Publications by Year: 2010

OBJECTIVE: To quantify size and localization differences between tumors presenting with seizures vs nonseizure neurological symptoms. DESIGN: Retrospective imaging survey. We performed magnetic resonance imaging-based morphometric analysis and nonparametric mapping in patients with brain tumors. SETTING: University-affiliated teaching hospital. PATIENTS OR OTHER PARTICIPANTS: One hundred twenty-four patients with newly diagnosed supratentorial glial tumors. MAIN OUTCOME MEASURES: Volumetric and mapping methods were used to evaluate differences in size and location of the tumors in patients who presented with seizures as compared with patients who presented with other symptoms. RESULTS: In high-grade gliomas, tumors presenting with seizures were smaller than tumors presenting with other neurological symptoms, whereas in low-grade gliomas, tumors presenting with seizures were larger. Tumor location maps revealed that in high-grade gliomas, deep-seated tumors in the pericallosal regions were more likely to present with nonseizure neurological symptoms. In low-grade gliomas, tumors of the temporal lobe as well as the insular region were more likely to present with seizures. CONCLUSIONS: The influence of size and location of the tumors on their propensity to cause seizures varies with the grade of the tumor. In high-grade gliomas, rapidly growing tumors, particularly those situated in deeper structures, present with non-seizure-related symptoms. In low-grade gliomas, lesions in the temporal lobe or the insula grow large without other symptoms and eventually cause seizures. Quantitative image analysis allows for the mapping of regions in each group that are more or less susceptible to seizures.

A compression cell designed to fit inside an NMR spectrometer was used to investigate the in situ mechanical strain response, structural changes to the internal pore structure, and the diffusion and flow of interstitial water in full-thickness cartilage samples as it was deforming dynamically under a constant compressive load (pressure). We distinguish between the hydrostatic pressure acting on the interstitial fluid and the pore pressure acting on the cartilage fibril network. Our results show that properties related to the pore matrix microstructure such as diffusion and hydraulic conductivity are strongly influenced by the hydrostatic pressure in the interstitial fluid of the dynamically deforming cartilage which differ significantly from the properties measured under static i.e. equilibrium loading conditions (when the hydrostatic pressure has relaxed back to zero). The magnitude of the hydrostatic fluid pressure also appears to affect the way cartilage’s pore matrix changes during deformation with implications for the diffusion and flow-driven fluid transport through the deforming pore matrix. We also show strong evidence for a highly anisotropic pore structure and deformational dynamics that allows cartilage to deform without significantly altering the axial porosity of the matrix even at very large strains. The insensitivity of the axial porosity to compressive strain may be playing a critical function in directing the flow of pressurized interstitial fluid in the compressed cartilage to the surface, to support the load, and provide a protective interfacial fluid film that ’weeps’ out from the deforming tissue and thereby enhances the (elasto)hydrodynamic efficacy of sliding joints. Our results appear to show a close synergy between the structure of cartilage and both the hydrodynamic and boundary lubrication mechanisms.

Disturbances in selective attention represent a core characteristic of schizophrenia, whose neural underpinnings have yet to be fully elucidated. Consequently, we recorded brain activation using functional magnetic resonance imaging (fMRI) while 15 patients with schizophrenia and 15 age-matched controls performed a well-established measure of selective attention-the color Stroop negative priming task. We focused on two aspects of performance: overriding pre-potent responses (Stroop effect) and inhibition of prior negatively primed trials (negative priming effect). Behaviorally, controls demonstrated both significant Stroop and negative priming effects, while schizophrenic subjects only showed the Stroop effect. For the Stroop effect, fMRI indicated significantly greater activation in frontal regions-medial frontal gyrus/anterior cingulate gyrus and middle frontal gyrus for controls-but greater activation in medial parietal regions (posterior cingulate gyrus/precuneus) for patients. Negative priming elicited significant activation in right dorsolateral prefrontal cortex for both groups, but also in left dorsolateral prefrontal cortex for patients. These different patterns of fMRI activation may reflect faulty interaction in schizophrenia within networks of brain regions that are vital to selective attention.

The authors examined the relationship between neuropsychological performance and MRI of the orbital frontal cortex (OFC) and diffusion tensor imaging (DTI) of the cingulum bundle (CB) within groups of patients with schizophrenia and healthy subjects. The authors analyzed data from subjects, who had participated in prior MRI, DTI, and neuropsychological studies (Nakamura et al., 2008; Nestor et al., 2008). In comparison to healthy subjects, patients showed the expected reductions across CB fractional anisotropy (white matter) and OFC gray matter volume as well as lower neuropsychological scores. In addition, in comparison to healthy subjects, patients showed a very different pattern of functional-anatomical correlates. For patients, CB white matter but not OFC gray matter correlated with various aspects of intelligence, including general abilities and working memory. For controls, OFC gray matter but not CB white matter correlated with scores on tests of intelligence and decision making. These results point to the potentially important role of CB white matter in the neuropsychological disturbance in schizophrenia.

Classic geometric active contour algorithms have the limitation of segmenting the image into only two regions: background and object of interest. A new multiphase level set algorithm for the segmentation of two or more regions of interest is proposed. This algorithm avoids by construction the presence of overlapped and void regions and no additional coupling terms are required. In addition, the number of iterations needed to reach convergence is small. The algorithm has been tested against a state-of-the-art multiphase method on both simulated and real Magnetic Resonance Imaging (MRI) volumes with favorable results.

BACKGROUND: Anxiety sensitivity (AS) is a dispositional trait involving fear of anxiety-related symptoms. Functional imaging research suggests that the activity of the anterior insular cortex, particularly the right insula, may both mediate AS and play a role in the pathophysiology of phobias. However, no imaging studies have examined whether AS relates to insula morphology. We examined whether AS was significantly correlated with right anterior insula volume and thickness among adults with specific animal phobia (SAP) and healthy comparison (HC) subjects. METHODS: Nineteen adults with SAP and 20 demographically group-matched HC subjects underwent magnetic resonance imaging at 3 Tesla. Subjects also completed the Anxiety Sensitivity Index (ASI). Regression and correlation analyses examined ASI scores in relation to anterior and posterior insular cortex volume and thickness within and across subject groups. RESULTS: SAP subjects had significantly higher ASI scores than HC, but did not differ in terms of insula volumes or thickness. ASI scores predicted right anterior insula thickness in SAP but not HC subjects, and right anterior insula volume in the sample as a whole. Correlations of ASI scores with the anterior and posterior insula volume and thickness were not significant in either group. CONCLUSIONS: These findings suggest that the right anterior insular cortex size is a neural substrate of AS within specific phobia, rather than an independent diagnostic marker of the disorder. Future investigations should examine whether heightened AS represents a shared intermediate phenotype across anxiety disorders, manifesting functionally as increased insular reactivity and clinically as a fear of anxiety symptoms.

BACKGROUND: Previous studies of major depressive disorder (MDD) have focused on abnormalities in the prefrontal cortex and medial temporal regions. There has been little investigation in MDD of midbrain and subcortical regions central to reward/aversion function, such as the ventral tegmental area/substantia nigra (VTA/SN), and medial forebrain bundle (MFB). METHODOLOGY/PRINCIPAL FINDINGS: We investigated the microstructural integrity of this circuitry using diffusion tensor imaging (DTI) in 22 MDD subjects and compared them with 22 matched healthy control subjects. Fractional anisotropy (FA) values were increased in the right VT and reduced in dorsolateral prefrontal white matter in MDD subjects. Follow-up analysis suggested two distinct subgroups of MDD patients, which exhibited non-overlapping abnormalities in reward/aversion circuitry. The MDD subgroup with abnormal FA values in VT exhibited significantly greater trait anxiety than the subgroup with normal FA values in VT, but the subgroups did not differ in levels of anhedonia, sadness, or overall depression severity. CONCLUSIONS/SIGNIFICANCE: These findings suggest that MDD may be associated with abnormal microstructure in brain reward/aversion regions, and that there may be at least two subtypes of microstructural abnormalities which each impact core symptoms of depression.

BACKGROUND: Regional prefrontal cortex gray matter reductions have been identified in schizophrenia, likely reflecting a combination of genetic vulnerability and disease effects. Few morphometric studies to date have examined regional prefrontal abnormalities in non-psychotic biological relatives who have not passed through the age range of peak risk for onset of psychosis. We conducted a region-of-interest morphometric study of prefrontal subregions in adolescent and young adult relatives of schizophrenia patients. METHODS: Twenty-seven familial high-risk (FHR) first-degree relatives of schizophrenia patients and forty-eight control subjects without a family history of psychosis (ages 13-28) underwent high-resolution magnetic resonance imaging at 1.5Tesla. The prefrontal cortex was parcellated into polar, dorsolateral, ventrolateral, ventromedial and orbital subregions. The Chapman scales measured subpsychotic symptoms. General linear models examined associations of prefrontal subregion volumes with familial risk and subpsychotic symptoms. RESULTS: FHR subjects had significantly reduced bilateral ventromedial prefrontal and frontal pole gray matter volumes compared with controls. Ventromedial volume was significantly negatively correlated with magical ideation and anhedonia scores in FHR subjects. CONCLUSIONS: Selective, regional prefrontal gray matter reductions may differentially mark genetic vulnerability and early symptom processes among non-psychotic young adults at familial risk for schizophrenia.

Blood flow and tissue velocity can be measured using phase-contrast MRI. In this work, the statistical properties of 4D phase-contrast images are derived, and a novel probabilistic blood flow mapping method based on sequential Monte Carlo sampling is presented. The resulting flow maps visualize and quantify the uncertainty in conventional flow visualization techniques such as streamlines and particle traces.

OBJECTIVE: To assess combined analysis of coronary arteries and delayed myocardial contrast enhancement based on co-registration of coronary CT angiography and late-phase CT and automatic segmentation. MATERIALS AND METHODS: Co-registration and late enhancement segmentation were applied to coronary CT angiography and late-phase CT images from six pigs with acute myocardial infarction (MI) and six patients with chronic MI. MI size was quantified by manual delineation, the established 3SD method, and a new mixture model approach. Correspondence between coronary artery lesions and MI was assessed visually from fused segmentation results.