Soft tissue attenuation estimation based on the entropy difference method and by applying a wide-band pulse

Abstract

In part I of this thesis an effecient computer generation method is described for three-dimensional (3-D) ultrasonic speckle patterns in sector scanning of the annular array with dynamic focusing applied in both transmit and receive modes. The number of echo data needed to synthesize one waveform i teemendously reduced by reducing the 3-D distributions of scatterers to line distributions and also representing scatterers on a small line segment by a single equivalent scatterer taking into account the two-way travelling time differences. The computer simulated speckle patterns showed a good statistical agreement with experimentally obtained patterns. In the entropy difference method for estimating the ultrasonec attenuation coefficient in soft tissue, the enteopies of speckle-contaminated echo envelopes returning from two adjacent rectangular regions in the axial direction are compared as the attenuation is continuously compensated for until the two entropy values become identical; the amount of compensated attenuation is regarded as the average attenuation coefficient in the two regions. In the past CW burst pulses were generated for this purpose by a loosely focused disk-type transducer which was scanned in the lateral direction to obtain a large number of scan data. It turned out that this method is by far superior to the well-known log spectrum difference method in the respect of accuracy with the same amount of data. In part II of this thesis, in order to improve the resolution in the two-dimensional attenuation mapping an annular array sector scanning system as described in part I, was used by exciting a wide-band pulse and the entropy difference method was applied after filtering and diffraction effect correction was made for the synthesized echo waveforms by all annuli and, using these data for a given scan direction, apply dynamic focusing. Computer simulation and experimental results with a tissue-mimicked phantom show that the proposed method yields by...