Terence M. Peters

Anatomic basis of amygdaloid and hippocampal volume measurement by magnetic resonance imaging

Both the amygdala and the hippocampus are involved in the pathogenesis of a number of neurologic conditions, including temporal lobe epilepsy, postanoxic amnesia, and Alzheimers disease. To enhance the investigation and management of patients with these disorders, we developed a protocol to measure the volumes of the amygdala and as much of the hippocampus as possible (approximately 90 to 95%) using high-resolution MRI. We present the anatomic basis of these two protocols and our results in normal control subjects. These volumetric studies of the amygdala may clarify the role of this structure in the pathogenesis of temporal lobe epilepsy.

Early childhood prolonged febrile convulsions, atrophy and sclerosis of mesial structures, and temporal lobe epilepsy An MRI volumetric study

We performed MRI volumetric measurements of the amygdala (AM) and hippocampal formation (HF) in a group of 43 patients with temporal lobe epilepsy not controlled by optimal drug treatment. Fifteen patients (35%) had a history of prolonged febrile convulsions (PFC) in early childhood; 30 patients underwent surgery, and histopathology was available in twenty-four. The mean values of AM and HF volumes ipsilateral to the EEG focus were significantly smaller than those of normal controls. The volumetric measurements showed a more pronounced atrophy of the AM in patients with a history of PFC, although the HF volumes were also smaller in this group. Patients with a history of PFC had a higher proportion of more severe mesial temporal sclerosis (MTS) compared with those with no PFC. These findings confirm a correlation between early childhood PFC, the severity of atrophy of mesial structures, and MTS.

MRI volumetric measurement of amygdala and hippocampus in temporal lobe epilepsy

We performed MRI volumetric measurements of the amygdala (AM), the hippocampal formation (HF), and the anterior temporal lobe in a group of 30 patients with intractable temporal lobe epilepsy (TLE) and in seven patients with extratemporal lobe foci. Measurements were analyzed with a semiautomated software program and the results compared with those of normal controls and correlated with the findings of all other investigations. In particular, we compared the results with the lateralization of epileptic abnormalities in the EEG. Volumetric studies of AM and HF showed lateralization of measurable atrophy consistent with that derived from extracranial and intracranial EEG examinations. The HF volumes were more sensitive and provided a lateralization in 87%. Combined measurements of AM and HF showed lateralization in 93%, always congruent with the results of EEG lateralization. This slight but important additional improvement in discrimination justifies using AM measurements in MRI volumetric studies of mesial temporal structures. Volumetric studies combined with other currently employed noninvasive techniques may diminish the need for invasive methods of investigation in patients with TLE.

Model-based segmentation of individual brain structures from MRI data

This paper proposes a methodology that enables an arbitrary 3-D MRI brain image-volume to be automatically segmented and classified into neuro-anatomical components using multiresolution registration and matching with a novel volumetric brain structure model (VBSM). This model contains both raster and geometric data. The raster component comprises the mean MRI volume after a set of individual volumes of normal volunteers have been transformed to a standardized brain-based coordinate space. The geometric data consists of polyhedral objects representing anatomically important structures such as cortical gyri and deep gray matter nuclei. The method consists of iteratively registering the data set to be segmented to the VBSM using deformations based on local image correlation. This segmentation process is performed hierarchically in scale-space. Each step in decreasing levels of scale refines the fit of the previous step and provides input to the next. Results from phantom and real MR data are presented.

Automated 3D nonlinear deformation procedure for determination of gross morphometric variability in human brain

We describe an automated method to register MRI volumetric datasets to a digital human brain model. The technique employs 3D non-linear warping based on the estimation of local deformation fields using cross-correlation of invariant intensity features derived from image data. Results of the non-linear registration on a simple phantom, a complex brain phantom and real MRI data are presented. Anatomical variability is expressed with respect to the Talairach-like standardized brain-based coordinate system of the model. We show that the automated non-linear registration reduces the inter-subject variability of homologous points in standardized space by 15% over linear registration methods. A 3D variability map is shown.

Multimodality image integration for stereotactic surgical planning

A method is presented for integrating stereotactic projection and tomographic image data to give composite 3-D images (stereo pairs) of cerebral anatomy and vasculature. The technique serves to combine complementary information from each modality and allows the imaged volume to be viewed directly. The procedure is largely automated and requires no additional apparatus or information beyond that which is ordinarily employed during stereotactic surgical planning. The two types of data are combined by superimposing the projection angiogram (DSA) onto a translucent volume rendered CT or MR image. Since the rendering algorithm employs an orthographic projection technique, the tomographic volume must first be reshaped and oriented to yield a perspective view that matches the DSA projection. During this process, the data undergo various interpolations which consequently affect the accuracy of target identification based on the resulting images. The integrity of the matching procedure was assessed using simulated data sets. Also, calculations were performed to estimate the resolution of measurements made from digitized stereoscopic images. The resulting sub-pixel accuracy of the matched images suggests that the technique has potential for stereotactic applications. Preliminary results are presented illustrating combined CT-DSA and MR-DSA data sets.

Integration of stereoscopic DSA and 3D MRI for image-guided neurosurgery

We demonstrate the feasibility and utility of using anatomical/vascular correlation in image-guided surgery, by interfacing a PC-based stereoscopic Digital Subtraction Angiography (DSA) analysis system to a three-dimensional (3D) image based surgical workstation that has been modified to allow presentation of stereoscopic images. Numerical values representing the position and angulation of a hand-held probe are transmitted to both systems simultaneously, enabling the probe to be visualized stereoscopically in both anatomical and vascular images during the surgical procedure. The integration of the patients vascular and anatomical data in this way provides the surgeon with a complete overview of brain structures through which he is passing the electrode-guiding cannulas, enabling him to avoid critical vessels en route to the targets.

Stereotactic neurosurgery planning on a personal-computer-based work station

Stereotactic surgery requires knowledge of cerebral structures derived from more than one image source. We have developed a PC-AT-based workstation that accepts patient images, made with the stereotactic frame in place, from CT, MRI, and DSA modalities. Reference markers on the frame are identified in the images to establish the coordinate geometry for each modality. Target points may be identified on each image type and trajectories of probe paths to these points defined. Targets identified on one set of images may be transferred automatically to other images of the same patient in order to guarantee a vessel-free path of approach to a target point deep within the brain. To date several hundred patients have had stereotactic surgery performed on the basis of plans using this system. Procedures included biopsy and aspiration of lesions, implantation of electrodes for the recording of deep EEG signals, and radiosurgical techniques. We present clinical examples of the use of this system in typical stereotactic neurosurgery procedures, address stereoscopic applications, and discuss the results of intermodality tests to establish the accuracy of the technique.

Dose distributions in radiosurgery

A PC-based, three-dimensional treatment planning system, which may be used for planning of radiosurgical treatments with the Gamma unit or with any of the radiosurgical techniques based on isocentric linear accelerators (linacs), is described and used to calculate isodose distributions for various linac-based radiosurgical techniques ranging from the single plane rotation to a 4-pi geometry. The latter gives an isotropic dose falloff outside the target volume but cannot be used for practical radiosurgery, while the single plane rotation is simple to use but gives unacceptably shallow dose falloffs in the transverse plane. Dose falloffs for several other techniques of varying degrees of complexity are shown and discussed. Also discussed is the effect of beam energy and beam profiles on radiosurgical dose distributions.

C.T. Aided Stereotaxy for Depth Electrode Implantation and Biopsy

We describe a computer program which facilitates the analysis of a series of C.T. scans made while a stereotaxic frame is fixed to the patient. The program has 2 modes of operation: a) The operator may select a region and determine the three-dimensional frame coordinate. b) The operator may select a set of frame coordinates and have the computer program display these at the appropriate sites on the C.T. scans. It these sites are the positions of depth electrodes, then a recording of the epileptic spike activity may be displayed at the appropriate sites on the scans.