Estimated fraction of tumor vascular blood contents sampled by near infrared spectroscopy and¹⁹F magnetic resonance spectroscopy

This study introduces an experimental approach to estimate percentage of hemoglobin content and volume sampled by near infrared spectroscopy (NIRS). Carbogen (5% CO₂, 95% O₂) respiratory intervention was used to induce physiological changes in a group of six Fisher rat breast tumors. Changes in total hemoglobin concentration, Δ[Hb]_total, and in total blood volume, ΔV_T-blood, of the tumors were measured by NIRS and ¹⁹F magnetic resonance spectroscopy of perflubron, respectively. The ratio of Δ[Hb]_total/ΔV _T-blood was used to calculate the fraction of hemoglobin contents sampled by NIRS. The results showed that the mean value of estimated fractions is within a range of 15-30% of total hemoglobin content in the tumor tissues. Based on the results, we suggest that NIRS does not sample the entire hemoglobin volume of the tissue vasculature, but is more sensitive to microvasculature. This study helps to understand the blood vascular volume sampled by NIRS, and demonstrates that the low cost, portable NIRS system may be a reliable, non-invasive, real-time, monitoring tool for changes in tumor blood contents.