Caudate shape discrimination in schizophrenia using template-free non-parametric tests

Abstract

This paper describes shape analysis of the caudate nucleus structure in a large schizophrenia study (30 controls, 60 schizophrenics). Although analysis of the caudate has not drawn the same attention as the hippocampus, it is a key basal ganglia structure shown to present differences in early development (e.g. autism) and also to present changes due to drug treatment. Left and right caudate were segmented from high resolution MRI using a reliable, semi-automated technique. Shapes were parametrized by a surface description, aligned, and finally represented as medial mesh structures (m-reps). Since schizophrenia patients were categorized based on treatment, we could test size and shape differences between normals, atypically and typically treated subjects. Statistical shape analysis used permutation tests on objects represented by medial representations. This allowed us to bypass the common problems of feature reduction inherent to low sample size and high dimensional feature vectors. Moreover, this test is non-parametric and does not require the choice of a shape template. The choice of medial shape representations led to a separate testing of global and local growth versus deformation. Results show significant caudate size and shape differences, not only between treatment groups and controls, but also among the treatment groups. Shape differences were not found when both treatment groups were grouped into one patient group and compared to controls. There was a clear localization of width and deformation change in the caudate head. As with other clinical studies utilizing shape analysis, results need to be confirmed in new, independent studies to get full confidence in the interpretation of these findings.