ULTRASONIC PROPAGATION PROPERTIES OF EXCISED HUMAN SKIN

Eight human skin samples were excised postmortem from the upper and lo wer back, chest and abdomen from two cadavers. The acoustical speed, a ttenuation and backscatter were measured as a function of frequency (2 0 to 30 MHz) at 100 positions on a uniform grid over a cross-sectional slice through each sample with the sound incident in a direction para llel to the skin surface. Measurements were made at 24 +/- 0.5 degrees C. Samples were then frozen, cut and stained for histological examina tion and quantification of fibrous proteins and fat content. The mean attenuation coefficients obtained for whole skin agreed well with prev iously published results. Employing the model alpha = alpha f(a) where alpha is the attenuation coefficient in decibels per centimeter, alph a(1) is the value of the attenuation coefficient at 1 MHz and f is fre quency raised to the power n, mean values (+/-1 standard deviation) fo r epidermis were alpha(1) = 0.44 +/- 0.26 and n = 1.55 +/- 0.12, and f or dermis alpha(1) = 0.264 +/- 0.17 dB cm(-1) and n = 1.69 +/- 0.084. Using a similar model the mean backscatter coefficient was defined by mu(1) = (5.01 +/- 25.76) x 10(-8) Sr-1 cm(-1) n = 3.77 +/- 1.5 for the epidermis, and mu(1) = (1.79 +/- 19.5) X 10(-6) and n = 2.76 +/- 1.4 for the dermis. The speed of sound values fell within the range to be found in the literature with a mean value in the epidermis of 1645 m s (-1) and in the dermis of 1595 m s(-1). Significant, strong correlatio n existed between the spatially averaged fibrous protein content in th e epidermis and dermis and the:spatially averaged integrated attenuati on measurements. Likewise, strong correlation existed between integrat ed backscatter and fibrous protein content in the epidermis but not in the dermis. Further research is required to confirm these preliminary findings and to evaluate the role of collagen fibre orientation as a source of variation in the backscattering coefficient of dermis.