Arterial spin labeling perfusion fMRI with very low task frequency

Abstract

Functional magnetic resonance imaging (fMRI) has become the most widely used modality for visualizing regional brain activation in response to sensorimotor or cognitive tasks. While the majority of fMRI studies have used blood oxygenation leveldependent (BOLD) contrast as a marker for neural activation, baseline drift effects result in poor sensitivity for detecting slow variations in neural activity. By contrast, drift effects are minimized in arterial spin labeling (ASL) perfusion contrast, primarily as a result of successive pairwise subtraction between images acquired with and without labeling. Recent data suggest that ASL contrast shows stable noise characteristics over the entire frequency spectrum, which makes it suitable for studying low-frequency events in brain function. The present study investigates the relative sensitivities of ASL and BOLD contrast in detecting changes in motor cortex activation over a spectrum of frequencies of experimental design, where the alternating period between the resting state and activation is varied from 30 s up to 24 hr. The results demonstrate that 1) ASL contrast can detect differences in motor cortex activation over periods of minutes, hours, and even days; 2) the functional sensitivity of ASL contrast becomes superior to that of BOLD contrast when the alternating period between the resting state and activation is greater than a few minutes; and 3) task activation measured by ASL tends to have less intersubject variability than BOLD contrast. The improved sensitivity of the ASL contrast for low task frequency and longitudinal studies, along with its superior power in group analysis, is expected to extend the range of experimental designs that can be studied using fMRI. Magn Reson Med 49:796 -802, 2003.

Tonotopic maps in human auditory cortex using arterial spin labeling

“…Vein voxels were defined using vein masks created from SWI images optimized to enhance venous vessels from the surrounding tissue. Our results are in agreement with previous studies reporting a venous bias of the BOLD signal whilst a higher specificity to the capillary beds for CBF signal (Aguirre et al, 2002; Tjandra et al, 2005; Wang et al, 2003). We hypothesized that such venous bias of the BOLD signal could explain the observed BOLD signal‐CBF tonotopy mismatches, but no significance difference was found between the BOLD signal‐CBF tonotopy correlations of vein versus non‐vein voxels.…”

“…ASL allows to quantify both stimulation‐induced and baseline CBF as an absolute marker of the physiological state of the tissue and its changes. Studies have shown that CBF, compared to the BOLD signal, is more spatially localized to neural activity, has lower intersubject variability and is more reproducible over time (Aguirre et al, 2002; Wang et al, 2003; Tjandra et al, 2005). However, CBF signal has a lower SNR and its quantitative estimation is challenged by MRI acquisition confounds such as transit delay, magnetization transfer and relaxation time effects.…”

CBT reduces CBF: cognitive‐behavioral therapy reduces cerebral blood flow in fear‐relevant brain regions in spider phobia

“…2003). ASL during the resting state is capable of detecting subtle changes in regional CBF within nodes of specific anxiety‐related networks; these may be modulated by CBT.…”

Propofol allows precise quantitative arterial spin labelling functional magnetic resonance imaging in the rat

“…ASL has advantages over other functional imaging methods; it has been reported to provide better localised mapping of neural activity compared to BOLD (Lee et al, 2002;Wang et al, 2003). ASL may also be superior to BOLD in tasks lasting longer than 1-2 minutes (Aguirre et al, 2002).…”