A Digital Pulse-Echo System Based on Acoustic Inversion

Abstract

At the 10th and 12th Acoustical Imaging Conferences we presented the theory of a multi-dimensional acoustic inversion technique. This theory is based on a quantitative description of the wave propagation through inhomogeneous media. During the last two years we have developed and built an imaging system for medical applications which utilizes our inversion technique for the reconsruction of images of 2D cross-sections. The system can be divided in four main parts: 1) data-acquisition system, 2) reconstruction system, 3) display system, 4) control and initialization system.

The data is acquired over a large aperture area (typical 100 mm) by means of a lineair array transducer. The nearly omnidirectional elements of the transducer are sequentially used for both the transmission of ultrasound pulses and the reception of the echos. So the medium is “illuminated” by very wide angle beams. The acquired r.f. data is digitized and stored in a semi-conductor bulk memory. The system can acquire in 100 msec a maximum of 1M samples. This data is the input for the reconstruction algorithm. For the reconstruction an array-processor is used. The reconstructed image, i.e. a high quality still-frame, is stored in a video-scanned memory and displayed on a t.v. screen. The lateral resolution in the plane of scanning obtained with this system is better than 0.4 mm (-6dB) and 1.0 mm (-20dB) over a depth range of 10 mm upto 150 mm. A typical reconstruction time for a dataset of 1 Msample is 1 minute. During the presentation examples will be shown.