Title :
Non-cylindrical transmission focusing for large depth of field
Author :
Umemura, Shin-ichiro ; Azuma, Takashi ; Miwa, Yuichi ; Sasaki, Kazuaki ; Sugiyama, Takashi ; Hayashi, Tatsuhiko ; Kuribara, Hiroshi
Author_Institution :
Central Res. Lab., Hitachi Ltd., Tokyo, Japan
Abstract :
In imaging with a microbubble contrast agent, which tends to make irreversible changes by transmission even at a low intensity, both transmission beamwidth and number of transmission per frame must be minimized. A transmission focusing technique based on a noncylindrical delay, which is applicable to a one-dimensional array, is proposed. Unlike X waves, the main beam propagates always coherently with the waves transmitted from the central part of the aperture. The non-cylindrical focusing delay was calculated by assuming a local focal length along the aperture, which increases gradually as the distance from the center increases. Numerical simulation of wave propagation predicted a large depth of field for a reasonably narrow main beam having longitudinally uniform intensity. The noncylindrical focusing was employed in a prototype beamformer, and the large depth of transmission field was confirmed with Shrielen measurements.
Keywords :
biomedical ultrasonics; ultrasonic focusing; ultrasonic imaging; ultrasonic propagation; Shrielen measurements; imaging; large depth of field; local focal length; microbubble contrast agent; noncylindrical transmission focusing; number of transmission per frame; transmission beamwidth; wave propagation; Acoustic beams; Apertures; Array signal processing; Biomedical imaging; Delay; Focusing; Laboratories; Numerical simulation; Prototypes; Testing;
Conference_Titel :
Ultrasonics Symposium, 2002. Proceedings. 2002 IEEE
Print_ISBN :
0-7803-7582-3
DOI :
10.1109/ULTSYM.2002.1192629