In this paper, we study the transient thermal response of skin layers to determine to which extent the surface temperature distribution reflects the properties of subsurface structures, such as benign or malignant lesions. Specifically, we conduct a detailed sensitivity analysis to interpret the changes in the surface temperature distribution as a function of variations in thermophysical properties, blood perfusion rate, metabolic heat generation and thicknesses of skin layers, using a multilayer computational model. These properties can vary from individual to individual or depend on location, external and internal influences, and in certain situations accurate property data are not available in the literature. Therefore, the uncertainties in these data could potentially affect the accuracy of the interpretation/diagnosis of a lesion in a clinical setting. In this study, relevant parameters were varied within characteristic physiological ranges, and differences in the surface temperature response were quantified. It was observed that variations in these parameters have a small influence on the surface temperature distribution. Analysis using this multilayer model was further conducted to determine the sensitivity of transient thermal response to different lesion sizes. This work validates the idea of examining the transient thermal response obtained using a thermal imaging system with the objective of lesion identification. The modeling effort and the sensitivity analysis reported in this paper comprise a portion of a comprehensive research effort involving experimentation on a skin phantom model as well as measurements on patients in a clinical setting, that are currently underway. One of the preliminary results from the ongoing clinical trial is also included to demonstrate the feasibility of the proposed approach.

In 2010 approximately 68,720 melanomas will be diagnosed in the US alone, with around 8,650 resulting in death 1 . To date, the only effective treatment for melanoma remains surgical excision, therefore, the key to extended survival is early detection 2,3 . Considering the large numbers of patients diagnosed every year and the limitations in accessing specialized care quickly, the development of objective in vivo diagnostic instruments to aid the diagnosis is essential. New techniques to detect skin cancer, especially non-invasive diagnostic tools, are being explored in numerous laboratories. Along with the surgical methods, techniques such as digital photography, dermoscopy, multispectral imaging systems (MelaFind), laser-based systems (confocal scanning laser microscopy, laser doppler perfusion imaging, optical coherence tomography), ultrasound, magnetic resonance imaging, are being tested. Each technique offers unique advantages and disadvantages, many of which pose a compromise between effectiveness and accuracy versus ease of use and cost considerations. Details about these techniques and comparisons are available in the literature 4 . Infrared (IR) imaging was shown to be a useful method to diagnose the signs of certain diseases by measuring the local skin temperature. There is a large body of evidence showing that disease or deviation from normal functioning are accompanied by changes of the temperature of the body, which again affect the temperature of the skin 5,6 . Accurate data about the temperature of the human body and skin can provide a wealth of information on the processes responsible for heat generation and thermoregulation, in particular the deviation from normal conditions, often caused by disease. However, IR imaging has not been widely recognized in medicine due to the premature use of the technology 7,8 several decades ago, when temperature measurement accuracy and the spatial resolution were inadequate and sophisticated image processing tools were unavailable. This situation changed dramatically in the late 1990s-2000s. Advances in IR instrumentation, implementation of digital image processing algorithms and dynamic IR imaging, which enables scientists to analyze not only the spatial, but also the temporal thermal behavior of the skin 9 , allowed breakthroughs in the field.In our research, we explore the feasibility of IR imaging, combined with theoretical and experimental studies, as a cost effective, non-invasive, in vivo optical measurement technique for tumor detection, with emphasis on the screening and early detection of melanoma [10][11][12][13] . In this study, we show data obtained in a patient study in which patients that possess a pigmented lesion with a clinical indication for biopsy are selected for imaging. We compared the difference in thermal responses between healthy and malignant tissue and compared our data with biopsy results. We concluded that the increased metabolic activity of the melanoma lesion can be detected by dynamic infrared imaging. Video LinkThe vide...

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Melanoma is the deadliest form of skin cancer. Each year more than 53,600 people learn that they have melanoma, and around 8700 people die from melanoma in the United States. Early detection is the key to improving survival in patients with malignant melanoma. We developed a thermal (infrared) imaging system that allows accurate measurements of small temperature differences on the skin surface with the aim to diagnose malignant pigmented skin lesions at an early stage of the disease. The imaging method we developed relies on active infrared imaging and a multimodal image analysis strategy, including involuntary body/limb motion correction and interactive lesion segmentation for detecting malignant lesions. The imaging system described in the paper was tested in a pilot patient study in which patients who possess a pigmented lesion with a clinical indication for biopsy were selected to participate. The lesion and the surrounding healthy skin were cooled by air at 15 °C for 30–60 s, and the thermal recovery was imaged with the infrared camera after the removal of this cooling stress. We found that the benign lesions have a thermal recovery similar to normal skin, whereas the thermal recovery of the melanoma lesion is different. It was observed that a malignant skin lesion has a higher temperature than healthy skin during the thermal recovery process (up to 2.2 °C higher for a Clark’s level II melanoma). The present study shows the feasibility of dynamic thermal imaging in distinguishing malignant pigmented lesions from benign, look-alike pigmented lesions.

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