title: Toward tract-specific fractional anisotropy (TSFA) at crossing-fiber regions with clinical diffusion MRI.
abstract: OBJECTIVE
  White matter fractional anisotropy (FA), a measure suggesting microstructure, is significantly underestimated with single diffusion tensor model at crossing-fiber regions (CFR). We propose a tract-specific FA (TSFA), corrected for the effects of crossing-fiber geometry and free water at CFR, and adapted for tract analysis with diffusion MRI (dMRI) in clinical research.
  
  
  METHODS
  At CFR voxels, the proposed technique estimates free water fraction (fiso ) as a linear function of mean apparent diffusion coefficient (mADC), fits the dual tensors and estimates TSFA. Digital phantoms were designed for testing the accuracy of fiso and fitted dual-anisotropies at CFR. The technique was applied to clinical dMRI of normal subjects and hereditary spastic paraplegia (HSP) patients to test the effectiveness of TSFA.
  
  
  RESULTS
  Phantom simulation showed unbiased estimates of dual-tensor anisotropies at CFR and high accuracy of fiso as a linear function of mADC. TSFA at CFR was highly consistent to the single tensor FA at non-CFR within the same tract with normal human dMRI. Additional HSP imaging biomarkers with significant correlation to clinical motor function scores could be identified with TSFA.
  
  
  CONCLUSIONS
  Results suggest the potential of the proposed technique in estimating unbiased TSFA at CFR and conducting tract analysis in clinical research.
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
authors.forename: Virendra
authors.initials: V
authors.lastname: Mishra
authors.affiliation: Department of Computer Science, University of Texas at Dallas, Richardson, Texas, USA.
authors.forename: Xiaohu
authors.initials: X
authors.lastname: Guo
authors.affiliation: Department of Neurology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
authors.forename: Mauricio R
authors.initials: MR
authors.lastname: Delgado
authors.affiliation: Advanced Imaging Research Center, University of Texas Southwestern Medical Center, Dallas, Texas, USA.|Department of Radiology, University of Texas Southwestern Medical Center, Dallas, Texas, USA.
authors.forename: Hao
authors.initials: H
authors.lastname: Huang
mesh_terms: D000465:Algorithms; D016880:Anisotropy; D001921:Brain / Q000033:anatomy & histology*; D002648:Child; D003198:Computer Simulation; D056324:Diffusion Tensor Imaging / Q000379:methods*; D006801:Humans; D007089:Image Enhancement / Q000379:methods; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008297:Male; D015233:Models, Statistical; D010363:Pattern Recognition, Automated / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D066127:White Matter / Q000033:anatomy & histology*; D055815:Young Adult
keywords: Gaussian mixture model; TSFA; diffusion MRI; dual-tensor; free water elimination; tract analysis; tract-specific fractional anisotropy