Impact of the structure of subcutaneous tissue on ultrasonic clutter

Subcutaneous tissue is often associated with ultrasonic clutter and phase aberration. However, the complexities of subcutaneous tissue are often replaced by far simpler models in phase aberration, and are not well defined in the case of ultrasonic clutter. We employed a nonlinear, full-wave simulation method to compare the impact of subcutaneous tissue structure on ultrasonic clutter. Simplified models of male and female connective tissue networks were created, including networks with varying degrees of fascial layer density and angles relative to the transducer probe. The models were given the speed of sound, density, and attenuation appropriate for the associated fat and connective tissue. The amount of ultrasonic clutter depended on the density and angle of the fascial layers, although the two factors were not necessarily independent. Increases in the density and angle of the fascial layers increased the magnitude of clutter. Differences were observed between the female and subcutaneous tissue structures, yielding approximately 3 to 15 dB higher clutter magnitude in the male structure. The human abdominal models generated relatively high clutter magnitude, ranging from near OdB just beneath the abdominal layer to approximately -33 dB and -27 dB for the two models. In these realistic models of human abdominal tissue, the high density of fascial layers increased the number of multipath reflections contributing to the clutter, and generated high clutter magnitude.