Measurement of cerebral blood volume in humans using hyperoxic MRI contrast

Purpose: To develop a new method of measuring quantitative regional cerebral blood volume (CBV) using epochs of hyperoxia as an intravenous contrast agent with T2*-weighted MRI. Materials and Methods: Images were acquired from six subjects (four male, two female, mean age 29 +/- 3.7 years) using a sequence combining pulsed arterial spin labeling interleaved with a gradient echo echo-planar imaging (EPI) blood oxygenation level-dependent (BOLD) sequence at 3T. The hyperoxia paradigm lasted 28 minutes consisting of 4 minutes of normoxia, two 6-minute blocks of hyperoxia. separated by 6 minutes of normoxia. During the hyperoxic blocks the subjects were delivered a fractional oxygen concentration of 0.5. Results: The mean CBV was calculated to be 3.77 +/- 1.05 mL/ 100 g globally, 3.93 +/- 0.90 mL/ 100 g in gray matter (GM), and 2.52 +/- 0.78 mL/ 100 g in white matter (WM). The mean GM/WM ratio was thus found to be 1.56. These values are comparable to those obtained in other studies. Conclusion: The hyperoxia technique for measuring CBV may be particularly useful for patient groups where an injected bolus of contrast agent is contraindicated. As more functional studies are employing epochs of inspired gases for calibration purposes, this method is easily incorporated into existing paradigms to produce a noninvashre, repeatable, easily tolerated, and quantitative measurement of regional CBV.