5 Doppler Instrumentation Flashcards
What are stand alone doppler and duplex doppler transducers?
Stand alone doppler transducers offer increased sensitivity to blood flow so assess blood flow velocity more accurately but do not offer a 2D image so are blind.
Duplex doppler transducers simultaneously visualise cardiac structures and assess blood flow velocity.
How is doppler displayed and how is it optimised?
The spectral doppler display plots frequency shift (velocity) on the y axis and time on the x axis. Flow towards the transducer is plotted above the line and flow away from the transducer is plotted below the line.
If the RBC velocity is greater than the Niquist limit, aliasing will occur, and the spectral doppler display will show the top of the waveform to be transposed to the opposite side of the baseline.
The spectral doppler display can be optimised by adjusting the speed, velocity scale and baseline.
How is the PWD sample volume optimised?
The shorter the gate length, the lower the velocity variation, so the narrower the spectral doppler. Therefore, the shorter the gate length higher the accuracy (e.g. stenosis assessment).
The shorter the distance between the sample volume and the transducer, the narrower the beam width, so the higher the focus. Therefore, the shorter the distance, the higher the spatial resolution.
What is image intensity?
The strength (amplitude) of the signal is displayed as the level of brightness (intensity).
What are image intensity threshold settings?
Intensity threshold settings control the minimum signal intensity (amplitude). The reject setting filters our low intensity signals. Low reject settings are used to assess low velocity structure and low amplitude signals. High reject settings are used to minimise noise and improve signal quality.
What are the principles of CFD?
CFD uses the principles of PWD but CFD assesses blood flow at multiple points in one area, not within one sample volume. The CFD box is superimposed on the 2D image. The CFD display colour codes the blood flow based on its direction and mean velocity within the area. Blood flow towards the transducer is red and blood flow away from the transducer is blue (BART – blue away red towards). Turbulent blood flow, areas with a high velocity variance, are green.
In CFD, what are the two methods to image the colour flow information on a 2D greyscale image?
Image domination is a method of displaying CFD information on the 2D greyscale image by superimposing the colour on the image.
Additive colour mode is a method of displaying CFD information on the 2D greyscale image by combining the colours with the greyscale pixels.
The methods involve balancing the visualisation of blood colour flow and cardiac structures by adjusting the colour flow transparency.
How are velocity and power displayed on CFD?
Velocity displays show the speed and direction of blood flow via CFD, CWD or PWD. Velocity displays are displayed by different colours or different spectral velocities.
Power displays shows the strength (amplitude) of the signal and is a measure of energy. Power displays are displayed as different levels of brightness.
What are the principles of TDI, PW TDI and colour TDI?
TDI assesses the movement of the myocardium. Typically, TDI assess the ventricular longitudinal systolic function.
PW TDI quantitatively assesses myocardial velocity in one area. The PW TDI trace shows the velocity of mitral annular movement towards the apex/transducer during systole (S’), the movement away from the apex/transducer during early diastole (E’), and the further movement away from the apex/transducer during atrial systole (A’).
Colour TDI qualitatively assesses myocardial velocity at multiple positions within one area. Colour TDI shows colour-coded myocardial velocity based on its direction and mean velocity within the sample volume. Movement towards the transducer is red and movement away from the transducer is blue.
How is TDI optimised?
TDI uses low pass low gain filters to remove high velocity/frequency low amplitude signals.
The lower the depth and the narrower the width, the higher the PRF so the higher the frame rate. Therefore, the higher the temporal resolution but the lower the spatial resolution.
The smaller the sample volume size, the higher the spatial resolution.
The smaller the angle, the lower the misalignment, the higher the velocity, and the more accurate the measurement.
What are the differences between PW TDI and colour TDI?
PW TDI measures peak velocity but colour TDI measures mean velocity. Therefore, PW TDI values are 25% higher.
PW-TDI is used to assess systolic and diastolic myocardial function by assessing myocardial velocities at specific points with a higher accuracy (higher temporal resolution). However, it is more angle dependent. It generates a spectral doppler display of velocity over time with S’, E’ and A’ representing the velocities at the different parts of the cardiac cycle to offer quantitative information.
C-TDI is used to assess regional and global myocardial function by assessing myocardial velocities over a bigger area with a lower accuracy (lower temporal resolution). It superimposes a colour map on the 2D image with the colours representing velocity and direction to offer qualitative information.
What is colour TDI tracking?
C-TDI tracking is a method which makes sure that the sample volume stays in the area of interest despite myocardial movement (motion and translation) to improves velocity measurements and minimise artefact. In C-TDI tracking, the sample volume is automatically adjusted to track the area of interest to follow myocardial motion using recent frames or current motion pattern.
How are myocardial translational movements minimised?
Myocardial translational movements can be minimised by optimising the patient position (minimising patient movement, minimising artefact and identifying the optimal windows) and breath holds, optimising the settings (stabilisation, frame rate averaging, focus etc), optimising image acquisition (acquiring images at end systole or end diastole when there is minimal myocardial movement), optimising image processing (algorithms minimising artefacts), and operator skill (minimise error artefacts).
What is curved M-mode TDI?
Curved M-mode TDI analyses myocardial motion, over time, along a set curved line of interest to assess regional and global ventricular function and dyssynchrony.
