A Phased Array Acoustic Imaging System for Medical Use

An experimental linear phased array acoustic imaging system has been developed for cardiac, obstetric, and radiological use. This is a real time, pulsed B scan system using either a 2.5 MHz or a 3.5 MHz hand held transducer. The display format is a sector scan with dimensions of 90° × 24 cm and the system is dynamically focussed. The system uses an analog heterodyne architecture to greatly simplify the electronics for a densely packed array and to allow use with transducers of different frequencies. With a 20 mm aperture segmented into 64 elements, at 2.5 MHz, the system achieves a 6 dB resolution at 7 cm in water of 2.5 mm in azimuth, 1 mm in range, and 3.5 mm in elevation. Emphasis was put on a system with wide dynamic range; side lobe levels of the array beam plot less than −65 dB have been achieved over the sector. A digital scan converter is used to convert the sector scan to a raster display and for image processing. Images will be shown to demonstrate system performance.