A COMPARISON OF ULTRASONIC WAVE-FRONT DISTORTION AND COMPENSATION IN ONE-DIMENSIONAL AND 2-DIMENSIONAL APERTURES

A comparison of wavefront distortion and compensation in one-dimension al and two-dimensional apertures is made using two dimensional transmi ssion measurements through 14 different specimens of human abdominal w all, The measurements were employed to emulate data in one dimension b y summing waveforms in the elevation direction after a geometric corre ction was performed using a fourth-order polynomial fit to the surface of arrival time, Distortion calculation and time-shift compensation w ere performed independently on waveforms in the one-dimensional and tw o-dimensional apertures and the waveforms were focussed using a Fourie r transform method to obtain the point-spread function in the central elevation plane. The results show that distortion is smoothed increasi ngly by one-dimensional apertures as the elevation dimension grows and that the smoothing is substantial for elevations similar to those emp loyed in present clinical imagers, The results also show that one-dime nsional compensation becomes less effective than two-dimensional compe nsation as the size of the elevation increases but that one-dimensiona l compensation performs almost as well as two-dimensional compensation in apertures with elevations like those in current imaging systems.