Publications by Year: 2007

INTRODUCTION: The aim of this work was to study the effects of restricted diffusion in a biological phantom consisting of green asparagus stems using q-space MRI at a clinical scanner. METHOD: Measurements of the full width at half maximum (FWHM) of the displacement distribution were performed with varied diffusion time (Td). The accuracy of the measurements was investigated with respect to the degree of violation of the short gradient pulse (SGP) condition, partial volume effects and a FWHM-based tensor model. RESULTS: The measurements showed a reasonably constant FWHM perpendicular to the capillaries in the vascular bundles and an increased FWHM parallel with the bundles when the Td was increased. A 15% decrease in FWHM perpendicular to the bundles was observed when the diffusion encoding duration was prolonged from 24 to 74 ms, owing to the violation of the SGP condition. For a population of different confinement sizes, simulations indicated that the FWHM reflects the smaller sizes rather then the mean size of the confinements. CONCLUSION: A new method allowing tensor analysis of FWHM was derived and yielded accurate results. In conclusion, we found it possible to measure the effects of restricted diffusion with q-space MRI using a clinical MRI scanner.

BACKGROUND/AIMS: The aim of this study was to report our experience of hepatolithiasis, diagnosed in 55 patients between June 1995 and March 2003. METHODS: Fifty-five patients who underwent endoscopic retrograde cholangiopancreatography for hepatolithiasis between June 1995 and March 2003 at our institution were evaluated. Diagnosis of hepatolithiasis was based on cholangiography, ultrasonography and computed tomography. Patients with hepatolithiasis were classified according to Tsunoda classification. RESULTS: Fifty-five patients with hepatolithiasis (22 female, 33 male; mean age: 48.2 +/-14.9, range: 22-83) were included in this study. The major causes of hepatolithiasis were previous bilio-digestive surgery and Caroli disease, with rates of 49% and 14.5%, respectively. While 37 of 55 patients (67.3%) presented with only intrahepatic lithiasis, 18 patients (32.7%) had intrahepatic lithiasis associated with common bile duct (16/18, 29%) or gallbladder (2/18, 3.6%) stones. According to Tsunoda classification, 4 patients were classified as type I, 32 type II, 9 type III and 10 type IV. Patients with types I and II had significantly better stone clearance rates in comparison to those with types III and IV (p

In this paper, novel methods for detecting steady-state visual evoked potentials using multiple electroencephalogram (EEG) signals are presented. The methods are tailored for brain-computer interfacing, where fast and accurate detection is of vital importance for achieving high information transfer rates. High detection accuracy using short time segments is obtained by finding combinations of electrode signals that cancel strong interference signals in the EEG data. Data from a test group consisting of 10 subjects are used to evaluate the new methods and to compare them to standard techniques. Using 1-s signal segments, six different visual stimulation frequencies could be discriminated with an average classification accuracy of 84%. An additional advantage of the presented methodology is that it is fully online, i.e., no calibration data for noise estimation, feature extraction, or electrode selection is needed.

In this study, we examined the role of the hippocampus in relational memory by comparing item recognition performance in amnesic patients with medial temporal lobe (MTL) damage and their matched controls. Specifically, we investigated the contribution of associative memory to item recognition using a cued recognition paradigm. Control subjects studied cue-target pairs once, whereas amnesic patients studied cue-target pairs six times. Following study, subjects made recognition judgments about targets that were presented either alone (no cue), with the originally presented cue (same cue), or with a cue that had been presented with a different target (recombined cue). Controls had higher recognition scores in the same cue than in the recombined cue condition, indicating that they benefited from the associative information provided by the same cue. By contrast, amnesic patients did not. This was true even for a subgroup of patients whose recognition performance in the no cue condition was matched to that of the controls. These data provide further support for the idea that the hippocampus plays a critical role in relational memory, even when associative information need not be retrieved intentionally.

In vivo quantification of neuroanatomical shape variations is possible due to recent advances in medical imaging and has proven useful in the study of neuropathology and neurodevelopment. In this paper, we apply a spherical wavelet transformation to extract shape features of cortical surfaces reconstructed from magnetic resonance images (MRIs) of a set of subjects. The spherical wavelet transformation can characterize the underlying functions in a local fashion in both space and frequency, in contrast to spherical harmonics that have a global basis set. We perform principal component analysis (PCA) on these wavelet shape features to study patterns of shape variation within normal population from coarse to fine resolution. In addition, we study the development of cortical folding in newborns using the Gompertz model in the wavelet domain, which allows us to characterize the order of development of large-scale and finer folding patterns independently. Given a limited amount of training data, we use a regularization framework to estimate the parameters of the Gompertz model to improve the prediction performance on new data. We develop an efficient method to estimate this regularized Gompertz model based on the Broyden-Fletcher-Goldfarb-Shannon (BFGS) approximation. Promising results are presented using both PCA and the folding development model in the wavelet domain. The cortical folding development model provides quantitative anatomic information regarding macroscopic cortical folding development and may be of potential use as a biomarker for early diagnosis of neurologic deficits in newborns.

BACKGROUND AND PURPOSE: Observing changes to water diffusivity and fractional anisotropy (FA) for particular hippocampal regions may improve the sensitivity and specificity of diffusion tensor MR imaging for hippocampal pathologies like Alzheimer disease and mesial temporal sclerosis. As a first step toward this goal, this study characterized the cytoarchitectural features underlying diffusion anisotropy in human hippocampus autopsy specimens at 60-microm in-plane resolution.

OBJECTIVE: This pilot study investigated whether our previous findings of disrupted normal sexual brain dimorphisms in language-associated regions in schizophrenia were linked with our previously reported sex differences in language dysfunction in schizophrenia. METHOD: Nineteen adults with schizophrenia and 15 normal comparisons were tested on phonology, semantics and grammar and underwent structural MRI. RESULTS: Among males, left hippocampal and left planum temporale (PT) abnormalities were associated with phonological, semantic and grammar deficits, accounting for 17-52% and 27-33%, respectively, of variance in diagnostic group differences. Anterior cingulate gyrus was significantly associated with semantics. Among females, right Heschl’s Gyrus (HG) and left PT were significantly associated with phonology, right HG with semantics and grammar and right hippocampus with semantics. CONCLUSIONS: These preliminary findings suggest disrupted sexual brain dimorphisms in schizophrenia are associated with sex-specific language deficits, and left hippocampal abnormalities, in particular, contribute to language dysfunction among men. Abnormalities in right cortical temporal regions showed stronger associations with language dysfunction among females.

BACKGROUND: Basal ganglia (BG) enlargement has been found in studies of adults with bipolar disorder (BPD), while the few studies of BPD youths have had mixed findings. The BG (caudate, putamen, globus pallidus, nucleus accumbens) is interconnected with limbic and prefrontal cortical structures and therefore may be implicated in BPD. METHODS: Sixty-eight youths (46 with BPD, 22 healthy controls) received neurological and psychiatric assessment, semi-structured interviews, and neuropsychological testing, followed by anatomic magnetic resonance imaging on a 1.5 Tesla scanner. After image segmentation, log BG volumes and asymmetry indices were analyzed using MANOVAs controlling for the effects of cerebral volume, age, sex, and diagnosis. These omnibus tests were followed by univariate linear regression models of each BG structure.

Our objective was to test for differences between subjects with obsessive-compulsive disorder (OCD) and healthy controls with respect to white matter architecture within the cingulum bundle (CB) and anterior limb of the internal capsule (ALIC). We studied eight subjects with active OCD and 10 matched healthy controls using diffusion tensor magnetic resonance imaging (DT-MRI) at 1.5 T (Tesla). Fractional anisotropy (FA) was evaluated in both CB and ALIC. Both voxelwise and region-of-interest methods of analysis were employed. Within both the left CB and the left ALIC, subjects with OCD exhibited significantly greater FA than healthy controls. In the right CB, subjects with OCD exhibited significantly decreased FA versus healthy control subjects. Additionally, the OCD group exhibited abnormal asymmetry (left > right) of FA in the CB. These results provide preliminary evidence for abnormal architecture within the CB and ALIC in OCD. FA differences in these areas are consistent with the presence of abnormal connections between the nodes linked by these tracts. This could explain why surgically severing these tracts is therapeutic. Additional studies are needed to replicate these findings and to clarify their pathological and clinical significance.

BACKGROUND: This is a unique hypothalamic magnetic resonance imaging (MRI) study in schizophrenia, an important region in the limbic system. We hypothesized abnormal volumetric increases, with greater severity in multiplex families (more than one ill member) compared with simplex families (one ill). We tested the hypothesis that normal hypothalamic sexual dimorphism is disrupted in schizophrenia. METHODS: Eighty-eight DSM-III-R schizophrenia cases (40 simplex and 48 multiplex), 43 first-degree nonpsychotic relatives, and 48 normal comparisons systematically were compared. A 1.5-Tesla General Electric scanner was used to acquire structural MRI scans, and contiguous 3.1-mm slices were used to segment anterior and posterior hypothalamus. General linear model for correlated data and generalized estimating equations were used to compare cases, relatives, and controls on right and left hypothalamus, controlled for age, sex, and total cerebral volume. Spearman’s correlations of hypothalamic volumes with anxiety were calculated to begin to examine arousal correlates with structural abnormalities. RESULTS: Findings demonstrated significantly increased hypothalamic volume in cases and nonpsychotic relatives, particularly in regions of paraventricular and mammillary body nuclei, respectively. This increase was linear from simplex to multiplex cases, was positively correlated with anxiety, and had a greater propensity in women. CONCLUSIONS: Findings suggest important implications for understanding genetic vulnerability of schizophrenia and the high rate of endocrine abnormalities.