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Publications (7)23.35 Total impact

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    ABSTRACT: Recent in vivo research using magnetic resonance spectroscopy demonstrated that chronic cigarette smoking exacerbates regional chronic alcohol-induced brain injury. Other studies associated cigarette smoking with gray matter volume reductions in healthy adults, with greater brain atrophy in aging, and with poorer neurocognition. Although cigarette smoking is common among alcohol-dependent individuals, previous research did not account for the potential effects of chronic smoking on regional brain volumes in alcoholism. High-resolution T1-weighted magnetic resonance images from one-week-abstinent, alcohol-dependent individuals and light drinkers were automatically segmented into gray matter, white matter, and cerebral spinal fluid of lobes and subcortical structures. A brief neuropsychological test battery was used to assess cognition in alcohol-dependent individuals. The alcoholic and nondrinking groups were retrospectively divided into chronic smokers and nonsmokers, and the volumetric data were analyzed as a function of alcohol and smoking status. Chronic alcohol dependence was associated with smaller volumes of frontal and parietal white matter, parietal and temporal gray matter, and thalami, accompanied by widespread sulcal but not ventricular enlargements. Chronic cigarette smoking was associated with less parietal and temporal gray matter and with more temporal white matter. Among alcoholics, better visuospatial learning and memory and greater visuomotor scanning speed were correlated with larger lobar white matter volumes in the nonsmoking alcohol-dependent group only. These data provide preliminary evidence that comorbid chronic cigarette smoking accounts for some of the variance associated with cortical gray matter loss and appears to alter relationships between brain structure and cognitive functions in alcohol-dependent individuals.
    Alcoholism Clinical and Experimental Research 09/2005; 29(8):1484-95. · 3.42 Impact Factor
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    ABSTRACT: Despite the clinical significance of event-related potential (ERP) latency abnormalities, little attention has focused on the anatomic substrate of latency variability. Volume conduction models do not identify the anatomy responsible for delayed neural transmission between neural sources. To explore the anatomic substrate of ERP latency variability in normal adults using automated measures derived from magnetic resonance imaging (MRI), ERPs were recorded in the visual three-stimulus oddball task in 59 healthy participants. Latencies of the P3a and P3b components were measured at the vertex. Measures of local anatomic size in the brain were estimated from structural MRI, using tissue segmentation and deformation morphometry. A general linear model was fitted relating latency to measures of local anatomic size, covarying for intracranial vault volume. Longer P3b latencies were related to contractions in thalamus extending superiorly into the corpus callosum, white matter (WM) anterior to the central sulcus on the left and right, left temporal WM, the right anterior limb of the internal capsule extending into the lenticular nucleus, and larger cerebrospinal fluid volumes. There was no evidence for a relationship between gray matter (GM) volumes and P3b latency. Longer P3a latencies were related to contractions in left temporal WM, and left parietal GM and WM near the interhemispheric fissure. P3b latency variability is related chiefly to WM, thalamus, and lenticular nucleus, whereas P3a latency variability is not related as strongly to anatomy. These results imply that the WM connectivity between generators influences P3b latency more than the generators themselves do.
    Human Brain Mapping 08/2005; 25(3):317-27. · 6.88 Impact Factor
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    ABSTRACT: The Committee of Human Research of the University of California San Francisco approved this study, and all volunteers provided written informed consent. The goal of this study was to prospectively determine the global and regional reliability and reproducibility of noninvasive brain perfusion measurements obtained with different pulsed arterial spin-labeling (ASL) magnetic resonance (MR) imaging methods and to determine the extent to which within-subject variability and random noise limit reliability and reproducibility. Thirteen healthy volunteers were examined twice within 2 hours. The pulsed ASL methods compared in this study differ mainly with regard to magnetization transfer and eddy current effects. There were two main results: (a) Pulsed ASL MR imaging consistently had high measurement reliability (intraclass correlation coefficients greater than 0.75) and reproducibility (coefficients of variation less than 8.5%), and (b) random noise rather than within-subject variability limited reliability and reproducibility. It was concluded that low signal-to-noise ratios substantially limit the reliability and reproducibility of perfusion measurements.
    Radiology 04/2005; 234(3):909-16. · 6.34 Impact Factor
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    ABSTRACT: The goals of this study were to measure if chronic active heavy drinking is associated with brain volume loss in non-treatment seeking men and women, and to assess the effect of positive family history of problem drinking on brain structure in heavy drinkers. Automated image processing was used to analyze high-resolution T1-weighted magnetic resonance images from 49 active heavy drinkers and 49 age- and sex-matched light drinkers, yielding gray matter, white matter and cerebrospinal fluid (CSF) volumes within the frontal, temporal, parietal and occipital lobes. Regional brain volume measures were compared as a function of group, sex and their interaction. Within heavy drinkers, volumes were correlated with measures of alcohol consumption and compared as a function of family history of problem drinking. Deformation morphometry explored localized patterns of atrophy associated with heavy drinking or severity of drinking. We found significant gray matter volume losses, but no white matter losses, in active heavy drinkers compared with light drinkers. Women had greater gray matter and smaller white matter and CSF volumes as a percentage of intracranial vault than men. Within heavy drinkers, smaller gray matter volumes were associated with higher current levels of drinking and older age, while a positive family history of problem drinking was associated with smaller CSF volumes. Community-dwelling heavy drinkers who are not in alcoholism treatment have dose-related gray matter volume losses, and family history of problem drinking ameliorates some structural consequences of heavy drinking.
    Psychiatry Research 03/2005; 138(2):115-30. · 2.68 Impact Factor
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    ABSTRACT: This paper examines an alternative approach to separating magnetic resonance imaging (MRI) intensity inhomogeneity from underlying tissue-intensity structure using a direct template-based paradigm. This permits the explicit spatial modeling of subtle intensity variations present in normal anatomy which may confound common retrospective correction techniques using criteria derived from a global intensity model. A fine-scale entropy driven spatial normalisation procedure is employed to map intensity distorted MR images to a tissue reference template. This allows a direct estimation of the relative bias field between template and subject MR images, from the ratio of their low-pass filtered intensity values. A tissue template for an aging individual is constructed and used to correct distortion in a set of data acquired as part of a study on dementia. A careful validation based on manual segmentation and correction of nine datasets with a range of anatomies and distortion levels is carried out. This reveals a consistent improvement in the removal of global intensity variation in terms of the agreement with a global manual bias estimate, and in the reduction in the coefficient of intensity variation in manually delineated regions of white matter.
    IEEE Transactions on Medical Imaging 02/2004; 23(1):99-110. · 4.03 Impact Factor
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    ABSTRACT: This paper examines a refinement to probabilistic intensity based tissue segmentation methods, which makes use of knowledge derived from an MRI bias field estimate. Intensity based labeling techniques have employed local smoothness priors to reduce voxel level tissue labeling errors, by making use of the assumption that, within uniform regions of tissue, a voxel should be highly likely to have a similar tissue assignment to its neighbors. Increasing the size of this neighborhood provides more robustness to noise, but reduces the ability to describe small structures. However, when intensity bias due to RF field inhomogeneity is present within the MRI data, local contrast to noise may vary across the image. We therefore propose an approach to refining the labeling by making use of the bias field estimate, to adapt the neighborhood size applied to reduce local labeling errors. We explore the use of a radially symmetric Gaussian weighted neighborhood, and the use of the mean and median of the adapted region probabilities, to refine local probabilistic labeling. The approach is evaluated using the Montreal brainweb MRI simulator as a gold standard providing known gray, white and CSF tissue segmentation. These results show that the method is capable of improving the local tissue labeling in areas most influenced by inhomogeneity. The method appears most promising in its application to regional tissue volume analysis or higher field MRI data where bias field inhomogeneity can be significant.
    Proc SPIE 01/2003;
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    ABSTRACT: Accurate segmentation of magnetic resonance images of the brain is of increasing interest in the study of many brain disorders. This paper reports our approach to obtain the segmentation by warping our segmented template to a target and then automatically modifying the boundary of each structure. Test results show that our approach can increase the overlap between the warped template of the lenticular nucleus and the manually delineated lenticular nucleus by 10% compared the approach with only warping. 17
    Proc SPIE 07/2001;