Assessment of an ultrasonic dermal scanner for skin thickness measurements

The measurement precision of a 20 MHz ultrasound dermal scanning system, Episcan, manufactured by Longport Inc. was investigated for its use in the measurement of skin thickness. Results from measurements of relatively ideal homogeneous, uniformly thick plastic plates indicate that the scanner can accurately measure to depths of 8-34 mm from the surface of the transducer or approximately 18 mm from the surface of the latex probe-cover with a high level of precision, less than 1% of the mean thickness. The precision was determined to be dependent on the depth of the scan. Using the measured optimal gain of 45%, a sample rate of 0.013 micros, and an A-scan record length of 1024 points, we determined the thickness resolution of the device is on the order of 0.003 mm for 2 mm thick layers and 0.01 mm for 5 mm thick layers. We conclude that variations greater than this value for clinical dermal thickness measurements are not due to instrument precision, but must result from the limitations of analyzing the data from real tissue.