Ultrasound B-mode imaging with electronically focused annular arrays has been associated in the past with fairly complex and expensive electronic circuits. When image quality rather than scanning speed is the prime concern, the concept of switched zone focusing offers an attractive alternative to true dynamic focusing previously reported. Strongly focused apertures used in both transmit and receive modes allow improved lateral resolution, lower side lobe levels, higher sensitivity, as well as simplified electronics.
This approach was investigated for the particular case of breast imaging. We outline some general design considerations for water path imaging with annular arrays, and describe the system adopted in the development of a high resolution breast scanner using a sealed, water filled head. Experimental results are compared to theoretical predictions, and grey scale images are presented to illustrate the performance of the instrument.