Recent activity in ultrasonic tomography

During the past two decades there have been significant developments in many aspects of acoustical imaging techniques for various applications. One aspect of this development has been the application of ultrasonic tomography to medical imaging and diagnosis instrumentation, and also to non-destructive evaluation of materials, to oceanographic systems for measurements of such factors as temperature and currents etc, and to seismic exploration. This paper reviews the theoretical and practical work in acoustical tomography to the present time.