Noninvasive Quantification Of Whole-brainmetabolic Function Based On T2-relaxation-under-spin-tagging And Phase-contrast MRI

Pilots of modern flight encounter gravity-induced loss of consciousness. As development of airplane and sophisticated tasks, analysis parameters cerebral blood flow and Cerebral Metabolic Rate of Oxygen from pilots can improve the accuracy of protection systems. The most commonly used method for measuring cerebral oxygen generation rate is Positron Emission Computerized Tomography, or use special equipment to analyze blood samples immediately. These experimental treatment processes require a relatively high cost, and take damage on the body, so that they can’t become a routine detection means.In this study, cerebral blood flow(CBF),oxygen extract fraction(OEF), and cerebral metabolic rate of oxygen( CMRO2) was measured noninvasively using the combined of T2-relaxation-under-spin-tagging and phase-contrast MRI techniques. Firstly, Venous oxygenation is measured by T2-relaxation-under-spin-tagging(TRUST) MRI. This method abandoned the traditional spin-echo sequence, replaced by a set of pre-saturated T2 pulse, which echo-time is respectively 0ms, 40 ms, 80 ms, and 160 ms. The T2-preparation scheme, instead of conventional T2-weighted sequence, is used to minimize the blood outflow effect. The sequence consists of interleaved acquisitions of label and control scanning, and each image type is acquired with four different effective echo times(eTEs) ranging from 0 to 160 ms. The T2 relaxation time can then be converted to venous oxygenation(Yv in %) with a calibration plot. And a nonselective saturation RF pulse was applied immediately after image acquisition to reset the magnetizations of all spins. Secondly, global CBF is measured by a PC quantitative flow technique applied at the four feeding arteries(Left ICA, Right ICA, Left VA, and Right VA), based on the principal of accumulated phase shift is proportional to the velocity of the spin. In addition, a T1-weighted magnetization-prepared rapid gradient-echo image was acquired of each subject to provide an estimation of the brain volume, so that variances in brain sizes can be accounted for when comparing across subjects. At last, CMRO2 was calculated by the Fick principle of arteriovenous difference.The value of Yv we measured(64.48±5.33)is correspond with that measured by magnetic resonance phase images(67.84±8.52). And the value of global CBF highly correlated with that measured by Arterial Spin Labeling(p<0.01). Then we did the coffee consumption control experiments. The result shows that, after ingestion of caffeine, the value of cerebral blood flow decreased, and the value of OEF and CMRO2 increased. The result has a good agreement with literature values obtained by PET techniques. The total duration of less than 6 minutes, may afford this technique great potential to become a standard pilot metabolism detection processes.