Image Processing Reference
Figure5.6 (a) Sonar scan of a lake with a drowning victim at the bottom; (b) detail of
drowning victim. (CourtesyofGaryKlein).
to a wavelength range of about 200-400 m in water. The ultrasound machine that
made this image can produce a 3D view that can be rotated.
Figure 5.8 shows a side view of a fetus with the addition of pseudocolor to
indicate the velocity of blood flow within the heart and main arteries. This view is
one of a series of real-time images that are displayed as a movie, allowing medical
workers to see the blood flow. The ultrasound machine has a mode in which it
detects slight shifts in the frequency of the reflected sound waves from the moving
blood. These Doppler shifts are similar to the shift in pitch of a train whistle that
a stationary observer hears as the train goes by. The orange false color denotes
blood flow away from the observer, and the blue denotes flow toward the observer.