Fresnel Zone Focusing of Linear Arrays Applied to B and C Echography

Abstract

For a long time, physicists have tried to get acoustical pictures like. ordinary X rays pictures. The through imaging techniques, holographic or ordinary imaging ones, have not yet proved to be of the same interest for medical use as echographic techniques. On the other hand, these later techniques give essentially cross-sectional B echograms, while the C echographic techniques remain quite limited due to the time required by X Y mechanical scanning. It is possible to run faster using an electronically X scanned one dimensional array, but the lateral resolution of such a device must be higher both in X and Y directicnsthan for B echography. Electronic focusing by delay lines may be combined to an X or θ scanner (1, 2) this technique requires high performance circuits able to handle the greatdynemic range of ultrasonic echoes. We want to present here a relatively simpler technique using holographic focusing useful for boti. B and C echography.