Dual wavelength handheld optical imager for human tissue imaging

Abstract

The proposed handheld optical imager displays dual wavelength LEDs of 660 nm and 940 nm and photodetectors as a Diffuse Optical System (DOS), linking its capability in detection and management of Rheumatoid Arthritis (RA). There are four sources, each followed by three detectors and arranged equidistant from one another. A switching circuit was implemented using a 555 timer in a stable mode to facilitate the switching of the LED at the aforementioned wavelengths. To acquire data, the rectangular-shaped scanner was kept on a volunteer’s palm and moved towards the tip of the finger. At each position of the imager, red and near-IR radiations were sent through the tissue, and the detectors received backscattered radiation. The current signals obtained from the photodiodes were converted into voltages using a trans-impedance amplifier and read into the computer using Data Acquisition (DAQ) system in twelve parallel channels. Using Beer–Lambert’s law, the attenuation coefficient was calculated and displayed as images. These images show the difference between bony structures and other tissue in the fingers. The distal and proximal phalangeal joints appear lower in intensity than the bony structure of the finger. The oxygen saturation map of the scanned area was also obtained. Subjects with arthritic conditions have inflamed joints. The arthritic joints are sensitive to changes in oxygen saturation. Therefore, the imager could distinguish between normal and inflamed joints and be a screening tool for arthritis. The Full Width at Half Maximum (FWHM) values and are compared with the actual width of the joints. The error values are found to be very minimal and the mean value absolute error calculated is 0.06 cm in the intermediate and 0.14 cm for the distal phalanges. These results serve as a premise for further advancements in the detection process.