Figure 10 illustrates the recently designed PPGI prototype device for distant monitoring of anesthesia efficiency during the palm surgery. The system was designed to record signals from the curved surface of the hand (dorsal or ventral aspect). The illuminator comprised four bispectral light sources, each consisting of two high-power LED emitters (Roithner LaserTechnik
GmbH; green:
l = 530 nm, 3 W; IR:
l = 810 nm, 1 W). To achieve uniform illumination of the skin surface, an adjustable LED intensity control was introduced via PC based custom developed software. The two wavelengths of illumination were chosen in order to control blood pulsations at two different vascular depths in real time [
38]. A microcontroller board (Arduino Nano, Arduino, USA) provided sequential switching of green and IR LEDs and triggering of the captured video frames. The camera control was performed using
uEye software in the manual trigger mode, with fixed exposure time, 2 × 2 pixel binning and triggered at 60 frames/s. A monochromatic camera (8 bit CMOS
IDS-uEye UI-1221LE) was equipped with
S-mount 1/2 inch
F = 4 mm low distortion, wide-field lens (Lensagon). The camera lens was placed at the distance of 15 cm from the skin surface, to ensure a full view of the adult palm (field of view, 20 cm × 15 cm). To reduce the skin specular reflectance, orthogonally oriented polarizers were placed behind the camera and all four light sources, respectively. The plastic parts were fabricated using a 3D printer (Prusa i3, custom made, Latvia). The device comprised a plastic enclosure filled with an adjustable vacuum pillow (40 × 20 AB Germa, Sweden) as the palm support.