Specificity of Quantitative Functional Brain Mapping with Arterial Spin-Labeling for Preoperative Assessment

Abstract

Background and purpose: Arterial spin-labeling is a noninvasive MR imaging technique allowing direct and quantitative measurement of brain perfusion. Arterial spin-labeling is well-established in clinics for investigating the overall cerebral perfusion, but it is still occasionally employed during tasks. The typical contrast for functional MR imaging is blood oxygen level-dependent (BOLD) imaging, whose specificity could be biased in neurologic patients due to altered neurovascular coupling. This work aimed to validate the use of functional ASL as a noninvasive tool for presurgical functional brain mapping. This is achieved by comparing the spatial accuracy of functional ASL with transcranial magnetic stimulation as the criterion standard.

Materials and methods: Twenty-eight healthy participants executed a motor task and received a somatosensory stimulation, while BOLD imaging and arterial spin-labeling were acquired simultaneously. Transcranial magnetic stimulation was subsequently used to define hand somatotopy.

Results: Functional ASL was found more adjacent to transcranial magnetic stimulation than BOLD imaging, with a significant shift along the inferior-to-superior direction. With respect to BOLD imaging, functional ASL was localized significantly more laterally, anteriorly, and inferiorly during motor tasks and pneumatic stimulation.

Conclusions: Our results confirm the specificity of functional ASL in targeting the regional neuronal excitability. Functional ASL could be considered as a valid supplementary technique to BOLD imaging for presurgical mapping when spatial accuracy is crucial for delineating eloquent cortex.

FIG 1.

Group analysis of clenching hand task. Results of the clenching of the right (A) and left (B) hand across the subjects are shown for BOLD (left side) and fASL (right side). Blue crosslines point at the global maxima of the group-level activation. Coordinates are reported in squared parentheses. Plots on top of each brain-view represent the BOLD (in blue) and fASL (green) timeseries of the individual global maxima. Straight lines and shaded areas indicate the means and the standard deviations evaluated at each timepoint across the subjects. The dashed black line represents the experimental design.

FIG 2.

Representation of CoG on MNI template. For each healthy participant, blue and green spheres are positioned on the MNI coordinates of the CoG for BOLD and fASL activations during the clenching motor task for each hand. The red spheres correspond to the MNI coordinates of the points with the highest motor evoked potential during TMS for each hand.