title: Diffusion imaging of reversible and irreversible microstructural changes within the corticospinal tract in idiopathic normal pressure hydrocephalus.
abstract: The symptoms of idiopathic normal pressure hydrocephalus (iNPH) can be improved by shunt surgery, but prediction of treatment outcome is not established. We investigated changes of the corticospinal tract (CST) in iNPH before and after shunt surgery by using diffusion microstructural imaging, which infers more specific tissue properties than conventional diffusion tensor imaging. Two biophysical models were used: neurite orientation dispersion and density imaging (NODDI) and white matter tract integrity (WMTI). In both methods, the orientational coherence within the CSTs was higher in patients than in controls, and some normalization occurred after the surgery in patients, indicating axon stretching and recovery. The estimated axon density was lower in patients than in controls but remained unchanged after the surgery, suggesting its potential as a marker for irreversible neuronal damage. In a Monte-Carlo simulation that represented model axons as undulating cylinders, both NODDI and WMTI separated the effects of axon density and undulation. Thus, diffusion MRI may distinguish between reversible and irreversible microstructural changes in iNPH. Our findings constitute a step towards a quantitative image biomarker that reflects pathological process and treatment outcomes of iNPH.
authors.affiliation: Department of Radiology, The University of Tokyo, Bunkyo, Tokyo, Japan; Department of Radiology, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Kouhei
authors.initials: K
authors.lastname: Kamiya
authors.affiliation: Department of Radiology, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Masaaki
authors.initials: M
authors.lastname: Hori
authors.affiliation: Department of Radiology, The University of Tokyo, Bunkyo, Tokyo, Japan; Department of Radiology, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Ryusuke
authors.initials: R
authors.lastname: Irie
authors.affiliation: Department of Neurosurgery, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Miyajima
authors.affiliation: Department of Neurosurgery, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Madoka
authors.initials: M
authors.lastname: Nakajima
authors.affiliation: Department of Radiology, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Kamagata
authors.affiliation: Department of Radiology, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Kouhei
authors.initials: K
authors.lastname: Tsuruta
authors.affiliation: Department of Radiology, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Asami
authors.initials: A
authors.lastname: Saito
authors.affiliation: Department of Radiological Sciences, Graduate School of Human Health Sciences, Tokyo Metropolitan University, Arakawa, Tokyo, Japan.
authors.forename: Misaki
authors.initials: M
authors.lastname: Nakazawa
authors.affiliation: Department of Radiology, The University of Tokyo Hospital, Bunkyo, Tokyo, Japan.
authors.forename: Yuichi
authors.initials: Y
authors.lastname: Suzuki
authors.affiliation: Department of Radiology, The University of Tokyo, Bunkyo, Tokyo, Japan.
authors.forename: Harushi
authors.initials: H
authors.lastname: Mori
authors.affiliation: Department of Radiology, The University of Tokyo, Bunkyo, Tokyo, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Kunimatsu
authors.affiliation: Department of Neurosurgery, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Arai
authors.affiliation: Department of Radiology, Juntendo University School of Medicine, Bunkyo, Tokyo, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Aoki
authors.affiliation: Department of Radiology, The University of Tokyo, Bunkyo, Tokyo, Japan.
authors.forename: Osamu
authors.initials: O
authors.lastname: Abe
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000704:Analysis of Variance; D016022:Case-Control Studies; D003198:Computer Simulation; D056324:Diffusion Tensor Imaging; D005260:Female; D006801:Humans; D006850:Hydrocephalus, Normal Pressure / Q000000981:diagnostic imaging*; D007091:Image Processing, Computer-Assisted; D008297:Male; D009010:Monte Carlo Method; D009415:Nerve Net / Q000000981:diagnostic imaging*; D011712:Pyramidal Tracts / Q000000981:diagnostic imaging*; D012720:Severity of Illness Index
keywords: AD, axial diffusivity; AWF, axonal water fraction; Axon density; Axon undulation; CSF, cerebrospinal fluid; CST, corticospinal tract; DTI, diffusion tensor imaging; Diffusion MRI; FA, fractional anisotropy; Idiopathic normal pressure hydrocephalus; MD, mean diffusivity; NODDI, neurite orientation dispersion and density imaging; ODI, orientation dispersion index; RD, radial diffusivity; ROI, region of interest; VF, volume fraction; VOI, volume of interest; WMTI, white matter tract integrity; iNPH, idiopathic normal pressure hydrocephalus