# Spectral Line Reflectance and Fluorescence Imaging Device for Skin Diagnostics
###### Abstract  
The multi-spectral-line imaging concept, which was recently implemented for the snapshot mapping of three main skin chromophores--melanin, oxy-hemoglobin, and deoxy-hemoglobin, is further explored for the snapshot capturing of four spectral line images at wavelengths of 450, 523, 638, and 850 nm, with the consecutive acquiring of a 405 nm excited fluorescence image. A corresponding laser-based prototype device was designed and assembled. Processing of the mentioned five images enables obtaining distribution maps of four skin chromophores within the malformation and comparing their mean fluorescence intensity with that of the surrounding healthy skin. This set of information is helpful for dermatologists, cosmetologists, oncologists, and other healthcare professionals to quantify the diagnosis of skin malformations (including cancers) and to follow up the recovery process after therapy. This paper describes the design of the developed proof-of-concept prototype device and initial test results. multi-spectral-line imaging; fluorescence imaging; non-contact skin diagnostics Article  
Spectral Line Reflectance and Fluorescence Imaging Device for Skin Diagnostics  
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22 October 202  
examined skin area. A set of several spectral images of the same skin target, captured within different wavelength bands, can be converted into a set of chromophore distribution maps [7]. There are two main approaches for obtaining spectral images--by narrowband spectral filtering of the image sensor at spectrally broadband illumination of the target area, or by means of spectrally narrowband illumination. The first approach is widely used in hyperspectral imaging (HSI) systems that capture sequential target images at several tens of adjacent spectral bands using interference filters [8], liquid crystal filters [9], or other means of spectral filtering. Commercial and custom-designed HSI systems were used for skin chromophore mapping [8; 10; 11; 12]; however, routine clinical applications of the HSI systems are limited due to their robustness, expensiveness, and the need for powerful computing resources. The set of processed data in the case of HSI may include a number of spectral images not containing any useful information. The HSI image acquisition process may last from several seconds [12] to a minute or longer [13], so movements of the skin target area during the procedure can cause image artefacts. Special image stabilization algorithms [14] could reduce or fully avoid the motion artefacts, but it takes extra time and computing resources. In addition, in many cases, calculations of complicated integrals comprising spectral features of the chromophore absorbance and the filtered HSI band shape are necessary. The second approach--spectrally selective illumination--has been mainly used in skin multi-spectral imaging (MSI) systems where sequentially switchable non-overlapping spectral bands of illumination (e.g., by several light-emitting diodes (LEDs) with different peak wavelengths at typical spectral full width at half maximum FWHM \(\approx\)20-50 nm) are exploited [15; 16]. Advanced MSI systems are portable and self-sustained, much cheaper than HSI systems, and better adapted for clinical use. The MSI processing procedure is also faster thanks to the lower number of the spectral images, typically between 3 and 8. Still, skin motion artefacts and the processing of relatively broadband spectral images may cause serious problems. Obviously, both the acquisition time of the spectral image set and the spectral bandwidth of each image have to be minimized. Ultimate performance can be achieved if the set of monochromatic (single-wavelength) spectral images is obtained by a single snapshot; this technique is provisionally called \"snapshot multi-spectral-line imaging\" or SMSLI [17; 18]. In this case, a set of spectral line images is obtained under uniform illumination of the target simultaneously by several spectral lines, e.g., emitted by lasers.