Objective: Optimization of Region of Interest (ROI) Analysis of the Superior Colliculus for Improved Activation Detection in Cervical Dystonia

Background: Cervical dystonia (CD) is a hyperkinetic movement disorder characterised by intermittent muscle contractions causing abnormal postures. Animal models suggest a role for the superior colliculus (SC) in its pathophysiology. The temporal discrimination threshold (a proposed mediational endophenotype of CD) is facilitated by the covert attention orienting system of which the SC is an important node. Imaging of the SC is technically challenging due its small size, its proximity to major blood vessels and the anatomical variations that exist between subjects. Noise artifacts, motion and the hemodynamic response function (HRF) can have an adverse impact on the signal to noise ratio (SNR). Therefore, accurate delineation, as well as tailored pre-processing steps are required for a high SNR and precise activation detection in the SC.

Methods: Functional MRI images were acquired from all 7 patients with CD and 7 healthy controls on a Philips 3T Achieva MRI scanner. A loom vs. recede task was used to activate the SC. A three-tier approach was followed for an accurate SC activation detection. This consisted of 1) Neuropathological dissection of human brainstem specimens by a consultant neuropathologist who identified the anatomical landmarks of the left and right superior colliculi. 2) Cardiac gating during acquisition for physiological noise correction. A photoplethysmographer was used during the functional runs to acquire the signal 3) Hand drawn ROIs on each subject followed by the comparison of outputs from different pre-processing pipelines obtained from combinations of smoothed (6 mm)/unsmoothed data, 4s/6s HRF and 1s/2.5s event durations.

Results: The diameter of each superior colliculus was measured to be 7mm. A significant difference (p<0.05) in SC activation for the 4s HRF and 2.5s event duration pipeline with the unsmoothed data was detected when compared to the other combinations. There was no significant difference detected with physiological noise correction (p =0.1276).

Conclusions: The results show the effect of various delineation parameters on SC activation and support optimum activation detection by a 4s HRF. The effect of physiological noise correction cannot be ruled out at this stage. Further powering the study can lead to the identification of the most optimal pipeline for SC activation detection in movement disorder patients.

References: 1. Hutchinson, M., et al., Cervical dystonia: a disorder of the midbrain network for covert attentional orienting. Front Neurol, 2014. 5: p. 54. 2. Billington, J., et al., Neural processing of imminent collision in humans. Proc Biol Sci, 2011. 278(1711): p. 1476-81.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/optimization-of-region-of-interest-analysis-of-the-superior-colliculus-for-improved-activation-detection-in-cervical-dystonia/