Digital image focussing in the near field of a sampled acoustic aperture

A study has been carried out to investigate digital techniques which can be used to form fully focussed acoustic images. An algebraic approach was used rather than a Fourier technique. Pulse-echo data was digitized from a 2.4 cm long, 32 element, 3 MHz linear array. Water bath tests have demonstrated azimuthal resolution close to beig diffraction limited throughout the field of view. Good images of tissue samples in-vitro have been obtained. Consideration of image sampling requirements and symmetry properties have led to the development of an efficient processing algorithm.