Fisher statistics for analysis of diffusion tensor directional information

Department of Neurology, University of Wisconsin, UW Medical Foundation Centennial Building, Madison, WI 53705, USA.
Journal of neuroscience methods (Impact Factor: 1.96). 02/2012; 206(1):40-5. DOI: 10.1016/j.jneumeth.2012.02.004
Source: PubMed

ABSTRACT A statistical approach is presented for the quantitative analysis of diffusion tensor imaging (DTI) directional information using Fisher statistics, which were originally developed for the analysis of vectors in the field of paleomagnetism. In this framework, descriptive and inferential statistics have been formulated based on the Fisher probability density function, a spherical analogue of the normal distribution. The Fisher approach was evaluated for investigation of rat brain DTI maps to characterize tissue orientation in the corpus callosum, fornix, and hilus of the dorsal hippocampal dentate gyrus, and to compare directional properties in these regions following status epilepticus (SE) or traumatic brain injury (TBI) with values in healthy brains. Direction vectors were determined for each region of interest (ROI) for each brain sample and Fisher statistics were applied to calculate the mean direction vector and variance parameters in the corpus callosum, fornix, and dentate gyrus of normal rats and rats that experienced TBI or SE. Hypothesis testing was performed by calculation of Watson's F-statistic and associated p-value giving the likelihood that grouped observations were from the same directional distribution. In the fornix and midline corpus callosum, no directional differences were detected between groups, however in the hilus, significant (p<0.0005) differences were found that robustly confirmed observations that were suggested by visual inspection of directionally encoded color DTI maps. The Fisher approach is a potentially useful analysis tool that may extend the current capabilities of DTI investigation by providing a means of statistical comparison of tissue structural orientation.

  • [Show abstract] [Hide abstract]
    ABSTRACT: Neural activity promotes circuit formation in developing systems and during critical periods permanently modifies circuit organization and functional properties. These observations suggest that excessive neural activity, as occurs during seizures, might influence developing neural circuitry with long-term outcomes that depend on age at the time of seizures. We systematically examined long-term structural and functional consequences of seizures induced in rats by kainic acid, pentylenetetrazol, and hyperthermia across postnatal ages from birth through postnatal day 90 in adulthood (P90). Magnetic resonance imaging (MRI), diffusion tensor imaging (DTI), and electrophysiological methods at ⩾P95 following seizures induced from P1 to P90 demonstrated consistent patterns of gross atrophy, microstructural abnormalities in the corpus callosum and hippocampus, and functional alterations in hippocampal circuitry at ⩾P95 that were independent of the method of seizure induction and varied systematically as a function of age at the time of seizures. Three distinct epochs were observed in which seizures resulted in distinct long-term structural and functional outcomes at ⩾P95. Seizures prior to P20 resulted in DTI abnormalities in corpus callosum and hippocampus in the absence of gross cerebral atrophy, and increased paired pulse inhibition (PPI) in the dentate gyrus at ⩾P95. Seizures after P30 induced a different pattern of DTI abnormalities in the fimbria and hippocampus accompanied by gross cerebral atrophy with increases in lateral ventricular volume, as well as increased PPI in the dentate gyrus at ⩾P95. In contrast, seizures between P20-P30 did not result in cerebral atrophy or significant imaging abnormalities in the hippocampus or white matter, but irreversibly decreased PPI in the dentate gyrus compared to normal adult controls. These age-specific long-term structural and functional outcomes identify P20-P30 as a potential critical period in hippocampal development defined by distinctive long-term structural and functional properties in adult hippocampal circuitry, including loss of capacity for seizure-induced plasticity in adulthood that could influence epileptogenesis and other hippocampal - dependent behaviors and functional properties. Copyright © 2014 IBRO. Published by Elsevier Ltd. All rights reserved.
    Neuroscience 12/2014; 288. DOI:10.1016/j.neuroscience.2014.12.017 · 3.33 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: PURPOSE: The purpose of this work is to investigate the hypothesis that uniform sampling measurements that are endowed with antipodal symmetry play an important role in image quality when the raw data and image data are related through the Fourier relationship. Currently, it is extremely challenging to generate large and uniform antipodally symmetric point sets suitable for three-dimensional radial MRI. A novel approach is proposed to solve this long-standing problem in a unique and optimal way. METHODS: The proposed method is based on constrained centroidal Voronoi tessellations of the upper hemisphere with a novel pseudometric. RESULTS: The time complexity of the proposed tessellations was shown to be effectively linear, i.e., on the order of the number of sampling measurements. For small sample size, the proposed method was comparable with the state-of-the-art method (a direct iterative minimization of the electrostatic potential energy of a collection of electrons antipodal-symmetrically distributed on the unit sphere) in terms of the sampling uniformity. For large sample size, in which the state-of-the-art method is infeasible, the reconstructed images from the proposed method has less streak and ringing artifacts, when compared with those of the commonly used methods. CONCLUSION: This work proposed a unique and optimal approach to solving a long-standing problem in generating uniform sampling points for three-dimensional radial MRI. Magn Reson Med, 2013. © 2013 Wiley Periodicals, Inc.
    Magnetic Resonance in Medicine 02/2014; 71(2). DOI:10.1002/mrm.24715 · 3.40 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The functional organization of the brain in segregated neuronal networks has become a leading paradigm in the study of brain diseases. Diffusion tensor imaging (DTI) allows testing the validity and clinical utility of this paradigm on the structural connectivity level. DTI in Alzheimer's disease (AD) suggests a selective impairment of intracortical projecting fiber tracts underlying the functional disorganization of neuronal networks supporting memory and other cognitive functions. These findings have already been tested for their utility as clinical markers of AD in large multicenter studies. Affective disorders, including major depressive disorder (MDD) and bipolar disorder (BP), show a high comorbidity with AD in geriatric populations and may even have a pathogenetic overlap with AD. DTI studies in MDD and BP are still limited to small-scale monocenter studies, revealing subtle abnormalities in cortico-subcortial networks associated with affect regulation and reward/aversion control. The clinical utility of these findings remains to be further explored. The present paper presents the methodological background of diffusion imaging, including DTI and diffusion spectrum imaging, and discusses key findings in AD and affective disorders. The results of our review strongly point toward the necessity of large-scale multicenter multimodal transnosological networks to study the structural and functional basis of neuronal disconnection underlying different neuropsychiatric diseases.
    European Archives of Psychiatry and Clinical Neuroscience 03/2014; 264(6). DOI:10.1007/s00406-014-0496-6 · 3.36 Impact Factor

Full-text (2 Sources)

Available from
May 21, 2014