Biomedical subjects

C Davatzikos

Publications and source records attributed to C Davatzikos.

8 recordsLinked to original sources

PubMed1998

Mapping image data to stereotaxic spaces: applications to brain mapping.

A methodology for spatial normalization of image data is presented. This methodology is based on a map between homologous features of an individual brain and the target brain, which is used to drive a three-dimensional elastic warping transformation. Functional or structural information present in the original, nonnormalized images is preserved during this transformation. In particular, information such as the volume or the total amount of a radioactive agent in any brain region can be calculated directly from the normalized images. Moreover, subtle morphological characteristics of an individual brain are captured by the properties of the spatial transformation applied to that brain. Intersubject or interpopulation comparisons are performed by comparing the corresponding transformations.

Algorithms↗

PubMed1997

Finding parametric representations of the cortical sulci using an active contour model.

The cortical sulci are brain structures resembling thin convoluted ribbons embedded in three dimensions. The importance of the sulci lies primarily in their relation to the cytoarchitectonic and functional organization of the underlying cortex and in their utilization as features in non-rigid registration methods. This paper presents a methodology for extracting parametric representations of the cerebral sulcus from magnetic resonance images. The proposed methodology is based on deformable models utilizing characteristics of the cortical shape. Specifically, a parametric representation of a sulcus is determined by the motion of an active contour along the medial surface of the corresponding cortical fold. The active contour is initialized along the outer boundary of the brain and deforms toward the deep root of a sulcus under the influence of an external force field, restricting it to lie along the medial surface of the particular cortical fold. A parametric representation of the medial surface of the sulcus is obtained as the active contour traverses the sulcus. Based on the first fundamental form of this representation, the location and degree of an interruption of a sulcus can be readily quantified; based on its second fundamental form, shape properties of the sulcus can be determined. This methodology is tested on magnetic resonance images and it is applied to three medical imaging problems: quantitative morphological analysis of the central sulcus; mapping of functional activation along the primary motor cortex and non-rigid registration of brain images.

Anatomy, Cross-Sectional↗

PubMed1992

Measurement of radiotracer concentration in brain gray matter using positron emission tomography: MRI-based correction for partial volume effects.

Accuracy in in vivo quantitation of brain function with positron emission tomography (PET) has often been limited by partial volume effects. This limitation becomes prominent in studies of aging and degenerative brain diseases where partial volume effects vary with different degrees of atrophy. The present study describes how the actual gray matter (GM) tracer concentration can be estimated using an algorithm that relates the regional fraction of GM to partial volume effects. The regional fraction of GM was determined by magnetic resonance imaging (MRI). The procedure is designated as GM PET. In computer simulations and phantom studies, the GM PET algorithm permitted a 100% recovery of the actual tracer concentration in neocortical GM and hippocampus, irrespective of the GM volume. GM PET was applied in a test case of temporal lobe epilepsy revealing an increase in radiotracer activity in GM that was undetected in the PET image before correction for partial volume effects. In computer simulations, errors in the segmentation of GM and errors in registration of PET and MRI images resulted in less than 15% inaccuracy in the GM PET image. In conclusion, GM PET permits accurate determination of the actual radiotracer concentration in human brain GM in vivo. The method differentiates whether a change in the apparent radiotracer concentration reflects solely an alteration in GM volume or rather a change in radiotracer concentration per unit volume of GM.

Algorithms↗

PubMedDate not supplied

Sex differences in anatomic measures of interhemispheric connectivity: correlations with cognition in women but not men.

A robust sex difference in the splenium of the corpus callosum, reflecting greater interhemispheric connectivity in women, was observed on magnetic resonance images from 114 individuals. In addition, bulbosity of the corpus callosum correlated with better cognitive performance in women but not in men, indicating that the degree of interhemispheric connectivity has different implications for men and women. These findings were based on a new image analysis technique which allows investigation of local variability in brain morphology.

Aged↗

PubMedDate not supplied

A computerized approach for morphological analysis of the corpus callosum.

OBJECTIVE: A new technique for analyzing the morphology of the corpus callosum is presented, and it is applied to a group of elderly subjects. MATERIALS AND METHODS: The proposed approach normalizes subject data into the Talairach space using an elastic deformation transformation. The properties of this transformation are used as a quantitative description of the callosal shape with respect to the Talairach atlas, which is treated as a standard. In particular, a deformation function measures the enlargement/shrinkage associated with this elastic deformation. Intersubject comparisons are made by comparing deformation functions. RESULTS: This technique was applied to eight male and eight female subjects. Based on the average deformation functions of each group, the posterior region of the female corpus callosum was found to be larger than its corresponding region in the males. The average callosal shape of each group was also found, demonstrating visually the callosal shape differences between the two groups in this sample. CONCLUSION: The proposed methodology utilizes the full resolution of the data, rather than relying on global descriptions such as area measurements. The application of this methodology to an elderly group indicated sex-related differences in the callosal shape and size.

Aged↗

PubMedDate not supplied

Spatial normalization of 3D brain images using deformable models.

PURPOSE: The spatial normalization and registration of tomographic images from different subjects is a major problem in several medical imaging areas, including functional image analysis, morphometrics, and computer-aided neurosurgery. The focus of this article is the development of a computerized methodology for the spatial normalization of 3D images. METHOD: We propose a technique that is based on geometric deformable models. In particular, we first describe a deformable surface algorithm that finds a mathematical representation of the outer cortical surface. Based on this representation, a procedure for obtaining a map between corresponding regions of the outer cortex in two different images is established. This map is subsequently used to derive a 3D elastic warping transformation, which brings two images into register. RESULTS: The performance of our algorithm is demonstrated on several datasets. In particular, we first test our deformable surface algorithm on MR images. We then register MR images to atlas images. In our third experiment, we apply a procedure for matching distinct cortical features identified through the curvature map of the outer cortex. Finally, we apply our technique to images from elderly individuals with substantial ventricular enlargement, and we show a good registration in the ventricular area and the surrounding brain structures. CONCLUSION: We present a highly automated methodology for spatial normalization of images, using deformable models. Applications of our methodology include stereotactic normalization of functional and structural images, morphological analysis of the brain, and computer-aided neurosurgery.

Algorithms↗

PubMedDate not supplied

An image-processing system for qualitative and quantitative volumetric analysis of brain images.

In this work, we developed, implemented, and validated an image-processing system for qualitative and quantitative volumetric analysis of brain images. This system allows the visualization and quantitation of global and regional brain volumes. Global volumes were obtained via an automated adaptive Bayesian segmentation technique that labels the brain into white matter, gray matter, and cerebrospinal fluid. Absolute volumetric errors for these compartments ranged between 1 and 3% as indicated by phantom studies. Quantitation of regional brain volumes was performed through normalization and tessellation of segmented brain images into the Talairach space with a 3D elastic warping model. Retest reliability of regional volumes measured in Talairach space indicated errors of < 1.5% for the frontal, parietal, temporal, and occipital brain regions. Additional regional analysis was performed with an automated hybrid method combining a region-of-interest approach and voxel-based analysis, named Regional Analysis of Volumes Examined in Normalized Space (RAVENS). RAVENS analysis for several subcortical structures showed good agreement with operator-defined volumes. This system has sufficient accuracy for longitudinal imaging data and is currently being used in the analysis of neuroimaging data of the Baltimore Longitudinal Study of Aging.

Aged↗

PubMedDate not supplied

A probabilistic ribbon model for shape analysis of the cerebral sulci: application to the central sulcus.

PURPOSE: An approach for quantifying the shapes of the cerebral sulci is presented, utilizing a probabilistic geometric model, and it is applied to the central sulcus. METHOD: The geometric structure of the central sulcus is determined from a set of outlines on cross-sectional images and is used by a procedure that automatically labels the major crest lines, i.e., curves of locally maximal curvature, along the sulcus. An automated procedure then determines a parametric representation of the central sulcus that is consistent across individuals, in that it assigns the same parametric coordinates to corresponding regions of the sulcus. RESULTS: The method is applied to the central sulci from 20 subjects. The use of this shape representation in cortical morphometric analysis applications is demonstrated, in particular in obtaining local depth and curvature measurements of a sulcus as well as in determining average shapes and variability. CONCLUSION: With this method, we were able to build parametric representations of the sulcal ribbons by preserving anatomical homologies.

Anatomy, Cross-Sectional↗