The Alzheimer's Disease Neuroimaging Initiative (ADNI): MRI methods

Abstract

The Alzheimer's Disease Neuroimaging Initiative (ADNI) is a longitudinal multisite observational study of healthy elders, mild cognitive impairment (MCI), and Alzheimer's disease. Magnetic resonance imaging (MRI), (18F)-fluorodeoxyglucose positron emission tomography (FDG PET), urine serum, and cerebrospinal fluid (CSF) biomarkers, as well as clinical/psychometric assessments are acquired at multiple time points. All data will be cross-linked and made available to the general scientific community. The purpose of this report is to describe the MRI methods employed in ADNI. The ADNI MRI core established specifications that guided protocol development. A major effort was devoted to evaluating 3D T(1)-weighted sequences for morphometric analyses. Several options for this sequence were optimized for the relevant manufacturer platforms and then compared in a reduced-scale clinical trial. The protocol selected for the ADNI study includes: back-to-back 3D magnetization prepared rapid gradient echo (MP-RAGE) scans; B(1)-calibration scans when applicable; and an axial proton density-T(2) dual contrast (i.e., echo) fast spin echo/turbo spin echo (FSE/TSE) for pathology detection. ADNI MRI methods seek to maximize scientific utility while minimizing the burden placed on participants. The approach taken in ADNI to standardization across sites and platforms of the MRI protocol, postacquisition corrections, and phantom-based monitoring of all scanners could be used as a model for other multisite trials.

Figure 1

Undesirable chemical shift. The manufacturer's default polarity of the readout gradient in the SI direction for sagittal acquisitions shifted fat over the base of the brain (arrow, left) in the first version of the protocol. This hinders automated brain extraction algorithms. Reversal of this shift (right) required custom alteration of the manufacturer's product imaging sequence.

Figure 2

Poor SNR with single-channel birdcage coils in first version of protocol. As indicated in Table 1, the protocol using a single-channel birdcage coil differs from the phased array protocol. Left: When 1.5 T images are acquired using the phased array protocol with a birdcage coil, poor SNR results. Right: Making the parameter adjustments listed in Table 1 resolves the problem without increasing chemical shift.

Figure 3

Example MP-RAGE images for each manufacturer at 1.5 T (left) and 3 T (right). a,b: GE. c,d: Philips. e,f: Siemens.

Figure 4

ADNI phantom. The ADNI phantom is spherical, with multiple inclusions that are used both for fiducial purposes and for SNR and contrast measurements. Image at the bottom is an MRI illustrating the central SNR inclusion as well as smaller spheres for fiducial measurements.

Figure 5

Effect of gradwarp. Spherical phantom with rectilinear grid inclusion before (left) and after (right) gradwarp correction.

Figure 6

Intensity in-homogeneity correction. Phased array coil acquisition at 1.5 T before (left) and after (right) intensity nonuniformity correction. Images have been reformatted from the sagittal into the axial plane to illustrate the intensity in-homogeneity anteriority prior to correction.