Two studies demonstrate the efficacy of a noninvasive MRI test for Alzheimer’s disease.
Researchers can diagnose and track Alzheimer’s disease with use of an innovative MRI technique called arterial spin labeling (ASL) to measure changes in brain function, as reported in a study published in the November 29 Neurology and in a separate study appearing in the October 29 online Alzheimer’s & Dementia. The investigators determined that the ASL-MRI test is a promising alternative to the current standard, a PET scan that requires exposure to small amounts of a radioactive glucose analog and costs approximately four times more than ASL-MRI.
ASL-MRI can be used to measure neurodegenerative changes in a similar way that fluorodeoxyglucose positron emission tomography (FDG-PET) scans are currently being used to measure glucose metabolism in the brain. Both tests correlate with cognitive decline in patients with Alzheimer’s disease.
In brain tissue, regional blood flow is tightly coupled to regional glucose consumption, which is the fuel the brain uses to function,” explained John A. Detre, MD, principal investigator of both studies and a Professor of Neurology and Radiology at the University of Pennsylvania in Philadelphia. “Increases or decreases in brain function are accompanied by changes in both blood flow and glucose metabolism. We designed ASL-MRI to allow cerebral blood flow to be imaged noninvasively and quantitatively using a routine MRI scanner.”
When Alzheimer’s disease is suspected, patients typically receive an MRI initially to look for structural changes that could indicate other medical causes, such as a stroke or brain tumor. Adding about 10 to 20 minutes to the test time, ASL can be incorporated into the routine MRI and capture functional measures to detect Alzheimer’s disease up front, turning a routine clinical test (structural MRI) into both a structural and functional test.
“If ASL-MRI were included in the initial diagnostic work-up routinely, it would save the time for obtaining an additional PET scan, which we often will order when there is diagnostic uncertainty, and would potentially speed up diagnosis,” said coauthor David Wolk, MD, Assistant Professor of Neurology and Assistant Director of the Penn Memory Center.
The studies show a comparison of ASL-MRI and FDG-PET in a group of patients with Alzheimer’s disease and age-matched controls. Cerebral blood flow and glucose metabolism were measured simultaneously by injecting the PET tracer during the MRI study. The data were then analyzed two different ways.
In the study appearing in Alzheimer’s & Dementia, ASL-MRI and FDG-PET images from 13 patients diagnosed with Alzheimer’s disease and 18 age-matched controls were analyzed by visual inspection. Independent, blinded review of the two tests by expert nuclear medicine physicians demonstrated similar abilities to rule out (sensitivity) and diagnose (specificity) Alzheimer’s disease. Neither ASL-MRI nor FDG-PET showed a clear advantage from quantitative testing.
In the Neurology study, the ASL-MRI and FDG-PET images were compared statistically at each location in the brain by computerized analysis. Data from 15 patients with Alzheimer’s disease were compared with data from 19 age-matched healthy adults. The patterns of reduction in cerebral blood flow were nearly identical to the patterns of reduced glucose metabolism by FDG-PET, both of which differed from the patterns of reduction in gray matter seen in Alzheimer’s disease.
"Given that ASL-MRI is entirely noninvasive, has no radiation exposure, is widely available, and easily incorporated into standard MRI routines, it is potentially more suitable for screening and longitudinal disease tracking than FDG-PET,” Dr. Detre and colleagues commented.
Additional studies will focus on larger sample sizes and include patients with mild cognitive impairment and other kinds of neurodegenerative conditions.