Transmural backscatter measurements of human scalp

Interest in transcranial ultrasound has motivated numerous ultrasonic studies of the skull and brain but reports of the ultrasonic properties of the scalp are limited. Scalp is a layered structure of dermis/epidermis followed by a fatty subcutaneous layer, a fibrous layer (galea aponeurotica) and lastly loose connective tissue. The goal of this study is to ultrasonically characterize the transmural tissue structure of the scalp. Sixty-four formalin-fixed specimens were prepared from four human donors from four scalp regions in two different orientations and scanned with a 25-MHz transducer. Apparent integrated backscatter (AIB) and integrated backscatter coefficient (IBC) were measured over a 10 × 12 mm region in the transmural plane. Parametric images and autocorrelated profile plots reveal how these parameters change throughout the layered structure. Regions of interest in the parametric images in each scalp layer were used to compute average values. The measured parameters were significantly lower in the connective tissue layer compared to both the epidermis/dermis and subcutaneous layers. Values varied from −45.7 ± 3.05 dB and 0.117 ± 0.102 cm−1str−1 in the dermis/epidermis layer to −51.2 ± 3.94 dB and 0.042 ± 0.073 cm−1str−1 in the connective tissue layer for AIB and IBC, respectively.