Author
Alex P. Zijdenbos
Other affiliations: McGill University, Vanderbilt University, Université de Montréal
Bio: Alex P. Zijdenbos is an academic researcher from Montreal Neurological Institute and Hospital. The author has contributed to research in topics: White matter & Hyperintensity. The author has an hindex of 44, co-authored 94 publications receiving 25241 citations. Previous affiliations of Alex P. Zijdenbos include McGill University & Vanderbilt University.
Topics: White matter, Hyperintensity, Voxel, Multiple sclerosis, Brain size
Papers published on a yearly basis
Papers
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TL;DR: This large-scale longitudinal pediatric neuroimaging study confirmed linear increases in white matter, but demonstrated nonlinear changes in cortical gray matter, with a preadolescent increase followed by a postadolescent decrease.
Abstract: Pediatric neuroimaging studies1,2,3,4,5, up to now exclusively cross sectional, identify linear decreases in cortical gray matter and increases in white matter across ages 4 to 20. In this large-scale longitudinal pediatric neuroimaging study, we confirmed linear increases in white matter, but demonstrated nonlinear changes in cortical gray matter, with a preadolescent increase followed by a postadolescent decrease. These changes in cortical gray matter were regionally specific, with developmental curves for the frontal and parietal lobe peaking at about age 12 and for the temporal lobe at about age 16, whereas cortical gray matter continued to increase in the occipital lobe through age 20.
5,140 citations
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TL;DR: A novel approach to correcting for intensity nonuniformity in magnetic resonance (MR) data is described that achieves high performance without requiring a model of the tissue classes present, and is applied at an early stage in an automated data analysis, before a tissue model is available.
Abstract: A novel approach to correcting for intensity nonuniformity in magnetic resonance (MR) data is described that achieves high performance without requiring a model of the tissue classes present. The method has the advantage that it can be applied at an early stage in an automated data analysis, before a tissue model is available. Described as nonparametric nonuniform intensity normalization (N3), the method is independent of pulse sequence and insensitive to pathological data that might otherwise violate model assumptions. To eliminate the dependence of the field estimate on anatomy, an iterative approach is employed to estimate both the multiplicative bias field and the distribution of the true tissue intensities. The performance of this method is evaluated using both real and simulated MR data.
4,613 citations
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TL;DR: The authors present a realistic, high-resolution, digital, volumetric phantom of the human brain, which can be used to simulate tomographic images of the head and is the ideal tool to test intermodality registration algorithms.
Abstract: After conception and implementation of any new medical image processing algorithm, validation is an important step to ensure that the procedure fulfils all requirements set forth at the initial design stage. Although the algorithm must be evaluated on real data, a comprehensive validation requires the additional use of simulated data since it is impossible to establish ground truth with in vivo data. Experiments with simulated data permit controlled evaluation over a wide range of conditions (e.g., different levels of noise, contrast, intensity artefacts, or geometric distortion). Such considerations have become increasingly important with the rapid growth of neuroimaging, i.e., computational analysis of brain structure and function using brain scanning methods such as positron emission tomography and magnetic resonance imaging. Since simple objects such as ellipsoids or parallelepipedes do not reflect the complexity of natural brain anatomy, the authors present the design and creation of a realistic, high-resolution, digital, volumetric phantom of the human brain. This three-dimensional digital brain phantom is made up of ten volumetric data sets that define the spatial distribution for different tissues (e.g., grey matter, white matter, muscle, skin, etc.), where voxel intensity is proportional to the fraction of tissue within the voxel. The digital brain phantom can be used to simulate tomographic images of the head. Since the contribution of each tissue type to each voxel in the brain phantom is known, it can be used as the gold standard to test analysis algorithms such as classification procedures which seek to identify the tissue "type" of each image voxel. Furthermore, since the same anatomical phantom may be used to drive simulators for different modalities, it is the ideal tool to test intermodality registration algorithms. The brain phantom and simulated MR images have been made publicly available on the Internet (http://www.bic.mni.mcgill.ca/brainweb).
1,811 citations
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TL;DR: Developmental trajectories for all structures, except caudate, remain roughly parallel for patients and controls during childhood and adolescence, suggesting that genetic and/or early environmental influences on brain development in ADHD are fixed, nonprogressive, and unrelated to stimulant treatment.
Abstract: ContextVarious anatomic brain abnormalities have been reported for attention-deficit/hyperactivity
disorder (ADHD), with varying methods, small samples, cross-sectional designs,
and without accounting for stimulant drug exposure.ObjectiveTo compare regional brain volumes at initial scan and their change over
time in medicated and previously unmedicated male and female patients with
ADHD and healthy controls.Design, Setting, and ParticipantsCase-control study conducted from 1991-2001 at the National Institute
of Mental Health, Bethesda, Md, of 152 children and adolescents with ADHD
(age range, 5-18 years) and 139 age- and sex-matched controls (age range,
4.5-19 years) recruited from the local community, who contributed 544 anatomic
magnetic resonance images.Main Outcome MeasuresUsing completely automated methods, initial volumes and prospective
age-related changes of total cerebrum, cerebellum, gray and white matter for
the 4 major lobes, and caudate nucleus of the brain were compared in patients
and controls.ResultsOn initial scan, patients with ADHD had significantly smaller brain
volumes in all regions, even after adjustment for significant covariates.
This global difference was reflected in smaller total cerebral volumes (−3.2%,
adjusted F1,280 = 8.30, P = .004) and
in significantly smaller cerebellar volumes (−3.5%, adjusted F1,280 = 12.29, P = .001). Compared with controls,
previously unmedicated children with ADHD demonstrated significantly smaller
total cerebral volumes (overall F2,288 = 6.65; all pairwise comparisons
Bonferroni corrected, −5.8%; P = .002) and
cerebellar volumes (−6.2%, F2,288 = 8.97, P<.001). Unmedicated children with ADHD also exhibited strikingly
smaller total white matter volumes (F2,288 = 11.65) compared with
controls (−10.7%, P<.001) and with medicated
children with ADHD (−8.9%, P<.001). Volumetric
abnormalities persisted with age in total and regional cerebral measures (P = .002) and in the cerebellum (P =
.003). Caudate nucleus volumes were initially abnormal for patients with ADHD
(P = .05), but diagnostic differences disappeared
as caudate volumes decreased for patients and controls during adolescence.
Results were comparable for male and female patients on all measures. Frontal
and temporal gray matter, caudate, and cerebellar volumes correlated significantly
with parent- and clinician-rated severity measures within the ADHD sample
(Pearson coefficients between −0.16 and −0.26; all P values were <.05).ConclusionsDevelopmental trajectories for all structures, except caudate, remain
roughly parallel for patients and controls during childhood and adolescence,
suggesting that genetic and/or early environmental influences on brain development
in ADHD are fixed, nonprogressive, and unrelated to stimulant treatment.
1,511 citations
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TL;DR: Findings provide evidence for a gradual maturation, during late childhood and adolescence, of fiber pathways presumably supporting motor and speech functions.
Abstract: Structural maturation of fiber tracts in the human brain, including an increase in the diameter and myelination of axons, may play a role in cognitive development during childhood and adolescence. A computational analysis of structural magnetic resonance images obtained in 111 children and adolescents revealed age-related increases in white matter density in fiber tracts constituting putative corticospinal and frontotemporal pathways. The maturation of the corticospinal tract was bilateral, whereas that of the frontotemporal pathway was found predominantly in the left (speech-dominant) hemisphere. These findings provide evidence for a gradual maturation, during late childhood and adolescence, of fiber pathways presumably supporting motor and speech functions.
1,309 citations
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TL;DR: An anatomical parcellation of the spatially normalized single-subject high-resolution T1 volume provided by the Montreal Neurological Institute was performed and it is believed that this tool is an improvement for the macroscopical labeling of activated area compared to labeling assessed using the Talairach atlas brain.
13,678 citations
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9,362 citations
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TL;DR: In this paper, the authors describe the steps involved in VBM, with particular emphasis on segmenting gray matter from MR images with non-uniformity artifact and provide evaluations of the assumptions that underpin the method, including the accuracy of the segmentation and the assumptions made about the statistical distribution of the data.
8,049 citations
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TL;DR: The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or her own research.
Abstract: I have developed "tennis elbow" from lugging this book around the past four weeks, but it is worth the pain, the effort, and the aspirin. It is also worth the (relatively speaking) bargain price. Including appendixes, this book contains 894 pages of text. The entire panorama of the neural sciences is surveyed and examined, and it is comprehensive in its scope, from genomes to social behaviors. The editors explicitly state that the book is designed as "an introductory text for students of biology, behavior, and medicine," but it is hard to imagine any audience, interested in any fragment of neuroscience at any level of sophistication, that would not enjoy this book. The editors have done a masterful job of weaving together the biologic, the behavioral, and the clinical sciences into a single tapestry in which everyone from the molecular biologist to the practicing psychiatrist can find and appreciate his or
7,563 citations
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TL;DR: This large-scale longitudinal pediatric neuroimaging study confirmed linear increases in white matter, but demonstrated nonlinear changes in cortical gray matter, with a preadolescent increase followed by a postadolescent decrease.
Abstract: Pediatric neuroimaging studies1,2,3,4,5, up to now exclusively cross sectional, identify linear decreases in cortical gray matter and increases in white matter across ages 4 to 20. In this large-scale longitudinal pediatric neuroimaging study, we confirmed linear increases in white matter, but demonstrated nonlinear changes in cortical gray matter, with a preadolescent increase followed by a postadolescent decrease. These changes in cortical gray matter were regionally specific, with developmental curves for the frontal and parietal lobe peaking at about age 12 and for the temporal lobe at about age 16, whereas cortical gray matter continued to increase in the occipital lobe through age 20.
5,140 citations