Question

The transducer you are using to image the liver transmits a wide-bandwidth beam of 3-5 MHz. Which of the following most correctly describes the reflected beam after it has traversed the liver?

a) the reflected bandwidth will be shifter down in frequency due to the increased attenuation of higher frequencies.
b) the reflected beam will be of reduced intensity but will have the same frequency content as the transmitted beam.
c) the reflected bandwidth will be shifted upward in frequency due to the increased absorption of the lower frequencies.
d) only the center frequency component of the bandwidth will be reflected back to the transducer.
e) the reflected beam will be identical to the transmitted beam.

Answer 1

The reflected ultrasound beam after traversing the liver will be of reduced intensity and have a downward-shifted frequency bandwidth due to higher frequency attenuation.

Step-by-step explanation:

The student is inquiring about the characteristics of an ultrasound beam after it has traversed through the liver with a transmitted wide-bandwidth beam of 3-5 MHz. The correct answer to this question is that the reflected beam will be of reduced intensity and will have a shifted frequency bandwidth. This frequency shift occurs because higher frequencies are attenuated more than lower frequencies within biological tissues, which leads to a predominance of lower frequencies in the reflected beam. In ultrasound imaging, this principle also underpins the Doppler shift technique, used to measure the velocity of moving blood by observing changes in the frequency of the reflected ultrasound waves.