Publications by Year: 2006

We develop a differential geometric framework for regularizing diffusion MRI data. The key idea is to model white matter fibres as 3D space curves and to then extend Parent and Zucker’s 2D curve inference approach [Parent, P., Zucker, S., 1989. Trace inference, curvature consistency, and curve detection. IEEE Transactions on Pattern Analysis and Machine Intelligence 11, 823-839] by using a notion of co-helicity to indicate compatibility between fibre orientations at each voxel with those in a local neighborhood. We argue that this provides several advantages over earlier regularization methods. We validate the approach quantitatively on a biological phantom and on synthetic data, and qualitatively on data acquired in vivo from a human brain. We also demonstrate the use of the technique to improve the performance of a fibre tracking algorithm.

A biological abnormality found to be associated with posttraumatic stress disorder (PTSD) may be, among other things, a pretrauma vulnerability factor, that is, it may have been present prior to the event’s occurrence and increased the individual’s likelihood of developing PTSD upon traumatic exposure. Alternately, it may be an acquired PTSD sign, that is, it may have developed after the traumatic exposure, along with the PTSD. We have studied pairs of Vietnam combat veterans and their noncombat-exposed, identical twins in an effort to resolve these competing origins. Combat veterans were diagnosed as current PTSD or non-PTSD (i.e., never had). Average heart rate responses (HRRs) to a series of sudden, loud-tone presentations were larger in Vietnam combat veteran twins with PTSD, but these larger responses were not shared by their noncombat-exposed cotwins, whose responses were similar to those of the non-PTSD combat veterans and their noncombat-exposed cotwins. These results suggest that larger HRRs to sudden, loud tones represent an acquired sign of PTSD. In contrast, increased neurological soft signs (NSSs), diminished hippocampal volume, and presence of abnormal cavum septum pellucidum (CSP) were found in Vietnam combat veteran twins with PTSD and their "high-risk," unexposed cotwins compared to Vietnam combat veteran twins without PTSD and their "low-risk," unexposed cotwins. These results support the conclusion that the latter abnormalities represent antecedent, familial vulnerability factors for developing chronic PTSD upon exposure to a traumatic event.

UNLABELLED: The purpose of this study was to evaluate the feasibility and performance of an augmented reality (AR) visualization prototype for virtual computed tomography (CT)-guided interventional procedures in a multimodality abdominal phantom. With the aid of AR guidance, three radiologists performed 30 attempts at targeting simulated liver lesions of different sizes (range, 5-15 mm) with a biopsy needle. The position of the needle tip relative to the lesion was verified by using ultrasonography and CT. With AR guidance, lesions were successfully targeted with the first needle pass in all cases. On the basis of these results, AR visualization for CT-guided intervention appears feasible and allows intuitive and accurate lesion targeting in a phantom. SUPPLEMENTAL MATERIAL: radiology.rsnajnls.org/cgi/content/full/2401040018/DC1

OBJECTIVE: Schizophrenia impairs many cognitive functions, including face perception. Veridical face perception is critical for social interaction, including distinguishing friend from foe and familiar from unfamiliar faces. The main aim of this study was to determine whether patients with schizophrenia show less activation in neural networks related to face processing, compared with healthy subjects, and to investigate the relationships between this functional abnormality and anatomical abnormalities in the fusiform gyrus shown with magnetic resonance imaging (MRI). METHOD: Twenty male chronic schizophrenia patients and 16 healthy comparison subjects matched with the patients for age, gender, handedness, and parental socioeconomic status underwent high-spatial-resolution MRI. Event-related potentials elicited by images of faces, cars, and hands were recorded in a separate session. RESULTS: Compared to the healthy subjects, the patients with schizophrenia showed bilateral N170 amplitude reduction in response to images of faces but not to images of other objects. The patients also had smaller bilateral anterior and posterior fusiform gyrus gray matter volumes, compared to the healthy subjects. In addition, right posterior fusiform gyrus volume was significantly correlated with N170 amplitude measured at the right posterior temporal electrode site in response to images of faces in the schizophrenia patients but not in the healthy comparison subjects. CONCLUSIONS: The results provide evidence for deficits in the early stages of face perception in schizophrenia. The association of these deficits with smaller fusiform gyrus volume in patients with schizophrenia, relative to healthy subjects, suggests that the fusiform gyrus is the site of a defective anatomical substrate for face processing in schizophrenia.

Finite gradient pulse lengths are traditionally considered a nuisance in q-space diffusion NMR and MRI, since the simple Fourier relation between the acquired signal and the displacement probability is invalidated. Increasing the value of the pulse length leads to an apparently smaller value of the estimated compartment size. We propose that q-space data at different gradient pulse lengths, but with the same effective diffusion time, can be used to identify and quantify components with free or restricted diffusion from multiexponential echo decay curves obtained on cellular systems. The method is demonstrated with experiments on excised human brain white matter and a series of model systems with well-defined free, restricted, and combined free and restricted diffusion behavior. Time-resolved diffusion MRI experiments are used to map the spatial distribution of the intracellular fraction in a yeast cell suspension during sedimentation, and observe the disappearance of this fraction after a heat treatment.

BACKGROUND: The caudate nucleus might contribute to the psychopathological and cognitive deficits observed in schizotypal personality disorder (SPD), a schizophrenia spectrum disorder. Here we focused on female patients, because this group is underrepresented in studies of SPD and schizophrenia, and we might learn more about the caudate and clinical and cognitive impairments that are unique to female patients diagnosed with SPD. METHODS: Magnetic resonance imaging scans, obtained on a 1.5-T magnet with 1.5-mm contiguous slices, were used to measure the caudate in 32 neuroleptic-na ıve women with SPD and in 29 female normal comparison subjects. Subjects were group-matched for age, parental socioeconomic status, and intelligence quotient. RESULTS: We found significantly reduced left and right caudate relative volume (8.3%, 7.7%) in female SPD subjects compared with normal comparison subjects. In female SPD subjects, we found significant correlations between smaller total caudate relative volume and worse performance on the Wisconsin Card Sorting test (nonperseverative errors) and on the California Verbal Learning Test (verbal memory and learning), and significant correlations between smaller total caudate relative volume and both positive and negative symptoms on the Structured Interview for Schizotypy. CONCLUSIONS: These findings demonstrate that, for female SPD subjects, smaller caudate volume is associated with poorer cognitive performance and more schizotypal symptomatology.

We examined semantic vs. associational influences on word priming in schizophrenia. Tested on three occasions, subjects made speeded lexical decisions to three kinds of prime-word relationships: semantic-only (e.g., Deer-Pony), associated-only (e.g., Bee-Honey), or semantic-and-associated (e.g., Doctor-Nurse). Controls showed greater priming of words related via two relationships (semantic-and-associated) than for words related only semantically.. However, patients showed greater priming for associated-only words than for words related only semantically. Schizophrenic patients may show an associational bias, restricting semantic integration and contributing to their disturbed thinking.

PURPOSE: The purpose of this study was to determine the range of fixed trajectory curvilinear distraction devices required to correct a variety of severe mandibular deformities. MATERIALS AND METHODS: Preoperative computed tomography (CT) scans from 18 patients with mandibular deformities were imported into a CT-based software program (Osteoplan). Three-dimensional virtual models of the individual skulls were made with landmarks to track movements. An ideal treatment plan was created for each patient. Upper and lower boundaries for the dimensions of curvilinear distractors were established based on manufacturing and geometric constraints. Then, anatomically acceptable distractor attachment points were identified on the models using proximal and distal grids. Treatment plans were simulated for a series of distractors with varying radii of curvature, elongations (arc-length of device), and placements along the grids. The outcomes using these distractors were compared with the ideal treatment plans. Discrepancies were quantified in millimeters by comparing landmarks in the simulated versus ideal movements. RESULTS: Approximately 400,000 simulated 3-dimensional movements, based on the distractor parameters and variations in placement were computationally evaluated for the 18 cases. It was determined that, by varying distractor placement, a family of 5 distractors, with 3, 5, 7, and 10 cm radii of curvature and a straight-line device, could be used to treat all 18 cases to within 1.8 mm of error. CONCLUSIONS: The results of this study indicate that a family of 5 curvilinear distractors may suffice to treat a broad range of mandibular deformities.

Shape analysis has become of increasing interest to the neuroimaging community due to its potential to precisely locate morphological changes between healthy and pathological structures. This manuscript presents a comprehensive set of tools for the computation of 3D structural statistical shape analysis. It has been applied in several studies on brain morphometry, but can potentially be employed in other 3D shape problems. Its main limitations is the necessity of spherical topology.The input of the proposed shape analysis is a set of binary segmentation of a single brain structure, such as the hippocampus or caudate. These segmentations are converted into a corresponding spherical harmonic description (SPHARM), which is then sampled into a triangulated surfaces (SPHARM-PDM). After alignment, differences between groups of surfaces are computed using the Hotelling T(2) two sample metric. Statistical p-values, both raw and corrected for multiple comparisons, result in significance maps. Additional visualization of the group tests are provided via mean difference magnitude and vector maps, as well as maps of the group covariance information.The correction for multiple comparisons is performed via two separate methods that each have a distinct view of the problem. The first one aims to control the family-wise error rate (FWER) or false-positives via the extrema histogram of non-parametric permutations. The second method controls the false discovery rate and results in a less conservative estimate of the false-negatives.

The use of surgical simulator systems for education and preoperative planning is likely to increase in the future. A natural course of development of these systems is to incorporate patient specific anatomical models. This step requires some kind of segmentation process in which the different anatomical parts are extracted. Anatomical datasets are, however, usually very large and manual processing would be too demanding. Hence, automatic, or semi-automatic, methods to handle this step are required. The framework presented in this paper uses nonrigid registration, based on the morphon method, to automatically segment the hip anatomy and generate models for a hip surgery simulator system.