting across the gate and that is because this is at a zero degree Doppler angle scan line is coming straight through here we are saying that the blood flow is Flowing directly at the scan line it is parallel it is a 0 de angle between scan line and flow of blood and again that is very very common in the heart so if you are an echo sonographer or an echo student this is where a lot of students get kind of confused they're like I never have to use that angle correct for the other parts of the body we have to use that angle correct we have to tell the machine which direction the blood is Flowing technically in heart applications you could angle correct through here you could say this is how the blood is Flowing maybe it'll be just a couple degrees off but because of the windows cardiac applications use we almost always just default that we're at that 0° this is also probably a really good time to mention too that you do not need to know Anatomy to pass your boards you do not need to know that this is is a crowed artery you do not need to know that this is a heart what you do need to know is that this is a scan line This is a sample gate this is the angle correct is the angle correct less than 60 can I find that information in the machine's display and does it make sense for creating a diagnostic image and just like continuous wave Doppler pulse wave Doppler also has some advantages and disadvantages again these are a little bit more clinical in practice so we will touch on these again in unit 20 the biggest advantage to pulse wave is that it has range resolution range resolution means that you can decide what depth what area where that Doppler information is coming from that is awesome about pulse wave Doppler the other great thing about it is that you can change the sample volume do you want to sample a very large area or do you want to sample a very small area you can make that decision the disadvantages of pulse wave Doppler though can be pretty detrimental to the diagnostic value of our ultrasound images pulse wave Doppler cannot detect High velocities there is a limit to how high of a velocity a pulse wave transducer can detect and that is called the Nyquist limit and again this is very clinical in application so we will cover this in much more depth but when the velocity reaches the Nyquist limit what we end up seeing is is alosine and alosine essentially is just on that graph this is the Nyquist limit here there is clearly more to the pulse wave more to the velocities that need to be graphed so they kind of wrap around and get placed in the wrong area this is considered artifact and this causes our information to be non-diagnostic so clinically we need to know how to fix this which is why we're going to cover it a little bit more in the next unit now when we're using the pulse wave Doppler application on our ultr sound machine the resulting wave form can be measured with machine calipers to accurately identify the velocities and this is because of the fast for your transform now the fast for your transform is the technique used by modern ultrasound machines to understand the doppers shift information returning to the machine and create the spectral waveform and we talked about that the red blood cells are going to send back different freen quencies based on if they're moving away or towards the transducer well there's more than just one red blood cell traveling through the gate and so there are going to be multiple red blood cell frequencies returning back to the transducer and the fast for your transform is going to be able to recognize that there are multiple frequencies coming back from multiple red blood cells and it's going to allow the machine then to display how those individual red blood cells cells are traveling in regards to the transducer so because the fast fa transform can analyze all this information we end up getting really detailed information in our pulse wave spectral tracings to talk about some terms that we've already heard the fast foror transform recognizes where those red blood cells are maps them onto the graph and now we can determine if flow is laminer or turbulent so in this example here we have very laminer flow the red blood cells are mostly moving all at the same speed or the same velocity because they're all kind of grouped together in this Thin Line the red arrow here is pointing to something called the spectral window again we'll talk a little bit more about this in the clinical portion but as those red blood cells start to travel at different speeds we start to see kind of a widening of that line and that's because this little red blood cell that the fast barrier transform recognize is traveling at a slower velocity than this little red blood cell reflection up here compared to this one and this one they're all different reflections of the speeds of the red blood cells so the fast for your transform allows the machine to be able to identify all these different velocities from the individual Reflections so this is starting to probably be a little bit more Disturbed flow and in this picture down here we're really seeing that chaotic flow we've got flow all the way from the Baseline zero velocity all the way up to the peak here and we've got a lot of different flows going through here again all these little Speckles that are in here all these little dots represent Echoes that are coming back from Individual red blood cells and it's the fast for your transform that is able to detect those and map them onto the graph so your spectral tracing is the mapping of the reflections from the red blood cells as they're translated through the fast for your transform modern machines use the fast foror transform it is a computer based analysis to look at the Doppler information now there used to be some older versions that were analog remember digital versus analog digital is what we're using now with the fast faor transform our analog options included a zero Crossing detector chirp Z transform and interval histograms so the only thing you need to know about these three terms is that that these these were the older analog ways in which spectral tracings were analyzed modern current machines use digital computer-based fast foror transform to analyze our Doppler shifts section 19.8 color Doppler so color Doppler is also a pulse wave technique but instead of giving measurable accurate velocities it is going to display average velocities as a 2d overlay so so the assigned colors are going to provide information about direction of flow now color Doppler uses pulse waves so we can choose where to get color Doppler information from but the problem is that it is also subject to aliasing now since color doler does not provide exact measurable velocities it is only considered kind of a semiquantitative method of velocity measurement and just like all of our other dopplers when we use color Doppler it is best when it's added an angle especially at zero and 90° should never be used because it cannot be calculated but we have a little bit more wiggle room with this one because we are only looking at the average velocities and we're not looking to measure an exact velocity we don't have to be as concerned about the accuracy of the Doppler angle when the colors come up on our display they will usually come up with a few different colors Reds Blues some yellows some greens and what the machine needs to know is what color to apply to certain velocity ranges so the machine gets the Doppler information back calculates the average velocity and then looks to the color map as a reference tool to match the velocities to a color now the map is usually displayed on the machine as a vertical bar it is adjustable in that you can change the scale or the prf of the color map which color is assigned as towards or away from the transduc producer and the Baseline of the color map as well the maps also come in different Hues you might see some that lean to like just Reds and blues and whites uh where a lot of them kind of use Reds oranges and yellows or Blues Light blues and greens either way though there are two types of color maps that we commonly use one is the velocity mode map or a variance mode map when we are using the velocity mode Maps which is probably the more common map that is used the velocity mode is going to show us Direction and velocity which I get is a little bit redundant because we need to have a direction in our velocity anyway but this is a map that allows us to easily recognize what direction is being displayed for the velocity so when we look at these color Maps whatever color is on the top of the bar is flow that is moving towards the transducer or producing a positive Doppler shift in the middle the map you will see a black bar this is the Baseline of the map and anything that shows up black is being recognized as having no Doppler shift now below the Baseline are colors that are going to represent flow that is away from the transducer or producing a negative shift so again above towards below away as a sonographer you can choose do you want blue on top or do do you want red on top do not be confused blue is not always towards red is not always towards you can decide as a sonographer how you want the map to be displayed so these three components show us the direction that is being recognized with the color that's being displayed now the velocity part of it is seeing more in these subtle differences of the color when we have a really dark blue or a really dark red it color that Maps closer to the Baseline of the center these are going to be slow velocities CU remember our Baseline is zero so this is a 5 cm/s velocity maybe right next to the Baseline As you move away from the Baseline note how the color changes we're kind of moving into like a lighter blue some maps even go into green uh with the Reds we usually go from red orange to a bright yellow so as we move away from the base sign velocities velocities that get matched to these colors are going to be higher so again if this is zero this might be like a positive 5 a positive 10 15 20 30 40 50 maybe 60 is the highest velocity that this map is going to map to so if you see bright yellow on your screen then you can assume that the average velocity through that area is about 60 cm/s same is true as we go away from the Baseline on the bottom side we're getting higher velocities they're just High velocities that are away from the transducer now the variance map is very similar but the variance map is not only going to show speed and direction but also adds in are we experiencing laminer or turbulent flow so in our variance mode again the color on top is showing towards the transducer colors mapped to the bottom of the color map are away from the transducer we again have our Baseline meaning these are areas that have no Doppler shift now the variance map adds in the laminer and turbulent flow so on the left of the map are colors that represent laminer flow so think left laminer l l left laminer that's true for above and below the Baseline these colors over here are laminer flow flowing towards the transducer these colors here are laminer flow flowing away from the transducer as the color goes across the map and starts to move towards the right side of the map these are going to be turbulent flows so any light blue in the map would be turbulent flow towards the transducer this would be turbulent Flow Away from the transducer you'll also see then that colors that match more towards the Baseline colors are slow velocities where they get to be higher velocities away from the Baseline so with variance Maps it's not uncommon to see the colors change not only from side to side but up and down as well now the variance maps are not as commonly used but again it is up to each individual lab and it's up to each radiologist provider or sonographer preference on which map they use so again no matter what map you are using top color is always going to represent flow that is towards the transducer or the bottom color is going to represent flow away from the transducer again it doesn't always have to be red towards or blue away or even vice versa it is whatever you a sonographer said it as so in these examples down here these are both velocity Maps we can see our Baseline black bar here we have darker Blues transitioning into brighter whites dark Reds transitioning into bright yellows Baseline anything black is zero Doppler shift dark Reds are slow velocities bright yellows or bright whites are high velocities so if we look at this example here this this is the portal vein in the liver this is our color box transducer is up here flow is red we know that it is towards the transducer you'll also notice that there are some like little tinges of yellow in here as well that little yellow bit through there indicates a little bit higher velocity being recorded and also note that those are through the center of the vessel on this side here again we have a velocity color map Black in the middle representing our are no flow red on the top meaning towards the transducer Blues on the bottom meaning away from the transducer the transducer is up here so if we were to take a look through this red area here we know that this is flow that is Flowing up towards the transducer which in this case is down at the bottom of the heart so we are seeing flow from the Atria to The ventricle we can see some areas of blue here these are representing areas that have flow moving away from the transducer you can see a little area of black here this indicates that there is no recognizable Doppler shift in this area so no color has been assigned and again the brighter the yellow the faster the speed the brighter the light blue the faster the speed where the dark blue and the dark red indicate slower velocities and just like pulse wave Doppler color Doppler does need to be performed with an array transducer CU we are going to have some of those crystals dedicated to obtaining the color Doppler information so typically find the area that we want to interrogate using our 2D Imaging and then we are going to activate the color by pressing a knob or button on the machine what's going to appear then is a color box and so the color box usually takes on the same shape as the sector so here is the color box and anything in this color box is going to be the area that pulse wave Doppler is going to be obtained from and then mapped to the color map as a stenographer you can change this color box you can make it bigger or smaller wider taller you can also move it if you wanted to be over here you can move it here you can move it to the top of the screen you can move it deeper into the screen now this is a curved linear transducer so we're seeing that type of sector here but if you were to be using a linear sequential transducer remember those produce rectangular 2D images you're going to actually have the option to steer your box as well to make it a parallelogram so the sonographer then will move this box to wherever they are interested in Remembering to not make the Box perpendicular to flow that they're trying to see again we can see our color map up in the corner here with red being towards blue being away and our black bar in the middle so we can see then without knowing Anatomy or anything that this blue area is representing flow that's moving away from the transducer and this red Anatomy is representing flow that is moving towards the transducer for the physics boards you will not need to know what these vessels are if they're flowing in the normal Direction you just need to be able to match what you're seeing to the color map and how that relates to the transducer now to obtain the information from the color box I mentioned earlier that there are going to be crystals dedicated to creating the color box information those crystals are going to send multiple ultrasound pulses and the multiple pulses that are sent from those crystals are known as a packet or Ensemble for most machines you need a minimum of three pulses to create color Doppler information but most of our machines are going to use 10 to 20 pulses per scan line to get the color Doppler information from the crystals creating the box now there are some benefits and drawbacks to using either a small or large packet size so if we look at the more pulses which means the large packet size or long ensembles we going to see greater accuracy in the color box so for example let's just say we have 10 crystals dedicated to make in our color box when we increase the size of the packets or create long ensembles we are telling each of those crystals to send more pulses so maybe each crystal is responsible for sending 15 pulses when we have those more pulses we're going to see greater accuracy we're going to get better information back from the flow in the area we're also going to be a lot more sensitive to slower flow in that area the more Pils that are being used gives the machine a chance to get more information kind of recognize those slow frequency shifts the problem is though that whenever we are needing more pulses to get more information that means we need more time because we can't send overlapping pulses so large packets or long ensembles are going to require more time which decreases our frame rate and temporal resolution so it'll be up to you as a sonographer you need to decide what is more important do I want better frame frame rate with less color sensitivity or do I want more color sensitivity and accuracy but sacrifice my frame rate to do so often times you're just going to choose kind of a balance between the two and quite honestly as a sonographer using modern machines The Ensemble packet size adjustment is rarely an issue it is not a machine tool that I change regularly typically whatever the machine is set up to use is sufficient for our purposes but again you should know that you have the ability to use more pulses or less pulses those pulses are called packets or ensembles and then if you're using a lot of pulses they're called large packets or long ensembles and you should know the benefits and drawbacks to using them recall that the pulse wave Doppler used fast for your transform to analyze the information that was coming back through the Doppler shifts and graph them the fast foror transform has to be very accurate because we want to go into that pulse wave spectral tracing and measure for exact velocities color because it's only doing average velocities does not need to be as accurate so it uses something called autocorrelation so autocorrelation again is another computer-based technique that is going to be used to analyze the color flow Doppler so as those velocities are coming back and it has to match it to the map that is where the autocorrelation comes in it doesn't take a whole lot of processing or data to get to that part of it so because of that the speed at which color Doppler can be obtained processed and displayed is actually pretty quick and we need it to be that way so we don't sacrifice our frame rate or temporal resolution more than necessary the last concept that we're going to talk about in regards to Doppler physics and instrumentation then is power color Doppler Now power color Doppler is a subset of color Doppler and it's also known as either energy mode or color angio sometimes it'll hear it referred to as just power doppler and I've got an example here of a kidney that is using power doppler notice there's still a color map here but notice that there's no Baseline we have from really bright yellow to a darker red now the cool thing about power color Doppler is that its sole purpose was just to recognize any sort of Doppler shift it didn't care if it was away or towards it totally skipped that portion of the analysis it just cared was there any sort of Doppler shift so it was a very simplified colorization of any motion detected by the machine now this kind of Doppler does have some advantages and disadvantages as well so powercolor Doppler is very very sensitive that meant that you could show very slow flow uh flow in very tiny vessels or even flow that was super deep into the body but because it's so sensitive it was really likely to show excessive color anytime the transducer moves or if the patient were to move it would recognize that as motion and then Show color so you might get kind of this blooming of color around the true Doppler information power color Doppler is also not angle dependent so we are not worried about keeping in with that 60° or trying to get to zero it is going to recognize motion at any degree except for 90° so any motion is able to be detected and then assigned a color to represent flow there is no alosine typically with color do again is just looking for motion it doesn't care if it's away below how fast how slow it just wants to know that there's motion and then it will sign color to it powerc color Doppler does require a lot of pulses though to be so sensitive and because of that it does cause a lower frame rate and lastly because there is no angle dependency then it was not able to provide direction information either so this can be considered a downfall a powercolor Doppler however newer machines more recently have been developed with power doppler that does allow for Direction so this is definitely a newer Improvement to our machines now if you're wondering if your power doppler provides Direction you can again look at your color map notice how this one again does not have that black bar there's no Baseline there's no zero so this is power doppler with no Direction when you are using a newer machine that does have power doppler with Direction you will see a very similar color map to like we saw before where it does have that black bar representing the zero or the Baseline and that brings us to the end of our Doppler physics and instrumentation discussion now I know that was a lot of information and the next unit is going to build on this information so before moving to the next unit make sure that you are comfortable with what the Doppler effect is what a Doppler shift is and what the Doppler equation is you should be able to recognize what each variable is why it's important and how it affects Doppler shift moving from that part of it then you need to take a look at velocity and the velocity equation re recognize those relationships that we saw from the Doppler equation now applied to Velocity and then start to put it together of how our angle to the direction of flow affects Doppler shift and how it affects velocity recognizing how that Doppler angle affects the Doppler and velocity information that's coming back is really going to help you with the clinical application of Doppler ultrasound looking more at the instrumentation side of things make sure to recognize what continuous wave Doppler is versus pulse wave Doppler recognize what the differences are between the transducers and then have a preliminary understanding of the advantages and disadvantages of continuous versus pulse wave again we're going to cover that a little bit more in unit 20 so if we can kind of have that base knowledge moving into that the clinical application of pulse Doppler versus continuous wave Doppler will be a little bit more apparent lastly then review the color Doppler information especially on how the color map is applied to the color displayed and then for all the instrumentation make sure that you go back and take a look at some of those key words phase quader bir directional Doppler autocorrelation packets ensembles angle correct scan lines sample gate sample volume all those terms are going to be used in the clinical setting so I want to make sure that you understand what they are and what they apply to so when we use them to discuss the clinical portion of it it'll come easier remember that you do have your activities in the workbook that go along with the lecture as well as the nerd check questions those open-ended questions that you can use to assess your knowledge of the information presented