Researchers Use Mikrotron CoaXPress Camera for Contactless Imaging of Large Skin Areas

Summary

March 8, 2023 - Photoplethysmography (PPG) is a noninvasive optical technology with applications including vital sign extraction and patient monitoring. However, its current use is primarily limited to heart rate and oxygenation monitoring. A 2023 study by researchers at Toronto Metropolitan University, Toronto, ON demonstrated the added utility of PPG for physiological investigations, in particular, of simultaneous data acquisition from several regions of tissue using remote/contactless PPG (rPPG).
 
Remote PPG is an extension of the reflection mode PPG to a "contactless" mode. In this case, the typical sensor is a camera placed some distance from the patient. This modality has several substantial advantages over traditional PPG. First, it does not require contact with the skin, which significantly simplifies clinical workflow, prevents potential cross-contamination, and is beneficial for patients with damaged or sensitive skin. Second, in contrast with the contact PPG, which is essentially a single-point measurement modality, rPPG allows the simultaneous collection of signals from large skin areas. 
 
In the study, the remote PPG was obtained with a Mikrotron EoSens 1.1CXP2 CoaXPress camera equipped with a Canon EF 50 mm f/1.8 STM lens. The camera features a 1.1 megapixel CMOS global shutter sensor with an area of 17.50 × 11.80 mm and a corresponding pixel size of 13.7 × 13.7 μm. It was mounted on a tripod and directed downwards in an orthogonal manner toward the tissue, in this case, two hands, resulting in a distance from the lens to the tissue of approximately 80 cm. Two diffuse light sources illuminated the hands from around 45 degrees (90 degrees from each other) to minimize the presence of shadows on the tissue.
 
Video data was captured at 500 fps at 512 × 512 pixels using the Bayer GR8 pixel format enabling subsequent extraction of RGB pixel data. Four coaxial cables transmitted the video data to an acquisition PC via a CoaXPress 2.0 frame grabber. The PC ran the Linux operating system and was equipped with an Intel i5 processor and 32 GB of RAM.
 
Twenty-two healthy adult subjects participated in the study. Their hands were placed on the video collection surface with the right palm facing up exposing the glabrous (devoid of hair) tissue and the left palm facing down exposing the non-glabrous (with hair) tissue. The video frame was configured to capture both hands simultaneously with the hands centered in the frame to facilitate subsequent division into each hand during processing Video was then recorded for 2 minutes. The recording was then repeated with the hands in the opposite position with the right palm down and the left palm up.
 
Toronto Metropolitan University researchers found that their results supported the utility of large-area mapping remote PPG measurements. Researchers believe that this technology can be used to extract and compare data from large skin areas of the body or several skin areas without the necessity of synchronizing data collection.