Wideband quantitative ultrasonic imaging by time-domain diffraction tomography

Abstract

A quantitative ultrasonic imaging method employing time-domain scattering data is presented. This method provides tomographic images of medium properties such as the sound speed contrast; these images are equivalent to multiple-frequency filtered-backpropagation reconstructions using all frequencies within the bandwidth of the incident pulse employed. However, image synthesis is performed directly in the time domain using coherent combination of far-field scattered pressure waveforms, delayed and summed to numerically focus on the unknown medium. The time-domain method is more efficient than multiple-frequency diffraction tomography methods, and can, in some cases, be more efficient than single-frequency diffraction tomography. Example reconstructions, obtained using synthetic data for two- and three-dimensional scattering of wideband pulses, show that the time-domain reconstruction method provides image quality superior to single-frequency reconstructions for objects of size and contrast relevant to medical imaging problems such as ultrasonic mammography. The present method is closely related to existing synthetic-aperture imaging methods such as those employed in clinical ultrasound scanners. Thus, the new method can be extended to incorporate available image-enhancement techniques such as time-gain compensation to correct for medium absorption and aberration correction methods to reduce error associated with weak scattering approximations.