Alzheimer's Imaging Consortium

Task-based functional Magnetic Resonance Imaging (tb-fMRI) leverages blood oxygenation to measure the brain's response to external stimuli. A lack of tb-fMRI equipment standardization is the well-recognized challenge when deploying this promising approach in multi-center clinical trials. We sought to implement and characterize visual task-based brain activation as an exploratory measurement in TRAILBLAZER-ALZ 6 (NCT05738486), a multicenter, randomized, double-blind, Phase 3b study of donanemab in adults with early symptomatic AD and confirmed amyloid pathology.

A total of 41 3 Tesla scanners were qualified for tb-fMRI, including 9 sites with established hardware (e.g. MR compatible Liquid Crystal Displays / goggles and triggering devices) and 32 sites lacking hardware (de novo) where a video-capable projector and an MRI coil mirror were provided. A 4-minute visual task (alternating 30s blocks of flashing annulus and crosshair) was disseminated either via a paradigm (established) or as a video (de novo). fMRI acquisition was an interleaved gradient recalled echo planar (GRE-EPI) sequence with TR(repetition time)/TE(echo time)= 3000ms/30ms, voxel size = 3x3x4mm³, and 35 slices. fMRI data was pre-processed and spatially normalized to brain atlas space using a validated Clario pipeline. Processed fMRI data was input to a general linear model (GLM) with outlier regression. Brain activation for each scan was quantified as the mean T-score and Blood Oxygenation Level Dependent (BOLD) contrast within a pre-specified region of interest (ROI) of atlas-space occipital subregions.

Task-based fMRI data was acquired from 799 participants (n established = 192, n de novo = 607). Brain activation within the entire ROI was significant across all participants for mean T-score (t > 7, p < 0.0001) and BOLD contrast value (t > 6.4, p < 0.0001). At the group-level, participants scanned on established equipment had significantly higher BOLD contrast values relative to de novo sites (two-tailed p < 0.03), but mean T-scores were not significantly different.

Task-based fMRI is viable in multi-center clinical trials. Novice sites can be trained to utilize off-the-shelf components and generate analyzable data. Variance due to fMRI equipment capabilities appears to impact the magnitude of ROI activation more than its significance level.