The radioactive tracer selected for tau positron emission tomography (PET) scanning can determine whether Alzheimer's-related brain changes are detected at all, according to research published in The Lancet. The finding raises questions about consistency in both clinical research and diagnostic practice.
What the Study Examined
Tau PET imaging is used to identify the abnormal protein tangles associated with Alzheimer's disease. Two tracers are currently in broad use: [18F]flortaucipir and [18F]MK6240. While both are designed to bind to tau deposits in the brain, the multicentre, prospective study — which enrolled participants across the ageing and Alzheimer's disease spectrum — tested them head-to-head within the same individuals.
The within-participant design is notable because it removes the variability that typically arises when comparing results across separate study populations, allowing a more direct assessment of how the two tracers perform under equivalent conditions.
Key Findings
Researchers reported that [18F]MK6240 identified a greater number of individuals with tau pathology than [18F]flortaucipir. This difference held across both cognitively unimpaired participants and those with measurable cognitive impairment, suggesting the gap in detection is not confined to any single stage of disease progression.
According to the study, the choice of tracer materially influences how frequently tau pathology is found across the broader spectrum of ageing and Alzheimer's disease — a finding with consequences that extend well beyond the imaging suite.
Implications for Clinical Trials and Treatment
The researchers noted that their results carry direct implications for how patients are selected and grouped in Alzheimer's clinical trials. Tracer choice could affect which individuals are deemed eligible for a given study, potentially skewing the populations enrolled and complicating comparisons between trials that use different imaging agents.
The findings also bear on therapeutic decision-making more broadly. If one tracer is less sensitive to early or mild tau accumulation, clinicians relying on that tool may reach different conclusions about a patient's disease status than those using the alternative.
Context
Tau pathology is one of the two hallmark features of Alzheimer's disease, alongside amyloid plaques. As tau-targeting therapies move through development pipelines, the ability to accurately and consistently detect tau burden becomes increasingly important. Standardisation of imaging methodology — including tracer selection — is an ongoing challenge in the field.
The study was cross-sectional in design, meaning it captured a single point in time for each participant rather than tracking changes over a longer period. Further longitudinal research may be needed to understand how tracer differences affect the monitoring of disease progression.