Non-Invasive Extraction of Mechanical Skin Parameters by Ultrasonic Image Processing: Validation by Invasive Tensiometric Method

Conventional methods for the skin aging are based mainly on physiological or biochemical observations. The aim of this study is to provide a non-invasive method based on the extraction of biomechanical parameters of the skin resulting from the processing of sequential high-frequency ultrasound images in order to investigate the process of skin lesions.

Consecutive ultrasound images of the epidermal and dermal layers were recorded and saved with a 40 MHz imaging system. In order to evaluate the process of skin damage, 25 C57BL6 mice were exposed to UVB radiation. The mechanical parameters of the skin derived from the processing of sequential ultrasound images were also estimated weekly with the motion estimation algorithm (gradient and block matching) during the injury generation process and results were reported as a mean and standard deviation. Validation of the method was performed by invasive tensiometric test. Correlation between the two methods was performed by Pearson correlation analysis. Statistical  repeated measures analysis of  variance was used to compare the statistical trend of changes over 5 weeks.

Significant correlation was obtained between elasticity extracted from non-invasive ultrasonic image processing method and invasive tensiometric method with a correlation coefficient of more than 0.79. By processing the sequential ultrasound images, the axial elastic and the shear modulus of the skin layers were significantly increased, which indicate the increased skin firmness during  the ultraviolet radiation (p <0.05). Also, the ratio of changes in the elastic modulus on the thirty-fifth day was 11 times more than zero-day. The shear modulus on the 35th day of ultraviolet radiation was 2.2 times more than zero-day. The results of repeated measures analysis of  variance showed that during irradiation with ultraviolet waves, the axial elastic modulus and the shear modulus of the skin layers obtained by processing sequential ultrasound images also increased significantly, indicating an increase in skin firmness (p <0.05).

Based on the findings of the present study a non-invasive method according to the extraction of local biomechanical parameters of skin based on the processing of sequential high-frequency ultrasound images for detecting the skin damage caused by ultraviolet radiation is proposed.