Defence of the PhD Thesis of Caroline CHARTIER

ABSTRACT

Nowadays, exploration of cutaneous tissue is limited by the few number of available approaches, known as quantitative methods, allowing an objective description of the me- chanical properties of skin tissue. Elastography allows a local exploration of a medium and offers the possibility for some strategies to quantitatively estimate the modulus of elasti- city (Young’s modulus). A 1-D high-frequency ultrasonic transient elastography method (HF-TE) allowing a micrometric description of the mechanical properties of skin tissue has been designed for cosmetic and dermatological applications. An experimental system of high-frequency transient elastography has been developed : software, hardware and mea- surement methodology. The HF-TE technique has been validated using simulation and measurements in monolayer and bilayer calibrated phantoms developed in the laboratory. The Young’s modulus values measured in monolayer media were then compared with those measured by two others dynamic techniques.

Finally, the HF-TE method was used in vivo for skin tissue characterization in cosmeto- logy and dermatology and then compared with standard echographic and cutometric mea- surements. In general, our results show the great ability of the HF-TE method to explore the Young’s modulus variations of healthy skin tissue as a function of depth of exploration with high resolution. Studies on the hypodermis of the thigh show promising results for the discrimination of different grades and types of cellulite. A clinical trial conducted in dermatology and comparing controls and patients with venous insufficiency, highlighted the discriminating power of the HF-TE method between the 2 groups but not between the different grades of this pathology. However, the combination based on a logistic regression of the thickness parameters of the dermis and the Young’s modulus resulted in a promising discriminating able to identify the grades.

Keywords : High-frequency transient elastography, HF-TE, Ultrasound, Young’s mo- dulus, Cutaneous tissue, Dermatology, Cosmetology, Cutometry