High temporal resolution MRI quantification of global cerebral metabolic rate of oxygen consumption in response to apneic challenge.

We present a technique for quantifying global cerebral metabolic rate of oxygen consumption (CMRO2) in absolute physiologic units at 3-second temporal resolution and apply the technique to quantify the dynamic CMRO2 response to volitional apnea. Temporal resolution of 3 seconds was achieved via a combination of view sharing and superior sagittal sinus-based estimation of total cerebral blood flow (tCBF) rather than tCBF measurement in the neck arteries. These modifications were first validated in three healthy adults and demonstrated to produce minimal errors in image-derived blood flow and venous oxygen saturation (SvO2) values. The technique was then applied in 10 healthy adults during an apnea paradigm of three repeated 30-second breath-holds. Subject-averaged baseline tCBF, arteriovenous oxygen difference (AVO2D), and CMRO2 were 48.6 ± 7.0 mL/100 g per minute, 29.4 ± 3.4 %HbO2, and 125.1 ± 11.4 μmol/100 g per minute, respectively. Subject-averaged maximum changes in tCBF and AVO2D were 43.5 ± 9.4% and -32.1 ± 5.7%, respectively, resulting in a small (6.0 ± 3.5%) but statistically significant (P=0.00044, two-tailed t-test) increase in average end-apneic CMRO2. This method could be used to investigate neurometabolic-hemodynamic relationships in normal physiology, to better define the biophysical origins of the BOLD signal, and to quantify neurometabolic responsiveness in diseases of altered neurovascular reactivity.