Intraoperative MR Research Articles

The Changing Role of Stereotaxis in Surgical Neuro-Oncology

Evaluate evolution and time course of stereotactic neurosurgery within surgical neuro-oncology. MEDLINE search 1966-2003 sub-stratified and analyzed for annual trends. AANS/CNS membership databases for Joint Sections. ACRC neuro-oncology program database 1998-2003. Tumor stereotaxis emerged in 1980 and became the dominant stereotactic publication topic by 1984. Frame-based tumor stereotaxis led publications through 1994, when supplanted by stereotactic radiosurgery (SR). Brachytherapy led SR 1982-1987, but then fell behind, reducing to pre-1983 levels by 1996. SR publications currently comprise 65% of stereotactic tumor articles and publication rate continues to rise at a steady rate. Frameless stereotaxis (FS) publications began to increase in 1993 and growth is larger than the corresponding fall in frame-based volumetric resection publications. Data suggest increased utilization for cases that would have otherwise utilized ultrasound or gone without image guidance. Intraoperative MR developed predominantly as complimentary technology to FS. Tumor diagnostic needle biopsy publications continue to be mostly frame-based, while FS techniques are largely resection focused. This may change as >80% of our tumors biopsied with frame-based techniques would be candidates for FS biopsy based solely on lesion size, location, and technique accuracy considerations. CNS parenchymal delivery of experimental therapies continues to be predominantly frame-based. The role of tumor stereotaxis in surgical neuro-oncology is important, but changing. SR is increasingly dominating the subspecialty. Stereotactic tumor resection has become a mainstream neurosurgical procedure due to FS, and this will likely occur with needle biopsy as well. Delivery of experimental therapies remains predominantly frame-based, but may need to transition to FS in order to gain wider mainstream acceptance and applicability once efficacy is demonstrated.

Registration of preoperative and intraoperative high-field MR image data allows automatic updating of neuronavigation

Updating of neuronavigation systems with intraoperative image data is possible without repeated patient registration. Tumor remnants depicted by intraoperative imaging can be localized reliably, as well as brain shift can be compensated for.

Strategies for brain shift evaluation

For the analysis of the brain shift phenomenon different strategies were applied. In 32 glioma cases pre- and intraoperative MR datasets were acquired in order to evaluate the maximum displacement of the brain surface and the deep tumor margin. After rigid registration using the software of the neuronavigation system, a direct comparison was made with 2D- and 3D visualizations. As a result, a great variability of the brain shift was observed ranging up to 24 mm for cortical displacement and exceeding 3 mm for the deep tumor margin in 66% of all cases. Following intraoperative imaging the neuronavigation system was updated in eight cases providing reliable guidance. For a more comprehensive analysis a voxel-based nonlinear registration was applied. Aiming at improved speed of alignment we performed all interpolation operations with 3D texture mapping based on OpenGL functions supported in graphics hardware. Further acceleration was achieved with an adaptive refinement of the underlying control point grid focusing on the main deformation areas. For a quick overview the registered datasets were evaluated with different 3D visualization approaches. Finally, the results were compared to the initial measurements contributing to a better understanding of the brain shift phenomenon. Overall, the experiments clearly demonstrate that deformations of the brain surface and deeper brain structures are uncorrelated.

An interactive augmented reality 3D visualization system for destroying liver tumor using cryoablation

Cryoablation is one of many local destruction techniques used to remove liver tumors. The procedure is cumbersome and time-consuming if there is no real-time access to intra-operative images as well as navigation information of instruments. In this paper, we propose a software-based solution that addresses issues like interactive, real-time navigation and visualization of cryoprobes, segmented tumor, intra-operative MR images, temperature maps, and isotherm surfaces. The system has an intuitive graphical user interface that provides access to a variety of functionalities. It enables the surgeon to perform the procedure safely, accurately, and rapidly by providing visual decision support mechanism.

Intraoperative MR at 1.5 Tesla--experience and future directions.

The objective of this report is to present and contrast the development of the different intraoperative MR systems that are currently in use. The manuscript focuses on the design and clinical experience of a 1.5 Tesla MR system, based on a movable magnet. This configuration is similar to the operating microscope and other surgical adjuncts, with MR technology moved to and from the patient as needed. The system has been used to monitor 294 neurosurgical procedures. including CNS neoplasia. epilepsy, cervical spine disorders, arteriovenous malformations, cavernomas and aneurysms. In many cases the surgical procedure was significantly altered by intraoperatively acquired MRI. Future developments include the construction of a 3 Tesla intraoperative MR system and an ambidextrous MR-compatible robot. This seamless integration of robotic technology into an intraoperative MR environment may well revolutionize neurosurgery.

Fast and Adaptive Finite Element Approach for Modeling Brain Shift

Objective: In this paper we introduce a finite element-based strategy for simulation of brain deformation occurring during neurosurgery. The phenomenon, known as brain shift, causes a decrease in the accuracy of neuronavigation systems that rely on preoperatively acquired data. This can be compensated for with a computational model of the brain deformation process. By applying model calculations to preoperative images, an update within the operating room can be performed.Methods: One of the crucial concerns in the context of developing a physical-based model is the choice of governing equations describing the physics of the phenomenon. In this work, deformation of brain tissue is expressed in terms of a 3D consolidation model for a linearly elastic and porous fluid. The next crucial issue is ensuring stable calculations within the chosen model. For this purpose, we developed a special technique for generating the underlying geometry for the simulation. With this technique an unstructured grid consisting of regular tetrahedra is created, whereupon time-dependent finite element simulation is performed in an adaptive manner.Results: We applied our algorithm to preoperative MR scans and investigated the value of the method. Due to the adaptivity of the method, only 5-10% of the computing time was needed as compared to traditional finite element approaches based on a uniformly subdivided grid. The results of the experiments were compared to the corresponding intraoperative MR scans. A close match between the computed deformation of the brain and the displacement resulting from the intraoperative data was observed.Conclusion: A model-based approach for the simulation of brain shift is presented. In this computational model the brain tissue is described as an elastic and porous material using Biot consolidation theory. Validating experiments conducted with MR data provided promising results.

Intracranial navigation by using low-field intraoperative magnetic resonance imaging: preliminary experience.

Intracranial navigation by using intraoperative magnetic resonance (iMR) imaging allows the surgeon to reassess anatomical relationships in near-real time during brain tumor surgery. The authors report their initial experience with a novel neuronavigation system coupled to a low-field iMR imaging system. Between October 2000 and December 2001, 70 neurosurgical procedures were performed using the mobile 0.12-tesla PoleStar N-10 iMR imaging system. The cases included 38 craniotomies, 15 brain biopsies, nine transsphenoidal approaches, and one drainage of a subdural hematoma. Tumor resection was performed using the awake method in seven of 38 cases. Of the craniotomies, image-confirmed complete or radical tumor resection was achieved in 28 cases, subtotal resection in eight cases, and open biopsies in two cases. Tumor resection was controlled with the use of image guidance until the final intraoperative images demonstrated that there was no residual tumor or that no critical brain tissue was at risk of compromise. In each stereotactic biopsy the location of the biopsy needle could be verified by intraoperative imaging and diagnostic tissue was obtained. Complications included a case of aseptic meningitis after a biopsy and one case of temporary intraoperative failure of the anesthesia machine. Awake craniotomies were performed successfully with no permanent neurological complications. Intraoperative MR image-based neuronavigation is feasible when using the Odin PoleStar N-10 system for tumor resections that require multiple other surgical adjuncts including awake procedures, cortical mapping, monitoring of somatosensory evoked potentials, or electrocorticography. Use of the system for brain biopsies offers the opportunity of immediate verification of the needle tip location. Standard neurosurgical drills, microscopes, and other equipment can be used safely in conjunction with this iMR imaging system.

Serial registration of intraoperative MR images of the brain

The increased use of image-guided surgery systems during neurosurgery has brought to prominence the inaccuracies of conventional intraoperative navigation systems caused by shape changes such as those due to brain shift. We propose a method to track the deformation of the brain and update preoperative images using intraoperative MR images acquired at different crucial time points during surgery. We use a deformable surface matching algorithm to capture the deformation of boundaries of key structures (cortical surface, ventricles and tumor) throughout the neurosurgical procedure, and a linear finite element elastic model to infer a volumetric deformation. The boundary data are extracted from intraoperative MR images using a real-time intraoperative segmentation algorithm. The algorithm has been applied to a sequence of intraoperative MR images of the brain exhibiting brain shift and tumor resection. Our results characterize the brain shift after opening of the dura and at the different stages of tumor resection, and brain swelling afterwards. Analysis of the average deformation capture was assessed by comparing landmarks identified manually and the results indicate an accuracy of 0.7±0.6 mm (mean±S.D.) for boundary surface landmarks, of 0.9±0.6 mm for landmarks inside the boundary surfaces, and 1.6±0.9 mm for landmarks in the vicinity of the tumor.

Model-driven brain shift compensation

Surgical navigation systems provide the surgeon with a display of preoperative and intraoperative data in the same coordinate system. However, the systems currently in use in neurosurgery are subject to inaccuracy caused by intraoperative brain deformation (brain shift), since they typically assume that the intracranial structures are rigid. Experiments show brain shift of up to 1 cm, making it the dominant error in the system. We propose a biomechanical-model-based approach for brain shift compensation. Two models are presented: a damped spring–mass model and a model based on continuum mechanics. Both models are guided by limited intraoperative (exposed brain) surface data, with the aim to recover the deformation in the full volume. The two models are compared and their advantages and disadvantages discussed. A partial validation using intraoperative MR image sequences indicates that the approach reduces the error caused by brain shift.

“Snapper-Stereoguide” – A New Device for Image Guided, Frameless Stereotactic Procedures in the Open MR

Summary A new device has been developed for planning, guiding and performing image guided stereotactic procedures. The burr hole mounted device is made of biocompatible composite (polyacetal) and consists of a probe holder within a ball-and-socket joint, to which a light-emitting diode reference stage is attached. In combination with intraoperative, near real-time imaging, this system aids in targeting burr hole entry points and trajectories. The open intraoperative MR (Signa SP, General Electric) used in this series fuses the anatomical space with imaging space and time space and transforms a “blind” stereotactic procedure into a visually controlled one. Planning and performing stereotactic interventions become a single step procedure without using registration, frames and fiducials. The snapper-stereoguide has been evaluated in more than 300 stereotactic procedures including biopsies, evacuations of cysts, abscesses, hematomas, insertion of laser fibres for laser induced interstitial thermotherapy (LITT) and guiding endoscopes. Although evaluated in an open MRI unit, this system could be used in all image guided procedures involving direction of a stereotactic instrument. On the basis of this clinical series this artefact free and frameless device for near real time stereotactic procedures proved to be easy to use, fast, accurate and safe. Taking into account the amount of brain and target shift observed in 30% of the procedures in this series, the dynamic accuracy of near real time MR imaging is not surpassed by any other system. The combination of the snapper-stereoguide and the OIMR was found to be a very helpful alternative to all currently used direct and indirect, frame-based and frameless systems.

847 Experience with Intraoperative Magnetic Resonance Imaging at 1.5 Tesla: 183 Cases

INTRODUCTION: An intraoperative MR imaging system, based on a moving, 1.5-tesla magnet, has been developed for neurosurgery. The high magnetic field allows the rapid acquisition of a variety of high-resolution MR sequences (i.e., T1, T2, MRA, EPI) during a surgical procedure. Intrusion upon neurosurgical techniques and equipment is minimized as the magnet is removed from the surgical field during operation. The data acquired during the development and application of this system has demonstrated its value. METHODS: The mobile MR system has been used to assist 176 craniotomies and 7 spinal procedures on patients harboring the spectrum of neurosurgical cranial and cervical disease. Lesions include glioma, meningioma, schwannoma, craniopharyngioma, AVM, cavernoma, mesial temporal sclerosis, cord tumor, etc. RESULTS: The value and effectiveness of this system was particularly evident in three patient groups. Among patients with pituitary adenoma intraoperative images showed unexpected residual tumor in 12 (67%) of 18 patients. In 9...

Enhanced CAS in head and neck-surgery: evaluation of intraoperative data modality iMRI and sonography

Purpose: Computer-assisted surgical procedures are well established in head/neck- and neurosurgery. Most systems are based on preoperative CT or MR data. To visualize the surgical change and re-registration, there is a need for intraoperative imaging. Currently, only few imaging methods are available to supply up-to-date information on the surgical progress, e.g., inter-/intraoperative MRI, interoperative CT, and sonography/ultrasound. The purpose of this study is to compare procedures and algorithms for intraoperative co-registration of iMRI and sonography in head/neck- and neurosurgery. Methods: Intraoperative imaging was performed by interventional MR (GE Signa SP) and high-resolution ultrasound (Siemens Sienna). iMRI: Localite Navigator Software (enhanced CAS) allows integration of preoperative data to intraoperative imaging of MR, fMR and CT. The co-registration was based on fiducial markers. The implementation was designed as a multimode real-time navigation system supplying images of bony structures/contours (derived from CT data) fused into real-time MR images. A total of 10 markers (three forehead, three temporal scalp, three mastoid, and one occipital scalp) were used in this study to define reproducible fixation points. Sonography: Based on neuronal networks, a recognize-algorithm for co-registration was developed using sonography data sets of the neck. Results: The statistical point-to-point accuracy (marker difference) of co-registration in the open MR was determined to be 1.2±0.1 mm. The co-registration CT preop and iMRI are reliable and nowadays established in selected surgical procedures of the skull base, e.g., biopsy of the petroclival region. The system yields a significantly better image quality and higher repetition rate than the standard real-time images. Typical for any marker-based registration, the matching accuracy for the registered data sets depends on the accuracy of locating the markers in the respective images, and the inherent displacement of the fiducial markers. The markerless co-registration Sono preop/Sono intraop based on neuronal networks is still less reliable with a positive recognition rate of 46/51 of structures with a maximal volume of 2.110 cm 3. Recognized structures can be used for co-registration with different data modalities, e.g., MR, CT or for single-modality navigation. Conclusions: Both interventional MRI as well as sonography allows intraoperative data update. The marker-based co-registration CT preop/iMRI is still more reliable than Sono preop/Sono intraop based on neuronal networks. Further developments tend towards the improvement of mutual information algorithm and marker-like landmarks to improve the recognition rate of integrated sonography. Low costs and less surgical tools expenditure are the advantages of sonography, and it will be a serious possibility for intraoperative CAS-update. Otherwise, the study demonstrates the possibility of combining intraoperative MR and sonography with other modalities for enhanced CAS in ORL and neurosurgery.

Postoperative fluid-attenuated inversion recovery MR imaging of cerebral gliomas: initial results.

Fluid-attenuated inversion-recovery (FLAIR) imaging has shown to be a valuable imaging modality in the assessment of intra-axial brain tumors; however, no data are available about the role of this technique in the clinically important postoperative stage. The purpose of this study was to evaluate the diagnostic potential of FLAIR MR imaging in residual tumor after surgical resection of cerebral gliomas. Fifteen patients with residual cerebral gliomas were examined within the first 18 days after partial surgical resection of cerebral gliomas. The imaging protocol included T1-weighted spin echo, T2- and proton-density-weighted fast spin echo, and FLAIR imaging with identical slice parameters. T1 and FLAIR were repeated after contrast media application. Detection and delineation of residual tumor were the primary parameters of the image analysis. Additionally, the influence of image artifacts on the image interpretation was assessed. On FLAIR images residual signal abnormalities at the border of the resection cavities were observed in all patients, whereas T2- and T1-weighted images present residual abnormalities in 13 of 15 and 10 of 15 patients, respectively. The FLAIR imaging was found to be superior to conventional imaging sequences in the delineation of these changes and comparable to contrast enhanced T1-weighted imaging in the delineation of residual enhancing lesions. Because of protein cell components and blood byproducts within the resection cavity, FLAIR imaging was unable to suppress the cerebrospinal fluid (CSF) in 4 patients. After the decomposition of proteins and blood, CSF could again be completely suppressed and residual or recurrent tumors were clearly identified. Our preliminary study has shown that FLAIR may be a valuable diagnostic modality in the early postoperative MR imaging after resection of cerebral gliomas due to its better delineation of residual pathologic signal at the border of the resection cavity. It should therefore be integrated into the early and/or intraoperative MR imaging protocol.

Intra-operative MR guidance during trans-sphenoidal pituitary resection: Preliminary results

The use of intra-operative MR image guidance has the potential to improve the precision, extent, and safety of trans-sphenoidal pituitary resections. The trans-sphenoidal approach to pituitary surgery has been performed for some time (1--3). Until now these surgeries have relied on direct visualization without the aid of image guidance. An open-bore configuration 0.5T SIGNA SP MR system (GE Medical Systems, Milwaukee, Wisconsin) has been used to provide image guidance for seventeen trans-sphenoidal pituitary adenoma resections (4). The intra-operative MRI system allowed the radiologist to successfully direct the surgeon toward the sella turcica while avoiding the cavernous sinus, optic chiasm and other critical structures. Imaging performed during the surgery monitored the extent of resection and allowed for removal of tumor beyond the surgeon's view in seven cases. Dynamic MR imaging was used to distinguish residual tumor from normal gland and postoperative changes, permitting more precise tumor localization. A heme-sensitive long TE gradient echo sequence was used to find the presence of hemorrhagic debris. All patients tolerated the procedure well without significant complications. J. Magn. Reson. Imaging 2001;13:136-141.

Three-Dimensional Optical Flow Method for Measurement of Volumetric Brain Deformation from Intraoperative MR Images

A three-dimensional optical flow method to measure volumetric brain deformation from sequential intraoperative MR images and preliminary clinical results from five cases are reported. Intraoperative MR images were scanned before and after dura opening, twice during tumor resection, and immediately after dura closure. The maximum cortical surface shift measured was 11 mm and subsurface shift was 4 mm. The computed deformation field was most satisfactory when the skin was segmented and removed from the images before the optical flow computation.

Model-Updated Image-Guided Neurosurgery: Preliminary Analysis Using Intraoperative MR.

In this paper, initial clinical data from an intraoperative MR system are compared to calculations made by a three-dimensional finite element model of brain deformation. The preoperative and intraoperative MR data was collected on a patient undergoing a resection of an astrocytoma, grade 3 with non-enhancing and enhancing regions. The image volumes were co-registered and cortical displacements as well as subsurface structure movements were measured retrospectively. These data were then compared to model predictions undergoing intraoperative conditions of gravity and simulated tumor decompression. Computed results demonstrate that gravity and decompression effects account for approximately 40% and 30%, respectively, totaling a 70% recovery of shifting structures with the model. The results also suggest that a non-uniform decompressive stress distribution may be present during tumor resection. Based on this preliminary experience, model predictions constrained by intraoperative surface data appear to be a promising avenue for correcting brain shift during surgery. However, additional clinical cases where volumetric intraoperative MR data is available are needed to improve the understanding of tissue mechanics during resection.

New developments in pituitary surgical techniques.

Despite ongoing advances in the pharmacological, radiotherapeutic and endocrine management of pituitary tumours, surgery remains the therapy of choice for the large majority of these lesions. As surgical efficacy is now being judged by more rigorous technical standards and by more stringent endocrine criteria than ever before, such scrutiny has only served to reinforce the fundamental role of surgery in pituitary tumour management. With the revival of the trans-sphenoidal approach, together with its ongoing technical evolution during the past three decades, pituitary tumours have emerged as eminently treatable lesions, with trans-sphenoidal microsurgery affording long-term, high-quality survival in many patients. Pituitary surgery is, however, not without limitation or liability. Even in experienced hands, endocrine and/or oncological remission is not uniformly achieved. Moreover, of those patients in whom such 'cures' can be induced, the durability of the response is not absolute, as tumour recurrence will continue to threaten a small but significant proportion of patients over time. Finally, and notwithstanding the fact that trans-sphenoidal surgery remains one of the safest procedures in contemporary, neurosurgical practice, complications can occur, some of which can be associated with significant morbidity and, on rare occasions, mortality. Clearly, there continue to be areas in need of improvement, and it has been in response to these limitations of contemporary pituitary surgery that neurosurgeons have sought to develop alternative strategies to improve surgical outcome. As a result, a variety of important innovations have been introduced during recent years. Among others, the most important and effective of these have been the application of neuronavigational techniques, trans-sphenoidal endoscopy and intraoperative MR resection control to the standard trans-sphenoidal approach to pituitary tumours. Whereas some advances are conceptual and others are technical, all are helping to push the limits of pituitary surgery to new frontiers of efficacy and safety. In this chapter, the current state of the art of pituitary surgery is reviewed along with those important new developments that, in the foreseeable future, hope to improve the quality of surgical care available to the pituitary tumour patient.

MR imaging-guided interventions

The spectrum of MR imaging-guided interventions includes biopsies, thermal ablation modalities, vascular applications, MR endoscopy and intraoperative MR imaging. The concept of MR guidance is based on the excellent morphologic and functional imaging achieved by MR. The most important recently published experimental and clinical results are discussed. In the future, MR imaging will play an important role in interventional radiology, minimal invasive therapy and guidance of surgical procedures.

MR imaging of the brain: tumors.

The radiologic modality that most likely provides the imaging information needed in a patient suspected of having a brain tumor is MR imaging. A brain tumor can be reliably ruled out if the MR examination is performed properly and experts interpret the results as negative. If there is a tumor, however, its exact location and topography must be determined. Important for therapy and prognosis are also tumor properties such as histologic type and grade, as well as effects on adjacent brain structures. Although potentially a noninvasive method of in vivo neuropathology, MR is still far from being sufficiently specific, as dissimilar lesions may look the same despite the use of refined imaging protocols. The evolution of MR imaging continues, however, making further methodologic improvement likely. Presently, advanced methods, such as diffusion- and perfusion-weighted MR imaging, functional MR imaging, neuronavigation based on MR imaging data, and the use of MR imaging during surgery (intraoperative MR imaging), influence the way patients are treated. Likewise, follow-up imaging (monitoring) of tumor patients by MR has become more effective, and experience has shown how to distinguish reactive changes from recurrent tumor. In the future, MR imaging may gain importance in the development of novel therapeutic concepts.

Laparoscopic surgery in a 0.5-t interventional magnetic resonance unit.

Intraoperative imaging using magnetic resonance imaging (MRI) is now possible in interventional MR (IMR) units. Magnetic resonance imaging has potential advantages over other methods used to guide surgery. These advantages include visualization of structures deep to the two-dimensional endoscopic image and clarification of surgical anatomy. This study investigates the feasibility of laparoscopic surgery with intraoperative imaging within an IMR unit. The procedures were performed in a 0. 5-T General Electric IMR scanner. Surgical ergonomics and intraoperative imaging were investigated by performing 10 laparoscopic cholecystectomies on porcine livers in a simulator using magnet-safe laparoscopic instruments and an ultrasonic scalpel for dissection. Intraoperative MR cholangiography (MRC) was performed using T2-weighted fast-spin-echo (FSE) and single-shot fast-spin-echo (ssFSE) techniques with maximal intensity projection (MIP) reconstruction. Two laparoscopic cholecystectomies then were performed on human patients with intraoperative MRC using similar techniques. The simulated procedures allowed the development of surgical techniques appropriate to this environment. Both FSE and ssFSE produced reasonable quality intraoperative images. Both patient procedures were performed without complication. The FSE imaging was of poor quality. However, ssFSE produced intraoperative images of the gallbladder with partial visualization of the extrahepatic biliary tree. Laparoscopic surgery in an IMR unit is technically possible. Currently, intraoperative MRC is difficult, and FSE imaging is very subject to movement artifact. However, the faster ssFSE, with further development, may be a useful technique for intraoperative imaging of the biliary tree during MR-guided surgery.