Delay and amplitude focusing through the body wall; a simulation study

The difficulties in focusing an ultrasound beam through regions consisting of spatial mixtures between smaller targets of fat and muscular tissue are demonstrated experimentally. Such inhomogeneities are observed in the muscles of obese patients. The focusing through a 5 mm thick region composed of layers of fat and muscular tissue is studied using a simulation program based on 3D ray-tracing. Simulation examples show to what extent the focusing (beam profile) is improved by delay compensation only, and how much the result can be improved by applying both amplitude and delay focusing. The conclusions for a realistic situation of a fat/muscle region located at a depth 15 mm are: 1) The delay and amplitude focusing (DAF) performs better corrections than delay corrections only. 2) The corrections for one beam can be used only for a few neighbor beams. 3) A 1.5D transducer with 11 elements in elevation seems to be sufficient to do the corrections