Improvement of the Spatial Resolution of Ultrasonic Imaging Using the Holographic Technique.

In the conventional synthetic aperture technique the antenna directivity is assumed to be wide enough that sufficient phase information can be obtained with antenna scanning. This assumption is made in the experimental studies as well. With a sharp antenna directivity, however, sufficient phase information cannot be obtained and the reconstructed Image obtained by the conventional synthetic aperture technique has poor resolution. On the other hand, if the real aperture technique is employed, an Image of improved quality can be obtained with a sharp antenna directivity and the resolution increases as the directivity becomes sharper. The present paper deals with the case of directivity which is too sharp for the synthetic aperture technique and too wide for the real aperture technique. Theoretical and experimental studies are made on ultrasonic imaging by using the modified synthetic aperture technique for this case. Specifically, the actually measured point spread function is used in the synthetic aperture technique and it. is confined that a higher resolution can be obtained in this way than by the conventional synthetic or real aperture technique. [ABSTRACT FROM AUTHOR]