Sonoelastography and transient elastography are two ultrasound-based techniques that facilitate noninvasive characterization of the viscoelastic properties of soft tissues by investigating their response to shear mechanical excitation. Young's modulus is the principle assessment parameter. Because it defines local tissue stiffness, it is of major interest for the medical imaging and cosmetic industries as it could replace subjective palpation by yielding local, quantitative information. In this paper, we describe a new high-resolution device capable of measuring local Young's modulus in very thin layers (1-5 mm) and devoted to the in vivo evaluation of the elastic properties of human skin. It uses an ultrasonic probe (50 MHz) for tracking the displacements induced by a 300 Hz shear wave generated by a ring surrounding the transducer. The displacements are measured using a conventional cross-correlation technique between successive ultrasonic back-scattered echoes. First, this noninvasive technique has been experimentally proven to be accurate for investigating elasticity in different skin-mimicking phantoms. Second, data were acquired in vivo on human forearms. As expected, Young's modulus was found to be higher in the dermis than in the hypodermis and other soft tissues.

Background: Little is still known concerning subcutaneous adipose tissue and cellulite, and controversial questions are still under discussion.Aims: Magnetic resonance imaging and spectroscopy were used to address two unresolved questions relating to the anatomy and physiology of subcutaneous adipose tissue.Methods: Using high spatial resolution magnetic resonance imaging we characterized the topography of the dermo- hypodermal junction, and the three-dimensional architecture of the subcutaneous fibrous septae. Using proton spectroscopy, we measured water and lipid fractions within a fat lobule, and T-1 and T-2 values of the detected compounds. All these data were analysed according to sex and presence of cellulite.Results: MR imaging quantified deeper indentations of adipose tissue into the dermis, and evidenced for the first time a great increase in the thickness of the inner fat layer in women with cellulite. Moreover, 3D reconstruction of the fibrous septae network showed a higher percentage of septae in a direction perpendicular to the skin surface in women with cellulite; but our study also depicted the tortuous aspect of this network. MR proton spectroscopy could not show any differences related to sex or presence of cellulite concerning T-1 and T-2 relaxation times of the detected compounds within a fat lobule, neither the unsaturated lipid fraction, the saturated lipid fraction, nor the water fraction.Conclusions: Magnetic resonance imaging showed that the 3D architecture of fibrous septae couldn't be modelled simply as perpendicular planes for women and tilted planes at 45degrees for men. MR spectroscopy did not confirm the hypothesis of increased water content in the adipose tissue of women with cellulite as suggested by others, except if such water would be located in the connective septae.