Imaging the mechanical stiffness of skin lesions by in vivo acousto-optical elastography.

Optical elastography is an imaging modality that relies on variations in the local mechanical properties of biological tissues as the contrast mechanism for image formation. Skin lesions, such as melanomas and other invasive conditions, are known to alter the arrangement of collagen fibers in the skin and thus should lead to alterations in local skin mechanical properties. We report on an acousto-optical elastography (AOE) imaging modality for quantifying the mechanical behavior of skin lesions. The method relies upon stimulating the tissue with a low frequency acoustic force and imaging the resulting strains in the tissue by means of quantifying the magnitude of the dynamic shift in a back-reflected laser speckle pattern from the skin. The magnitude of the shift reflects the local stiffness of the tissue. We demonstrate AOE on a tissue-mimicking phantom, an in vivo mouse melanoma lesion and two types of in vivo human melanocytic nevi. The skin lesions we examined were found to have distinct mechanical properties that appear to correlate with the varying degrees of dermal involvement of the lesions.