OASIS-2

OASIS-2 is the second release of the Open Access Series of Imaging Studies, also called OASIS Longitudinal. It contains repeated structural brain MRI of older adults from the longitudinal pool of the Washington University Alzheimer Disease Research Center, and is used to study brain volume loss in normal ageing and early Alzheimer's disease and to develop and test morphometry tools.

Composition

There are 150 right-handed participants (88 women, 62 men) aged 60 to 96 at entry, each scanned on two or more visits (on average 719 days apart), for 373 imaging sessions. Dementia status was staged with the Clinical Dementia Rating (CDR). 72 participants stayed nondemented throughout, 64 had a CDR above 0 at their first visit and 14 converted from CDR 0 to dementia at a later visit. Each session holds 3 or 4 individual T1-weighted scans. Age, sex, education, socioeconomic status, MMSE, CDR, estimated intracranial volume, atlas scaling factor and normalized whole-brain volume come as a spreadsheet. Many participants also appear in OASIS-1 under different identifiers.

Acquisition

All sessions were acquired on the same 1.5 T Siemens Vision scanner with an unchanged MP-RAGE protocol (sagittal, 1.25 mm slices, 1 x 1 mm in-plane). Images are distributed as NIfTI. Besides the raw scans, each session includes the motion-corrected average, a bias-corrected image registered to the Talairach atlas, and a brain-masked version.

Annotations

No manual labels. Each session comes with an automated grey matter, white matter and CSF segmentation in atlas space, and the clinical CDR rating per visit.

Known limitations

• A single scanner and a single T1-weighted sequence: no FLAIR, T2 or other contrasts.
• The images were not defaced. The OASIS terms forbid any use that could reconstruct or recognise faces.
• Exclusion of non-Alzheimer dementias, stroke and large lesions makes the cohort cleaner than a clinical population.
• 25 sessions were dropped for poor quality; some borderline scans remain.
• The paper gives 51 participants with CDR 0.5 at entry in the text and Table 3, but 52 in Table 2.
• The 2010 paper describes the usage policy as liberal; current access goes through the OASIS data use agreement.