"So what the heck is aliasing and power doppler?"

Aliasing

Aliasing is an artifact that is seen both in color and spectral doppler modalities. It reflects the point at which the maximum measurable velocity has been reached for a given PRF and Gain setting.

If you see aliasing on the screen, first turn back the overall gain knob to just before aliasing is present; if this does not satisfactorlly reduce the alias, you may adjust the PRF to improve the image. Below is a picture in color doppler reflecting aliasing.

Aliasing in Color Mode





Aliasing in Spectral Doppler Mode (notice the waveforms (spikes) are off the screen)


Power Doppler

A final mode used frequently in the ED is "power doppler". Power doppler is particularly handy for very low flow states including imaging gonadal flow, suspected occlusions, small or tortuous vessels and tumor vasculartiy. Power doppler, in contrast to color doppler, measures the amount (quantitiy and distribution) of red cells passing by the beam in contrast to the frequency changes of the transmitting and receiving beam. Power doppler does NOT indicate flow direction, as does color doppler. The intensity of flow is indicated by how close to white the color is on the screen (i.e. yellows are indicatave of faster moving blood than reds).



Power Doppler of the Hepatic Veins



Thanks for looking, and grab me if you have any questions!

Hunter


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