<title>In-vitro correlation between reduced scattering coefficient and hemoglobin concentration of human blood determined by near-infrared spectroscopy</title>

Abstract

We study the correlation between (mu) <SUB>s</SUB>' and THC obtained in vitro, in a highly scattering medium containing human blood. We used a frequency domain near infrared spectrometer (modulation frequency: 110 MHz, wavelengths: 758 and 830 nm) to measure in real time (acquisition time: 0.64 s) (mu) <SUB>s</SUB>' and THC. We used Liposyn suspension and red blood cells in saline buffer solution. After a couple of minutes of baseline acquisition, several consecutive increments of 3-5 ml blood were added to the solution yielding THC equals 15-100 (mu) M and (mu) <SUB>a</SUB> equals 0.03-0.3 1/cm. At the last amount of blood added, increments of glucose in the range of 0.5-20 g/L were added. For each step of blood and glucose added, data were acquired for a couple of minutes. This was repeated 6 times. Average of data was calculated for both (mu) <SUB>s</SUB>' and THC for each of the red blood cells and glucose increments added. We found a high correlation between (mu) <SUB>s</SUB>' and THC (0.018 X THC + 4.51, R<SUP>2</SUP> equals 0.98 at 758 nm and 0.012 X THC + 4.86, R<SUP>2</SUP> equals 0.97 at 830 nm). We studied the effect of glucose on (mu) <SUB>s</SUB>' and we found a high correlation between the glucose added to the suspension and the decrease in (mu) <SUB>s</SUB>' for the case of high glucose concentrations. The slope of this correlation is -0.011 at both wavelengths and the correlation factors were R<SUP>2</SUP> X 0.96 at 830 nm and R<SUP>2</SUP> equals 0.91 at 758 nm (case shown). The effect of glucose was less significant at 830 nm than at 758 nm in general. This work is a proof of principle for detection of (mu) <SUB>s</SUB>' changes with glucose. This approach also establishes limits for glucose detection in physiological conditions.