Metabolism of oxygen via T2 and interleaved velocity encoding: A rapid method to quantify whole-brain cerebral metabolic rate of oxygen
Rajiv S. Deshpande, Michael C. Langham, Cheng-Chieh Cheng, Felix W. Wehrli
Abstract
Purpose
Cerebral metabolic rate of oxygen (CMRO2) is an important biomarker of brain function. Key physiological parameters required to quantify CMRO2 include blood flow rate in the feeding arteries and venous oxygen saturation (SvO2) in the draining vein. Here, a pulse sequence, metabolism of oxygen via T2 and interleaved velocity encoding (MOTIVE), was developed to measure both parameters simultaneously and enable CMRO2 quantification in a single pass.
Methods
The MOTIVE sequence interleaves a phase-contrast module between a nonselective saturation and a background-suppressed T2-prepared EPI readout (BGS-EPI) to measure T2 of blood water protons and cerebral blood flow in 20 s or less. The MOTIVE and standalone BGS-EPI sequences were compared against TRUST (“T2 relaxation under spin tagging”) in the brain in healthy subjects (N = 24). Variants of MOTIVE to enhance resolution or shorten scan time were explored. Intrasession and intersession reproducibility studies were performed.
Results
MOTIVE experiments yielded an average SvO2 of 61 ± 6% in the superior sagittal sinus of the brain and an average cerebral blood flow of 56 ± 10 ml/min/100 g. The bias in SvO2 of MOTIVE and BGS-EPI to TRUST was +2 ± 4% and +1 ± 3%, respectively. The bias in cerebral blood flow of MOTIVE to Cartesian phase-contrast reference was +1 ± 6 ml/min/100 g.
Conclusions
The MOTIVE sequence is an advance over existing T2-based oximetric methods. It does not require a control image and simultaneously measures SvO2 and flow velocity. The measurements agree well with TRUST and reference phase-contrast sequences. This noninvasive technique enables CMRO2 quantification in under 20 s and is reproducible for in vivo applications.