Multi‐Slice MRI of Rat Brain Perfusion During Amphetamine Stimulation Using Arterial Spin Labeling

Abstract

When a single coil is used to measure perfusion by arterial spin labeling, saturation of macromolecular protons occurs during the labeling period. Induced magnetization transfer contrast (MTC) effects decrease tissue water signal intensity, reducing the sensitivity of the technique. In addition, MTC effects must be properly accounted for in acquiring a control image. This forces the image to a single slice centered between the labeling plane and the control plane. In this work, a two-coil system is presented as a way to avoid saturation of macromolecular spins during arterial spin labeling. The system consists of one small surface coil for labeling the arterial water spins, and a head coil for MRI, actively decoupled from the labeling coil by using PIN diodes. It is shown that no signal loss occurs due to MTC effects when the two-coil system is used for MRI of rat brain perfusion, enabling three-dimensional perfusion imaging. Using the two-coil system, a multi-slice MRI sequence was used to study the regional effects of amphetamine on brain perfusion. Amphetamine causes significant increases in perfusion in many areas of the brain including the cortex, cingulate, and caudate putamen, in agreement with previous results using deoxyglucose uptake to monitor brain activation.

Relative changes of cerebral arterial and venous blood volumes during increased cerebral blood flow: Implications for BOLD fMRI

“…Relative arterial and venous CBV (rCBV) were determined by diffusionweighted 19 F NMR, while relative CBF (rCBF) was measured using a two-coil continuous arterial spin labeling method (17). To correlate our NMR results, changes in arterial and venous vessel diameters induced by hypercapnia were also measured by in vivo optical microscopy (14).…”

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.…”

“…1b. This minimum separation is given by: [1] Therefore, higher lateral separability is obtained using narrow RF coils (an essential feature to avoid MT effects (42)) and high angles.…”