Normal and diabetic foot sole skin mimicking tissue phantom fulfillment for spectroscopic-based DFU diagnostics perspective

The development and advancement of spectroscopy techniques for the timely diagnosis of diabetic foot ulcers (DFUs) requires foot-skin equivalent reference objects, such as tissue phantoms. Therefore, herein, we describe the fabrication and characterization of a solid and single-layered tissue-mimicking phantom, which mimics the optical properties of the sole skin of the normal and diabetic foot. We found that 600 µl of 7% w/v titanium dioxide (TiO2) per 100 ml epoxy solution could provide a solid tissue phantom with the optical properties equivalent to those of a healthy foot. On the contrary, adding 10 µl of India ink to the same phantom concentration could provide a phantom with optical properties equivalent to those of diabetic foot sole skin. Monte Carlo simulations have been performed based on the calculated optical properties and geometry of the developed phantom and found that the fluence distribution was higher in the normal foot compared to the diabetic foot. To investigate the feasibility of the developed phantoms in spectroscopy study, diffuse reflectance measurements have been performed. The diffuse reflectance of the normal phantom plate was higher than that of the diabetic phantom plate. Furthermore, phantom inhomogeneity error was measured and found to be less than 2%, indicating that nearly homogeneous phantoms have been developed. The stability study confirmed that the optical properties of the developed phantoms do not change significantly after a six-month period, which potentially makes them a suitable controlled reference object that may be used in spectroscopy studies for DFU diagnosis and assessment of its severity.