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BackgroundThe promise of Alzheimer's disease biomarkers has led to their incorporation in new diagnostic criteria and in therapeutic trials; however, significant barriers exist to widespread use. Chief among these is the lack of internationally accepted standards for quantitative metrics. Hippocampal volumetry is the most widely studied quantitative magnetic resonance imaging measure in Alzheimer's disease and thus represents the most rational target for an initial effort at standardization.Methods and ResultsThe authors of this position paper propose a path toward this goal. The steps include the following: (1) Establish and empower an oversight board to manage and assess the effort, (2) adopt the standardized definition of anatomic hippocampal boundaries on magnetic resonance imaging arising from the European Alzheimer's Disease Centers–Alzheimer's Disease Neuroimaging Initiative hippocampal harmonization effort as a reference standard, (3) establish a scientifically appropriate, publicly available reference standard data set based on manual delineation of the hippocampus in an appropriate sample of subjects (Alzheimer's Disease Neuroimaging Initiative), and (4) define minimum technical and prognostic performance metrics for validation of new measurement techniques using the reference standard data set as a benchmark.ConclusionsAlthough manual delineation of the hippocampus is the best available reference standard, practical application of hippocampal volumetry will require automated methods. Our intent was to establish a mechanism for credentialing automated software applications to achieve internationally recognized accuracy and prognostic performance standards that lead to the systematic evaluation and then widespread acceptance and use of hippocampal volumetry. The standardization and assay validation process outlined for hippocampal volumetry was envisioned as a template that could be applied to other imaging biomarkers.

BackgroundCerebral vasogenic edema (VE) has been reported to occur during antiamyloid immunotherapy. VE may be associated with central nervous system pathology with blood–brain barrier disruptions; however, less is known about the prevalence of naturally occurring VE in patients with Alzheimer's disease (AD).MethodsFluid‐attenuated inversion recovery imaging sequences were obtained from four ongoing multicenter, randomized, double‐blind, placebo‐controlled, phase 3 trials in patients with mild‐to‐moderate AD. The first set of baseline scans was from patients in volumetric magnetic resonance imaging addenda in the Interrupting Alzheimer's Dementia by EvaluatiNg Treatment of Amyloid PaThologY (IDENTITY) studies examining semagacestat, a γ‐secretase inhibitor (cohort 1, n = 621). The second set of baseline scans was from the EXPanding Alzheimer's Disease InvestigaTIONs (EXPEDITION) studies examining solanezumab, an anti‐Aβ monoclonal antibody (cohort 2, n = 2141). Readers were blinded to patient‐identifying information and future treatment. A third set of baseline scans was from the first 700 patients who underwent protocol‐specified magnetic resonance imaging before randomization in the EXPEDITION studies (cohort 3). The analysis used three neuroradiologists: two performed independent primary interpretations and the third was the adjudicator. Readers were blinded to patient information, treatment, protocol, and time point.ResultsFour cases of asymptomatic VE were detected at baseline/screening. Two VE cases were due to underlying extra‐axial mass lesions. The third VE case was associated with numerous microhemorrhages in keeping with cerebral amyloid angiopathy‐related inflammation or Aβ‐related angiitis. The final VE case demonstrated localized sulcal fluid‐attenuated inversion recovery imaging hyperintensity. No VE was detected in cohort 3 by readers blinded to patient baseline status.ConclusionsVE seems to be rare at baseline in patients with AD in clinical trials, 2 of 2762 associated with AD. Additional cohorts should be evaluated to support these findings.