Design and technical evaluation of fibre-coupled Raman probes for the image-guided discrimination of cancerous skin

Two different designs for fibre-coupled Raman probes are presented that are optimized for discriminating cancerous and normal skin by achieving high epithelial sensitivity to detect a major component of the Raman signal from the depth range of the epithelium. This is achieved by optimizing Raman spot diameters to the range of ≈200 µm, which distinguishes this approach from the common applications of either Raman microspectroscopy (1–5 µm) or measurements on larger sampling volume using spot sizes of a few mm. Video imaging with a depicted area in the order of a few cm, to allow comparing Raman measurements to the location of the histo-pathologic findings, is integrated in both designs. This is important due to the inhomogeneity of cancerous lesions. Video image acquisition is achieved using white light LED illumination, which avoids ambient light artefacts. The design requirements focus either on a compact light-weight configuration, for pen-like handling, or on a video-visible measurement spot to enable increased positioning accuracy. Both probes are evaluated with regard to spot size, Rayleigh suppression, background fluorescence, depth sensitivity, clinical handling and ambient light suppression. Ex vivo measurements on porcine ear skin correlates well with findings of other groups.