Investigating the characteristics of the region-of-interest for calculating the diffusion tensor imaging along perivascular spaces index

Motivation: Several parameters affect diffusion tensor imaging along the perivascular spaces (DTI-ALPS) index calculation. However, the impact of ROI size, shape, and relative orientation to the lateral ventricle remains unclear, potentially hindering cross-study comparability. Goal(s): To investigate the influence of ROI characteristics in estimating the DTI-ALPS index. Approach: Differences in DTI-ALPS index and correlations among 8 ROI types (size, shape, and orientation) were investigated. Results: DTI-ALPS index calculation depends on ROI size, shape, and orientation. Single-voxel and parallel rectangular ROIs exhibit strong agreement; parallel-parallel and orthogonal-orthogonal ROIs show excellent correlation. However, larger, rectangular ROIs with orthogonal placement result in significant differences and poor correlation. Impact: Our analysis shows that ROI size, shape, and relative orientation to the lateral ventricle impact DTI-ALPS index calculation. Therefore, in addition to imaging parameters, ROI characteristics also need to be considered for comparison among studies.