Non-invasive Serum Cholesterol Detection Using Near-infrared Light Transmission

Abstract

Abstract-This paper investigated whether a simple, non-invasive blood vessel visualization technique using near-infrared light is suitable for determining serum cholesterol levels. Six-week-old male Wistar rats were divided into 6 groups (n = 10/group) and were fed either control diet alone or control diet with 0.5%, 1.0%, 1.25%, 1.5%, or 2.0% cholesterol for 8 weeks. A cuff was subsequently placed on the proximal part of the tail (cuff pressure, 80 mmHg), the tail distal to the compression site was exposed to near-infrared light (wavelength, 850 nm), and transmitted light was photographed. Near-infrared transmission images were acquired before and after cuff inflation, and hemoglobin and haematocrit levels in veins distal to the compression site were determined. Increased dietary cholesterol levels resulted in increased total serum cholesterol levels. Before cuff inflation, rats that were fed the 2.0% cholesterol diet had significantly lower hemoglobin levels than those that fed the control diet (P < 0.01). There were no significant differences in hemoglobin and haematocrit levels at 5 min after cuff inflation. From the association between total serum cholesterol levels and differences in hemoglobin levels, the differences in hemoglobin levels were almost constant when total serum cholesterol levels increased to near 150 mg/dL, but the differences significantly elevated at total serum cholesterol levels >150 mg/dL (r = 0.449, P < 0.001). The correlation between total serum cholesterol levels and relative changes in near-infrared light transmission significantly adhered to that between total serum cholesterol levels and differences in hemoglobin levels (r = 0.452, P < 0.005). At total serum cholesterol levels >150 mg/dL, increased cholesterol levels affected erythrocyte membranes and probably reduced their deformability, resulting in decreased hemoglobin levels (anemia) with erythrocyte destruction in the spleen as the rate-determining factor. This decrease was detected as changes in near-infrared light transmission.