Objective: To assess the changes in R2* occurring in PD patients compared to controls, a multicenter transversal study was carried out in a large cohort of PD patients going from the early to the late stage of the disease and matched controls.

Background: Several postmortem studies have shown an accumulation of iron in the substantia nigra (SN) in Parkinson’s disease (PD). The iron concentration can be estimated by the MRI-R2* mapping.

Method: Images acquired at 3T in 12 clinical centers were registered, then normalized to the MNI space using DARTEL approach for level group analyses. R2* values were measured in different subcortical regions of interest (ROI) segmented from an automatic atlas. In this study, the observed inter-subject variability was significantly higher than the disease effect. For this reason, an original strategy (intrasubject subcortical quantitative referencing, ISQR) was developed using the measurement of R2* in the red nucleus (RN) as an intra-subject reference. This structure is not directly involved in the PD circuit but exhibits non-specific variability equivalent to that presented in the ROI. ISQR is based on the calculation of the difference between a structure of interest and the RN: R2*(ISQR) (ROI,subject)=R2*(ROI,subject)-R2*(RN,subject)

Results: An increased R2* value was only achieved in the SN of PD patients compared to controls (P_left-SN<0.001, P_right-SN=0.001). After stratification of patients into 4 subgroups according to the disease duration (G1<5 years; G2, between 5 and 10 years; G3, between 10 and 15 years and G4>15 years), no significant difference for R2* was found between PD subgroups, for all ROI (figure1). These results can be explained by the high inter-subject variability in all subcortical regions of R2*. By applying our ISQR strategy, increased R2*(ISQR) values were obtained in the SN when comparing; PD patients to controls (P_right-SN, P_left-SN<10^-4), each PD subgroup to controls (P_right-SN, P_left-SN<10^-3), and between PD subgroups (P_right-SN=0.03, P_left-SN=0.01) with an overall increase of R2*(ISQR) magnitude values (figure2). A significant difference was found when compared G3 to G1 (P_left-SN=0.04, P_right-SN=0.02) and G4 to G1 (P_left-SN=0.006, P_right-SN<0.001) (figure3).

Conclusion: Our results support the use of ISQR to reduce variations not directly related to PD. These findings demonstrate that our original ISQR strategy is useful for PD progression.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/intrasubject-subcortical-quantitative-referencing-to-make-quantitative-mri-sensitive-to-parkinsons-disease/