Andreas Staubert

Intraoperative diagnostic and interventional magnetic resonance imaging in neurosurgery

OBJECTIVE The benefits of intraoperative magnetic resonance (MR) imaging for diagnostic and therapeutic measures are as follows: 1) intraoperative update of data sets for navigational systems, 2) intraoperative resection control of brain tumors, and 3) frameless and frame-based on-line MR-guided interventions. The concept of an intraoperative MR scanner in the sterile environment of operating theater is presented, and its advantages, disadvantages, and limitations are discussed. METHODS A 0.2-tesla magnet (Magnetom Open; Siemens AG, Erlangen, Germany) inside a radiofrequency cabin with a radiofrequency-shielded sliding door was installed adjacent to one of the operating theaters. A specially designed patient transport system carried the patient in a fixed position on an air cushion to the scanner and back to the surgeon. RESULTS In a series of 27 patients, intraoperative resection control was performed in 13 cases, with intraoperative reregistration in 4 cases. Biopsies, cyst aspirations, and catheter placements (mainly frameless) were performed under direct MR visualization with fast image sequences. The MR-compatible equipment and the patient transport system are safe and reliable. CONCLUSION Intraoperative MR imaging is a safe and successful tool for surgical resection control and is clearly superior to computed tomography. Intraoperative acquisition of data sets eliminates the problem of brain shift in conventional navigational systems. Finally, on-line MR-guided interventional procedures can be performed easily with this setting. As with all MR systems, individual testing with phantoms, application of correction programs, and determination of the optimal amount of contrast media are absolute prerequisites to guarantee patient safety and surgical success.

Clinical evaluation and follow-up results for intraoperative magnetic resonance imaging in neurosurgery.

OBJECTIVE The use of intraoperative magnetic resonance imaging (MRI) in neurosurgery has increased rapidly, and a variety of concepts have recently been presented. Although the feasibility of the procedure has been demonstrated repeatedly, no conclusive analysis of its effects on the surgical procedures, the extent of tumor removal, and outcomes, or its possible problems, has been performed. METHODS Of 242 operations performed with intraoperative MRI, 97 procedures for supratentorial glioma treatment were analyzed with respect to intraoperative imaging results and postoperative outcomes. Analysis of the images included assessment of imaging artifacts, image quality, and extent of tumor removal. Patients were monitored to determine radiological progression, survival times, postoperative complications, and morbidity rates. RESULTS No intraoperative complications related to the imaging procedure were observed. Image quality was good or fair in 85.5% of the cases. Different types of surgically induced imaging changes could be identified. In 56 cases, resection was continued using navigation with intraoperative MRI data sets (rereferencing accuracy, 0.9 mm). For high-grade gliomas, the percentage of cases in which residual tumor was identified by MRI could be significantly reduced from 62% intraoperatively to 33% postoperatively, which was paralleled by a significant increase in survival times for patients without residual tumor. Complication and morbidity rates were within the ranges reported for other studies. CONCLUSION Intraoperative MRI is safe and allows reliable updating of neuronavigational data, with compensation for brain shifting. Surgically induced imaging changes, which have been identified as a possible problem with intraoperative MRI in general, necessitated comparisons with preoperative scans and require future attention. The extent of tumor removal and survival times were increased significantly. Overall, patients seemed to benefit from the method.

Intraoperative Magnetic Resonance Imaging to Update Interactive Navigation in Neurosurgery: Method and Preliminary Experience

We report on the first successful intraoperative update of interactive image guidance based on an intraoperatively acquired magnetic resonance imaging (MRI) date set. To date, intraoperative imaging methods such as ultrasound, computerized tomography (CT), or MRI have not been successfully used to update interactive navigation. We developed a method of imaging patients intraoperatively with the surgical field exposed in an MRI scanner (Magnetom Open; Siemens Corp., Erlangen, Germany). In 12 patients, intraoperatively acquired 3D data sets were used for successful recalibration of neuronavigation, accounting for any anatomical changes caused by surgical manipulations. The MKM Microscope (Zeiss Corp., Oberkochen, Germany) was used as navigational system. With implantable fiducial markers, an accuracy of 0.84 +/- 0.4 mm for intraoperative reregistration was achieved. Residual tumor detected on MRI was consequently resected using navigation with the intraoperative data. No adverse effects were observed from intraoperative imaging or the use of navigation with intraoperative images, demonstrating the feasibility of recalibrating navigation with intraoperative MRI.

Image-guided neurosurgery with intraoperative MRI : update of frameless stereotaxy and radicality control

Intraoperative shifts and resulting inaccuracies have been a concern in frame based and frameless stereotactically guided interventions, particularly in open microsurgical procedures. Trying to solve this problem, we developed a method to perform intraoperative MRI (0.2 tesla, Magnetom Open) and use intraoperatively acquired data sets to update neuronavigation. In 21 patients, intraoperative images could be used to reference navigation (mean accuracy of 0.83 +/- 0.31 mm). The operation was continued in 10 cases to resect detected tumor remnants using navigation, leaving 4 patients (19%) with residual tumor postoperatively. We showed that update of frameless stereotaxy to compensate for brain shift is feasible and might increase the number of cases where radiologically complete resection can be achieved.

Intraoperative MRI to control the extent of brain tumor surgery

Purpose: The main aim of our study was to find out whether the combined use of neuronavigation and intraoperative MRI can increase the rate of “complete tumor removal”. The second aim was to characterize the different forms of surgically induced enhancement in order to differentiate them from residual tumor. Materials and methods: Surgery was performed in 18 patients with high-grade glioma. Using a neuronavigation device, the surgeons operated up to the point where they would otherwise have terminated surgery. Intraoperative MRI was then performed to determine whether residual enhancing had been left behind and to update the neuronavigation device. If necessary, feasible surgery was continued. On days 1–3 after surgery early postoperative MRI (1.5 T) was performed. The proportion of patients in whom the enhancing tumor was completely removed was compared with a series of 60 patients with glioblastoma multiforme, who had been operated on using neither neuronavigation nor intraoperative MRI . We also looked for and characterized different types of surgically induced enhancement. Results: Intraoperative MRI definitely showed residual tumor in 6 of the 18 patients and resulted in ambiguous findings in 3 patients. In 7 patients surgery was continued. Early postoperative MRI showed residual tumor in 3 patients and resulted in uncertain findings in 2 patients. The rate of patients in whom complete removal of enhancing tumor could be achieved was 50 % at the time of the intraoperative MR examination and 72 % at the time of the early postoperative MR control. The difference in proportion of patients with “complete tumor removal” between the groups who had been operated on using neuronavigation (NN) and intraoperative MRI (ioMRI) and those who had been operated on using only modern neurosurgical techniques except NN and ioMRI was statistically highly significant (Fisher exact test; P = 0.008). Four different types of surgically induced contrast enhancement were observed. These phenomena carry different confounding potentials with residual tumor. Conclusion: Our preliminary experience with intraoperative MRI in patients with enhancing intraaxial tumors is encouraging. Combined use of neuronavigation and intraoperative MRI was able to increase the proportion of patients in whom complete removal of the enhancing parts of the tumor was achieved. Surgically induced enhancement requires careful analysis of the intraoperative MRI in order not to confuse it with residual tumor.ZusammenfassungAuch für erfahrene Neurochirurgen ist es außerordentlich schwierig bis unmöglich, intraoperativ die Grenze eines hirneigenen Tumors zu erkennen und entsprechend dieser Grenze eine „Totalentfernung“ des Tumors durchzuführen. Verschiedene Studien zeigten die Unzuverlässigkeit der intraoperativen Einschätzung der Operationsradikalität. Während intraoperative CT-Kontrollen und intraoperative Ultraschallkontrollen bereits seit längerem eingesetzt werden, wurde der Magnetresonanztomographie – der bildgebenden Methode mit der höchsten Weichteilauflösung – dieser Anwendungsbereich erst kürzlich durch die Entwicklung „offener“ MR-Systeme erschlossen. Im Operationstrakt der neurochirurgischen Klinik der Universität Heidelberg wurde ein offener MR-Tomograph installiert, an dem neben Biopsieentnahmen und neurochirurgischen Interventionen auch intraoperative MR-Kontrollen der Operationsradikalität durchgeführt werden. Unsere ersten Erfahrungen deuten darauf hin, daß durch den Einsatz intraoperativer MRT die Operationsradikalität neurochirurgischer Eingriffe gesteigert werden kann. Allerdings war bei allen Patienten durch die chirurgische Manipulation selbst verursachtes Kontrastmittelenhancement nachweisbar, das z. T. Verwechslungspotential mit Resttumor besaß.

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.

Virtuelle Realität in der Neurochirurgie

ZusammenfassungDefinition: Virtuelle Realität (VR) erlaubt dem Benutzer, in eine dreidimensionale Welt einzutauchen (engl.: to immerse, daher immersive VR) und in dieser virtuellen Welt zu agieren. Damit unterscheidet sich die VR von den bekannten Vorstellungen, z.B. in Computerspielen, wo man aktiv in einer irrealen Welt agiert, oder in Spielfilmen, wo man passiv an einer realen Welt teilnimmt. In der virtuellen Realität agiert man aktiv in einer Welt mit realistisch erscheinenden Elementen, die ihr Erscheinungsbild ändern können und daher „weitgehend unberechenbar” sind. Anwendung: Virtuelle Realität hat den Einzug nicht nur in Spielhallen und die Unterhaltungsindustrie gefunden, sondern auch in industrielle Fertigungsanlagen (Autos, Möbel usw.), militärische Bereiche und die Medizin. Gerade die beiden letzten Bereiche sind eng verknüpft, denn mit dem Begriff Telemedizin verband sich ursprünglich die Idee, im Kriegsfall Operationen an verwundeten Soldaten mit ferngesteuerten Robotern aus sicherem Abstand heraus durchzuführen oder Astronauten von der Erde aus zu behandeln. In der Medizin, speziell in der Neurochirurgie, werden heute bereits virtuelle Methoden zu Ausbildungszwecken, zur Operationsplanung und zu Operationen am virtuellen Patienten eingesetzt.SummaryDefinition: Virtual reality enables users to immerse themselves in a virtual three-dimensional world and to interact in this world. The simulation is different from the kind in computer games, in which the viewer is active but acts in a nonrealistic world, or on the TV screen, where we are passively driven in an active world. In virtual reality elements look realistic, they change their characteristics and have almost real-world unpredictability. Use of virtual reality: Virtual reality is not only implemented in gambling dens and the entertainment industry but also in manufacturing processes (cars, furniture etc.), military applications and medicine. Especially the last two areas are strongly correlated, because telemedicine or telesurgery was originated for military reasons to operate on war victims from a secure distance or to perform surgery on astronauts in an orbiting space station. In medicine and especially neurosurgery virtual-reality methods are used for education, surgical planning and simulation on a virtual patient.

Ein Visualisierungssystem zur Unterstutzung der intraoperativen Resektionskontrolle

Trotz ihrer hohen Leistungsfahigkeit konnen etablierte Navigationstechniken bei neurochirurgischen Eingriffen bestimmte Situationen, beispielsweise den Einsatz bei einer ungunstigen Geometrie der Resektionshohle, nicht meistem. Urn in solchen Problemfallen dennoch eine Radikalitatskontrolle der durchgefuhrten Resektion anhand intraoperativer MR-Volumenscans vomehmen zu konnen, bedarf es erganzender Werkzeuge. In der vorliegenden Arbeit stell en wir ein Softwaretool vor, mit dessen Hilfe intraoperative MR-Aufnahmen oder Ausschnitte derselben schnell und einfach dreidimensional dargestellt werden konnen mit dem Ziel, Resttumorgewebe aufzufinden und die zugehorige Position visuell auf den Patienten ubertragen zu konnen. Das flexible, interaktive System wurde in enger Zusammenarbeit mit den klinisch tatigen Neurochirurgen konzipiert und ist demnach auf deren Bedurfnisse zugeschnitten

Ein computerbasiertes Hirnatlas-System nach Talairach

Computerisierte Hirnatlanten sind ein wertvolles Hilfsmittel und Werkzeug fur viele neurologische Fragestellungen. Die Rechenleistung moderner Computersysteme ermoglicht potentiell eine Vielzahl von Darstellungs- und Interaktionsoptionen, die rechnergestutzte Atlanten gegenuber den konventionellen gedruckten Buchern aufwerten. Wir stellen in dieser Arbeit eine digitale Version des etablierten Stereotaxieatlas’ von Talairach und Tournoux vor. Der Atlas kann auf Datensatze von Patienten abgebildet werden und kann so zur Unterstutzung der neurochirurgischen Operationsplanung dienen. Durch viele Visualisierungsmoglichkeiten und das Angebot von anatomischen und funktionellen Hintergrundinformationen zu einzelnen Strukturen eingnet sich das System auch zur visuellen Erkundung der Hirnanatomie.

Ein digitaler Gehirnatlas

Aufgrund der hohen Genauigkeitsanforderungen bei neurochirurgischen Eingriffen ist eine Operationsplanung unerlaslich. Ein Hilfsmittel in der Planungsphase sind Gehimatlanten, die die Interpretation der praoperativen dreidimensionalen Bilddatensatze der Patienten unterstutzen. Um die unbequeme Handhabung von in Buchform vorliegenden Atlanten zu verbessern, haben wir eine digitale Version des etablierten Stereotaxieatlas’ von Talairach und Toumoux entwickelt, die gegenuber dem gedruckten Original eine Reihe von Vorzugen aufweist. Z.B. kann das computerisierte Atlassystem kann mit funktionellen MR-Aufnahmen gematcht werden. Anhand dieser Eigenschaft soll die Atlasgenauigkeit im Cortexbereich, speziell am motorischen Gyrus praecentralis, evaluiert werden.