Mean Apparent Propagator MRI: A Potential Imaging Biomarker of Brain Microstructural Alterations in Basic-Type Intermittent Exotropia

Purpose: This study aimed to investigate brain microstructural alterations in children with basic-type intermittent exotropia (IXT) using mean apparent propagator magnetic resonance imaging (MAP-MRI) and to analyze their correlations with clinical signs. Methods: MRI was performed on individuals with basic-type IXT and healthy controls using a 3T Siemens scanner with a 64-channel head coil. Three-dimensional T1-weighted and diffusion-weighted images were acquired. MAP-MRI parametric maps were reconstructed using the Laplace-constrained algorithm, with diffusion tensor imaging maps serving as a reference. Voxel-wise analysis and deterministic fiber tractography were conducted to investigate microstructural changes of cortical regions and visual pathway in basic-type IXT. Receiver operating characteristic analysis was performed to assess the discriminative performance of the MAP-MRI metrics. The correlations between MAP-MRI metrics in significant brain regions and clinical signs were also analyzed. Results: Seventy-eight individuals with basic-type IXT and 96 healthy controls were enrolled. MAP-MRI revealed extensive microstructural alterations in brain regions associated with binocular vision and oculomotor control, as well as cognition and emotion regulation (P < 0.01 at both the voxel and cluster levels). Receiver operating characteristic analysis demonstrated that MAP-MRI metrics exhibited excellent discriminative performance, with the highest area under the curve of 0.986. In addition, MAP-MRI metrics were correlated with disease severity and disease duration (P < 0.05). Conclusions: MAP-MRI identified widespread microstructural alterations and their associations with clinical signs, providing valuable insights into the neural correlates underlying impaired binocular vision and oculomotor control in children with basic-type IXT. MAP-MRI metrics have the potential to serve as noninvasive imaging biomarkers for detecting IXT-related microstructural changes.