A comparison of ultrasonic wavefront distortion and compensation in one-dimensional and two-dimensional apertures

A comparison of wavefront distortion and compensation in one-dimensional and two-dimensional apertures is made using two-dimensional transmission measurements through 14 different specimens of human abdominal wall. The measurements were employed to emulate data in one dimension by summing waveforms in the elevation direction after a geometric correction was performed using a fourth-order polynomial fit to the surface of arrival time. Distortion calculation and time-shift compensation were performed independently on waveforms in the one-dimensional and two-dimensional apertures and the waveforms were focussed using a Fourier transform method to obtain the point-spread function in the central elevation plane. The results show that distortion is smoothed increasingly by one-dimensional apertures as the elevation dimension grows and that the smoothing is substantial for elevations similar to those employed in present clinical imagers. The results also show that one-dimensional compensation becomes less effective than two-dimensional compensation as the size of the elevation increases but that one-dimensional compensation performs almost as well as two-dimensional compensation in apertures with elevations like those in current imaging systems.<>