Biomedical subjects

C R Wirtz

Publications and source records attributed to C R Wirtz.

At least 19 recordsLinked to original sources

PubMed2002

[A computer system for planning and carrying out neurosurgical interventions].

Neurosurgical interventions have to be planned carefully using different sources of information like anatomical MR images, segmented brain structures, functional data (EEG, MEG, fMRI) and atlas information. We developed a 3D planning system that incorporates this important data. The planning procedure is performed by the neurosurgeon in less than 15 minutes. The results of the planning phase, i.e. an optimal trajectory, localizations of the electrical sources and information about the brain tissue can be used intraoperatively. Therefore the planning system is connected with a navigation system. The simultaneous visualization of the planning information and the actual position of the instrument during the surgical procedure is extremely valuable for the outcome and quality of the intervention.

Brain Neoplasms↗

PubMed2001

Low-field interventional MRI in neurosurgery: finding the right dose of contrast medium.

MRI is increasingly being used as an interventional tool in neurosurgery. The field strength of "intraoperative" MR systems is usually lower than that of imagers commonly used for diagnostic purposes. However, lesion enhancement and apparent lesion extent depend on field strength. The aim of this study was to compare the contrast between intracranial, contrast-enhancing space-occupying lesions and the surrounding white matter obtained with low-field (0.2 T) and high-field (1.5 T) MR imaging and to find the contrast medium dosage for low-field MRI that produces the same lesion-to-white-matter contrast as the one obtained with high-field MRI after the administration of a standard dose of the contrast medium. A total of 38 patients with intracranial metastases or high-grade glioma were enrolled in this study. T1-weighted spin-echo sequences were acquired. High-field (1.5 T) studies were performed after the i.v. administration of 0.1 mmol gadolinium-DTPA/kg body weight. For low-field MRI (0.2 T) a dose escalation technique was used. T1-weighted sequences were repeated after each of three i. v. injections of 0.1 mmol gadolinium-DTPA/kg body weight. Thus, at the low-field examinations three T1-weighted sequences with a contrast medium dosage of 0.1, 0.2 and 0.3 mmol gadolinium-DTPA/kg body weight were obtained. Lesion-to-white-matter contrasts were calculated and compared. The average lesion-to-white-matter contrast obtained with high-field MR examinations was 1.63 (standard deviation 0.32). In the low-field MR examinations the average lesion-to-white-matter contrast was 1.34 (0.2) after a single dose, 1.57 (0.2) after a double dose, and 1.71 (.19) after a triple dose of contrast medium. The lesion-to-white-matter contrast of the high-field MR examination after a single dose of contrast medium was significantly higher than that of the low-field study after a single dose (P < 0.0001), but did not differ significantly from the low-field studies after a double (P = 0.28) or a triple dose (P = 0.17) of contrast medium. In a series of patients with contrast-enhancing space occupying brain lesions low-field MRI (0.2 T) after a double dose of contrast medium yielded the same lesion-to-white-matter contrasts as high-field MRI (1.5 T) after a standard dose. This is an important finding to avoid errors in intraoperative MRI due to the immanently lower degree of lesion enhancement in low-field MR imaging.

Adult↗

PubMed2001

Initial experience with an ultrasound-integrated single-RACK neuronavigation system.

A prototype ultrasound-integrated neuronavigation system was tested in 34 operations as regards image quality, stability, and handling during daily use in the operating theatre. The system consists of a high-end ultrasound scanner, a navigation computer, and an active optical positioning and digitiser system, all integrated in a single rack. An Ethernet interface between the two hardware devices enables digital data transfer between the ultrasound scanner and the navigation device without loss of image quality. The integration of an ultrasound scanner and a navigation device offers the opportunity of navigating directly to an intracranial or intraspinal lesion using intra-operative 3D ultrasound images. The brainshift problem is thus avoided. The ability to directly compare MR images and 3D ultrasound simplifies the interpretation of ultrasound images. The single-rack solution is an advantage in times of restricted space in the operating theatre caused by the increasing volume of technical equipment needed for a neurosurgical operation. In 30 cases the prototype system showed good reliability. In four cases the navigation system failed during the operation; however, the capacity of the ultrasound scanner was still available as a stand-alone function. With the single-rack concept, the flexibility of the system is high and the complete device can easily be moved from one operating theatre to another.

Equipment Design↗

PubMed2001

Monocrystalline iron oxide nanoparticles: possible solution to the problem of surgically induced intracranial contrast enhancement in intraoperative MR imaging.

BACKGROUND AND PURPOSE: Intraoperative MR imaging is increasingly being used to control the extent of surgical resection; however, surgical manipulation itself causes intracranial contrast enhancement, which is a source of error. Our purpose was to investigate the potential of monocrystalline iron oxide nanoparticles (MIONs) to solve this problem in an animal model. METHODS: In male Wistar rats, surgical lesions of the brain were produced. The animals underwent MR examination immediately afterward. In the first group, a paramagnetic contrast agent was administered, whereas the second group of animals received MIONs 1 day before surgery. In a third group of animals, malignant glioma cells were stereotactically implanted in the caudoputamen. Two weeks later, MIONs were IV injected and the tumor was (partially) resected. Immediately after resection, MR examination was performed to determine the extent of residual tumor. RESULTS: Surgically induced intracranial contrast enhancement was seen in all animals in which a paramagnetic contrast agent was used. Conversely, when MIONs had been injected, no signal changes that could be confused with residual tumor were detected. In the animals that had undergone (partial) resection of experimental gliomas, MR assessment of residual tumor was possible without any interfering surgically induced phenomena. CONCLUSION: Because MIONs are stored in malignant brain tumor cells longer than they circulate in the blood, their use offers a promising strategy to avoid surgically induced intracranial contrast enhancement, which is known to be a potential source of error in intraoperative MR imaging.

Animals↗

PubMed2000

An integrated head-holder/coil for intraoperative MRI in open neurosurgery.

With the invention of "open" magnetic resonance imaging (MRI) systems, access to the patient is possible during the imaging procedure. An important application of these systems is intraoperative MRI to control the extent of resection during tumor surgery. Up to now flexible surface coils wrapped around, or placed at each side of the head, were used for imaging. These flexible coils have several disadvantages such as unreliability, interindividual problems, difficult handling, poor hygienic properties, and often unsatisfactory or inhomogeneous image quality. To solve most of these problems, an MR-compatible head-holder in combination with an integrated surface coil for use in a 0.2 T C-shaped magnet was developed. Forty-eight patients with known cranial tumors underwent MRI intraoperatively. In 32 patients (67%), residual tumor was found, and additional surgical resection was performed. The integrated head-holder/coil is a safe and practical tool for intraoperative MRI, providing efficient and reliable resection control during neurosurgical procedures.

Brain↗

PubMed2000

Interventional MRI-guided brain biopsies using inductively coupled surface coils.

The technical realization of inductively coupled surface coils for interventional MR-guided procedures, and the application to brain biopsies in a 0.2 T magnet is described. The advantages compared to standard coils are discussed, and the results of 26 biopsies on eight different neuropathologic diagnoses from varying locations within the brain are presented. Initial experience shows that inductively coupled coils can offer an increased number of indications for interventional procedures in the brain, easier handling of sterility, and often a better access for the surgeon, compared to the use of standard MR head coils.

Biopsy, Needle↗

PubMed2000

[Virtual reality in neurosurgery].

DEFINITION: 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.

Endoscopes↗

PubMed2000

The benefit of neuronavigation for neurosurgery analyzed by its impact on glioblastoma surgery.

Neuronavigation, today a routine method in neurosurgery, has not yet been systematically assessed in direct comparison with conventional microsurgical techniques. The aim of the present study was the direct comparison of the impact of neuronavigation on glioblastoma surgery regarding time consumption, extent of tumor removal and survival. For each of 52 patients operated for primary glioblastoma with neuronavigation, a patient operated on without navigation was matched. Completeness of tumor resection, including volumetric analysis, was examined by early post-operative MRI. Operating and survival times were obtained for all patients. At a rate of 86.5%, surgeons' opinions about neuronavigation were positive. Operating times were identical in the two groups, while preparation times were 30.4 min longer with navigation. Radiological radicality was achieved in 31% of navigation cases vs. 19% in conventional operations. The absolute and relative residual tumor volumes were significantly lower with neuronavigation. Radical tumor resection was associated with a highly significant prolongation in survival (median 18.3 vs. 10.3 months, p < 0.0001). Survival was longer in patients operated on using neuronavigation (median 13.4 vs. 11.1 months). Neuronavigation increases radicality in glioblastoma resection without prolonging operating time. Regarding the problem of brain shift, neuronavigation should be optimized by intraoperative real-time imaging.

Adult↗

PubMed2000

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.

Adolescent↗

PubMed1999

Surgically induced intracranial contrast enhancement: potential source of diagnostic error in intraoperative MR imaging.

BACKGROUND AND PURPOSE: Intraoperative MR imaging is being used increasingly during neurosurgical interventions. The aim of this study was to describe and classify different forms of surgically induced intracranial contrast enhancement observed during intraoperative MR examinations. METHODS: A total of 51 intraoperative MR examinations were performed to assess the extent of brain tumor removal. The intraoperative MR results (T1-weighted images, unenhanced and obtained serially after the IV administration of paramagnetic contrast material) were compared with preoperative and early postoperative MR findings. Animal experiments were conducted to obtain further evidence of the mechanism of surgically induced contrast enhancement. RESULTS: Four different types of surgically induced contrast enhancement were found: meningeal enhancement, increased enhancement of the choroid plexus, delayed enhancement at the resection margins, and immediate intraparenchymal contrast enhancement. The types of surgically induced contrast enhancement differ regarding their location, configuration, and time course. Their potential to be confused with contrast-enhancing, residual tumor also varies. Three of the four types of surgically induced contrast enhancement were reproducible in an animal model. CONCLUSION: Surgically induced contrast enhancement is a potential source of error in intraoperative MR imaging. Careful analysis of the location, configuration, and time course of intraoperatively observed intracranial enhancement is critical to avoid confusing surgically induced contrast enhancement with contrast-enhancing, residual tumor.

Animals↗

PubMed1999

Intraoperative MR imaging increases the extent of tumor resection in patients with high-grade gliomas.

BACKGROUND AND PURPOSE: MR is being used increasingly as an intraoperative imaging technique. The purpose of this study was to test the hypothesis that intraoperative MR imaging increases the extent of tumor resection, thus improving surgical results in patients with high-grade gliomas. METHODS: Thirty-eight patients with intracranial high-grade gliomas underwent 41 operations. Using a neuronavigation system, tumors were resected in all patients to the point at which the neurosurgeon would have terminated the operation because he thought that all enhancing tumor had been removed. Intraoperative MR imaging (0.2 T) was performed, and surgery, if necessary and feasible, was continued. All patients underwent early postoperative MR imaging (1.5 T). By comparing the proportions of patients in whom complete resection of all enhancing tumor was shown by intraoperative and early postoperative MR imaging, respectively, the impact of intraoperative MR imaging on surgery was determined. RESULTS: Intraoperative MR imaging showed residual enhancing tumor in 22 cases (53.7%). In 15 patients (36.6%), no residual tumor was seen, whereas the results of the remaining four intraoperative MR examinations (9.7%) were inconclusive. In 17 of the 22 cases in which residual tumor was seen, surgery was continued. Early postoperative MR imaging showed residual tumor in eight patients (19.5%) and no residual tumor in 31 cases (75.6%); findings were uncertain in two patients (4.9%). The difference in the proportion of "complete removals" was statistically highly significant (P = .0004). CONCLUSION: Intraoperative MR imaging significantly increases the rate of complete tumor removal. The rate of complete removal of all enhancing tumor parts was only 36.6% when neuronavigation alone was used, which suggests the benefits of intraoperative imaging.

Adult↗

PubMed1998

[Neuronavigation. Methods and prospects].

With the recent developments in computer technology and the improvements in modern neuroimaging, frame-based stereotactic guidance for open microsurgical procedures has been increasingly replaced by neuronavigation, also called frameless stereotaxy. It allows transfer of individual patientís images onto the operative field to assist the neurosurgeon intraoperatively in defining the tumor margins or identifying functionally important brain areas. The different localization techniques employed are articulated position-sensing arms, infrared or ultrasound systems working with the principle of satellite navigation and robotic systems integrated with the operating microscope. In 200 operations performed with different systems (arm-based, robotic and infrared) the method proved to be helpful, enabling fewer invasive procedures to be performed. With a mean deviation of 2.87 +/- 1.9 mm for intraoperative localization, the accuracy was only slightly worse than in frame-based stereotaxy with deviations below 2 mm. Neuronavigation was most helpful for operations on deeply seated lesions, skull-base tumors and lesions in brain areas with high functionality. The major disadvantage is the use of preoperative data for navigation, leading to inaccuracies when anatomical structures are altered during the operation by resection of tumors or shift of intracranial soft tissue. Intraoperative magnetic resonance imaging (MRI) might be a solution for this problem. With the method of intraoperative MRI developed in our department it has already been possible to update neuronavigation with images reflecting intraoperative changes in anatomy. Therefore, neuronavigation is definitely a method with growing importance in operative routine, and it will also spread into other surgical specialties.

Brain Diseases↗

PubMed1998

[Intraoperative magnetic resonance tomography for control of extent of neurosurgical operations].

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.

Astrocytoma↗

PubMed1998

Preoperative planning and intraoperative navigation in skull base surgery.

Experience with the commercially available, 3-D navigation systems Viewing Wand (ISG, Mississauga, Ontario, Canada) and SPOCS (Aesculap, Germany) in skull base surgery is presented. Having meanwhile been tested in over 60 clinical trials, the systems achieved an accuracy of < or = 2.7 mm which, at the moment, we deem sufficiently acceptable to proceed with their clinical evaluation. There was no difference in intraoperative accuracy between the mechanical and the optical navigation systems. The systems proved to be very helpful in identifying the extent of the tumours and in visualizing the proximity of vital structures. 3-D-planning, simulation and intraoperative navigation especially facilitates surgery in anatomically complicated situations, without risk of damaging neighbouring structures. The SPOCS (Surgical Planning and Orientation Computer System) revealed a considerably improved flexibility in handling and a better integration into the surgical procedure in comparison with the relatively inflexible and space-demanding Viewing Wand arm. Especially, the 'offset' function of the SPOCS offers the possibility of a virtual elongation of the instrument and thus, in combination with the on-line visualization of the corresponding images, of a 'look ahead' operation. By using computer-assisted simulation and navigation systems, we can expect quality improvement and risk reduction. More extensive and radical interventions seem possible.

Computer Simulation↗

PubMed1998

Modified Headholder and operating table for intra-operative MRI in neurosurgery.

In order to facilitate intra-operative use of magnetic resonance imaging (MRI) in neurosurgery an MRI-compatible headholder was developed and adapted to a modified MR-couch simultaneously serving as tabletop for the operating table. To allow shock-free transport into the scanner the wheels of the operating table were replaced by an air cushion mechanism. In 75 procedures the system proved to be reliable and safe. Image quality was not impaired by the fixation device. With growing routine the transfer became straightforward, requiring approximately 10 min. Intra-operative MRI is thus made possible with minimal changes to the standard surgical environment. Its benefit however, still remains to be critically investigated.

Equipment Design↗

PubMed1998

Neuronavigation--first experiences with three different commercially available systems.

Growing interest in neuronavigation also referred to as frameless stereotaxy has led to the development of various navigational devices employing different localization methods. In 152 procedures the authors have used neuronavigation. Cases included 89 intracranial- and 26 skull base tumours, 9 biopsies, 21 vascular and 7 functional procedures on 144 patients since July 1993. In 75 cases the lesions were located in eloquent areas. In 82% (124) MRI, 13% (18) CT and 5% (8) both imaging methods were employed. Three neuronavigational devices with different localization methods were used for the procedures. The Viewing Wand (VW, ISG, Canada), a multijointed arm was used in 101 procedures. In 15 cases the SPOCS (Aesculap, Germany) consisting of cameras detecting infrared light from LED's mounted on instruments and in 51 cases the microscope-integrated MKM (ZEISS, Germany) was investigated, 15 times two systems were used simultaneously. Mean time necessary for preoperative registration was 23 +/- 13 min (VW), 21 +/- 16 min (SPOCS) and 27 +/- 22 min (MKM) respectively. The mean accuracy of registration measured as RMS was 2.9 +/- 1.2 mm (VW), 3.3 +/- 0.9 mm (SPOCS) and 3.1 +/- 1.0 (MKM) respectively. Regarding intraoperative handling the VW was found to be a robust but sometimes bulky and hindering device whereas the SPOCS was more flexible but with the need of unobstructed visibility between cameras and pointers. The MKM without these restrictions required training to get used to handling.

Adolescent↗

PubMed1997

Image guided excision of a ruptured feeding artery "pedicle aneurysm" associated with an arteriovenous malformation in a child: case report.

Excision of a ruptured aneurysm located at a lenticulostriate feeding artery associated with an arteriovenous malformation was performed using image guided neuronavigation in an 8-year-old child. The management of this lesion, which is rare in childhood, demonstrates the potential of combining frameless stereotaxy for precise target approach with conventional open microneurosurgery to minimize morbidity. Because of the unavoidable shifting of the brain that occurs during surgery, a catheter pointing towards the dome of the aneurysm was placed using image guidance prior to insertion of spatulae.

Aneurysm, Ruptured↗

PubMed1997

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.

Adult↗