MRI diffusion in Parkinson's disease: using the technique's inherent directional information to study the olfactory bulb and substantia nigra.

Pathological studies have shown that Parkinson's disease (PD) at early stages affects the olfactory bulb (OB) followed by an involvement of substantia nigra (SN) and other brain regions. Emerging imaging methodologies detect alterations in certain brain regions of living PD patients, which may support proper diagnosis and monitor disease progression. Here we used a novel approach of diffusion tensor imaging (DTI), taking advantage of the technique's inherent diffusion directional information, for region of interest (ROI) placement and diffusion measurements in the OB and SN. 16 healthy individuals and 18 early-moderate patients with PD, supported by reduced ¹²³I-Ioflupane putaminal binding, were examined with two identical DTI series. Olfaction was assessed with the 40-item UPSIT and Parkinsonian severity with UPDRS and Hoehn&Yahr. DTI measurements showed reduced fractional anisotropy (FA) for SN in the PD group in both DTI series. In OBs there was reduced FA in the PD group in the first series, but not in the second. As OBs are located in an area susceptible to artifacts, the coefficient of variation between the two DTI series was higher than for other brain regions. The UPSIT scores were much lower in the PD group than in healthy individuals. In conclusion, we describe a novel approach for more objective ROI placement in DTI, which enabled us to detect altered diffusion in the SN and OBs in PD. These data provides further support that diffusion MRI can be of high clinical utility as a biomarker to facilitate diagnosis and follow disease progression in PD.