HIGH-SPEED DATA-ACQUISITION IN A DIFFRACTION TOMOGRAPHY SYSTEM EMPLOYING LARGE-SCALE TOROIDAL ARRAYS

This report describes the development of an experimental system for ul trasound computed tomography and its application to breast imaging. De tails of the system design and methods of highspeed data acquisition a re presented. The method uses low-power discrete frequency sound in th e range of 0.3-1.2 MHz, two cylindrical arrays of 512 and 1024 PZT tra nsducers, high spatial sampling of the wavefront, and unique diffracti on tomographic reconstruction methods. One transducer at a time is act ivated and allowed to reach steady state at which point the remaining measure phase and amplitude of the ultrasound signal. A total of 64 MB of data are acquired in <1 s for the 512-element array and 128 MB in <3 s for the 1024 array. Several algorithms have been developed to pro duce the diffraction tomogram which is reconstructed as either a 512 x 512 or 1024 x 1024 matrix of the scattering potential of the object d ependent on speed of sound and attenuation. The effects of aberration are greatly diminished by a hybrid iterative algorithm. To date, human images have been made of the female breast which show good depiction of glandular structures and differentiation of gland and fat, and the coronal format provides a novel of the entire breast in life-size disp lay. The results demonstrate that the technique provides a unique quan titative ultrasound image with high resolution over a very large globa l field of view of the breast. The method shows promise for improved i maging of the breast. (C) 1997 John Wiley & Sons, Inc.