Solving inverse bioheat problems of skin tumour identification by dynamic thermography

Abstract

Dynamic thermography is a promising new non-invasive diagnostic technique for skin cancer, not just to identify the skin tumour in its early stage but also to evaluate some of tumour parameters showing the stage and invasiveness. This paper covers the solution of inverse bioheat problems of simultaneous identification of tumour diameter, thickness, blood perfusion rate and thermoregulation coefficient based on the surface temperature difference between healthy skin and lesion during the rewarming period of dynamic thermography. The problem has been treated using numerically generated measurement data for Clark II and Clark IV tumours by adding noise to mimic real measurement data. The solution is based on a more realistic 3D numerical model, composed of different layers including the thermoregulation response of the skin, tumour and surrounding tissue using a deterministic Levenberg–Marquardt optimisation algorithm that is robust and fast. The paper covers the analysis of the starting point of the solution, randomness and level of added noise, as well as the effect of numerical model error on the inverse solution. Tumour diameter and thermoregulation response can be estimated accurately regardless of noise and stage, while blood perfusion and tumour thickness can only be estimated accurately for low noise level or later tumour stage. The solution sensitivity to metabolic heat generation, thickness, blood perfusion rate and thermoregulation coefficient of skin and fat was low, while heat capacity and thermal conductivity of skin and tumour should be determined precisely in the numerical model to be able to evaluate all four tumour parameters as accurately as possible.