Innovative PET Scans Could Improve Alzheimer's Disease Evaluation

Positron emission tomography (PET) scanning should help non-invasive assessment of the formation of Alzheimer's disease- (AD)-related plaques in the brain, according to a new study.

Alzheimer's disease is degenerative neurologic disease characterized by dementia. It usually affects older individuals, although a small subset of early-onset victims exists. ß-amyloid and other plaques are often used as a basis for AD diagnosis and evaluation, according to the investigators. At present, these aggregates are studied through analysis of brain tissue samples that are obtained during life or observed after death. According to the researchers, this marks, "a major methodological obstacle considering clinical drug trials of early Alzheimer's disease,” as this makes it very difficult to assess the progression of the disease.

Normal-pressure hydrocephalus, which is an increase in the levels of cerebrospinal fluid in the brain, shares some common symptoms with AD, including cognitive impairment. Between 22% and 42% of patients with normal-pressure hydrocephalus symptoms also have the brain lesions that are hallmarks of AD.

PET scanning is a medical imaging technique that measures the location of tracer molecules in a three-dimensional image. A non-invasive, relatively standard procedure, PET has enormous potential as an assessment method for AD if the correct tracer marker is used. To assess this technique, Ville Leinonen, M.D., Ph.D., from the University of Kuopio (Finland), and colleagues examined 10 patients who did not have severe dementia but had undergone biopsy of the frontal cortex because they were suspected of having normal-pressure hydrocephalus. Of these, six were found to have samples with ß-amyloid plaques, while four displayed no AD-related tissue. Carbon 11-labeled Pittsburgh Compound B ([¹¹C]PiB) was injected into each subject as a tracer before undergoing a 90-minute PET scan. The investigators published their findings on August 11, 2008, in the journal Archives of Neurology.

Those patients with ß-amyloid plaques in their brain biopsies also displayed a higher update of [¹¹C]PiB in certain brain areas. In comparison, patients without Alzheimer's plaques did not show this result. The researchers indicated that this means PET using this marker could be a viable option for future diagnosis of AD. "This study supports the use of [¹¹C]PiB PET in the evaluation of beta-amyloid deposition in, for example, mild cognitive impairment, Alzheimer's disease, or normal-pressure hydrocephalus,” they reported. "Large and prospective studies are required to verify whether [¹¹C]PiB PET will become a tool in diagnosing Alzheimer's disease. Another potential use of [¹¹C]PiB would be the quantitative monitoring of beta-amyloid deposits in the brain in subjects under treatment in pharmaceutical trials of early Alzheimer's disease targeting amyloid accumulation.”

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University of Kuopio