A transducer is used to send an ultrasound pulse toward a stone and to receive ultrasound reflections from the stone. The recorded time between a pulse that is reflected from the proximal surface and a pulse that is reflected either from the distal surface of the stone or from a surface supporting the stone is used to calculate the stone size. The size of the stone is a function of the time between the two pulses and the speed of sound through the stone (or through the surrounding fluid if the second pulse was reflected by the surface supporting the stone). This technique is equally applicable to measure the size of other in vivo objects, including soft tissue masses, cysts, uterine fibroids, tumors, and polyps.
