In medical diagnostic imaging, an ultrasonic transducer produces short bursts of sound that travel through soft tissue, reflect from internal structures, and return to the detector. For one transducer setting, the time interval between the start of one burst and the start of the next is 4.0×10−7s. Within soft tissue, sound propagates at approximately 1540m/s.
(a) Compute the wavelength of the ultrasound in soft tissue.
(b) An echo is received from a tissue interface located 3.0cm beneath the transducer face. Determine the round-trip travel time for the sound burst.
(c) On an oscilloscope display, the horizontal axis represents time with a sweep speed of 5.0×10−7scm−1. Calculate the horizontal separation on the display (in cm) between the emitted pulse and the received echo from the interface in part (b).
(d) Suppose the ultrasound enters a region where the propagation speed is 10% lower than in the surrounding tissue. Analyze qualitatively how this speed change would affect both the wavelength of the ultrasound in that region and the image resolution. Support your answer with appropriate reasoning.