Whole‐brain 3D perfusion MRI at 3.0 T using CASL with a separate labeling coil

Abstract

A variety of continuous and pulsed arterial spin labeling (ASL) perfusion MRI techniques have been demonstrated in recent years. One of the reasons these methods are still not routinely used is the limited extent of the imaging region. Of the ASL methods proposed to date, continuous ASL (CASL) with a separate labeling coil is particularly attractive for whole-brain studies at high fields. This approach can provide an increased signal-to-noise ratio (SNR) in perfusion images because there are no magnetization transfer (MT) effects, and lessen concerns regarding RF power deposition at high field because it uses a local labeling coil. In this work, we demonstrate CASL whole-brain quantitative perfusion imaging at 3.0 T using a combination of strategies: 3D volume acquisition, background tissue signal suppression, and a separate labeling coil. The results show that this approach can be used to acquire perfusion images in all brain regions with good sensitivity. Further, it is shown that the method can be performed safely on humans without exceeding the current RF power deposition limits. The current method can be extended to higher fields, and further improved by the use of multiple receiver coils and parallel imaging techniques to reduce scan time or provide increased resolution.

Continuous ASL perfusion fMRI investigation of higher cognition: Quantification of tonic CBF changes during sustained attention and working memory tasks

“…Utilizing our amplitude-modulated CASL MRI imaging protocol with a single coil at 3 T field strength (Wang et al, 2005), we were able to characterize tonic CBF changes associated with an uninterrupted 6 min continuous performance of the two high-level cognitive tasks-i.e., visual sustained attention and verbal working memory. Appropriate image quality and whole brain coverage were obtained without using any additional hardware, such as a separate labeling coil (Talagala et al, 2004;Zaharchuk et al, 1999).…”

Towards quantification of blood-flow changes during cognitive task activation using perfusion-based fMRI

“…Labeling of both carotid arteries, an improved coverage of the imaging coil, and active detuning of the labeling coil are straightforward steps towards whole-brain coverage (Talagala et al, 2004;Zaharchuk et al, 1999). An even stronger main magnetic field (leading to a prolonged longitudinal relaxation time in the arteries, T 1a ) would reduce losses of the label during the transit, and thereby, on top of an overall improved SNR of the images, increase the sensitivity.…”

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.…”