Time-domain ultrasound diffraction tomography

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 farfield 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-dimensional and three-dimensional scattering of wideband pulses as well as measured scattering data from a 2048-element ring transducer, 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.