PET has the potential to differentiate between types of dementia and to identify pharmaceuticals to slow the progress of the disease, according to two studies published in the August issue of the Journal of Nuclear Medicine.
In one study, researchers from the nuclear medicine department and PET center at Austin Health in Heidelberg, Australia, led by Dr. Victor Villemagne, compared cortical amyloid deposition using F-18 florbetaben and PET in a total of 109 participants in three clinical studies.
Among these 109 participants, there were 32 control subjects, 20 patients with mild cognitive impairment (MCI), and 30 patients with Alzheimer's disease. The researchers also included 11 subjects with frontotemporal lobar degeneration, seven individuals with dementia with Lewy bodies, five people with Parkinson's disease, and four patients with vascular dementia (JNM, August 2011, Vol. 52:8, pp. 1210-1217).
All individuals received PET scans after intravenous injection of 300 MBq of F-18 florbetaben. Standardized uptake value ratios (SUVRs) using the cerebellar cortex as a reference region were calculated between 90 and 110 minutes after injection.
Higher SUVRs
The researchers found that the Alzheimer's patients demonstrated "significantly higher" SUVRs (p < 0.0001) in neocortical areas, with 96% of Alzheimer's patients and 60% of subjects with mild cognitive impairment showing diffuse cortical F-18 florbetaben retention.
By comparison, only 9% of the patients with frontotemporal lobar degeneration, 25% of those with vascular dementia, 29% of those with dementia with Lewy bodies, and no Parkinson's disease patients showed cortical binding. Cortical binding was present in 16% of the control subjects.
Villemagne and colleagues concluded that F-18 florbetaben performs with the same high accuracy as previously reported with the most widely used amyloid agent, carbon-11 Pittsburgh Compound B, for distinguishing between certain types of neurodegenerative dementia, particularly for diagnosis of Alzheimer's disease from frontotemporal dementia.
F-18 florbetaben also has the benefit of a longer half-life and is more affordable, making it appropriate for clinical use, added study co-author Dr. Christopher Rowe.
PET scores
In the second study, researchers from Wolfson Molecular Imaging Centre at the University of Manchester in the U.K. developed a "PET score" that was extracted automatically from FDG-PET scans using a sample of controls, patients with mild cognitive impairment, and patients with Alzheimer's disease (JNM, pp. 1218-1226).
Lead study author Dr. Karl Herholz and colleagues theorized that the PET scores would provide greater test-retest reliability than standard neuropsychologic test scores, and that they would be a better measure of progression of Alzheimer's disease and cognitive impairment.
The researchers found that the number of patients diagnosed with Alzheimer's disease increased over 24 months, while the number of patients diagnosed with mild cognitive impairment decreased. In addition, the number of control subjects increased slightly, because more MCI patients were reclassified as controls during follow-up.
Herholz and colleagues also found no substantial changes in PET scores among the control group and in patients with MCI at follow-up at six, 12, and 24 months.
Drug trials
The finding was "expected because subjects with substantial clinical progression moved to the Alzheimer's disease group," the authors wrote. "In contrast, there was a steady increase of PET scores in Alzheimer's patients, because those who already had Alzheimer's at entry remained in this group while the disease progressed."
There is an urgent need for tools to more efficiently conduct drug trials for mild cognitive impairment, according to Herholz.
"Clinical outcome parameters show large variability and little sensitivity to progression at that stage, making these trials extremely costly and cumbersome," he said. "Prevention of dementia by drugs applied at MCI stage would greatly improve quality of life for patients and reduce costs of dementia care and treatment."
