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

Abstract

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 T 1 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-oxygenationlevel-dependent) fMRI associated with hypercapnia and hyperoxia were made with 8-s temporal resolution. CBF fMRI responses to 5% CO 2 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% O 2 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.

Measurement of cerebral perfusion territories using arterial spin labelling

“…While some methods were proposed to extend the coverage of both PASL and CASL to multiple slices (39)(40)(41), MT effects still imposed a few hard to overcome constraints, such as imaging slice orientation restricted to the labeling direction (39,40) and reduction of the effective degree of spin labeling (41). Complete elimination of MT effects could only be achieved with the use of a separate, dedicated labeling RF coil (15,30,31,(42)(43)(44). The use of a small labeling RF coil located outside the imaging region eliminated MT effects, turning the multi-slice implementation trivial and allowing the imaging planes to be arbitrarily positioned in space.…”

“…Both in small animals as well as in humans, the labeling RF coil is positioned over the neck (15,30,31,(42)(43)(44), producing ASL of the common carotid arteries (CCA) and the vertebral arteries (VA), which supply the anterior and posterior brain circulation, respectively. High degrees of labeling efficiency, in the range of 0.75 -0.92, have been obtained with a separate labeling RF coil and the average RF power deposited on the neck was smaller than 2 W both in animals (42,44) as well as in humans (43), corresponding to less than 3.8W/kg specific absorption rate (SAR).…”

“…High degrees of labeling efficiency, in the range of 0.75 -0.92, have been obtained with a separate labeling RF coil and the average RF power deposited on the neck was smaller than 2 W both in animals (42,44) as well as in humans (43), corresponding to less than 3.8W/kg specific absorption rate (SAR). However, because of the close proximity of the labeling RF coil to the skin in the neck and the individual variability in the location of the CCAs and VAs, a careful calibration of the mean RF power required to produce efficient labeling is advised to minimize quantification errors of CBF.…”

Analysis of Cerebral Hemodynamics in Healthy Adult Rhesus with Dynamic Susceptibility Contrast Perfusion (DSC-MR) Imaging

“…Mild hypothermia has been widely used nowadays and deep hypothermia is still being studied. As primate animals are close to humans, rhesus has been studied gradually since 2003 [5][6][7][8][9][10][11]. Theoretically, low brain temperature could improve the brain tolerance to hypoxia.…”

Continuous arterial spin labeling of mouse cerebral blood flow using an actively-detuned two-coil system at 9.4T

“…In contrast to FAIR, CASL using an actively-detuned twocoil system presents higher sensitivity and minimizes magnetization transfer effects and thus is extensively used for studying rat brains [3][4][5][6][7][8]. However, non-invasive MR studies of CBF in mice using CASL remain challenging due to limiting factors such as reduced sensitivities because of the small volume of interest, amplified magnetic susceptibility and elevated physiological motion contributions.…”