To illustrate the proposed differentiation parameter,
shows ordinary color RGB and parametric images of a melanoma and a nevus (a) and a pigmented nevus alone (b). The average p-value of healthy skin in these images is set to 0, in order to make the results comparable regardless of the individual skin type or color. The nevi regions in both cases are darker, while the melanoma region is lighter than the healthy skin background.
RGB images (left) and parametric p-images (right) of melanoma (a) and pigmented nevus (b). The p-value of healthy skin is set to 0.
Most of the parametric p-maps of the examined lesions showed the same tendency—melanoma’s areas (or parts of them) showed notably higher p-values than the surrounding skin, and the nevus areas showed lower p-values than the healthy skin, or, in some cases, similar p-values. Consequently, the criterion p > p0, where p0 is related to the surrounding healthy skin, may be regarded as indication to melanoma.
shows the scatter plot of the mean p-values (averaged over the selected pathology areas) for all examined cases of melanoma and common nevus, when p0 is set to 0.
As the result of our diagnostic test, sensitivity, specificity, positive predictive value and negative predictive value were calculated. After analysis of the 17 available melanoma multi-spectral image sets, 16 showed clear response accordingly to the above-mentioned criterion p (true positives or TP), and only one case - melanoma with ulceration - did not support the criterion (false negative or FN). After analysis of 65 nevi, 58 of them showed lower p-parameter values than the surrounding skin, (true negatives or TN), and 7 cases did not meet the criterion (false positive or FP). Sensitivity of this test is TP/(TP + FN) = 94%, specificity is TN/(FP + TN) = 89%, positive predictive value (PPV) = TP/(TP + FP) = 70% and negative predictive value (NPV) = TN/(FN + TN) = 98%.