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

We study the correlation between μs 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) μs 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=15-100 μM and μa=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 μs and THC for each of the red blood cells and glucose increments added. We found a high correlation between μs and THC (0.018×THC+4.51, R2=0.98 at 758 nm and 0.012×THC+4.86, R2=0,97 at 830 nm). We studied the effect of glucose on μs and we found a high correlation between the glucose added to the suspension and the decrease in μs for the case of high glucose concentrations. The slope of this correlation is -0.011 at both wavelengths and the correlation factors were R2=0.96 at 830 nm and R2=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 μs changes with glucose. This approach also establishes limits for glucose detection in physiological conditions