The different types of Doppler ultrasound

 The different types of Doppler ultrasound

 The differences between the different types of Doppler imaging commonly used in radiology.

 Pulse wave Doppler ultrasound:

When you use pulse wave Doppler

ultrasound you are measuring frequency shifts within a narrowly defined doppler gate or sample that doppler gate tends to be only a tiny fraction of your field of view, you want to place that doppler gate in the center of the vessel of interest and recognize that you are only measuring frequency shifts between these two little parallel lines those frequency shifts are then recorded to generate a waveform and that waveform is a reflection of the relative change in velocity over the cardiac cycle when we angle correct for the direction of flow relative to our ultrasound beam we can then generate velocity measurements that is accurate when angling correction is accurate.

Spectral wave 

doppler ultrasound image

 The importance of the 

different lines or markings on the image first we have

the gate 

or the sample volume when we are doing spectral wave doppler ultrasound we are only measuring the frequency shifts that are occurring within that small gate or small field of view that gate is adjustable we can make it wider we can make it broader but it should fit nicely within the vessel of interest and hopefully be centered within that vessel in addition to the gate outlined in yellow we will have the line of insulation this is a representation of the direction that our ultrasound waves are traveling in realize that the motion that we are trying to measure is not necessarily traveling in parallel with our ultrasound waves because it is not they are not traveling in parallel we need to angle correct to determine the angle of insulation we angle correct with a user-defined line that is typically a small white line I have now been highlighted in purple we adjust that white line to reflect the expected direction of movement or motion or flow within the gate so if we think the blood is flowing this way within the gate, we adjust the line to reflect that expected direction of flow once we have adjusted for the expected direction of flow we calculate the angle of insulation as the angle between that direction of flow and the angle our ultrasound waves are traveling in we can then take the cosine of that angle to accurately calculate the velocity of flow within our gate.

The 

waves generated by our spectral wave imaging

The wave is a representation of the 

relative velocity across the cardiac cycle waves above the baseline tend to reflect motion towards the probe waves below the baseline tend to reflect motion away from the probe remember the motion we're talking about is only the motion within the gate we can adjust our scale and we can correct for the angle of motion to calculate accurate velocities.

 The key features of 

an arterial waveform

Typically the highest velocity point in 

an arterial waveform is peak systole that occurs at the end of left ventricular contraction we are often going to compare peak systole to end-diastole which is the end of passive flow just before left ventricular contraction one common way we assess the change in velocity over time is with the systolic upstroke also known as acceleration is defined as the change in velocity over time so how long from in diastole to peak systolic and what is the change from in diastole to peak systole a normal arterial waveform has a brisk upstroke when we have delayed acceleration or blunting of that systolic upstroke that can indicate proximal stenosis and is commonly referred to as Parvus tardis we also often look at the resisted index particularly in transplant organs the resistant index is an assessment of the difference between peak systole and in diastole with respect to peak systole in a high resistance system like a transplanted organ that is undergoing rejection or a transplanted organ that has a venous thrombosis there will be decreased passive flow in diastolic velocity will be less than normal and the resistive index will go up in a low resistive system such as a system with an arteriovenous fistula there will be increased passive flow increased in diastolic velocity and therefore the resistant index will go down if there is proximal stenosis that causes a decrease in peak systole  the difference between peak systole and industry will be decreased and your resistive index will drop.

 Color Doppler 

ultrasound

Spectral wave doppler ultrasound is a 

more quantitative form of doppler ultrasound and color doppler ultrasound is a more qualitative form of ultrasound with color doppler imaging you are encoding the direction and velocity of flow with color brighter pixels tend to mean higher velocity darker pixels mean a lower velocity and the scale can be adjusted so that it is a reflection of the expected velocity within the vessel of interest typically flow that is encoded as red is the flow that is moving in the direction of the probe flow that is encoded as blue is the flow that is moving away from the probe although in some limited clinical applications you may flip that scale one advantage color doppler imaging has over spectral wave doppler is a much larger sample volume as possible instead of being limited to a small gate or sample volume you have a look you can adjust your sample volume based on the size of your vessel of interest and it can be made taller wider and it can be moved around within your field of view so that you can sample all different size vessels in various sized fields of view.

Power Doppler:

 power doppler use the most are when there's a markedly hypoechoic lesion whether it's in the breast or the neck or the parotid gland that may be a cyst but could also be a markedly hypoechoic solid nodule and you want to try to see if you can detect flow within that solid nodule and and breast would probably be one of the most common applications m mode imaging is not a true form of Doppler imaging but it is a useful low power form of imaging to detect and quantify motion in m mode imaging a grayscale reference image is obtained a point of reference is then set and the motion with respect to that initial reference image is recorded over time that motion can then be quantified

 In the case of the first trimester 

ultrasound 

Doppler  be used to determining 

the fetal heart rate in echocardiography, it can be used to calculate the excursion of the valve leaflets it is a low power form of imaging, and therefore it is safe to use in the first trimester because of its low thermal index and its low mechanical index relative to power doppler or relative to spectral wave doppler it is felt to be much safer to use and in fact, we try to avoid any forms of spectral wave or color doppler in the first-trimester fetus