AN IN-VIVO METHOD FOR MEASURING THE MECHANICAL-PROPERTIES OF THE SKINUSING ULTRASOUND

In this study, we report a new and original device called the ''echorh eometer,'' comprising a suction system with an ultrasound scanner (A-m ode, TM-mode and B-mode) that enables the simultaneous visualization a nd measurement of the deformation of skin structures in vivo. With the scanner described here, high resolution is obtained using a strongly focused, wide-band 20-MHz center frequency transducer, with an axial r esolution of 0.07 mm. This device can determine, noninvasively, not on ly those skin structures that are involved in the deformation, but als o their morphological variation and their extent of involvement with t he degree of stress applied. Using this device, the behavior of the de rmis and subcutaneous fat, while under suction, was investigated on th e volar forearm of 10 volunteers. The results showed that the resistan ce to the applied vertical stress is essentially due to the dermis rat her than the subcutaneous fat, and that there is a certain amount of i nfiltration of fluid into the tissues under suction. In addition, it w as shown that the dermal response to an applied suction is initially d ue to its own natural tension and that, with increasing deformation, t he intrinsic dermal elasticity has a greater contribution to the resis tance of stress. With this information, we hope to develop a mechanica l model to define appropriate mechanical parameters for skin. This wil l allow the evaluation of changes in the dermis and also enable therap eutic intervention to be assessed. Furthermore, it could also be appli ed to studies of skin ageing and the assessment of cosmetic product ef ficacy (emolliency, hydratation, etc.). (C) 1998 World Federation for Ultrasound in Medicine & Biology.