Quantitative basal CBF and CBF fMRI of rhesus monkeys using three-coil continuous arterial spin labeling

A three-coil continuous arterial-spin-labeling technique with a separate neck labeling coil was implemented on a Siemens 3T Trio for quantitative cerebral blood flow (CBF) and CBF fMRI measurements in non-human primates (rhesus monkeys). The optimal labeling power was 2 W, labeling efficiency was 92 ± 2%, and optimal post-labeling delay was 0.8 s. Gray matter (GM) and white matter (WM) were segmented based on T₁ maps. Quantitative CBF were obtained in 3 min with 1.5-mm isotropic resolution. Whole-brain average ΔS/S was 1.0-1.5%. GM CBF was 104 ± 3 ml/100 g/min (n = 6, SD) and WM CBF was 45 ± 6 ml/100 g/min in isoflurane-anesthetized rhesus monkeys, with the CBF GM/WM ratio of 2.3 ± 0.2. Combined CBF and BOLD (blood-oxygenation-level-dependent) fMRI associated with hypercapnia and hyperoxia were made with 8-s temporal resolution. CBF fMRI responses to 5% CO₂ were 59 ± 10% (GM) and 37 ± 4% (WM); BOLD fMRI responses were 2.0 ± 0.4% (GM) and 1.2 ± 0.4% (WM). CBF fMRI responses to 100% O₂ were - 9.4 ± 2% (GM) and - 3.9 ± 2.6% (WM); BOLD responses were 2.4 ± 0.7% (GM) and 0.8 ± 0.2% (WM). The use of a separate neck coil for spin labeling significantly increased CBF signal-to-noise ratio and the use of small receive-only surface coil significantly increased signal-to-noise ratio and spatial resolution. This study sets the stage for quantitative perfusion imaging and CBF fMRI for neurological diseases in anesthetized and awake monkeys.