## 3 Thermographic Techniques for Skin Cancer Diagnosis
### Dynamic Infrared Thermography
#### 3.2.2 Dynamic IR Thermography Using a Cold Provocation  
Dynamic IR thermography was successfully applied by [PERSON] et al. [23] to detect a BCC. In particular, a cool gel pack was used to cool down to 27 \({}^{\circ}\)C on a skin area of 10 \(\times\) 10 cm\({}^{2}\). The thermal recovery was then recorded by an FLIR SC 3000 camera with a temperature resolution of 0.03 K for 5 min with a frame rate of 1 Hz. The involuntary movements of the patients were compensated by detecting the bore holes of a fiducial marker in the frame sequence using the generalized Hough transformation. In 2006, the work of [PERSON] et al. revealed dynamic thermography as a powerful diagnostic tool. In 2009, [PERSON] et al. began an experimental program aimed at investigating the feasibility of dynamic infrared thermography for follow-up melanoma patients treated with Boron Neutron Capture Therapy (BNCT) [37]. The patients remained at rest for 15-20 min in order to allow the examined region to reach an approximate thermal equilibrium with the environment. Then, the initial temperature distribution was recorded for 30 s (basal study); after that, an immersion in water at 15 \({}^{\circ}\)C for 2 min or an alcohol spray followed by fan currents over the region (to induce cooling by forced evaporation) were used as cold stimuli. Again, a second thermal acquisition was recorded for 3 min or more. In order to compare the steady and post-stimulus temperature distributions, the examined region was immobilized, and anatomical landmarks were used for image acquisition. In the early phase of this study, two patients were followed up for 30 weeks after the BNCT treatment, revealing dynamic thermography as a useful tool for melanoma monitoring during BNCT treatments as well as for optimizing the treatment itself. [PERSON] and [PERSON] developed a thermal infrared imaging system aimed at early diagnosing malignant pigmented skin lesions [38]. This system allows for small temperature differences on the skin surface to be accurately measured. In their pilot study, 37 patients with a pigmented lesion with a clinical indication for biopsy were tested. A 50 mm diameter skin region containing the lesion was cooled by a stream of cold air at 15 \({}^{\circ}\)C for 1 min. The thermal recovery phase was recorded for 3-4 min by an infrared camera (equipped with a 320 \(\times\) 256 pixel InSb focal plane array and having a sensitivity of 0.025 \({}^{\circ}\)C) located 30 cm away from the patient. The acquisition frequency was set at 2 s. To analyze the infrared images, an involuntary movement correction and an interactive lesion segmentation were applied. In particular, to align the recorded thermal image sequence, the corners of an adhesive marker were used as landmarks in a quadratic motion model. Then, an interactive image segmentation algorithm was used to create a mask image delineating the lesion, which in turn was used to identify the lesion region in each of the thermal images. [PERSON] and [PERSON] reported the detection of two melanoma cases at a very early stage, for which temperature differences of 0.5 \({}^{\circ}\)C and 2.2 \({}^{\circ}\)C, respectively, between the lesion and healthy tissue were observed. Thirty-six chronic sun-exposed subjects affected by 87 actinic keratosis and 48 BCC lesions were examined by [PERSON] et al. [39] using both dynamic IR thermography and dermoscopy. A cold stress at 5 \({}^{\circ}\)C on the skin area containing the lesion was applied for 20 s, and after that, the thermal recovery of this region was recorded by an FLIR3000 Thermocam. The thermal images showed well-distinct thermal patterns for the two kinds of lesions: all the actinic keratosis lesions exhibited a hyperthermic pattern, while the BCC lesions showed a hypothermic one. On the contrary, dermoscopic examination a 22% of cases for which no diagnostic indications were achievable. However, the authors stated that to confirm IR thermography as a diagnostic tool, a larger sample of subjects has to be enrolled. [PERSON] et al.