ADNI-3 MRI ACQUISITIONS

Abstract

Phase three of the Alzheimer's Disease Neuroimaging Initiative (ADNI-3) began in late 2016. MRI for ADNI-1 focused on consistent longitudinal structural imaging on 1.5T scanners. ADNI-2 imaging was performed at 3T with structural imaging similar to ADNI-1, adding 2D FLAIR and T2*-weighted imaging at all sites. Advanced imaging (diffusion imaging, resting state fMRI, or arterial spin labeling) was included depending on scanner manufacturer. ADNI-3 implements these three advanced sequences from ADNI-2 across all sites. To maximize protocol utility for other studies, only product sequences are used. MR sequence parameters are summarized in Table 1. Consistency across scanner models is important to support pooling of data across the 57 scanners used by 59 ADNI enrollment sites. Completely consistent protocols would, however, be limited by the least capable scanner. As a compromise, two sets of protocols (“basic” and “advanced”) were developed. The basic and advanced protocols share several sequences. Whole brain structure is assessed with T1-weighted inversion recovery and 3D FLAIR images. Higher spatial resolution images are acquired over a limited field of view centered on the hippocampus. T2-weighted images are acquired for assessment of cerebral microbleeds. Arterial spin labeling (ASL) images are acquired via 3D pCASL, 2D PASL or 3D PASL sequences, depending on availability. The protocols diverge for resting state fMRI and diffusion imaging. The bifurcation is driven largely by the availability of simultaneous multi-slice (SMS) accelerated imaging. Diffusion imaging is done using a single b=1000 s/mm2 shell in the basic protocol and with three shells (b=500, 1000 and 2000 s/mm2) in the advanced protocol. Resting state data are acquired with TR ∼600 ms in the advanced protocol and 3000 ms in the basic protocol. The breakdown of scanner manufacturers and models for the 57 scanners is shown in Table 2. The commercial availability of SMS in the U.S. is new and still increasing; initially all scanners have been outfitted with the basic protocol. As scanners are upgraded, it is estimated that approximately 30–45% of scanners upgrade to an advanced protocol by 2019. ADNI-3 data will be collected using basic and advanced protocols. Structural imaging is implemented consistently across the protocols.