Comparison of cerebral blood volume measured by near infrared spectroscopy and contrast enhanced magnetic resonance imaging

Monitoring angiogenesis noninvasively with near-infrared spectroscopy

Near-infrared (NIR) spectroscopy is used to quantify cerebral blood volume (CBV) as a marker of angiogenesis (formation of new blood vessels). Rats are exposed to chronic hypoxia for 3 weeks at half atmospheric pressure to stimulate angiogenesis, and second-differential NIR spectroscopy is used to quantify total cerebral hemoglobin before and after angiogenesis. The cerebral hemoglobin (from broadband NIR spectroscopy), and the large vessel hemoglobin and hematocrit (from blood samples), are used to derive values for the calculation of CBV. The total hemoglobin in brain is 46.6+/-1.9 micromoll (mean+/-SD, n=5) preacclimation and increases by 72% postacclimation. CBV is initially 3.26+/-0.41% v/v and increases by 31% with acclimation. Each individual animal shows a measureable increase in CBV. This study indicates that NIR broadband spectroscopy can be used for repeated measurements of CBV and can be applied as a noninvasive method to study angiogenesis.

Reproducibility of cerebral blood volume measurements by near infrared spectroscopy in 16 healthy elderly subjects

Near infrared spectroscopy (NIRS) is a non-invasive method to monitor cerebral haemodynamics. Used either alone or in combination with other non-invasive methods such as transcranial Doppler sonography, this technique is well suited for use in cerebrovascular research in ageing. Reproducibility of NIRS, however, has only been determined in neonates and adults. We applied controlled desaturation (the O(2)-method) to measure the cerebral blood volume (CBV) with NIRS in 16 healthy subjects aged 65 to 88. This method uses deoxygenated haemoglobin (the concentration of which is manipulated by desaturation) as an intravascular tracer for NIRS. We determined repeatability (between tests interval: 2 min), short-term reproducibility (intervals of 20 and 40 min) and long-term reproducibility (interval > 2 weeks). We found a coefficient of variation (CV) of 12.5% for repeatability and a CV of 11.7% for short-term reproducibility. The CV for long-term reproducibility was 15%. We conclude that NIRS can reproducibly measure CBV in subjects aged 65 and older, using the O(2)-method. In this group of healthy subjects, this method was well tolerated.

Correlation between near-infrared spectroscopy and magnetic resonance imaging of rat brain oxygenation modulation

We measure the tissue oxygen and haemoglobin concentrations in the rat brain during modulation of inhaled oxygen concentration (FiO2), using non-invasive frequency domain near-infrared oximetry. The rise in oxygenated haemoglobin concentration and the decline in deoxygenated haemoglobin concentration are demonstrated in correspondence with the modulation of FiO2, which is changed from 20% to 100% in increments of 20%. Furthermore, the tissue oxygenation saturation also shows the corresponding trend and changes ranging from approximately 70% to 90%. The relative changes in deoxygenated haemoglobin concentration are compared to the blood-oxygenation-level-dependent (BOLD) MRI signal recorded during a similar FiO2 protocol. A linear relationship with high correlation coefficient between the relative changes in the BOLD MRI signal and the NIRS signal is observed.

Measurement of absolute values of hemoglobin oxygenation in the brain of small rodents by near infrared reflection spectrophotometry

Reflection near infrared spectroscopy (reNIRS) has been proposed as a novel technique for the measurement of absolute values of total hemoglobin (tHb), oxygenated hemoglobin (oxHb), hemoglobin saturation (SO2), and cytochrome aa3 oxidation status (oxCyt aa3) in living tissue. In this study, we evaluated reNIRS during physiological cerebral blood flow conditions in rats (n=6) and during the induction of global cerebral ischemia in gerbils (n=6). ReNIRS parameters were assessed over the exposed cerebral cortex and compared to regional cerebral blood flow (rCBF) data obtained by laser Doppler flowmetry. Under physiological conditions, reNIRS measurements reflected the large intra- and interindividual variability of oxHb and tHb in the brain. The absolute values obtained by reNIRS for tHb (6.3 +/- 1.7 mg/ml), oxHb (3.7 +/- 1.1 mg/ml), and SO2 (61 +/- 5%) matched expected values. In contrast, measurements of oxCyt aa3 were unstable and results unreliable. reNIRS reliably detected cerebral ischemia, verified by a reduction of rCBF to 11% of baseline. tHb dropped to 74 +/- 7% of baseline (P<0.001), reflecting ischemic microvascular vasoconstriction. oxHb and SO2 dropped to expected near-zero values (2 +/- 4 and 3 +/- 5% of baseline, respectively; P<0.001). We conclude that reNIRS provides reliable and reproducible absolute values for brain tissue tHb, oxHb, and SO2 in small rodents. Determination of physiological values requires measurements at multiple locations, while cerebral ischemia is reliably detected by continuous recordings at a single location.