Dynamic susceptibility contrast MRI could tip off early-stage Alzheimer’s

Cerebral blood flow (CBF) is an emerging indication of Alzheimer’s pathology and dynamic susceptibility contrast (DSC) MRI may be an ideal modality to track CBF in high-risk patients with mild cognitive impairment, as well as those already diagnosed with the disease, according to a study published in the June issue of Academic Radiology.

Thomas Hauser, MD, from the department of radiology at the German Cancer Research Center in Heidelberg, Germany, and colleagues compared (DSC) MRI brain studies for CBF with previous CBF studies using other modalities such as FDG PET and SPECT.

Changes in tau proteins and accumulation of beta-amyloid plaques are the key indicators of Alzheimer’s pathology. Amyloid plaque can form inside blood vessels of the brain, thereby altering CBF. All three of these predictors worsen over a long period of years prior to full onset of Alzheimer’s during a phase of mild cognitive impairment (MCI). Hauser and colleagues assessed perfusion and tissue microcirculation in several regions of the brain using MRI after intravenous bolus injection of contrast medium.

A total of 85 patients with a mean age of 72 years participated in the study. Of these, 51 were indicated as MCI and 34 as Alzheimer’s patients. For comparison, 23 age-matched healthy controls were included. All patients were given a clinical evaluation and scanned with either a 1.5T or a 3T MRI scanner.

“Although a slight regional reduction of CBV [ceberbral blood volume] was seen in our analysis in various brain areas in patients with MCI compared to [healthy controls] (pronounced in the frontal and temporoparietal cortices bilaterally, the right temporal cortex, the right anterior cingulate gyri, and the left lentiform nucleus), it reached the level of significance only in the left frontal cortex,” wrote the authors. “In patients with AD, no further significant reduction of CBV could be recognized.”

The decrease in CBV was found to be statistically significant (P < 0.05) for Alzheimer’s patients compared to healthy controls. These results were compared to a number of studies with similar findings, except a number of studies indicated marked reductions in CBV in Alzheimer’s patients, whereas this study showed an insignificant decrease. In contrast, hyperactivation of CBF (P < 0.05) was found in the hippocampal area and posterior cingulate gyrus.

“These changes may reflect a complex mechanism of degeneration and compensatory response to accumulating [Alzheimer’s disease] neuropathology and differences in the neuroplasticity,” the authors wrote. “According to these results, our findings of slight increases of CBF in patients with MCI in some regions such as the medial temporal lobe may be the result of an early compensatory mechanism, probably determined by an elevation of neuronal activity, inflammation, or production of vasodilators.”

Although the majority of the results were complementary with other imaging modalities, the authors did not consider DSC-MRI a means of definitive diagnosis.

“The long-lasting transition from normal cognition to AD comes along with both a decrease of perfusion and several slight increases of perfusion in different regions in the early stage," the researchers wrote. "This supports the concepts of regional compensatory cellular mechanisms. However, a definitive diagnosis of MCI based only on DSC-MRI is not possible yet. Nevertheless, various changes of perfusion in AD, most notable in the CBF analyses, correlated well with findings from other studies, such as PET studies. DSC-MRI therefore provides noninvasively new insights into the early pathophysiologic changes of dementing disorders and may improve early diagnosis of [Alzheimer's disease]."