Sound waves have added new dimensions to noninvasive diagnostic techniques. Visualization of the gallbladder is a case in point. A report in the March 7 issue shows the value of ultrasound in diagnosing hydrops of the gallbladder, while an article in the Archives of Surgery (112:273-275, 1977) describes three instances where sonography delineated gallbladders not visualized by roentgenography. As the first article illustrates, correct diagnosis allowed the surgeon to substitute low hazard cholecystostomy for laparotomy in a poor-risk patient.
Vibrations beyond the upper limits of human hearing (about 20 kHz) are named "ultrasound." The frequencies currently used in medical sonography range between 1 and 15 MHz. Since tissues transmit (and absorb) wave energy at different rates, a portion of the energy contained in an ultrasonic wave beam is reflected at the interface between sonically dissimilar structures.1,2 Illustrative wave velocities are 330 m/sec in air, 1,480 m/sec in water and