Towards automatic detection of malignant melanoma by laser speckle

The incidence of malignant melanoma (MM), the most aggressive and deadly form of skin cancer, has been increasing rapidly since the last few decades. Clinical differentiation between MM and pigmented benign skin lesions based on visual assessment can be challenging because some of benign lesions such as melanocytic lesions (ML) and seborrheic keratoses (SK) resemble MM. In this paper we introduce a novel, non-invasive, "optical biopsy" method based on laser speckle. Propagating inside the skin tissues, photons undergo optical path dispersion due to scattering. Therefore the emerging light loses the initial state of coherence, which influences the backscattered speckle pattern if the light optical path deviation in a tissue is comparable with the length of coherence. Speckle contrast is a measure of this decorrelation process. Histology shows that MM, ML, and SK have diverse morphology. We hypothesized that the morphological differences can be detected by polychromatic speckle, and the technique can be used to differentiate these lesions in vivo. In a study with 12 MMs, 24 MLs, and 37 SKs, we computed the speckle contrast related to their superficial skin region. The mean contrast of MM, ML and SK were 0.78 (standard error (SE) = 0.02, 0.63 (SE = 0.01), and 0.67 (SE = 0.01), respectively. Statistical test showed that there was a significant difference among the contrast of the three types of lesions (p < 0.001, Kruskal-Wallis), and intergroup pair-wise tests showed significant differences in distribution between all three groups. Potentially, speckle imaging can differentiate these lesions.