Answer #26

The correct answer is A: Increases by a factor of 2.

This question requires you to know that for pulsed wave Doppler the frequency depends on both the thickness of the crystal and the velocity of propagation of sound within the crystal.

This is given by the equation: frequency = (propagation velocity in the crystal)/(2x crystal thickness).

Thus if we cut the thickness of the crystal in half then the frequency will increase 2 fold. None of the other answers are correct.

Note that for continuous wave (CW) Doppler the frequency depends only on the transmit voltage since the crystal is constantly being stimulated and is always "on" emitting ultrasound. Thus it is not dependent on crystal thickness. Hence choice E would be correct if this were CW Doppler.