Transillumination is a very well-known non-invasive optical technique, that relies on the use of non-ionizing radiation to obtain information about the internal morphology of biological tissues. In a previous work , we implemented a laser-based illuminator operating at a wavelength of 850 nm that, combined with a CMOS digital camera and narrow-band optical detection, showed a great potential for in vivo imaging. A great advantage is the use of low-cost semiconductor lasers, driven by a very low current (about 11 mA), that are spatially distributed as a 6 by 6 matrix covering a 25 cm2 area. Thanks to the strong absorption of haemoglobin at this wavelength, we have collected raw data that can be further processed to achieve better quality images. In particular, here we show that a higher contrast can be attained by expansion of grey level histograms to exploit the full range 0-255. This elaboration can be exploited for the recognition of vascular structures with better resolution. Examples are reported about hand dorsal vein pattern and alive chick embryo blood vessels. Analyses can be successfully performed without applying any thermal or mechanical stress to the human tissue under test and without damaging or puncturing any parts of the eggshells.
 Merlo, S.; Bello, V.; Bodo, E.; Pizzurro, S. A VCSEL-Based NIR Transillumination System for Morpho-Functional Imaging, Sensors, 2019, 19, 1-13