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Comparison Of Baseline 123?I Ioflupane SPECT Striatal Binding Ratios With Diffusion Tensor Images From The Parkinson's Progression Marker Initiative

Gallagher, C.L.; Sojkova, J; Bendlin, B.B.; Okonkwo, O; Alexander, A; Wu, I.W.; Schuff, N
MDS: San Diego, CA
Download Presentation: Gallagher-MDS poster-2015.pdf
To compare fractional anisotropy (FA), an MRI?based index of white matter microstructural integrity, to striatal binding ratio (SBR), a SPECT?based index of nigrostriatal dopaminergic projections, in Parkinson's disease (PD) and control subjects.

Several studies have shown diffusion tensor MRI (DTI) differences in cerebral white matter in PD patients when compared with healthy controls. Whether these differences are a consistent finding in large datasets, and whether they reflect pathological changes related to PD, is not known. The Parkinson's Progression marker initiative (PPMI) is a multicenter, longitudinal study that collects both DTI and 123?I Ioflupane SPECT. We hypothesized that this dataset would show lower SBR to be associated with lower FA in major white matter tracts.

Data from 162 PPMI subjects (92 PD, 52 HC, 18 SWEDDs) with both SPECT and DTI (mean intra?scan interval 1.6 months) available as of January 2014 were analyzed. Using a voxel?wise approach, we compared FA within major white matter tracts (FA .15 or higher) to mean hemispheric SBR for caudate nucleus and putamen. FA maps were first normalized in tract?based spatial statistics (TBSS; Smith, NeuroImage 2006); voxel?wise analyses were then conducted in SPM12 (http://www.fil.ion.ucl.ac.uk) using a regression design with covariates of age, gender, years of education, and scanner model (Siemens TrioTrim or Verio, both 3T). We also compared FA between PD and control groups and with SBR in the PD group. Reported clusters included at least 20 voxels at P?
Greater age was associated with diffusely lower FA throughout hemispheric white mater (T=3.2?7.0). [figure1] With the exception of a small parietal?occipital cluster (T=5.2; MNI 35, ?70, 6), the relationship between FA and either putamen or caudate nucleus SBR was opposite that expected; higher FA was associated with lower SBR in several clusters (T=3.5?4.9). [figure2] Within the PD group, higher FA was associated with lower SBR; PD subjects had clusters of higher FA than controls.

In comparison to age, dopamine deficiency (based on SBR) was a weak predictor of FA variations, and furthermore yielded an effect opposite that hypothesized. Several factors, including laterality of PD onset, may have influenced this outcome and require further investigations.