| Popis: |
Present ultrasound imaging simulations rely on pulse-echoes from amplitude-weighted point scatterer models rather than a model based on wave propagation. Aberration has been most often modeled as a phase screen adjacent to the aperture rather than as a distributed effect. A more realistic model which accounts for diffraction, absorption, refraction, and aberration effects has been implemented. Based on two layer measurements of fat and muscle in abdominal walls[1], the new model projects the layer data three-dimensionally to their correct physical locations so that spatially local heterogeneous aberration effects vary with array geometry to the field point. Frequency-dependent effects in the original data are removed and combined with wave propagation effects calculated along ray paths from a multilayer time domain model that includes material impulse response functions[2] for power law media and reverberations. The net result is a set of temporal functions that can be convolved with diffraction responses from the FOCUS software program [3,4] for more efficient simulations. Beam contours calculated for a 5 MHz, 76 element linear array demonstrate that beam quality has greater local dependence on combined propagation and aberration effects than shown in earlier work. New simulations indicate that phase screen is a poor approximation and that absorption has a small effect. This new scalable model for beam and eventual image simulation, which includes aberration, absorption and effects, is adaptable to different array geometries, frequencies, waveforms, and tissue combinations. |
