Change in Blood Vessel Images of the Human Finger Using Near-Infrared Radiation While Compressing the Upper Arm

We can observe the pattern of blood vessel easily by photographing near-infrared (NIR) light that is transmitted through an organism. The experimental system consists of two parts: a cuff compression device and a blood vessel observation device. The blood vessel observation device consists of a NIR light (wavelength 850 nm), and a CCD camera. The finger of a subject was put between the NIR light and the CCD camera. The NIR light that was transmitted through the finger was captured by the CCD camera, and the grayscale images of blood vessels were stored in a PC. We investigated the effects of two parameters on the grayscale image: the compression pressure applied to the upper arm, and the age of the subjects. Forty-five normal men and women (aged 20-64 years) participated in this study. The grayscale image of blood vessels during compression changed to black, and the grayscale image after compression returned to the same image as before compression. The average brightness of an image was calculated by averaging the shades of gray in all pixels. The results for the influence of compression of the upper arm showed that up to 80 mmHg, an increase in pressure caused a significant increase (p<0.05) in the change in the average brightness. However, the change in the average brightness for a compression of 150 mmHg was significantly (p<0.01) lower than those for compressions of 80 mmHg and 100 mmHg; this is thought to be due to the arterial and venous compliance. There was a negative correlation (r= (0.61, p<0.001) between the age of the subjects and the time to reach half the convergent value for the change in the average brightness. One of the contributing factors for this result is considered to be the reduction in the venous compliance with age.