Integration of plantar soft tissue stiffness measurements in routine MRI of the diabetic foot

Objective. A method of measuring mechanical properties of plantar soft tissues in vivo by integrating a photoelastic technique into an MRI system is presented. Background. Plantar tissue stiffening in the diabetic foot is associated with development of ulcers at the highest-pressure sites. MRI is used as an effective means of demonstrating tissue damage caused by diabetic ulceration. Design. The new measurement method uses the indentation of a sphere into the plantar tissue, which is simultaneously scanned by MRI. The indentation force is obtained using the photoelastic technique while tissue deflection is measured on the MRI scans, to yield a characteristic load–displacement curve. Methods. Applicability of the proposed method in characterizing the plantar tissue stiffness and indentation patterns of two young normal subjects and two older diabetic patients was tested. Results. Significantly higher effective shear and elastic moduli were measured for the diabetic plantar tissue compared with that of normal. For the diabetic patients, local stiffness in proximity of the 1st metatarsal head was substantially larger than in other sites, and this could be associated with initial tissue ulceration at this location.