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Biomedical subjects

Alan Evans

Publications and source records attributed to Alan Evans.

12 recordsLinked to original sources
PubMed2006

An unbiased iterative group registration template for cortical surface analysis.

Accurate alignment of explicit surface representations of human cerebral cortices is necessary in order to compare local individual differences in cortical morphometric measurements (thickness, surface area, gyrification, etc.) in both normal and clinical populations. This paper presents a methodology for developing unbiased, high resolution iterative registration templates from a group of 222 subject hemispheres and shows that the resulting template provides better alignment of a separate set of test data than single-subject templates. It demonstrates that between 30 and 50 subjects are required to generate a stable iterative template. It also explores the way in which fold variants in registration templates affect the quality of registration. Finally, it shows that hemisphere-specific group registration templates systematically better register subject hemispheres of the same laterality, underlining the need to develop templates free of hemisphere bias for asymmetry analysis.

Adolescent↗
PubMed2006

Comprehensive dissection of the medial temporal lobe in AD: measurement of hippocampus, amygdala, entorhinal, perirhinal and parahippocampal cortices using MRI.

BACKGROUND: Early pathological involvement of specific medial temporal lobe areas is characteristic for Alzheimer's disease (AD). OBJECTIVE: To determine the extent of regional medial temporal lobe atrophy, including hippocampus, amygdala, and entorhinal, perirhinal, and parahippocampal cortices in mild AD patients and healthy controls, and to compare diagnostic accuracy across volumetric markers. METHODS: We studied 34 patients with clinically probable AD and 22 healthy elderly control subjects. Regional volumetric measures were obtained from volumetric T1-weighted MRI scans after accounting for global brain atrophy using affine transformation into standard space. RESULTS: Volumes of medial temporal lobe structures were significantly smaller in AD patients than in controls with exception of the left entorhinal cortex. The degree of atrophy was comparable between all structures. Diagnostic accuracy (number of correctly allocated cases divided by number of all cases) was highest for the right parahippocampal cortex with 85%, but only slightly lower for the right hippocampus and right entorhinal cortex with 82% and 84%. Using a linear combination of markers, the unilateral volumes of the right hippocampus, parahippocampal cortex and perirhinal cortex yielded an accuracy of 93%. CONCLUSION: Extent of atrophy is similar between the different regions of the medial temporal lobe in mild AD.Volume measurements of medial temporal lobe structures in addition to the hippocampus only yield improved diagnostic accuracy if a combination of these structures is used.

Aged↗
PubMed2006

Longitudinal mapping of cortical thickness and clinical outcome in children and adolescents with attention-deficit/hyperactivity disorder.

CONTEXT: Data from a previous prospective study of lobar volumes in children with attention-deficit/hyperactivity disorder (ADHD) are reexamined using a measure of cortical thickness. OBJECTIVE: To determine whether regional differences in cortical thickness or cortical changes across time characterize ADHD and predict or reflect its clinical outcome. DESIGN, SETTING, AND PARTICIPANTS: Longitudinal study of 163 children with ADHD (mean age at entry, 8.9 years) and 166 controls recruited mainly from a local community in Maryland. Participants were assessed with magnetic resonance imaging. Ninety-seven patients with ADHD (60%) had 2 or more images and baseline and follow-up clinical evaluations (mean follow-up, 5.7 years). MAIN OUTCOME MEASURES: Cortical thickness across the cerebrum. Patients with ADHD were divided into better and worse outcome groups on the basis of a mean split in scores on the Children's Global Assessment Scale and persistence/remission of DSM-IV-defined ADHD. RESULTS: Children with ADHD had global thinning of the cortex (mean reduction, -0.09 mm; P=.02), most prominently in the medial and superior prefrontal and precentral regions. Children with worse clinical outcome had a thinner left medial prefrontal cortex at baseline than the better outcome group (-0.38 mm; P=.003) and controls (-0.25 mm; P=.002). Cortical thickness developmental trajectories did not differ significantly between the ADHD and control groups throughout except in the right parietal cortex, where trajectories converged. This normalization of cortical thickness occurred only in the better outcome group. CONCLUSIONS: Children with ADHD show relative cortical thinning in regions important for attentional control. Children with a worse outcome have "fixed" thinning of the left medial prefrontal cortex, which may compromise the anterior attentional network and encumber clinical improvement. Right parietal cortex thickness normalization in patients with a better outcome may represent compensatory cortical change.

Adolescent↗
PubMed2006

The clinical spectrum of developmental language impairment in school-aged children: language, cognitive, and motor findings.

OBJECTIVE: Our goal was to evaluate detailed school-age language, nonverbal cognitive, and motor development in children with developmental language impairment compared with age-matched controls. METHODS: Children with developmental language impairment or normal language development (controls) aged 7 to 13 years were recruited. Children underwent language assessment (Clinical Evaluation of Language Fundamentals-4, Peabody Picture Vocabulary-3, Goldman-Fristoe Test of Articulation-2), nonverbal cognitive assessment (Wechsler Intelligence Scale for Children-IV), and motor assessment (Movement Assessment Battery for Children). Exclusion criteria were nonverbal IQ below the 5th percentile or an acquired language, hearing, autistic spectrum, or neurologic disorder. RESULTS: Eleven children with developmental language impairment (7:4 boys/girls; mean age: 10.1 +/- 0.8 years) and 12 controls (5:7 boys/girls; mean age: 9.5 +/- 1.8 years) were recruited. Children with developmental language impairment showed lower mean scores on language (Clinical Evaluation of Language Fundamentals-4--developmental language impairment: 79.7 +/- 16.5; controls: 109.2 +/- 9.6; Goldman-Fristoe Test of Articulation-2--developmental language impairment: 94.1 +/- 10.6; controls: 104.0 +/- 2.8; Peabody Picture Vocabulary-3--developmental language impairment: 90.5 +/- 13.8; controls: 100.1 +/- 11.6), cognitive (Wechsler Intelligence Scale for Children-IV--developmental language impairment: 99.5 +/- 15.5; controls: 113.5 +/- 11.9), and motor measures (Movement Assessment Battery for Children percentile--developmental language impairment: 12.7 +/- 16.7; controls: 66.1 +/- 30.6) and greater discrepancies between cognitive and language scores (Wechsler Intelligence Scale for Children-IV/Clinical Evaluation of Language Fundamentals-4--developmental language impairment: 17.8 +/- 17.8; controls: 1.2 +/- 12.7). Motor impairment was more common in children with developmental language impairment (70%) than controls (8%). CONCLUSIONS: Developmental language impairment is characterized by a broad spectrum of developmental impairments. Children identified on the basis of language impairment show significant motor comorbidity. Motor assessment should form part of the evaluation and follow-up of children with developmental language impairment.

Child↗
PubMed2004

Comparison of progressive cortical gray matter loss in childhood-onset schizophrenia with that in childhood-onset atypical psychoses.

BACKGROUND: Recent anatomical brain magnetic resonance imaging (MRI) studies show a striking postpsychotic progressive loss of cortical gray matter (GM) in patients with childhood-onset schizophrenia (COS), which appears greater than that seen for adult patients. However, the diagnostic specificity and the relationship of these changes to drug treatment and cognitive functioning remain unclear. We performed a comparative prospective brain MRI study in patients with COS and pediatric patients with transient psychosis with behavior problems (psychosis not otherwise specified) provisionally considered multidimensionally impaired (MDI). We hypothesized that cortical GM loss would occur in patients with COS but not in adolescents with atypical psychoses. METHODS: Anatomical brain MRI was performed at baseline and follow-up in 19 patients in the MDI group (mean [SD] age of 13.3 [3.1] years); in 23 patients with COS matched for age, sex, IQ score, and drug treatment (mean [SD] age of 13.9 [2.5] years); and 38 healthy control subjects matched for age and sex (mean [SD] age of 13.3 [3.1] years). The mean (SD) follow-up was 2.5 (0.8) years. Volumes of the cerebrum and total and regional GM were obtained by using automated analysis, and percent change in volume across time was calculated. One-way analyses of variance with post hoc Tukey Honestly Significantly Different comparisons were performed to examine group differences in the percent change in GM across follow-up. RESULTS: The COS group had significantly greater total, frontal, temporal, and parietal GM loss than did the MDI or healthy control groups; analysis of variance post hoc P values ranged from.03 to.001. The MDI and control groups did not differ significantly from each other. CONCLUSIONS: The cortical GM volume loss in COS appears diagnostically specific; it was not seen in children and adolescents with atypical psychosis. Because both patient groups had similar early developmental patterns, cognitive functioning, medications, and hospitalizations, this progressive loss appears to be intrinsic to COS. An ongoing neurodevelopmental process and/or brain response specific to the illness could account for these changes.

Adolescent↗
PubMed2004

Voxel-based morphometry of human brain with age and cerebrovascular risk factors.

The objectives of this study were to evaluate the correlations of the volumes of the gray matter and white matter with age, and the correlations of the tissue probabilities of the gray matter and white matter with age and several cerebrovascular risk factors. We obtained magnetic resonance (MR) images of the brain and clinical information from 769 normal Japanese subjects. We processed the MR images automatically by correcting for inter-individual differences in brain size and shape, and by segmenting the MR images into the gray matter and white matter. Volumetry of the brain revealed a significant negative correlation between the gray matter volume and age, which was not observed between white matter volume and age. Voxel-based morphometry showed that age, systolic blood pressure, and alcohol drinking correlated with the regional tissue probabilities of the gray matter and white matter.

Adolescent↗
PubMed2004

Fast and robust parameter estimation for statistical partial volume models in brain MRI.

Due to the finite spatial resolution of imaging devices, a single voxel in a medical image may be composed of mixture of tissue types, an effect known as partial volume effect (PVE). Partial volume estimation, that is, the estimation of the amount of each tissue type within each voxel, has received considerable interest in recent years. Much of this work has been focused on the mixel model, a statistical model of PVE. We propose a novel trimmed minimum covariance determinant (TMCD) method for the estimation of the parameters of the mixel PVE model. In this method, each voxel is first labeled according to the most dominant tissue type. Voxels that are prone to PVE are removed from this labeled set, following which robust location estimators with high breakdown points are used to estimate the mean and the covariance of each tissue class. Comparisons between different methods for parameter estimation based on classified images as well as expectation--maximization-like (EM-like) procedure for simultaneous parameter and partial volume estimation are reported. The robust estimators based on a pruned classification as presented here are shown to perform well even if the initial classification is of poor quality. The results obtained are comparable to those obtained using the EM-like procedure, but require considerably less computation time. Segmentation results of real data based on partial volume estimation are also reported. In addition to considering the parameter estimation problem, we discuss differences between different approximations to the complete mixel model. In summary, the proposed TMCD method allows for the accurate, robust, and efficient estimation of partial volume model parameters, which is crucial to a variety of brain MRI data analysis procedures such as the accurate estimation of tissue volumes and the accurate delineation of the cortical surface.

Artifacts↗
PubMed2003

Do we have the training? The ethics of workplace drug testing and the GP.

BACKGROUND: Workplace drug testing has been in place in Australia since the early 1990s. In some industries it is required by legislation, while in others, employers have introduced it as an apparent cost effective way of improving productivity, safety and the health of its workforce while reducing absenteeism, accident rates and even deaths. There are national standards in place for workplace drug testing regarding specimen collection and testing, and well documented processes to follow in establishing a drug screening program within a workforce. OBJECTIVE: This article explores the ethics of workplace drug testing and questions the assumed rights and obligations of employer, employee and the clinician involved in occupational medicine. DISCUSSION: It is questionable whether most general practitioners have the appropriate training to deal with these ethical issues comprehensively.

Australia↗
PubMed2002

Incidence of and survival from malignant melanoma in Scotland: an epidemiological study.

BACKGROUND: We aimed to assess the incidence and survival for all patients with invasive primary cutaneous malignant melanoma diagnosed in Scotland, UK, during 1979-98. METHODS: The Scottish Melanoma Group obtained data for 8830 patients (3301 male and 5529 female) first diagnosed with invasive cutaneous malignant melanoma. FINDINGS: Age-standardised incidence rose from 3.5 in 1979 to 10.6 per 10(5) population in 1998 for men, and from 7.0 to 13.1 for women, a rise of 303% and 187%, respectively. After 1995, the rate of increase levelled in women younger than 65 years at diagnosis. Melanoma incidence increased most in men on the trunk, head, and neck and in women on the leg. 5-year survival rose from 58% to 80% for men diagnosed in 1979 and 1993, respectively, and from 74% to 85% for women; improvements of 38% (p<0.001) and 15% (p<0.001), respectively. Most improvement was attributable to a higher proportion of thinner tumours. Male mortality from melanoma was 1.9/10(5) population per year at the start and end of the study, whereas mortality for men younger than 65 years at diagnosis rose from 1.2 to 1.35 (p=0.24). For all women, mortality fell slightly from 1.9 to 1.85/10(5) population per year (p=0.61), whereas for women younger than 65 years at diagnosis, mortality fell from 1.3 to 1.15 (p=0.62). INTERPRETATION: Interventions aimed at both primary and secondary prevention of melanoma are justified. Specialist tumour registers for entire countries can be used to plan and monitor public health interventions.

Adult↗