A mobile high-field magnetic resonance system for neurosurgery

Intraoperative magnetic resonance imaging to determine the extent of resection of pituitary macroadenomas during transsphenoidal microsurgery

OBJECTIVE

Well-established surgical goals for pituitary macroadenomas include gross total resection for noninvasive tumors and debulking with optic chiasm decompression for invasive tumors. In this report, we examine the safety, reliability, and outcome of intraoperative magnetic resonance imaging (iMRI) used to assess the extent of resection, and thus the achievement of preoperative surgical goals, during transsphenoidal microneurosurgery.

METHODS

Our magnetic resonance operating room contains a Hitachi AIRIS II 0.3-T, vertical-field open magnet (Hitachi Medical Systems America, Inc., Twinsburg, OH). A motorized scanner tabletop moves the patient between the imaging and operative positions. For transsphenoidal surgery, the patient is positioned directly on the scanner tabletop so that the surgical field is located between 1.2 and 1.6 m from the magnet isocenter. At this location, the magnetic field strength is low (<20 G), thus permitting the use of many conventional surgical instruments. Thirty consecutive patients with pituitary macroadenomas underwent tumor resection in our magnetic resonance operating room by use of a standard transsphenoidal approach. After initial resection, the patient was advanced into the scanner for imaging. If residual tumor was demonstrated and deemed surgically accessible, the patient underwent immediate re-exploration.

RESULTS

iMRI was performed successfully in all 30 patients. In one patient, iMRI was used to clarify the significance of hemorrhage from the sellar region and resulted in immediate conversion of the procedure to a craniotomy. In the remaining 29 patients, initial iMRI demonstrated that the endpoint for extent of resection had been achieved in only 10 patients (34%) after an initial resection attempt, whereas 19 patients (66%) still had unacceptable residual tumor. All 19 of these latter patients underwent re-exploration. Ultimately, re-exploration resulted in the achievement of the planned endpoint for extent of resection in all of the 29 completed transsphenoidal explorations. Operative time was extended in all cases by at least 20 minutes.

CONCLUSION

iMRI can be used to safely, reliably, and objectively assess the extent of resection of pituitary macroadenomas during the transsphenoidal approach. The surgeon is frequently surprised by the extent of residual tumor after an initial resection attempt and finds the intraoperative images useful for guiding further resection.

Transoral resection of axial lesions augmented by intraoperative magnetic resonance imaging. Report of three cases

Transoral decompression of the cervicomedullary junction may be compromised by a narrow corridor in which surgery is performed, and thus the adequacy of surgical decompression/resection may be difficult to determine. This is problematic as the presence of spinal instrumentation may obscure the accuracy of postoperative radiological assessment, or the patient may require reoperation. The authors describe three patients in whom high-field intraoperative magnetic resonance (MR) images were acquired at various stages during the transoral resection of C-2 disease that had caused craniocervical junction compression. All three patients harbored different lesions involving the cervicomedullary junction: one each of plasmacytoma and metastatic breast carcinoma involving the odontoid process and C-2 vertebral body, and basilar invagination with a Chiari I malformation. All patients presented with progressive myelopathy. Surgical planning MR imaging studies performed after the induction of anesthesia demonstrated the lesion and its relationship to the planned surgical corridor. Transoral exposure was achieved through placement of a Crockard retractor system. In one case the soft palate was divided. Interdissection MR imaging revealed that adequate decompression had been achieved in all cases. The two patients with carcinoma required placement of posterior instrumentation for stabilization. Planned suboccipital decompression and placement of instrumentation were averted in the third case as the intraoperative MR images demonstrated that excellent decompression had been achieved. Intraoperatively acquired MR images were instrumental in determining the adequacy of the decompressive surgery. In one of the three cases, examination of the images led the authors to change the planned surgical procedure. Importantly, the acquisition of intraoperative MR images did not adversely affect operating time or neurosurgical techniques, including instrumentation requirements.

Intraoperative magnetic resonance imaging during transsphenoidal surgery

OBJECT

The aim of this study was to evaluate whether intraoperative magnetic resonance (MR) imaging can increase the efficacy of transsphenoidal microsurgery, primarily in non-hormone-secreting intra- and suprasellar pituitary macroadenomas.

METHODS

Intraoperative imaging was performed using a 0.2-tesla MR imager, which was located in a specially designed operating room. The patient was placed supine on the sliding table of the MR imager, with the head placed near the 5-gauss line. A standard flexible coil was placed around the patient's forehead. Microsurgery was performed using MR-compatible instruments. Image acquisition was started after the sliding table had been moved into the center of the magnet. Coronal and sagittal T1-weighted images each required over 8 minutes to acquire, and T2-weighted images were obtained optionally. To assess the reliability of intraoperative evaluation of tumor resection, the intraoperative findings were compared with those on conventional postoperative 1.5-tesla MR images, which were obtained 2 to 3 months after surgery. Among 44 patients with large intra- and suprasellar pituitary adenomas that were mainly hormonally inactive, intraoperative MR imaging allowed an ultra-early evaluation of tumor resection in 73% of cases; such an evaluation is normally only possible 2 to 3 months after surgery. A second intraoperative examination of 24 patients for suspected tumor remnants led to additional resection in 15 patients (34%).

CONCLUSIONS

Intraoperative MR imaging undoubtedly offers the option of a second look within the same surgical procedure, if incomplete tumor resection is suspected. Thus, the rate of procedures during which complete tumor removal is achieved can be improved. Furthermore, additional treatments for those patients in whom tumor removal was incomplete can be planned at an early stage, namely just after surgery.

Intraoperative magnetic resonance imaging for skull base surgery

OBJECTIVES/HYPOTHESIS

Skull base surgery has evolved over the past several decades. Major improvements in the imaging of skull base pathology led to better target localization and better surgical planning. The objectives of this study were to assess the use of intraoperative magnetic resonance (MR) imaging in the management of a series of patients with skull base pathology. We hypothesized that high-quality intraoperative MR imaging would have an impact on surgery in this patient group.

STUDY DESIGN

Prospective, non-randomized, cohort study.

METHODS

Thirty-one patients with skull base lesions underwent surgery in a 1.5-Tesla intraoperative MR suite. The concepts of a moving magnet, high magnetic field strength, and radiofrequency coil design are presented.

RESULTS

Eleven of 31 patients had the course of surgery significantly altered by the information acquired from the images obtained during surgery.

CONCLUSIONS

Intraoperative MR imaging is a valuable adjunct to skull base surgery. One third of patients had altered surgery as a result of this adjunct. Intraoperative MR imaging is of particular value in the treatment of pituitary adenomas and benign skull base tumors.

Intraoperative magnetic resonance imaging: considerations for the operating room of the future

Recent technological advances have made possible the introduction of the magnetic resonance imaging (MRI) system into the operating room to guide neurosurgical interventions. We review the possibilities and limitations associated with various open-configuration magnet designs, including systems from the Phillips, Siemens, General Electric, Odin and IMRIS designs. This technology has been shown to be a feasible adjunct to current neurosurgical management of intracranial brain tumors for both biopsy and resection procedures and shows significant potential applications for epilepsy surgery, spine surgery and for minimally invasive interventional techniques. Combined with other surgical planning modalities, intra-operative MRI scanners provide an evolutionary influence on the design of today's operating room.

Cranial surgery navigation aided by a compact intraoperative magnetic resonance imager

OBJECT

In this article the authors report on a novel, compact device for magnetic resonance (MR) imaging that has been developed for use in a standard neurosurgical operating room.

METHODS

The device includes a permanent magnet with a field strength of 0.12 tesla. The poles of the magnet are vertically aligned, with a gap of 25 cm. When not in use the magnet is stored in a shielded cage in a corner of the operating room; it is easily moved into position and attaches to a regular operating table. The magnet is raised for imaging when needed and may be lowered to allow surgery to proceed unencumbered. Surgical navigation with optical and/or magnetic probes is incorporated into the system. Twenty-five patients have undergone removal of intracranial lesions with the aid of this device. Operations included craniotomy for tumor or other lesion in 18 patients and transsphenoidal resection of tumor in seven. The number of scans ranged from two to five per surgery (average 3.4); image quality was excellent in 45%, adequate in 43%, and poor in 12%. In four patients MR imaging revealed additional tumor that was then resected; in five others visual examination of the operative field was inconclusive but complete tumor removal was confirmed on MR imaging. In 21 patients early postoperative diagnostic MR studies corroborated the findings on the final intraoperative MR image. Using a water-covered phantom, the accuracy of the navigational tools was assessed; 120 data points were measured. The accuracy of the magnetic probe averaged 1.3 mm and 2.1 mm in the coronal and axial planes, respectively; the optical probe accuracy was 2.1 mm and 1.8 mm in those planes.

CONCLUSIONS

This device provides high-quality intraoperative imaging and accurate surgical navigation with minimal disruption in a standard neurosurgical operating room.

Intraoperative magnetic resonance imaging combined with neuronavigation: a new concept

OBJECTIVE

Intraoperative image data may be used not only to evaluate the extent of a tumor resection but also to update neuronavigation, compensating for brain shift. To date, however, intraoperative magnetic resonance imaging (MRI) can be combined only with navigation microscopes that are separated from the magnetic field, thus requiring time-consuming intraoperative patient transport. To help solve this problem, we investigated whether a new navigation microscope can be used within the fringe field of the MRI scanner.

METHODS

The navigation microscope was placed at the 5-G line of a 0.2 MRI device. Patients were positioned lying down directly on the table of the scanner, with their heads placed approximately 1.5 m from the center of the magnet, fixed in an MRI-compatible ceramic head holder. Standard operating instruments were used. For intraoperative imaging, we slid the table into the center of the magnet in less than 30 seconds.

RESULTS

By use of this setup, we operated on 22 patients. In all patients, anatomic neuronavigation could be used in combination with intraoperative MRI. In addition, in 12 patients, functional data from magnetoencephalographic or functional MRI studies were integrated, resulting in functional neuronavigation. We did not encounter adverse effects of the low magnetic field during navigation. Moreover, intraoperative imaging was not disturbed by the navigation microscope and vice versa.

CONCLUSION

Functional neuronavigation and intraoperative MRI can be used essentially simultaneously without the need for lengthy intraoperative patient transport. The combination of intraoperative imaging with functional neuronavigation offers the opportunity for more radical resections and fewer complications.

Glioma resection in a shared-resource magnetic resonance operating room after optimal image-guided frameless stereotactic resection

OBJECTIVE

We describe a shared-resource intraoperative magnetic resonance imaging (MRI) design that allocates time for both surgical procedures and routine diagnostic imaging. We investigated the safety and efficacy of this design as applied to the detection of residual glioma immediately after an optimal image-guided frameless stereotactic resection (IGFSR).

METHODS

Based on the twin operating rooms (ORs) concept, we installed a commercially available Hitachi AIRIS II, 0.3-tesla, vertical field, open MRI unit in its own specially designed OR (designated the magnetic resonance OR) immediately adjacent to a conventional neurosurgical OR. Between May 1998 and October 1999, this facility was used for both routine diagnostic imaging (969 diagnostic scans) and surgical procedures (50 craniotomies for tumor resection, 27 transsphenoidal explorations, and 5 biopsies). Our study group, from which prospective data were collected, consisted of 40 of these patients who had glioma (World Health Organization Grades II-IV). These 40 patients first underwent optimal IGFSRs in the adjacent conventional OR, where resection continued until the surgeon believed that all of the accessible tumor had been removed. Patients were then transferred to the magnetic resonance OR to check the completeness of the resection. If accessible residual tumor was observed, then a biopsy and an additional resection were performed. To validate intraoperative MRI findings, early postoperative MRI using a 1.5-tesla magnet was performed.

RESULTS

Intraoperative images that were suitable for interpretation were obtained for all 40 patients after optimal IGFSRs. In 19 patients (47%), intraoperative MRI studies confirmed that adequate resection had been achieved after IGFSR alone. Intraoperative MRI studies showed accessible residual tumors in the remaining 21 patients (53%), all of whom underwent additional resections. Early postoperative MRI studies were obtained in 39 patients, confirming that the desired final extent of resection had been achieved in all of these patients. One patient developed a superficial wound infection, and no hazardous equipment or instrumentation problems occurred.

CONCLUSION

Use of an intraoperative MRI facility that permits both diagnostic imaging and surgical procedures is safe and may represent a more cost-effective approach than dedicated intraoperative units for some hospital centers. Although we clearly demonstrate an improvement in volumetric glioma resection as compared with IGFSR alone, further study is required to determine the impact of this approach on patient survival.

Serial intraoperative magnetic resonance imaging of brain shift

OBJECTIVE

A major shortcoming of image-guided navigational systems is the use of preoperatively acquired image data, which does not account for intraoperative changes in brain morphology. The occurrence of these surgically induced volumetric deformations ("brain shift") has been well established. Maximal measurements for surface and midline shifts have been reported. There has been no detailed analysis, however, of the changes that occur during surgery. The use of intraoperative magnetic resonance imaging provides a unique opportunity to obtain serial image data and characterize the time course of brain deformations during surgery.

METHODS

The vertically open intraoperative magnetic resonance imaging system (SignaSP, 0.5 T; GE Medical Systems, Milwaukee, WI) permits access to the surgical field and allows multiple intraoperative image updates without the need to move the patient. We developed volumetric display software (the 3D Slicer) that allows quantitative analysis of the degree and direction of brain shift. For 25 patients, four or more intraoperative volumetric image acquisitions were extensively evaluated.

RESULTS

Serial acquisitions allow comprehensive sequential descriptions of the direction and magnitude of intraoperative deformations. Brain shift occurs at various surgical stages and in different regions. Surface shift occurs throughout surgery and is mainly attributable to gravity. Subsurface shift occurs during resection and involves collapse of the resection cavity and intraparenchymal changes that are difficult to model.

CONCLUSION

Brain shift is a continuous dynamic process that evolves differently in distinct brain regions. Therefore, only serial imaging or continuous data acquisition can provide consistently accurate image guidance. Furthermore, only serial intraoperative magnetic resonance imaging provides an accurate basis for the computational analysis of brain deformations, which might lead to an understanding and eventual simulation of brain shift for intraoperative guidance.

Novel, compact, intraoperative magnetic resonance imaging-guided system for conventional neurosurgical operating rooms

OBJECTIVE

Preliminary clinical experience with a novel, compact, intraoperative magnetic resonance imaging (MRI)-guided system that can be used in an ordinary operating room is presented.

DESCRIPTION OF INSTRUMENTATION

The system features an MRI scanner integrated with an optical and MRI tracking system. Scanning and navigation, which are operated by the surgeon, are controlled by an in-room computer workstation with a liquid crystal display screen. The scanner includes a 0.12-T permanent magnet with a 25-cm vertical gap, accommodating the patient's head. The field of view is 11 x 16 cm, encompassing the surgical area of interest. The magnet is mounted on a transportable gantry that can be positioned under the surgical table when not in use for scanning, thus rendering the surgical environment unmodified and allowing the use of standard instruments. The features of the integrated navigation system allow flap planning and intraoperative tracking based on updated images acquired during surgery.

OPERATIVE TECHNIQUE

Twenty patients with brain tumors were surgically treated using craniotomy or trans-sphenoidal approaches. One patient underwent conscious craniotomy with cortical mapping, and two underwent electrocorticography.

EXPERIENCE AND RESULTS

Planning was accurate. Resection control images were obtained for all patients during surgery, with precise localization of residual tumor tissue. There were no surgical complications related to the use of the system.

CONCLUSION

This intraoperative MRI system can function in a normal operating room modified only to eliminate radiofrequency interference. The operative environment is normal, and standard instruments can be used. The scanning and navigation capabilities of the system eliminate the inaccuracies that may result from brain shift. This novel type of intraoperative MRI system represents another step toward the introduction of the modality as a standard method in neurosurgery.

Comparison of intraoperative MR imaging and 3D-navigated ultrasonography in the detection and resection control of lesions

Object

The authors undertook a study to compare two intraoperative imaging modalities, low-field magnetic resonance (MR) imaging and a prototype of a three-dimensional (3D)–navigated ultrasonography in terms of imaging quality in lesion detection and intraoperative resection control.

Methods

Low-field MR imaging was used for intraoperative resection control and update of navigational data in 101 patients with supratentorial gliomas. Thirty-five patients with different lesions underwent surgery in which the prototype of a 3D-navigated ultrasonography system was used. A prospective comparative study of both intraoperative imaging modalities was initiated with the first seven cases presented here.

In 35 patients (70%) in whom ultrasonography was performed, accurate tumor delineation was demonstrated prior to tumor resection. In the remaining 30% comparison of preoperative MR imaging data and ultrasonography data allowed sufficient anatomical localization to be achieved. Detection of metastases and high-grade gliomas and intra-operative delineation of tumor remnants were comparable between both imaging modalities. In one case of a low-grade glioma better visibility was achieved with ultrasonography. However, intraoperative findings after resection were still difficult to interpret with ultrasonography alone most likely due to the beginning of a learning curve.

Conclusions

Based on these preliminary results, intraoperative MR imaging remains superior to intraoperative ultrasonography in terms of resection control in glioma surgery. Nevertheless, the different features (different planes of slices, any-plane slicing, and creation of a 3D volume and matching of images) of this new ultrasonography system make this tool a very attractive alternative. The intended study of both imaging modalities will hopefully allow a comparison regarding sensitivity and specificity of intraoperative tumor remnant detection, as well as cost effectiveness.

Intraoperative magnetic resonance imaging–augmented transoral resection of axial disease

Object

Because transoral decompression of the cervicomedullary junction is compromised by a narrow surgical corridor, the adequacy of decompression/resection may be difficult to determine. This is problematic as spinal hardware may obscure postoperative radiological assessment, or the patient may require reoperation. The authors report three patients in whom high-field intraoperative magnetic resonance (MR) images were acquired at various stages during the transoral resection of C-2 lesions causing craniocervical junction compression.

Methods

In all three patients the lesions involved the cervicomedullary junction: one case each of plasmacytoma and metastatic breast carcinoma involving the odontoid process and C-2 vertebral body, and one case of basilar invagination with a Chiari type I malformation. All three patients presented with progressive myelopathy. Surgery-planning MR imaging studies, performed after the induction of anesthesia, demonstrated the lesion and its relationship to the planned surgical corridor. Transoral exposure was achieved through placement of a Crockard retractor system. In one case the soft palate was divided. Interdissection MR imaging revealed that adequate decompression had been achieved in all cases. In the two patients with carcinoma, posterior instrumentation was placed to achieve spinal stabilization. Planned suboccipital decompression and fixation was averted in the third case because MR imaging demonstrated that excellent decompression had been achieved.

Conclusions

Intraoperatively acquired MR images were instrumental in determining the adequacy of surgical decompression. In one patient the MR images changed the planned surgical procedure. Importantly, the acquisition of intraoperative MR images did not adversely affect operative time or neurosurgical techniques, including the instrumentation procedure.

The engineering of an interventional MRI with a movable 1.5 Tesla magnet

The engineering of a novel intra-operative MRI system is described. A movable, 1.5 Tesla MRI magnet was placed in a neurosurgical operating room without affecting established neurosurgical procedure. The system allows fast, high-quality MR intra-operative imaging of the brain and spine without the necessity of patient transportation. A neuro-navigational device capable of displaying and updating spatially referenced MR images in the operating room was integrated with the MRI system. Over 100 procedures have been carried out with this system without limiting surgical access and without compromising traditional neurosurgical, nursing or anesthetic techniques. J. Magn. Reson. Imaging 2001;13:78-86.

Brain biopsy sampling by using prospective stereotaxis and a trajectory guide

OBJECT

The authors describe their initial results obtained using a skull-mounted trajectory guide for intraoperative magnetic resonance (MR) imaging-guided brain biopsy sampling. The device was used in conjunction with a new methodology known as prospective stereotaxis for surgical trajectory alignment.

METHODS

Between January 1999 and March 2000, 38 patients underwent 40 brain biopsy procedures in which prospective stereotaxis was performed with the trajectory guide in a short-bore 1.5-tesla MR imager. In most cases, orthogonal T2-weighted half-Fourier acquisition single-shot turbo spin-echo (HASTE) images were used to determine the desired trajectory and align the device. The surgical trajectory was defined as a line connecting three points: the target, pivot, and alignment stem points. In all cases, surgical specimens were submitted for frozen section and pathological examination. Postoperative turbofluid-attenuated inversion-recovery and gradient-echo images were obtained to exclude the presence of hemorrhage. Trajectory determination and alignment was simple and efficient, requiring less than 5 minutes. Confirmatory HASTE images were obtained along the biopsy needle as it was being advanced or after reaching the target. All biopsy procedures yielded diagnostic tissue. One patient with a lesion near the motor strip experienced a transient hemiparesis of the hand related to passage of the biopsy needle, and another sustained a fatal postoperative myocardial infarction. No patient suffered a clinically significant or radiologically visible hemorrhage.

CONCLUSIONS

In combination with prospective stereotaxis, the trajectory guide provided a safe and accurate way to perform brain biopsy procedures.

Intraoperative magnetic resonance image guidance in neurosurgery

Recently, there has been a burgeoning interest in the use of image-guided navigation to improve the safety and effectiveness of neurosurgical procedures. The intraoperative use of magnetic resonance imaging (MRI) provides the most accurate guidance available. This report discusses the hardware and software improvements that have made intraoperative MRI a reality and describes the use of this technology for neurosurgical intraoperative guidance.

Intraoperative magnetic resonance imaging in epilepsy surgery

The aim of this study was to investigate how intraoperative magnetic resonance imaging (MRI) can help in epilepsy surgery to asses immediately whether a resection or disconnection procedure is tailored to the individual needs of a patient, thus ideally meeting the treatment plan and enhancing the efficiency of the procedure. The recently proposed concept of an individually tailored procedure with as limited tissue removal as possible would support a more conservative resection than initially advocated by many centers; such limited removal would preserve as much brain as possible that is not necessarily epileptogenic or involved in propagation of seizures. For intraoperative imaging we used a Magnetom Open 0.2-T scanner located in our "twin-OR" in 61 patients with pharmacoresistant epilepsy. A three-dimensional sequence was used, allowing free slice reformatting. In the nonlesional cases (n = 32) the extent of the tailored temporal resection (n = 28) or callosotomy (n = 4) could be documented exactly. In the 29 lesional cases the complete resection was primarily proved in 23 patients. In three glioma patients a lesion that extended into eloquent areas did not allow for complete removal. A second look (n = 3) could increase the rate of total resection in the lesional cases from 79% to 90%. Intraoperative MRI allowed a reliable evaluation of the extent of resection or disconnection in epilepsy surgery within the operative procedure. It also provided the possibility of a second look in cases of incomplete resection, especially in the lesional cases. Increased knowledge of structure-function relationships as partially defined by intraoperative imaging may reduce the adverse neuropsychological sequelae of epilepsy surgery in the future.

Advances in mobile intraoperative magnetic resonance imaging

OBJECTIVE

The goal was to enhance a mobile magnetic resonance imaging system developed for neurosurgery. Components of the system included an actively shielded, 1.5-T superconducting magnet, a titanium operating room table, a radiofrequency (RF) head coil that could be disassembled, and local RF shielding.

METHODS

The system was designed and implemented by the Division of Neurosurgery, University of Calgary (Calgary, Alberta, Canada), in collaboration with the National Research Council of Canada Institute for Biodiagnostics (Winnipeg, Manitoba, Canada). The ceiling-mounted, 1.5-T magnet was moved into and out of the surgical field as required. After initial success in monitoring the resection of various intracranial and cranial base lesions, significant modifications to the system were made by Innovative Magnetic Resonance Imaging Systems, Inc. (Winnipeg, Manitoba, Canada), and BrainLAB (Heimstetten, Germany). These modifications included the design and construction of a shorter magnet with a larger bore and stronger gradients, widening of the titanium operating room table, modification of the RF coil housing to allow vertical movement and incorporation of a three-pin head-clamp, construction of a transparent, copper-impregnated RF shield, and integration with a surgical navigation system.

RESULTS

The movable intraoperative imaging system has now been used for 101 neurosurgical procedures, including the previously reported cases.

CONCLUSION

The modifications to the system have enhanced its integration with established neurosurgical techniques and have improved patient safety. The larger magnet bore size, together with the ability to move the RF coil vertically, allows placement of patients in prone or lateral positions. Surgical navigation has been successfully integrated with the intraoperatively acquired high-resolution images. The ability to identify and resect residual lesions before wound closure remains a tremendous immediate advantage of this technology.

Magnetic resonance imaging-guided neurosurgery in the magnetic fringe fields: the next step in neuronavigation

OBJECTIVE

We describe the development of an alternative approach to intraoperative magnetic resonance imaging (iMR)-guided neurosurgery and report our initial experience with 22 craniotomies and 16 brain biopsies. The advantages and disadvantages of each approach are examined.

METHODS

An iMR suite houses a 0.2-T open configuration system (Siemens Medical Systems, Erlangen, Germany) and is equipped with anesthetic gases and a magnetic resonance imaging (MRI)-compatible anesthesia machine and monitor. Standard operating instruments and equipment were tested for safety and compatibility in the magnetic fringe fields surrounding the open MRI system. We then performed brain biopsies and craniotomies in the iMR suite.

RESULTS

Standard operating equipment functioned properly in the 0.5- to 10-mT zone and was not affected by the magnet's attractive force. Twenty-two craniotomies and 16 brain biopsies were performed in the interventional suite, using serial intraoperative MRI guidance, without injury to patients or operating room staff.

CONCLUSION

Full neurosurgical procedures may be performed in the weak fringe fields surrounding an MRI system, using standard operating room equipment. This approach to iMR-guided neurosurgery offers a significant cost advantage over retrofitting an entire operative suite with "MRI-compatible" surgical equipment. The surgeon's familiarity with standard equipment and the reliability of the equipment are additional advantages. Neurosurgery in the fringe fields allows the neurosurgeon to utilize serial MRI with a minimum of inconvenience, disruption, and change to the standard neurosurgical procedure. Serial intraoperative imaging to visualize the changes in the brain that are associated with neurosurgical intervention seems to enhance the ability to safely and effectively accomplish neurosurgical goals.