# Chapter 19 Book Flashcards

Change in frequency due to doppler shift is also called what?

Doppler frequency

The motion between the sound _______ and the _________ creates a frequency change.

source, receiver

The process of extracting the low Doppler frequency from the transducer’s carrier frequency is called _________.

Demodulation

Doppler shift = _____________ - _____________

reflected frequency - transmitted frequency

A positive doppler shift occurs when a receiver moves __________ the source.

towards

What is the doppler equation?

∆ƒ = (2 x v x ƒo x cos ø) / propagation speed

Doppler shift is directly related to what property of RBCs?

Velocity

The entire velocity of blood cells are measured when the sound beam is pointed _________ to them.

Parallel

The measured velocity of RBCs = the ____________ x _________.

true velocity x cos ø

cos 0º = _______

1.0

cos 30º = _______

0.87

cos 60º = ________

0.50

cos 45º = _________

0.71

cos 90º = __________

0

What is the greatest advantage of continuous wave doppler?

its ability to accurately measure very high velocities

The fact that signals arise from all blood cells in the region of overlap in continuous wave doppler is known as __________ _____________.

range ambiguity

Simultaneous anatomic imaging and Doppler is called ___________ ____________.

Duplex imaging

The greatest advantage of pulsed wave doppler is what?

being able to select the exact location where velocities are measured

Describe Aliasing

the false representation of very high velocities going in the opposite direction

The very top of a spectral display is called the ________ ___________.

Nyquist limit

When does aliasing occur?

when the Doppler smiling rate is too low in comparison to the velocities

What are ways to avoid aliasing?

Increase the scale decrease the frequency adjust the baseline Select a shallower sample volume Use continuous wave doppler

Color Doppler measures ________ velocity, whereas pulsed and continuous wave Doppler measure ________ velocity.

mean, peak