Final answer:
The minimal information required for an ultrasound examination to image fetal motion is the speed of the sound and the frequencies of the sound waves emitted and observed, due to the Doppler effect.
So the correct answer is option (C).
Step-by-step explanation:
In order to image the motion of a fetus during an ultrasound examination, the minimal information required is the speed of the sound and the frequencies of the sound waves emitted and observed. This is because of the Doppler-shifted ultrasound, which is a method used in medical diagnostics to detect motion and determine velocity through the Doppler shift of an echo. The Doppler shift is the actual change in frequency due to the relative motion of the source and observer. Specifically, when the ultrasound hits the moving fetus, the reflected sound, or echo, is at a different frequency. This change in frequency is used to calculate the velocity of the moving fetus.
The ultrasound machine emits sound waves at a known frequency toward the area of interest. Because the fetus is moving, the frequency of the reflected sound waves will be altered, which is observed by the ultrasound machine. Using the known speed of sound in the human body, the machine can use the difference between the emitted and reflected frequencies to calculate the speed and motion of the fetus.