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Comparison of global and local estimations of ultrasonic parameters at 20 MHz: in vivo normal skin

Measurements of ultrasound integrated backscatter (IBS) and frequency dependence of backscatter (n) can be used to characterize tissue composition and structure. Their high resolution estimation and presentation in quantitative images could further help evaluate local variations in tissue composition. In this work, local estimates of IBS and n are made using 20-MHz radio frequency (RF) data acquired in skin in vivo, and used to construct parametric images. Comparison is made between global estimates (made directly from a block of RF data) and the average of the local estimates over matched regions of interest in parametric images. IBS estimated by the local technique presents a mean bias of -1.05 dB in comparison with global estimates whereas local estimates of n did not demonstrate bias. Sensitivity to measurement depths in the dermis and pressure of the probe against the skin identified with global estimates was maintained with local estimates.