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A stereotactic brain biopsy system that is magnetic resonance (MR) imaging-guided has not been validated in dogs. Our purpose was to determine the mean needle placement error in the caudate nucleus, thalamus, and midbrain of a canine cadaver brain using the modified Brainsight stereotactic system. Relocatable reference markers (fiducial markers) were attached to the cadaver head using a dental bite block. A T1-weighted gradient echo three-dimensional (3D) sequence was acquired using set parameters. Fiducial markers were used to register the head to the acquired MR images in reference to a 3D position sensor. This allowed the planning of trajectory path to brain targets in real time. Coordinates (X, Y, Z) were established for each target and 0.5 microl of diluted gadolinium was injected at each target using a 26-gauge needle to create a lesion. The center of the gadolinium deposition was identified on the postoperative MR images and coordinates (X', Y', Z') were established. The precision of this system in bringing the needle to target (needle placement error) was calculated. Seventeen sites were targeted in the brain. The mean needle placement error for all target sites was 1.79 +/- 0.87 mm. The upper bound of error for this stereotactic system was 3.31 mm. There was no statistically significant relationship between needle placement error and target depth (P = 0.23). The ease of use and precision of this stereotactic system support its development for clinical use in dogs with brain lesions > 3.31 mm.

The authors address the use of multimodality imaging as an aid to the planning and guidance of neurosurgical procedures, and discuss the integration of anatomical (CT and MRI), vascular (DSA), and functional (PET) data for presentation to the surgeon during surgery. The authors' workstation is an enhancement of a commercially available system, and in addition to the guidance offered via a hand-held probe, it incorporates the use of multimodality imaging and adds enhanced realism to the surgeon through the use of a stereoscopic three-dimensional (3-D) image display. The probe may be visualized stereoscopically in single or multimodality images. The integration of multimodality data in this manner provides the surgeon with a complete overview of brain structures on which he is performing surgery, or through which he is passing probes or cannulas, enabling him to avoid critical vessels and/or structures of functional significance.

Movements of brain tissue during neurosurgical procedures reduce the effectiveness of using pre-operative images for intra-operative surgical guidance. In this paper, we explore the use of acquiring intra-operative ultrasound (US) images for the quantification of and correction for non-linear brain deformations.We will present a multi-modal registration strategy that automatically matches pre-operative images (e.g., MRI) to intra-operative US to correct for these deformations. The strategy involves using the predicted appearance of neuroanatomical structures in US images to build "pseudo ultrasound" images based on pre-operative segmented MRI. These images can then be non-linearly registered to intra-operative US using cross-correlation measurements within the ANIMAL package. The feasibility of the theory is demonstrated through its application to clinical patient data acquired during 12 neurosurgical procedures.Results of applying the method to 12 surgical cases, including those with brain tumors and selective amygdalo-hippocampectomies, indicate that our strategy significantly recovers from non-linear brain deformations occurring during surgery. Quantitative results at tumor boundaries indicate up to 87% correction for brain shift.Qualitative and quantitative examination of the results indicate that the system is able to correct for non-linear brain deformations in clinical patient data.

The authors demonstrate the use of multi-modality and 3-D stereoscopic imaging in the context of image-guided neurosurgery. They consider here, the integration of anatomical data (MRI), vascular data (DSA) and functional data (PET) derived from the same patient. The authors' workstation, incorporating, a stereoscopic 3-D image display, is interfaced to a hand-held probe whose position coordinates in real space are constantly relayed to the computer during the procedure. This enables the probe to be visualized stereoscopically in images relating to the individual or combined modalities during the surgical procedure. The integration of multi-modality data in this manner provides the surgeon with a complete overview of brain structures on which he is performing surgery, or through which he is passing probes or cannulas, enabling him to avoid critical vessels and/or structures of functional significance. >

With the advent of magnetic resonance imaging (MRI), it is possible to obtain high-resolution anatomical images of the monkey brain. Accuracy, however, is lost in the laboratory or surgical setting when the localization of brain structures depends on nonstereotaxic tracking methods. Here we present an image-guided stereotaxic system that is able to localize and access anatomical brain structures using the monkey's MRI. This system, which is also known as frameless stereotaxy, is capable of computing the relation of the physical “real space” of the monkey's head to the corresponding image space, while a position sensor enables the tracking of the animal's head and the localization of brain areas and favorable paths to targets within the brain using real time display software. Surgical procedures make use of an adjustable upright chair and a surgical headclamp instead of the traditional restrictive head holder with ear bars. This novel system allows for the flexible positioning of the animal and the ability to reach areas of the brain that were difficult to access in the past. The headclamp also serves as a tool holder, which in the present application guided a cannula of retrograde tracer to the desired location in the frontal lobe. Histological examination of the brain showed that the injection reached the target site, and tests using an MRI compatible phantom demonstrated that the precision of the system in bringing an injection to target is less than 1.2 mm. This system can be used to inject accurately tracers for anatomical tract-tracing, to make precise lesions, and to position electrodes for electrophysiological studies.

The Image-guided Neurosurgery laboratory (IGNSL) at the Montreal Neurological Institute has developed a system aimed at optimizing and extending the utility of image-guidance in neurosurgery, through the integration of images from a variety of imaging modalities. Based upon the ISG Viewing-wand, it allows images incorporating functional, electrophysiological as well as anatomical data to be displayed, along with a representation of a hand-held probe, to the surgeon in the operating room during a surgical procedure. In addition the three-dimensional composite images may be presented to the surgeon stereoscopically in order to enhance the appreciation and quantitative assessment of the imaged volume.

When image-guided neurosurgery is used in procedures that require a craniotomy, targeting accuracy can often be compromised because of the brain shift that occurs due to pressure, gravitational and resection effects. Errors between the positions of homologous structures in the pre-operative images and within the brain itself of up to 25 mm have been reported. We have recently completed a study of the use of tracked 2D intra-operative ultrasound, integrated with 3D MRI as a means of visualizing and measuring the shift of the brain tissue during neurosurgical procedures, as well as correcting the pre-operative MR images on a slice-by-slice basis to conform with the intra-operative ultrasound images. More than 15 surgical cases have been performed thus far with the 2D system. We are extending this study to incorporate tracked 3D ultrasound. To date we have developed new tools for real-time overlay of the 3D ultrasound volumes and with the pre-operative MRI volumes. These facilities include a stereoscopic virtual-reality view of the ultrasound probe with live ultrasound video superimposed over a 3D-rendered MRI of the brain, as well as 3D ultrasound/MRI transparency overlay views. In addition, algorithms to automatically extract homologous landmarks from MRI and 3D ultrasound images are under development. These landmarks will be used to automatically generate nonlinear warp transformations to correct the pre-operative MRI as well as surgical target coordinates for brain shift.

Movements of brain tissue during neurosurgical procedures reduce the effectiveness of using pre-operative images for intraoperative surgical guidance. In this paper, we explore the use of acquiring intraoperative ultrasound (US) images for the quantification of and correction for non-linear brain deformations. We will present a multi-modal, automatic registration strategy that matches pre-operative images (e.g. MRI) to intra-operative ultrasound to correct for the non-linear brain deformations. The strategy involves using the predicted appearance of neuroanatomical structures in ultrasound images to build "pseudo ultrasound" images based on pre-operative segmented MRI. These images can then be registered to intra-operative US in a strategy based on cross-correlation measurements generated from the ANIMAL [1] registration package. The feasibility of the theory is demonstrated through its application to clinical patient data acquired during 12 neurosurgical procedures. Qualitative examination of the results indicate that the system is able to correct for non-linear brain deformations.

We present a surgical guidance system that incorporates pre-operative image information (e.g., MRI) with intraoperative ultrasound (US) imaging to detect and correct for brain tissue deformation during image-guided neurosurgery (IGNS). Many interactive IGNS implementations employ pre-operative images as a guide to the surgeons throughout the procedure. However, when a craniotomy is involved, tissue movement during a procedure can be a significant source of error in these systems. By incorporating intraoperative US imaging, the target volume can be scanned at any time, and two-dimensional US images may be compared directly to the corresponding slice from the pre-operative image. Homologous points may be mapped from the intraoperative to the pre-operative image space with an accuracy of better than 2 mm, enabling the surgeon to use this information to assess the accuracy of the guidance system along with the progress of the procedure (e.g., extent of lesion removal) at any time during the operation. Anatomical features may be identified on both the pre-operative and intraoperative images and used to generate a deformation map, which can be used to warp the pre-operative image to match the intraoperative US image. System validation is achieved using a deformable multi-modality imaging phantom, and preliminary clinical results are presented.

Performing a craniotomy will cause brain tissue to shift. As a result of the craniotomy, the accuracy of stereotactic localization techniques is reduced unless the brain shift can be accurately measured. If an ultrasound probe is tracked by a 3D optical tracking system, intra-operative ultrasound images acquired through the craniotomy can be compared to pre-operative MRI images to quantify the shift. We have developed 2D and 3D image overlay tools which allow interactive, real-time visualization of the shift as well as software that uses homologous landmarks between the ultrasound and MRI image volumes to create a thin-plate-spline warp transformation that provides a mapping between pre-operative imaging coordinates and the shifted intra-operative coordinages. Our techniques have been demonstrated on poly vinyl alcohol cryogel phantoms which exhibit mechanical and imaging properties similar to those of the human brain.

Object. To investigate the utility of [15O]H2O positron emission tomography (PET) activation studies in the presurgical mapping of primary somatosensory cortex, the authors compared the magnitude and location of activation foci obtained using PET scanning with the results of intraoperative cortical stimulation (ICS).Methods. The authors used PET scanning and vibrotactile stimulation (of the face, hand, or foot) to localize the primary somatosensory cortex before surgical resection of mass lesions or epileptogenic foci affecting the central area in 20 patients. With the aid of image-guided surgical systems, the locations of significant activation foci on PET scanning were compared with those of positive ICS performed at craniotomy after the patient had received a local anesthetic agent. In addition, the relationship between the magnitude and statistical significance of blood flow changes and the presence of positive ICS was examined.In 22 (95.6%) of 23 statistically significant (p < 0.05) PET activation foci, spatially concordant sites on ICS were also observed. Intraoperative cortical stimulation was positive in 40% of the PET activation studies that did not result in statistically significant activation. In the patients showing these results, there was a clearly identifiable t-statistic peak that was spatially concordant with the site of positive ICS in the sensorimotor area. All PET activation foci with a t statistic greater than 4.75 were associated with spatially concordant sites of positive ICS. All PET activation foci with a t statistic less than 3.2 were associated with negative ICS.Conclusions. Positron emission tomography is an accurate method for mapping the primary somatosensory cortex before surgery. The need for ICS, which requires local anesthesia, may be eliminated when PET foci with high (> 4.75) or low (< 3.20) t-statistic peaks are elicited by vibrotactile stimulation.

Stereotactic techniques are prevalent in neurosurgery. A fundamental assumption of stereotaxis is that the brain is a rigid body. It has been demonstrated, however, that following a craniotomy the brain tissue will shift by 10 mm on average. We are investigating intra-operative ultrasound, using an optical tracking system to record the position and orientation of the ultrasound probe, as a method of measuring and correcting for brain shift. We have determined that the accuracy to which ultrasound image coordinates can be tracked (including the errors involved in calibration) is better than 0.5 mm within the ultrasound image plane, and better than 2 mm perpendicular to the plane. We apply two visualization methods to compare the ultrasound and the pre-operative MRI: the first is real-time overlay of the ultrasound with the co-planar MR slice, and the second is the real-time texture mapping of the ultrasound video into a 3D view with the MRI. Our technique is demonstrated on a poly vinyl alcohol cryogel phantom.

Tissue movement can be a significant source of error in image-guided neurosurgery. A surgical guidance system that incorporates preoperative image information (eg, magnetic resonance [MR] imaging data) and intraoperative ultrasound (US) allows detection of tissue deformation during neurosurgery. An interactive image overlay tool allows a region of interest (ROl) to be defined and permits the operator to move the ROI over the MR or US image and overlay the associated image (US or MR) within the ROl. The system can be validated with a deformable multimodality phantom. Before deformation of the phantom, good agreement between the MR imaging and US data overlay confirms proper registration of the MR and US images; after deformation, the overlay demonstrates significant distortion of ventricles and movement of simulated blood vessels. Intraoperatively, this information helps establish the orientation of the US image being displayed by providing an oblique MR image that coincides with the live US view. The superior anatomic display of MR imaging also helps the surgeon interpret the corresponding US images. Finally, the system enables the surgeon to evaluate the patient-MR image registration by comparing structures on the MR images and live US images and using the overlay tool to visualize discrepancies.

We present a surgical guidance system that incorporates preoperative image information (e.g. MRI or CT) and intraoperative ultrasound imaging to detect brain tissue deformation during image guided neurosurgery. Many interactive IGNS implementations involve using pre-operative image information (e.g. MRI or CT) as a guide to the surgeons throughout the procedure. Tissue movement during a procedure can be a significant source of error in these systems. By incorporating intraoperative imaging, the target volume can be scanned at any time, and mapped into the pre- operative image space. The surgeon can use this information to assess the accuracy of the guidance system at any time during the procedure. In addition, the system can be used to provide updated information of the progress of this procedure (e.g. extent of lesion removal). Validation results using a deformable multimodality imaging phantom are presented as well as initial examples of the system used in surgery.

Image-guided surgery has evolved over the past 15 years from stereotactic planning, where the surgeon planned approaches to intracranial targets on the basis of 2D images presented on a simple workstation, to the use of sophisticated multi- modality 3D image integration in the operating room, with guidance being provided by mechanically, optically or electro-magnetically tracked probes or microscopes. In addition, sophisticated procedures such as thalamotomies and pallidotomies to relieve the symptoms of Parkinson's disease, are performed with the aid of volumetric atlases integrated with the 3D image data. Operations that are performed stereotactically, that is to say via a small burr- hole in the skull, are able to assume that the information contained in the pre-operative imaging study, accurately represents the brain morphology during the surgical procedure. On the other hand, preforming a procedure via an open craniotomy presents a problem. Not only does tissue shift when the operation begins, even the act of opening the skull can cause significant shift of the brain tissue due to the relief of intra-cranial pressure, or the effect of drugs. Means of tracking and correcting such shifts from an important part of the work in the field of image-guided surgery today. One approach has ben through the development of intra-operative MRI imaging systems. We describe an alternative approach which integrates intra-operative ultrasound with pre-operative MRI to track such changes in tissue morphology.

We describe a new technique permitting the mapping of neural connections in the living human brain. The method combines two well established tools of brain research: transcranial magnetic stimulation (TMS) and positron emission tomography (PET). We use TMS to stimulate directly a selected cortical area while simultaneously measuring changes in brain activity, indexed by cerebral blood flow (CBF), with PET. The exact location of the stimulation site is achieved by means of frameless stereotaxy. In the first study using this technique, we found significant positive correlations between CBF and the number of TMS pulse trains at the stimulation site, namely the left frontal eye field (FEF) and, most importantly, in the visual cortex of the superior parietal and medial parieto-occipital regions. The pattern of these distal effects was consistent with the known anatomic connectivity of the monkey FEF. We suggest that the combined TMS/PET technique offers an objective tool for assessing the state of functional connectivity without requiring the subject to engage in any specific behavior.

Interactive image-guided techniques used in conjunction with three-dimensional images allow accurate planning and performance of a variety of neurosurgical procedures. The authors have used the frameless stereotactic Allegro Viewing Wand System to provide real-time correlation of the operating field and computerized images in over 200 neurosurgical operations carried out for intractable epilepsy. The authors experience shows that the viewing wand system is most helpful as an adjunctive navigational device in the microsurgical treatment of epilepsy.