C. Henri

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.

Experience with a computerized stereoscopic workstation for neurosurgical planning

The authors describe a PC AT-based workstation that allows stereotactic neurosurgery to be planned using stereoscopic digital subtraction angiography (DSA) projections in conjunction with computed tomography (CT) and/or magnetic resonance (MR) image data. Techniques for correlating the positions of targets and for performing measurements in images acquired from different modalities (i.e., CT, MR and DSA) are presented. The stereoscopic approach is discussed and compared with conventional methods of planning stereotactic neurosurgery. This method is found to be enlightening in terms of its ability to provide the observer with a 3D appreciation of the imaged structure. The ability to perform quantitative measurements, as well as view projection image data in 3D, is an attractive feature of the stereoscopic workstation and is considered crucial to planning many stereotactic procedures.<<ETX>>

Integration of Stereoscopic DSA with Three-Dimensional Image Reconstruction for Stereotactic Planning

Following 4 years of experience using a microcomputer-based system for the planning of stereotactic neurosurgery, we have now developed a workstation with the capability of displaying and analyzing three-dimensional images for this purpose. In addition to viewing volumetrically rendered three-dimensional computer tomograms and magnetic resonance images, we may directly view and analyze stereoscopic digital angiograms. In addition to each set of images being viewed in isolation, we may also combine the three-dimensional anatomical images with the stereoscopic angiograms. This new system is based on a computer equipped with a light polarization switched screen capable of displaying stereoscopic images directly to the observer, thus permitting him to interact with the three-dimensional volume directly, determining coordinates and positioning probe trajectories.

Stereotactic Neurosurgery Planning On A PC Based Workstation.

Stereotactic surgery requires knowledge of cerebral structures derived from more than one image source. We have developed a PC-AT based workstation which 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, for example, to guarantee a vascular 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 based on the use of a high energy linear accelerator. We present clinical examples of the use of this system in typical stereotactic neurosurgery procedures, address stereoscopic applications, and discuss the results of inter-modality tests to establish the accuracy of the technique.

3-D Correlative Imaging And Segmentation Of Cerebral Anatomy, Function And Vasculature

We describe the 3-D integration and simultaneous display of images of brain anatomy, metabolism and vasculature. Data are registered with interactive software or with transformation algorithms which match homologous points from each volume. For neurosurgical procedures, a rigid frame, fixed to the patients head, is equipped with fiducial markers that map images into a common coordinate system. A computerized 3-D brain atlas, customized to individual anatomy by non-linear warping and/or by interactive modification, measures regional volume or metabolism. 3-D vascular images are correlated with anatomy by direct voxel merging or by overlaying stereoscopic angiograms.

Evaluation of perceived distortions in stereoscopic images (projection radiography)

The effects of several imaging parameters on the perceived shape of a test pattern have been studied geometrically. Distortions in the perceived shape, which arise when the images are acquired and viewed using different geometries, are clearly demonstrated, allowing their severity to be assessed and quantified. The specific application in which stereoscopic images have been quantitatively employed is described. Additional results that provide an estimate of the smallest resolvable depth that may be measured from a digitized stereo-pair acquired using either of two different approaches are presented.<<ETX>>

Clinical experience with a stereoscopic image workstation

Stereoscopic radiography has been used routinely at the Montreal Neurological Institute for many years. Recently, with the advent of stereoscopic acquisition and display techniques for digital angiography, together with the increased use of 3-D display techniques for medical images, we have developed and implemented a stereoscopic display workstation for use in a clinical context. The system is based on standard AT-bus computer hardware and includes a high performance monitor equipped with a liquid-crystal polarizing shutter to display the stereoscopic images. The most significant application of this system has been planning for the stereotactic implantation of EEG recording electrodes. Here the surgeon has the ability not only to view the imaged anatomy in three-dimensions, but he is also able to interact with the images and to plan surgical procedures in a more realistic manner than traditional 2-D approaches. Display modes include vascular anatomy (from stereoscopic digital subtraction or MR angiography), or a combination of DSA images and 3-D volume-rendered MR or CT reconstructions.