Arterial Spin Labeling MRI Identifies Evidence of Cognitive Decline Before Symptoms Present

The technique has the potential to be used as a biomarker in very early diagnosis of preclinical dementia.

The World Health Organization (WHO; Geneva, Switzerland) stated that dementia affects more than 35 million people worldwide, a number expected to more than double by 2030. Problems in the brain related to dementia, such as lessened blood flow, might be present for a long time but are not evident because of cognitive reserve, a phenomenon where other areas of the brain compensate for deficits in one region. Early detection of cognitive decline is vital, because treatments for Alzheimer’s disease (AD), the most common type of dementia, are most effective in this early phase.

Researchers recently examined arterial spin labeling (ASL), a new MRI technique that measures brain perfusion and does not require the injection of a contrast agent. “ASL MRI is simple to perform, doesn’t require special equipment and only adds a few minutes to the exam,” said study author Sven Haller, MD, from the University of Geneva (Geneva, Switzerland). The findings were published online October 2014 in the journal Radiology.

The study group included 148 healthy elderly study participants and 65 individuals with mild cognitive impairment (MCI). The participants underwent brain MRI and a neuropsychologic evaluation, a typical battery of tests used to determine cognitive ability. Of the 148 healthy individuals, 75 remained stable, while 73 worsened cognitively at 18 months clinical follow-up. Those who deteriorated had shown reduced perfusion at their baseline ASL MRI scans, especially in the posterior cingulate cortex, an area in the middle of the brain that is associated with the default mode network, the neural network that is active when the brain is not concentrating on a specific task. Declines in this network are seen in MCI patients and are more pronounced in those with Alzheimer’s disease (AD).

The pattern of diminished perfusion in the brains of healthy individuals who went on to develop cognitive deficits was similar to that of patients with MCI. “There is a known close link between neural activity and brain perfusion in the posterior cingulate cortex,” Dr. Haller said. “Less perfusion indicates decreased neural activity.”

The study findings suggest that individuals with decreased perfusion identified with ASL MRI may temporarily maintain their cognitive status through the mobilization of their cognitive reserve, but will ultimately develop slight cognitive deficits.

Previous research conducted with positron emission tomography (PET) imaging, the current gold standard for brain metabolism imaging, revealed that patients with AD had decreased metabolism in the same area of the brain where the perfusion abnormalities were found using ASL MRI. This is evidence of a close association between brain metabolism and perfusion, according to Dr. Haller.

ASL MRI has potential as a standalone test or as an adjunct to PET for dementia screening, Dr. Haller said. While PET can identify markers of AD in the brain and cerebrospinal fluid, it exposes the patient to radiation. ASL does not expose the patient to radiation and is easy to perform in routine clinical settings. “ASL might replace the classic yet unspecific fluordesoxyglucose PET that measures brain metabolism. Instead, PET could be done with the new and specific amyloid PET tracers,” Dr. Haller said.

The findings also support a role for ASL MRI as an alternative to neuropsychologic testing, according to the researchers. They plan to perform follow-up research on the patient group to learn more about ASL and long-term cognitive changes.

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