Objective: The aim of this study was to explore a novel method of analyzing positron emission tomography (PET) data using graph theory analysis. To this end, we investigated if there were any differences in network topology in the dopamine D2 receptor (D2R) network between three groups: healthy controls (HC), cognitively unimpaired Parkinson’s disease patients (PD-CU), and Parkinson’s disease patients with mild cognitive impairment (PD-MCI).

Background: Cognitive decline in Parkinson’s disease (PD) is a common sequela of the disorder and previous research has found that there is a decrease in D2R in the cortex of PD patients as parkinsonism increases. However, the pathology of cognitive impairment in PD remains poorly understood. Graph theory analysis is a method of investigating whole-brain communication patterns that may be disrupted in PD.

Method: Forty three participants (13 HC, 13 PD-CU, 17 PD-MCI) underwent high-resolution 90 minute PET scans using the radiotracer [11C]FLB 457, which binds with high affinity to extrastriatal D2R in the cortex. An MRI scan was also performed for coregistration. The imaging data was preprocessed using two methodologies: without partial volume correction (PVC) using ROMI, an in-house PET image processing software, as well as with PVC using PMOD v4.005, a PET imaging analysis software package. The non-displaceable binding potential values for each region of interest (ROI) in the AAL atlas was acquired then analyzed using the Graph Analysis Toolbox for MATLAB.

Results: We examined two dopamine subnetworks: a dorsal dopamine network made up of 16 bilateral ROIs and a mesolimbic dopamine network made up of 28 bilateral ROIs. In the method without PVC, the dorsal dopamine network was found to be more efficient in the PD-CU group compared to PD-MCI group, with increased small-worldness, clustering and local efficiency (p<0.05). The mesolimbic dopamine network had reduced clustering in PD-CU compared to HC (p<0.05). In the method using PVC, we found increased assortativity in the PD-CU group compared to the HC group (p<0.05) in the dorsal network.

Conclusion: We observed network topology differences between PD-CU and PD-MCI groups, suggesting network level dopaminergic dysregulation in PD. We found more efficient brain network architecture in PD-CU patients compared to PD-MCI, suggesting compensatory mechanisms may be involved.

References: Kaasinen V, Aalto S, Någren K, Hietala J, Sonninen P, Rinne JO. Extrastriatal dopamine D2 receptors in Parkinson’s disease: a longitudinal study. Journal of neural transmission. 2003 Jun 1;110(6):591-601.

« Back to MDS Virtual Congress 2020

MDS Abstracts - https://www.mdsabstracts.org/abstract/graph-theory-analysis-of-dopamine-d2-receptor-network-in-parkinsons-disease-patients/