MR's ability to chart structural atrophy associated with cognitive decline has constituted its primary use in imaging Alzheimer's disease. Now researchers have demonstrated an MR perfusion technique that shows hypoperfusion in similar brain regions to those seen in FDG-PET and HMPAO-SPECT studies.
The technique, arterial spin-labeled perfusion MRI (ASL-MRI), can be performed in 10 minutes on a commercial scanner. The sequence inverts polarity of water protons, which then flow into the region of interest and perfuse into extravascular space. The inverted protons, mixing with protons of a different polarity, are readily distinguished.
"Given the coupling between metabolism and perfusion in the cortex, ASL-MRI may detect similar functional changes to PET and SPECT, while offering several advantages over these modalities," said co-investigator Dr. Norbert Schuff at the International Conference on Alzheimer's Disease and Related Disorders in Philadelphia in July.
Dr. Nathan A. Johnson and colleagues from the VA Medical Center in San Francisco and several other sites in California studied 20 subjects with AD, 18 with mild cognitive impairment, and 23 healthy controls with pulsed ASL-MRI, as well as a 3D T1-weighted sequence.
The AD group showed significant regional hypoperfusion in the parietal lobes, posterior cingulate gyri, and prefrontal cortices when compared with controls. These findings are very similar to PET and SPECT perfusion studies, Schuff said.
The MCI group did not show statistically significant regional hypoperfusion relative to the control group, but there was a trend toward hypoperfusion in the inferior left parietal lobe, the region of greatest significance in the AD group.
To demonstrate that the hypoperfusion is independent of tissue loss, the researchers corrected for atrophy and measured the corrected data against the uncorrected. The findings were similar.
A subpopulation of cognitively impaired nondemented subjects (CIND), which includes amnestic MCI and other dementias, was found to have a dominant hypoperfusion in the lateral posterior area and some spotty hypoperfusion in the posterior cingulate.
"The AD patients have more hypoperfusion than the CIND group," Schuff said.
Schuff concluded that ASL-MRI is similar to PET and SPECT in terms of showing hypoperfusion in similar brain regions and demonstrating that hypoperfusion is independent of volume loss. ASL-MRI can improve disease classification compared with hippocampal volume alone, he said.
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