Objective: To investigate the iron distribution in STN in PD patients using QSM images.

Background: Subthalamic Deep Brain Stimulation (DBS) is considered an effective treatment for Parkinson’s disease (PD). The subthalamic nucleus (STN) has been functionally subdivided in three portions: the somatomotor part which lies dorsolaterally, the limbic part which corresponds to the anteromedial pole and the intermediate portion which corresponds to the associative territory. The goal of DBS is to stimulate the motor part of the STN to obtain optimal motor outcome. Histological studies have revealed an inhomogeneous iron distribution within the STN, which has been related to the subdivisions within this nucleus, and the tissue iron content can be assessed in vivo using Quantitative Susceptibility Mapping (QSM).

Method: Thirty-one PD patients were enrolled and underwent a 3T-MRI exam of the brain including a 3D multi-echo T2*-weighted sequence, that sequence was used to generate QSM map. The segmentation of the STN in the three portions was performed on the QSM maps by an experienced neurologist. For each patient, three ROIs were drawn in the location of the anteromedial, intermediate and dorsolateral portion of both STN in the axial and coronal planes; the mean values of magnetic susceptibility (χ) in each ROI of each patient were recorded. Δχ values of the different parts of the STN were compared between each other.

Results: Significant differences were found between anteromedial and intermediate ROIs, intermediate and dorsolateral ROIs, anteromedial and dorsolateral ROIs (p<0.0001 for each pair of ROIs in both sides). The highest susceptibility values were recorded in the anteromedial part (96,95±36.41 ppb in the right side and 83,68±45,34 ppb in the left side) while the smallest susceptibility values were found in the dorsolateral part of the nucleus (24,29±24,66 ppb in the right side and 12,21±22,06 ppb in the left side).

Conclusion: Using quantitative images we found a significant difference of Δχ values between anteromedial, intermediate and dorsolateral ROIs of STN. The highest values were recorded in the anteromedial part and the smallest ones in the dorsolateral part of the nucleus. These results are in line with evidences of iron distribution within STN .
QSM images could be a promising MR technique to parcel the nucleus improving DBS targeting in patients with PD.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/quantitative-susceptibility-mapping-images-for-the-parcellation-of-the-subthalamic-nucleus-a-possible-role-for-targeting-deep-brain-stimulation/