Advances in MR imaging of the skin

MR imaging of the skin is challenging because of the small size of the structures to be visualized. By increasing the gradient amplitude and/or duration, skin layers can be visualized with a voxel size of the order of 20 microm, clearly the smallest obtained for in vivo images in a whole-body imager. Currently, the gradient strength of most commercial systems enables acquisition of such a small voxel size, and the main difficulty has thus become to achieve sufficient detection sensitivity. The signal-to-noise ratio (SNR) can be increased either by increasing the magnetic field strength or by minimizing noise with small coils; cooling copper coils or superconducting coils can enhance the SNR by a factor of 3 or more. MR imaging, because of the large number of parameters it is able to measure, can provide more than the microscopic architecture of the skin: physical parameters such as relaxation times, magnetization transfer or diffusion, and chemical parameters such as the water and fat contents or phosphorus metabolism. In spite of the amount of information they have provided to date, MR imaging and spectroscopy have had limited clinical applications, mainly because cutaneous pathologies are easily accessible to the naked eye and surgery. However, MR technologies indeed represent powerful research tools to study normal and diseased skin.