Relationship between skin-collagen micro-architecture and ultrasonic backscatter parameters at 20 MHz

This in vitro study investigates the role of skin-collagen in the variation of the integrated backscatter coefficient (IBS) and the frequency dependence of backscatter (n). IBS and n (11-27 MHz) were estimated from spectral analysis of radio frequency (RF) signals acquired in 31 human skin specimens of abdomen and breast dermis at depths of 370, 620 and 880 μm beneath the skin surface. Microscopic morphometrical analysis was applied at matched depths of histologic sections from each specimen to estimate mean thickness of collagen bundles (TH), mean space between bundles (SP) and percent fractional-area occupied by the collagen (%A). Both IBS and n decreased with depth of the measurement region beneath the skin surface and were significantly different for abdomen and breast. For abdomen specimens, n was inversely correlated to TH and %A in the most superficial depth. IBS was inversely correlated to %A in the most superficial depth. For breast samples, IBS significantly decreased as SP increased at all three depths. Knowledge of the relationship between dermal collagen distribution and acoustic properties should aid interpretation of in vivo ultrasound measurements.