by
Brendon Nafziger, DOTmed News Associate Editor | January 12, 2010
The final answer might come later in the decade, as Dr. Carlesimo hopes a three-year follow-up study of the participants in the current experiment, now underway, will confirm "the high predictive value of the association between memory deficit...and hippocampal ultrastructural changes."
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The follow-up experiments could also put to rest any concerns about the study's limitations.
The DTI scans weren't terribly predictive for patients under 50, a finding Dr. Carlesimo attributes "to the fact [that] both neuronal rearrangement in the hippocampi of healthy individuals and pathological changes in the brain of individuals who will develop Alzheimer's disease actually start later in...life."
And perhaps more seriously, the researchers can't completely rule out the presence of visual artifacts distorting the results. The doctors used a computer program to compare voxels from different images, which can be hard to link up. Still, Dr. Carlesimo says they controlled for possible artifacts the best they could, by only including images with good contrast-to-noise ratio, having slides inspected by a radiologist, and eliminating subjects from the study with poor co-registration.
"Nevertheless, we acknowledge that it remains a challenge to obtain perfect segmentation of anatomical nuclei and co-registration of different images with different voxel dimensions. Consequently, partial volume effects might have impacted our results," Dr. Carlesimo admits.
And don't discount traditional MR imaging just yet. There's always a chance that standard MRI scans, using more advanced technology, can also be used to pick up subtle, age-related changes to the hippocampus by imaging subfields of the brain region older MR equipment can't detect.
"[The subfields] appear to be more susceptible to pathological changes (as those produced by hypoxia or AD [Alzheimer's disease]) than others," Dr. Carlesimo writes. "So, structural changes affecting these regions are likely to be more predictive of memory loss."
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