title: Restriction spectrum imaging reveals decreased neurite density in patients with temporal lobe epilepsy.
abstract: Diffusion tensor imaging (DTI) has become a popular tool for delineating the location and extent of white matter injury in temporal lobe epilepsy (TLE). However, DTI yields nonspecific measures that are confounded by changes occurring within both the intracellular and extracellular environments. This study investigated whether an advanced diffusion method, restriction spectrum imaging (RSI) could provide a more robust measure of white matter injury in TLE relative to DTI due to RSI's ability to separate intraaxonal diffusion (i.e., neurite density; ND) from diffusion associated with extraaxonal factors (e.g., inflammation; crossing fibers).
  
  
  
  RSI and DTI scans were obtained on 21 patients with TLE and 11 age-matched controls. RSI-derived maps of ND, isotropic-hindered (IH) and isotropic-free (IF) water, and crossing fibers (CFs) were compared to DTI-derived fractional anisotropy (FA) maps. Voxelwise and tract-based analyses were performed comparing patients with TLE to controls on each diffusion metric.
  
  
  
  Reductions in FA were seen primarily in frontotemporal white matter in TLE, and they were most pronounced proximal to the seizure focus. Reductions in ND corresponded to those seen in the FA maps; however, ND reductions were greater in magnitude, more lateralized to the epileptogenic hemisphere, and showed a broader pattern. Increases in IF/IH and effects from CFs also contributed to reduced FA in the ipsilateral parahippocampal cingulum and fornix, with decreases in IH extending into extratemporal regions. Reduced ND of the uncinate fasciculus was associated with longer disease duration, whereas FA was not associated with any clinical variables.
  
  
  
  RSI may provide a more specific measure of white matter pathology in TLE, distinguishing regions primarily affected by axonal/myelin loss from those where CFs and increases in extracellular water also play a role. By providing a more specific measure of axonal/myelin loss, RSI-derived ND may better reflect overall white matter burden in epilepsy.
authors.affiliation: Multimodal Imaging Laboratory, University of California, San Diego, La Jolla, California, U.S.A.
authors.forename: Richard Q
authors.initials: RQ
authors.lastname: Loi
authors.affiliation: Multimodal Imaging Laboratory, University of California, San Diego, La Jolla, California, U.S.A.
authors.forename: Kelly M
authors.initials: KM
authors.lastname: Leyden
authors.affiliation: Multimodal Imaging Laboratory, University of California, San Diego, La Jolla, California, U.S.A.
authors.forename: Akshara
authors.initials: A
authors.lastname: Balachandra
authors.affiliation: Multimodal Imaging Laboratory, University of California, San Diego, La Jolla, California, U.S.A.
authors.forename: Vedang
authors.initials: V
authors.lastname: Uttarwar
authors.affiliation: Multimodal Imaging Laboratory, University of California, San Diego, La Jolla, California, U.S.A.|Department of Radiology, University of California, San Diego, La Jolla, California, U.S.A.
authors.forename: Donald J
authors.initials: DJ
authors.lastname: Hagler
authors.affiliation: Department of Neurology, University of California, San Francisco, California, U.S.A.|UCSF Comprehensive Epilepsy Center, University of California, San Francisco, California, U.S.A.
authors.forename: Brianna M
authors.initials: BM
authors.lastname: Paul
authors.affiliation: Multimodal Imaging Laboratory, University of California, San Diego, La Jolla, California, U.S.A.|Department of Radiology, University of California, San Diego, La Jolla, California, U.S.A.
authors.forename: Anders M
authors.initials: AM
authors.lastname: Dale
authors.affiliation: Multimodal Imaging Laboratory, University of California, San Diego, La Jolla, California, U.S.A.|Department of Radiology, University of California, San Diego, La Jolla, California, U.S.A.
authors.forename: Nathan S
authors.initials: NS
authors.lastname: White
authors.affiliation: Multimodal Imaging Laboratory, University of California, San Diego, La Jolla, California, U.S.A.|Department of Psychiatry, University of California, San Diego, La Jolla, CA, U.S.A.
authors.forename: Carrie R
authors.initials: CR
authors.lastname: McDonald
mesh_terms: D000328:Adult; D016880:Anisotropy; D016022:Case-Control Studies; D056324:Diffusion Tensor Imaging / Q000379:methods; D004569:Electroencephalography; D004833:Epilepsy, Temporal Lobe / Q000000981:diagnostic imaging*; D005260:Female; D007839:Functional Laterality; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009413:Nerve Fibers, Myelinated / Q000473:pathology*; D066127:White Matter / Q000000981:diagnostic imaging*; D055815:Young Adult
keywords: Crossing fibers; Diffusion tensor imaging; Fractional anisotropy; Intracellular diffusion; Restricted diffusion