BACKGROUND/AIMS: A new method for the in vivo characterization of the mechanical properties of skin has been developed. This comprises a suction chamber and an ultrasound device to measure both the vertical displacement of the skin's surface, and the skin's thickness. METHODS: A mathematical model of the mechanical behaviour of a taught elastic membrane is used to obtain a set of parameters intrinsic to the skin, such as Young's modulus (E) and the initial stress (sigma0), which reflect the stiffness and the natural tension of the skin, respectively. We also calculated an index of non-elasticity of the skin (unrestored energy ratio, UER), which takes into account the volume of tissue mobilized. It determines a ratio between the energy input to the skin and the energy it dissipates. These parameters were evaluated from the volar forearm of 10 normal male volunteers. RESULTS: The results were: 129+/-88 kPa for E, 13.5+/-5 kPa for sigma0, and 0.42+/-0.04 for UER; with reproducibilities of 9.5%, 12.4% and 6.4%, respectively. CONCLUSIONS: This new suction device was found useful for the study of the behaviour of the skin, and the device may be used for the evaluation of certain skin diseases and their therapy.

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BACKGROUND/AIMS: The vast number of existing dedicated techniques proves that skin blood flow estimation is an unsolved problem. Specificities of cutaneous vascularization (very low blood velocity, noisy environment, complexity of the vascularization architecture) result in the unsuitability of conventional ultrasonic Doppler techniques (long acquisition time, low spatial resolution). The object here was to present a high-frequency time-domain correlation METHOD: In particular, the difficulties of adaptating this type of measurement (data processing, hardware problem) are pointed out. METHODS: Radio-frequency (RF) backscattered signals, obtained with a modified version of a home-made 20 MHz skin imaging system, are studied. Time shifts between successive windowed sections of the RF signals are determined by the mean of the cross-correlation algorithm. A realignment procedure (to remove the artefacts caused by the movements of the patient and the manipulator) and a stationary echo cancelling procedure (to remove the signals coming from the cutaneous tissues and to permit the detection of very small vessels) are used. RESULTS: In vitro results show that velocity measurements as low as 0.1 mm/s are attainable with a 80 &mgr;m axial resolution, and blood vessels of 100 &mgr;m are detectable. Our technique has also been validated by means of in vivo experiment on an erysipelas located on a human leg. In this way, a 180-&mgr;m-diameter blood vessel has been detected on a M-mode RF image and the corresponding velocity profile has been obtained. CONCLUSION: Further improvements can be expected, and the level of performance obtained in vitro in this work should be also attainable in vivo and should then provide an effective tool for skin physiology and pathology.

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