P. W. A. Willems

Frameless stereotactic subcaudate tractotomy for intractable obsessive–compulsive disorder

SummaryObsessive–compulsive disorder (OCD) is a chronic, disabling disorder. Psychosurgery may be indicated for a subset of patients for whom no conventional treatment is satisfactory. This paper focuses on the stereotactic subcaudate tractotomy (SST). Thus far, these procedures have been carried out using frame-based stereotactic techniques. However, modern – highly accurate – frameless stereotactic procedures have successfully been introduced in neurosurgical practice. We developed a novel frameless stereotactic subcaudate tractotomy procedure with promising initial results in a patient suffering from intractable OCD. This is the first report on frameless SST. Future studies should examine whether other ablative stereotactic psychosurgery procedures can be done using frameless stereotactic methods.

Clinical evaluation of stereotactic brain biopsies with an MKM-mounted instrument holder.

Summary¶Object. The aim of this study was to assess the clinical usefulness and accuracy of robot-assisted frameless stereotactic brain biopsies with a recently introduced MKM-mounted instrument holder.n Methods. Twenty-three patients with intracranial lesions participated in this study. Depending on the size of the intracranial lesion, fiducials for image-to-patient co-ordinate transformation consisted either of bone screws or adhesive markers. Shortly after surgery, postoperative MRI-imaging was performed to demonstrate the location of the biopsy site. These images were compared with the preoperative images to assess the biopsy localisation error.n Results. Postoperative biopsy sites could be demonstrated in six patients with bone screws and in 14 with adhesive markers. These two subgroups yielded average biopsy localisation errors of 3.3u2009mm (SD 1.7u2009mm) and 4.5u2009mm (SD 2.0u2009mm) respectively. This difference was not statistically significant. One biopsy was located in a liquefied haematoma. All others yielded pathological tissue. There were two postoperative haemorrhages, of which only one was temporarily symptomatic. There was no mortality in the first 30 days after surgery.n Conclusions. Robot-assisted frameless point-stereotactic techniques represent an alternative to frame-based techniques for the performance of stereotactic biopsies.

Frameless stereotactic placement of ventriculoperitoneal shunts in undersized ventricles: a simple modification to free-hand procedures

The aim of this report is to introduce a simple modification to the free-hand frameless stereotactic placement of ventriculoperitoneal shunts in undersized ventricles. In this technical note, we describe our experience with ventricular catheter placement in two children suffering from shunt dependent idiopathic intracranial hypertension using an image-guided instrument holder with a catheter guide. In both patients, the surgical procedure proved to be easy and accurate, with good initial clinical results. The use of an image-guided instrument holder is a modification to the free-hand frameless stereotactic placement of ventriculoperitoneal shunts in undersized ventricles.

Repeated quantitative perfusion and contrast permeability measurement in the MRI examination of a CNS tumor

Abstract. This study reports on the results of quantitative MRI perfusion and contrast permeability measurement on two occasions in one patient. The measurements were separated 81 days in time. The tumor grew considerably in this period, but no change was found with respect to perfusion and contrast permeability. Non-involved white matter values were reproduced to demonstrate repeatability. The presented approach to dynamic susceptibility contrast MRI allows fast and repeatable quantitative assessment of perfusion and is easily integrated in a conventional brain tumor protocol.

The Impact of Workflow and Volumetric Feedback on Frameless Image-guided Neurosurgery

OBJECTIVE During image-guided neurosurgery, if the surgeon is not fully orientated to the surgical position, he or she will briefly shift attention toward the visualization interface of an image guidance station, receiving only momentary “point-in-space” information. The aim of this study was to develop a novel visual interface for neuronavigation during brain tumor surgery, enabling intraoperative feedback on the entire progress of surgery relative to the anatomy of the brain and its pathology, regardless of the interval at which the surgeon chooses to look. METHODS New software written in Java (Sun Microsystems, Inc., Santa Clara, CA) was developed to visualize the cumulative recorded instrument positions intraoperatively. This allowed surgeons to see all previous instrument positions during the elapsed surgery. This new interactive interface was then used in 17 frameless image-guided neurosurgical procedures. The purpose of the first 11 cases was to obtain clinical experience with this new interface. In these cases, workflow and volumetric feedback (WVF) were available at the surgeons discretion (Protocol A). In the next 6 cases, WVF was provided only after a complete resection was claimed (Protocol B). RESULTS With the novel interactive interface, dynamics of surgical resection, displacement of cortical anatomy, and digitized functional data could be visualized intraoperatively. In the first group (Protocol A), surgeons expressed the view that WVF had affected their decision making and aided resection (10 of 11 cases). In 3 of 6 cases in the second group (Protocol B), tumor resections were extended after evaluation of WVF. By digitizing the cortical surface, an impression of the cortical shift could be acquired in all 17 cases. The maximal cortical shift measured 20 mm, but it typically varied between 0 and 10 mm. CONCLUSION Our first clinical results suggest that the embedding of WVF contributes to improvement of surgical awareness and tumor resection in image-guided neurosurgery in a swift and simple manner.

The effect of repetitive manual fiducial localization on target localization in image space.

OBJECTIVE In this clinical study, we quantify intra- and interobserver variability of manual fiducial localization in image space, as the effect of repetitive manual fiducial localization is still unclear, especially on a target position. METHODS After uploading eight imaging datasets with a total of 56 skin adhesive fiducial markers in a commercially available image-guidance system, the centroids of the fiducial markers were tagged. This task was executed repeatedly at three separate moments by six different observers. The fiducial localization variability and its target shift effect in image space were determined out of 1008 tagged fiducial markers. RESULTS The maximal intraobserver target shift effect measured 0.72 ± 0.14 mm in computed tomographic image space and 0.95 ± 0.21 mm in magnetic resonance image space. CONCLUSION If a fiducial tagging task is well understood, repetitive manual detection of fiducial markers can be done with a low intraobserver fiducial localization variability, resulting in a submillimetric effect on a target position, either in computed tomographic or magnetic resonance image space. Therefore, we think it is justified to determine the centroids of a skin adhesive fiducial marker in the image space by hand.

Comparison of adhesive markers, anatomical landmarks and surface matching in patient-to-image registration for frameless stereotaxy

The application accuracy of frameless stereotaxy depends partly on the accuracy of the patient-to-image registration procedure. We compared the application accuracy of registration procedures based on anatomical landmarks, surface matching, and adhesive markers. After acquisition of a 3D-MRI volume, 30 patients were subjected to all three registration procedures. Frameless stereotaxy was performed with the STN system (Carl Zeiss, Germany). Following each registration procedure, the root-mean-squared-error (RMSE) and the target registration error (TRE) of an extra adhesive marker (target) were recorded. The first represents the goodness-of-fit of the registration procedure (not available in surface matching) while the second represents the application accuracy. The mean TRE+/- SD for each type of registration was 5.3+/- 2.1mm, 9.4+/- 6.6mm, and 3.6+/- 1.6mm (paired t-tests: p<0.01). When anatomical landmarks were used, anterior targets generated smaller TREs than posterior targets (4.6+/- 2.0mm and 6.8+/- 1.3mm respectively, t-test: p<0.01). There was no significant correlation between the RMSE and the TRE (anatomical landmarks: R2=0.071, adhesive markers: R2=0.004). A more detailed evaluation of surface matching, using a plastic skull phantom, also could not demonstrate an improvement in application accuracy due to surface matching. In conclusion, our results indicate that adhesive markers offer the most accurate alternative to bonescrews. However, we believe anatomical landmarks to provide sufficient accuracy for many neurosurgical procedures concerning frontally located targets, reducing the need for extra preoperative imaging.

Acquisition of 3D ultrasound images during neuronavigation

Intraoperative brain deformation is the most important cause affecting the overall accuracy of image guided neurosurgical procedures. One option for correcting this deformation is to acquire 3D ultrasound images during the operation and use these to update the information provided by the preoperatively acquired MR data.

The impact of auditive feedback on neuronavigation

Abstract To improve the usefulness of the information offered by neuronavigation systems, we developed an auditive feedback system which can be used in addition to regular neuronavigation. Using a serial connection, instrument coordinates determined by a commercially available neuronavigation system were transferred to a laptop computer. Based on preoperative segmentation of the images, the software on the laptop computer produced an audible signal whenever the instrument moved into an area the surgeon wanted to avoid. Phantom experiments were conducted to evaluate the impact of this setup on volumetric resections. These consisted of the ‘resection’ of a preoperatively defined target-volume from eight blocks of floral foam using CT-based navigation, four with and four without the auditive feedback extension. The resemblance between the resection cavity, as demonstrated by a postoperative CT scan, and the target-volume was greater each time auditive feedback had been used. This corresponded with more complete removal of the target-volume in all cases and the removal of more nontarget ‘tissue’ in two out of four cases. Our results make the usefulness of auditive feedback plausible and, consequently, we recommend the relatively inexpensive incorporation of auditive feedback in commercially available neuronavigation systems.

Monte Carlo simulation for anisotropic error prediction in frameless stereotaxy

Typically, frameless stereotactic systems present a crosshair indicating the localisation of an instrument relative to preoperative images. We aim to develop a model that enables three-dimensional graphical presentation of confidence intervals at the instrument’s position, during a surgical procedure. This requires the prediction of frameless stereotactic accuracy confidence intervals at any position within the surgical volume.