Personalized microstructural evaluation using a Mahalanobis-distance based outlier detection strategy on epilepsy patients' DTI data - Theory, simulations and example cases

PLoS One. 2019 Sep 23;14(9):e0222720. doi: 10.1371/journal.pone.0222720. eCollection 2019.

Abstract

Quantitative MRI methods have recently gained extensive interest and are seeing substantial developments; however, their application in single patient vs control group comparisons is often limited by inherent statistical difficulties. One such application is detecting malformations of cortical development (MCDs) behind drug resistant epilepsies, a task that, especially when based solely on conventional MR images, may represent a serious challenge. We aimed to develop a novel straightforward voxel-wise evaluation method based on the Mahalanobis-distance, combining quantitative MRI data into a multidimensional parameter space and detecting lesion voxels as outliers. Simulations with standard multivariate Gaussian distribution and resampled DTI-eigenvalue data of 45 healthy control subjects determined the optimal critical value, cluster size threshold, and the expectable lesion detection performance through ROC-analyses. To reduce the effect of false positives emanating from registration artefacts and gyrification differences, an automatic classification method was applied, fine-tuned using a leave-one-out strategy based on diffusion and T1-weighted data of the controls. DWI processing, including thorough corrections and robust tensor fitting was performed with ExploreDTI, spatial coregistration was achieved with the DARTEL tools of SPM12. Additional to simulations, clusters of outlying diffusion profile, concordant with neuroradiological evaluation and independent calculations with the MAP07 toolbox were identified in 12 cases of a 13 patient example population with various types of MCDs. The multidimensional approach proved sufficiently sensitive in pinpointing regions of abnormal tissue microstructure using DTI data both in simulations and in the heterogeneous example population. Inherent limitations posed by registration artefacts, age-related differences, and the different or mixed pathologies limit the generalization of specificity estimation. Nevertheless, the proposed statistical method may aid the everyday examination of individual subjects, ever so more upon extending the framework with quantitative information from other modalities, e.g. susceptibility mapping, relaxometry, or perfusion.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adolescent
  • Adult
  • Algorithms
  • Child
  • Diffusion Tensor Imaging / methods*
  • Epilepsy / diagnostic imaging*
  • Epilepsy / pathology
  • Female
  • Gray Matter / diagnostic imaging
  • Gray Matter / pathology
  • Humans
  • Image Processing, Computer-Assisted / methods*
  • Magnetic Resonance Imaging / methods*
  • Male
  • Middle Aged
  • Precision Medicine / methods
  • ROC Curve
  • White Matter / diagnostic imaging
  • White Matter / pathology
  • Young Adult

Grants and funding

This study was supported by the EFOP-3.6.3-VEKOP-16-2017-00009 project, the Hungarian National Brain Research Program grants KTIA/NAP_13-1-2013-0001:5 and 2017-1.2.1-NKP-2017-00002, and the Hungarian NRDIO (National Research, Development and Innovation Office) Grant: K128040. LRK also received support from the Bolyai Research Fellowship Program of the Hungarian Academy of Sciences.