iMRI System Research Articles

First ground-based, high-field, cryogen-free, mobile intraoperative magnetic resonance imaging system

Background/ObjectiveAccurately targeting specific regions of interest in the brain is pivotal for the success of neurosurgical procedures. For example, the outcome of brain tumor resection is improved dramatically when surgeons are better able to define surgical borders. Intraoperative magnetic resonance imaging (iMRI) helps reduce the risk of damaging critical areas of the brain and makes it possible to confirm a successful resection or determine the need for further resection prior to closing a patient’s head and finalizing the surgery. Here we present a ground-based, iMRI system with a mobile 1-T cryogen-free imager. MethodsAn ex-vivo experimental test of the novel iMRI system is performed to demonstrate preoperative and intraoperative imaging. ResultsThe ground-based, mobile iMRI system presented here was successfully used to obtain intraoperative MR images without moving the imaging target or compromising conventional surgical techniques. ConclusionThe success of this experiment constitutes a major milestone towards the installation of a ground-based, high-field, mobile iMRI system in a hospital setting.

The impact of intra-operative magnetic resonance imaging and 5-ALA in the achievement of gross total resection of gliomas: A systematic literature review and meta-analysis.

In an effort to maximize extent of resection (EOR) regarding gliomas, intraoperative MRI (i-MRI) and 5-aminolevulinic acid (5-ALA) have been developed. Our study aimed to investigate the comparative contribution of 5-aminolevulinic acid and i-MRI in maximizing EOR in gliomas. We searched the PubMed and ScienceDirect services for randomized controlled trials, controlled trials and interrupted time series studies evaluating the effect of i-MRI on gross total resection (GTR) rates and on overall survival in glioma patients. Our primary study endpoint was the definition of the percentage of patients who were offered GTR. Other relevant points of interest included the determination of overall and progression-free survival and subgroup analyses for level of evidence. I-MRI aids in achieving GTR (odds ratio 2.71, p<0.0001). Magnet field strength does not affect significantly either GTR rates (p=0.08). The cost of the procedure is dependent on the workload of the i-MRI system. These data suggest that i-MRI or 5-ALA improves progression-free and overall survival, although there are several restrictions related to their effectiveness and reliability. I-MRI and 5-ALA are considered to be effective adjuncts in the achievement of GTR of gliomas. When these methods are compared, there is no definite conclusion regarding which method is more effective.

Utility and pitfalls of high field 3 tesla intraoperative MRI in neurosurgery: A single centre experience of 100 cases.

In India, few centers are using 1.5 Tesla intraoperative MRI systems. We are using a 3 Tesla iMRI system. We share our initial experience of 3T iMRI in neurosurgical procedures with evaluation of its utility and pitfalls. A prospective observational study conducted between August 2017 to July 2018 at Yashoda Hospital, Secunderabad. All patients undergoing iMRI guided resection of intracranial SOL were included. First 100 patients with various intracranial SOLs were included. The mean time required in shifting and image acquisition was 85.6 minutes in first 20 cases which was reduced to 37.4 minutes in next the next cases. Primary GTR was achieved in 44% cases, and residues were detected in 56%, secondary GTR was achieved in 37% cases, and surgery was discontinued in 19%. Maximum residues were detected in intraaxial sols and pituitary macroadenomas. No major iMRI associated complications were seen, minor issues involving transportation and minor contact burns were seen in 4 cases, insignificant anesthetic procedure related complications in 19 cases. As per our experience iMRI is an excellent tool to guide and improve the extent of safe resection by 37% in brain tumor surgeries. Good image quality, less time for image acquisition was observed advantages of 3T system. iMRI success depends on multidepartment coordinated teamwork and multiple iterations of the process to smoothen the workflow.

Review of first clinical experiences with a 1.5 Tesla ceiling-mounted moveable intraoperative MRI system in Europe.

High-field intraoperative MRI (iMRI) systems provide excellent imaging quality and are used for resection control and update of image guidance systems in a number of centers. A ceiling-mounted intraoperative MRI system has several advantages compared to a conventional iMRI system. In this article, we report on first clinical experience with using such a state-of-the-art, the 1.5T iMRI system, in Europe. A total of 50 consecutive patients with intracranial tumors and vascular lesions were operated in the iMRI unit. We analyzed the patients' data, surgery preparation times, intraoperative scans, surgical time, and radicality of tumor removal. Patients' mean age was 46 years (range 8 to 77 years) and the median surgical procedure time was 5 hours (range 1 to 11 hours). The lesions included 6 low-grade gliomas, 8 grade III astrocytomas, 10 glioblastomas, 7 metastases, 7 pituitary adenomas, 2 cavernomas, 2 lymphomas, 1 cortical dysplasia, 3 aneurysms, 1 arterio-venous malformation and 1 extracranial-intracranial bypass, 1 clival chordoma, and 1 Chiari malformation. In the surgical treatment of tumor lesions, intraoperative imaging depicted tumor remnant in 29.7% of the cases, which led to a change in the intraoperative strategy. The mobile 1.5T iMRI system proved to be safe and allowed an optimal workflow in the iMRI unit. Due to the fact that the MRI scanner is moved into the operating room only for imaging, the working environment is comparable to a regular operating room.

TU‐H‐BRA‐05: A System Design for Integration of An Interior MRI and a Linear Accelerator

Purpose:MRI is a highly desirable modality to guide radiation therapy but it is difficult to combine a conventional MRI scanner directly with a linear accelerator (linac). An interior MRI (iMRI) concept has been proposed to acquire MRI images within a small field of view only covering targets and immediate surrounding tissues. The objective of this project is to design an interior MRI system to work with a linac using a magnet to provide a field around 0.2T in a cube of 20cm per side, and perform image reconstruction with a slightly inhomogeneous static magnetic fields.Methods:All the results are simulated using a commercially available software package, FARADY. In our design, a ring structure holds the iMRI system and also imbeds a linac treatment head. The ring is synchronized to the linac gantry rotation. Half of the ring is made of steel and becomes a magnetic flux return path (yoke) so that a strong magnetic field will be limited inside the iron circuit and fringe fields will be very weak. In order to increase the static magnetic field homogeneity, special steel magnet boots or tips were simulated. Three curved boots were designed based on two‐dimensional curves: arc, parabola and hyperbola.Results:Different boot surfaces modify magnetic field distributions differently. With the same pair of neodymium‐iron‐boron (NdFeB) magnets, the magnetic induction at the centers are 0.217T, 0.201T, 0.204T, and 0.212T for flat, arc, parabola and hyperbola boots, respectively. The hyperbola boots lead to the most homogeneous results, the static magnetic field deviations are within 0.5% in a cube of 20cm, and can be further improved using shimming techniques.Conclusion:This study supports the concept of an iMRI design. Successful development of iMRI will provide crucial information for tumor delineation in radiation therapy.

Intraoperative MRI in pediatric brain tumors.

Intraoperative magnetic resonance imaging (iMRI) has emerged as an important tool in guiding the surgical management of children with brain tumors. Recent advances have allowed utilization of high field strength systems, including 3-tesla MRI, resulting in diagnostic-quality scans that can be performed while the child is on the operating table. By providing information about the possible presence of residual tumor, it allows the neurosurgeon to both identify and resect any remaining tumor that is thought to be safely accessible. By fusing the newly obtained images with the surgical guidance software, the images have the added value of aiding in navigation to any residual tumor. This is important because parenchyma often shifts during surgery. It also gives the neurosurgeon insight into whether any immediate postoperative complications have occurred. If any complications have occurred, the child is already in the operating room and precious minutes lost in transport and communications are saved. In this article we review the three main approaches to an iMRI system design. We discuss the possible roles for iMRI during intraoperative planning and provide guidance to help radiologists and neurosurgeons alike in the collaborative management of these children.

Movable intraoperative magnetic resonance imaging incorporating a seismic system

IntroductionA high-field ceiling-mounted and movable intraoperative MR imaging (iMRI) can minimize additional risks for MRI and enhance safety by not moving the patient. In this system, hanging the heavy magnet from the ceiling requires structural stability; this stability was confirmed in earlier studies, but not proved during a seismic event. ObjectiveWe have installed a 1.5T movable iMRI system with an incorporated seismic system in our hospital in Japan, a seismic event-prone region. This arrangement is the first in the world, to our knowledge. The objective of this study was to describe the mechanism of this seismic system and the first clinical experience using this system. MethodsThe seismic system consists of a stabilizer pad that is mounted directly under the magnet, in addition to the structural stability. The seismic system was tested with using a shaker table testing at a test laboratory. ResultsNinety-one patients underwent neurosurgical intervention using this iMRI and seismic system at our hospital. In all patients, intra-, pre, and/or postoperative MR images were successfully obtained, and image quality was excellent. The workflow of moving the magnet and scanning were smooth and unproblematic. We had 169 seismic events in our city during this time period, but had no incidental or accidental events related to the seismic events. ConclusionWith the use of the seismic system, a ceiling-mounted, movable iMRI system can be more safely used. This seismic system may contribute to the spread of movable iMRI systems in countries where seismic events occur.

Application of intraoperative magnetic resonance imaging in large invasive pituitary adenoma surgery

To investigate the clinical application value of intraoperative magnetic resonance imaging (iMRI) in large invasive pituitary adenoma surgery. A total of 30 patients with large pituitary adenoma underwent microscopic tumor resection under the assistance of an iMRI system; 26 cases received surgery through the nasal-transsphenoidal approach, and the remaining four cases received surgery through the pterion approach. iMRI was performed one or two times depending on the need of the surgeon. If a residual tumor was found, further resection was conducted under iMRI guidance. iMRI revealed residual tumors in 12 cases, among which nine cases received further resection. Of these nine cases, iMRI rescanning confirmed complete resection in six cases, and subtotal resection in the remaining three. Overall, 24 cases of tumor were totally resected, and six cases were subtotally resected. The total resection rate of tumors increased from 60% to 80%. iMRI can effectively determine the resection extent of pituitary adenomas. In addition, it provides an objective basis for real-time judgment of surgical outcome, subsequently improving surgical accuracy and safety, and increasing the total tumor resection rate.

NI-86 * COMBINED AWAKE BRAIN MAPPING AND LOW-FIELD INTRAOPERATIVE MRI FOR BRAIN TUMOR RESECTION

BACKGROUND: Surgery for patients with intraparenchymal brain tumors is often reported as being done with intraoperative MRI guidance or with awake mapping, but rarely with these two methods in tandem. We report our experience performing awake image-guided surgery using a compact iMRI. METHODS: Surgery in 25 patients was done using the PoleStar iMRI system (Medtronic Surgical Technologies). All patients had a glioma in the dominant hemisphere for language. Patients were divided into 4 groups depending on how mapping and imaging effected surgery: Group A: gross total resection (GTR) without imaging; Group B: GTR with the aid of iMRI; Group C: language mapping stopped surgery before further imaging; Group D: language mapping stopped surgery after iMRI revealed residual tumor. RESULTS: The number of iMRI scans acquired ranged from 1 to 5 (mean 2.6), adding an average of 1.4 hours to surgery. There were 7/25 patients in Group A, 6/25 in Group B, 3/25 in Group C, and 9/25 in Group D. Overall, intraoperative imaging led to further resection in 15/25 patients, while language mapping stopped surgery in 12/25. Gross total resection was achieved in 13 patients. A mean follow up of 16.9 months revealed no major new postoperative deficits. Minor deficits of language, calculation, contralateral weakness occurred in 12/25 patients, while language function worsened in 3 patients (12%). CONCLUSIONS: Neurosurgeons should not have to choose between these two modalities, removing the guesswork out of intracranial tumor surgery. Compact iMRI is easily integrated with awake surgery and cortical mapping to ensure accurate resection of gliomas in the dominant hemisphere, while preserving neurological function. In only a small minority of patients with such tumors can a GTR be safely achieved without the use of iMRI and/or language mapping.

Awake language mapping and 3-Tesla intraoperative MRI-guided volumetric resection for gliomas in language areas

The use of both awake surgery and intraoperative MRI (iMRI) has been reported to optimize the maximal safe resection of gliomas. However, there has been little research into combining these two demanding procedures. We report our unique experience with, and methodology of, awake surgery in a movable iMRI system, and we quantitatively evaluate the contribution of the combination on the extent of resection (EOR) and functional outcome of patients with gliomas involving language areas. From March 2011 to November 2011, 30 consecutive patients who underwent awake surgery with iMRI guidance were prospectively investigated. The EOR was assessed by volumetric analysis. Language assessment was conducted before surgery and 1week, 1month, 3months and 6months after surgery using the Aphasia Battery of Chinese. Awake language mapping integrated with 3.0Tesla iMRI was safely performed for all patients. An additional resection was conducted in 11 of 30 patients (36.7%) after iMRI. The median EOR significantly increased from 92.5% (range, 75.1–97.0%) to 100% (range, 92.6–100%) as a result of iMRI (p<0.01). Gross total resection was achieved in 18 patients (60.0%), and in seven of those patients (23.3%), the gross total resection could be attributed to iMRI. A total of 12 patients (40.0%) suffered from transient language deficits; however, only one (3.3%) patient developed a permanent deficit. This study demonstrates the potential utility of combining awake craniotomy with iMRI; it is safe and reliable to perform awake surgery using a movable iMRI.

Research on the application of intraoperative magnetic resonance in transnasal ⁃sphenoidal surgery for pituitary adenoma

Objective To discuss the application of the intraoperative magnetic resonance imaging (iMRI) ⁃ based neuronavigation system in transnasal ⁃ sphenoidal surgery for pituitary adenoma. Methods Thirty ⁃ eight pituitary adenomas were resected via nasal ⁃ sphenoidal approach with assistance of the American GE Signa 1.5T intraoperative magnetic resonance system associating German Brain LAB neuronavigation system. The clinical materials, iMRI quality and its influence on the surgical process and results were analyzed. Results Intraoperative scanning was performed 2 or 3 times in each patient, averaging (2.11 + 0.41) times. The scanning time was 3-5 min, and adding the packaging and transporting process, the whole procedure required 15-20 min. Posing the position, fixing the head rest and navigation registering took 32-40 min in all. So the total operation may last 47-60 min, averaging (51.20 + 0.66) min. The iMRI was used to scan and collect pictures. Residual tumor tissue was revealed in 11 cases. Eight of the 11 cases underwent total resection according to the new neuronavigation plan. The other 3 cases under⁃ went subtotal resection because the adenomas were tenacious and adhered closely to the surrounding significant structures. By using this iMRI system, the total resection rate (TRR) of adenoma increased from 71.05% (27/38) to 92.10% (35/38). It was raised by 21.05% (8/38; χ2 = 4.290, P = 0.018). There was no iMRI related complication occurred. Conclusion The application of iMRI ⁃ based neuronavigation technology in transnasal ⁃ sphenoidal operations for pituitary adenoma provides objective evidence for the guidance of surgical procedure and real time assessment of surgical results, which may lead to higher TRR and avoid deviation of navigation caused by brain⁃drift in transnasal⁃sphenoidal operation. DOI：10.3969/j.issn.1672⁃6731.2012.02.022

Intraoperative MRI electrical noise and monitor ECG filters affect arrhythmia detection and identification

Most electrical equipment in the modern operating room (OR) radiates electrical noise (EN) that can interfere with patient monitors. We have described the EN that an intraoperative magnetic resonance imaging (iMRI) system emits and have shown that this high-energy EN diminishes the quality of the ECG waveform during iMRI scans in our neurosurgical OR. We have also shown that the ECG signal filters in our iMRI-compatible patient monitor reduce this interference but, in the process, disturb the true morphology of the displayed waveform. This simulation study evaluates how iMRI-generated EN affects the ability of the anesthetist to detect and identify ECG arrhythmias and whether the patient monitor's ECG signal filters can improve arrhythmia recognition. Using an ECG simulator, we generated Lead II and V5 ECG signal segments that contained either no arrhythmia or one of four common cardiac arrhythmias. We filtered the ECG segments with four filters available on our iMRI-compatible monitor (Veris MR, MEDRAD Inc., Indianola, PA USA). We then digitized the segments and mixed simulated iMRI EN into the resultant tracings. With institutional approval and written informed consent, board-certified anesthesiologists reviewed the tracings, determined if an arrhythmia was present and identified the arrhythmia. We conducted the study anonymously. We reported the data as percent correct arrhythmia detection and correct arrhythmia identification. Thirty-one anesthesiologists completed the study. Overall, the participants correctly detected 79.5% (95% CI: 77.2, 81.7%) of the arrhythmias and correctly identified 62.5% (95% CI: 59.8, 65.3%) of the arrhythmias, regardless of EN presence. Although the proportions among monitor noise filters studied were not significant, the manufacturer-designated MR5 Veris MR filter optimized arrhythmia detection and arrhythmia identification for our participants, regardless if EN was present in the ECG tracings. In the neurosurgical OR, the anesthetist must be able to effectively monitor a patient in the presence of iMRI-generated EN. Depending on the OR design, the patient may be out of the anesthetist's direct view during a scan procedure. The anesthetist must rely on monitored physiologic parameters to assess patient status during this time. He/she should be familiar with his/her monitor's filtering capabilities and routinely adjust the ECG filters to achieve the best compromise between minimized EN effects and maximized displayed ECG signal quality.

Use of an ultra-low field intraoperative MRI system for pediatric brain tumor cases: initial experience with ?polestar n20?

Use of intraoperative MRI (iMRI) is the highest contemporary supportive means for brain tumor surgery. In this article we describe the issues related to iMRI use in pediatric cranial operations. Pediatric cases operated with the aid of Polestar N20 iMRI system are defined and the pros and cons of the system are emphasized. Patient positioning is easier and the obtained images are better in pediatric cases, particularly for posterior fossa tumors. iMRI should be used in all pediatric brain tumor operations when possible.

Intraoperative MRI for transphenoidal procedures: Short-term outcome for 100 consecutive cases

Background The majority of pituitary lesions are benign and can be cured with complete surgical resection. However, the transsphenoidal technique (the most common approach for pathology in this region) is limited by poor visualization and anatomical constraints. This can lead to incomplete tumor resection and thus increased recurrence rates. The use of iMRI during these procedures offers the advantage of radiographic confirmation during the procedure and may improve extent of resection. We reviewed our experience with this technology in 100 consecutive cases and compared the outcomes to published results. Methods 100 patients were treated via transnasal transsphenoidal approach using the GE Signa SP 0.5 Tesla (double doughnut design) iMRI system between July 2002 and August 2009 and followed prospectively. Intraoperative findings, imaging results, postoperative MRI and clinical outcome were evaluated to determine the extent of tumor resection, monitor for recurrence and determine outcome. Results There were 100 patients studied, 81 macroadenomas, 9 microadenomas, and 10 other pathological diagnosis. The average extent of resection was 96% with gross total resection based on iMRI in 76 patients (76%). Four patients (4%) all with macroadenomas greater than 4 cm experienced major perioperative complications (hydrocephalus 2, thalamic infarct 1, major arterial bleeding 1), six patients (6%) developed post-operative CSF leaks, one patient (1%) had post-operative worsening of visual fields, and five patients (5%) had abdominal fat graft infections. Nine patients (9%) including five with known residual tumor required post-operative adjuvant treatment during the follow-up period secondary to either disease progression or failure to achieve endocrinological cure. Conclusions iMRI-guided transsphenoidal pituitary surgery provides the surgeon with immediate radiographic feedback during the procedure and aides in overcoming the limitations in direct visualization during such procedures. As a result of this it may enable surgeons to perform such procedures with fewer complications and increased rate of gross total resection. However, the impact of this technology on long-term tumor control still needs to be determined with further follow-up.

Feasibility of Intraoperative MRI Guidance for Craniotomy and Tumor Resection in the Semisitting Position

Intraoperative magnetic resonance imaging (iMRI) has emerged as a reliable and useful tool in intracranial brain tumor surgery. Patient placement in a semisitting position may be advantageous in certain cases, but has so far seemed incompatible with conductance of iMRI-guided procedures. The general iMRI setup and the imaging protocol were tested and described earlier. Having performed a preliminary phantom study and a minimally invasive burr-hole procedure in the semisitting position, we have transferred our setup into craniotomy: an iMRI-guided microsurgical tumor resection was performed in a patient with a recurrent glioblastoma in the occipital lobe extending to the corpus callosum using a mobile 0.15 Tesla iMRI system. All safety precautions commonly used in semisitting craniotomy were also applied. Patient positioning as well as preoperative and intraoperative image acquisition could be accomplished. Tumor resection was performed in a standard microsurgical image-guided manner using neuronavigation. On intraoperative imaging, we could demonstrate complete resection of enhancing tissue, which was later confirmed by early postoperative high-field MRI. After our established protocol of patient monitoring, no complications or adverse events were noted intraoperatively or in the early or late postoperative phases. The iMRI-guided brain tumor resection is feasible in combination with semisitting patient positioning. However, special safety precautions must be followed.

A Moveable 3-Tesla Intraoperative Magnetic Resonance Imaging System

Based on success with a prototype 1.5T intraoperative magnetic resonance imaging (iMRI) system and the desire for increased signal-to-noise ratio, along with its relationship to image quality and advanced applications, a 3.0T system that uses the same novel moveable magnet configuration was developed. To assess clinical applicability by prospectively applying the higher-field system to a neurosurgical cohort. Upgrading to 3.0T required substantial modification of an existing iMRI-equipped operating room. The 1.5T magnet was replaced with a ceiling-mounted, moveable 3.0T magnet with a 70-cm working aperture. Local radiofrequency shielding was replaced with whole-room shielding. A new hydraulic operating table, high-performance gradients, and advanced image processing software were also installed. The new system was used as an adjunct to standard neurosurgical practice. The iMRI system upgrade required 6 months. Since completion, the 3.0T iMRI system has successfully guided neurosurgery in 120 patients without system failure in a patient-focused environment. Intraoperative image quality was superior to that obtained at 1.5T and enabled intraoperative acquisition of advanced imaging sequences, including tractography. Intraoperative imaging was found to modify surgery in a substantial number of patients. Implementation of an iMRI system based on a moveable 3.0T magnet is feasible. From clinical experience with 120 patients, iMRI at 3.0T is safe, reliable, and capable of directing image-guided surgery with exceptional image quality.

Stereotactic Brain Biopsy With a Low-Field Intraoperative Magnetic Resonance Imager

Techniques for stereotactic brain biopsy have evolved in parallel with the imaging modalities used to visualize the brain. To describe our technique for performing stereotactic brain biopsy using a compact, low-field, intraoperative magnetic resonance imager (iMRI). Thirty-three patients underwent stereotactic brain biopsies with the PoleStar N-20 iMRI system (Medtronic Navigation, Louisville, Colorado). Preoperative iMRI scans were obtained for biopsy target identification and trajectory planning. A skull-mounted device (Navigus, Medtronic Navigation) was used to guide an MRI-compatible cannula to the target. An intraoperative image was acquired to confirm accurate cannula placement within the lesion. Serial images were obtained to track cannula movement and to rule out hemorrhage. Frozen sections were obtained in all but 1 patient with a brain abscess. Diagnostic tissue was obtained in 32 of 33 patients. In all cases, imaging demonstrated cannula placement within the lesion. Histological diagnoses included 22 primary brain tumors and 10 nonneoplastic lesions. In 61% of the cases, initial trajectory was corrected on the basis of the intraoperative scans. In 1 patient, biopsy was nondiagnostic despite accurate cannula placement. No patient suffered a clinically or radiographically significant hemorrhage during or after surgery. There were no intraoperative complications. Stereotactic biopsy with a low-field iMRI is an accurate way to obtain specimens with a high diagnostic yield. This accuracy, combined with the acceptable additional procedural time, may obviate the need for frozen section. The ability to correct biopsy cannula placement during surgery eliminates the chance of misdiagnosis because of faulty targeting, as well as the risks associated with inconclusive frozen sections and "blind" replacement of the cannula.

Real-time image guided brain biopsy using low-field intraoperative magnetic resonance imaging: preliminary clinical report

Objective To study the preliminary clinical experience,advantage and disadvantage of the brain biopsy procedure guided by low-field intraoperative magnetic resonance imaging(iMRI).Methods Between August 2006 and February 2009,6 consecutive brain biopsy procedures were performed using the mobile 0.15-tesla PoleStar N-20 iMRI system in order to identify the pathological diagnosis of the intracranial lesions in these patients.Results All biopsy samples comprised pathological tissue,leading to a diagnostic yield of 100%.A tiny hematoma was detected at the region of biopsy of the left basal ganglion on postoperative CT scans in only one patient with intracranial muhi-lesions.Conclusiom iMRI-basedneuronavigation is feasible when using the mobile 0.15-tesla PoleStar N-20 iMRI system for brain biopsy procedures.The most obvious advantage of using the system for brain biopsies is offering the opportunity of immediate verification of the location of needle tip,and this method produces a hish histological yield and low complication rate. Key words: Biopsy,needle; Neuronavigation; Intraoperative magnetic resonance imaging

MINIMAL ACCESS NERVE SURGERY AND INTERVENTIONAL MAGNETIC RESONANCE IMAGING

Develop and assess the utility of novel minimal access techniques including percutaneous open-configuration interventional magnetic resonance imaging (iMRI), open surgery using open or closed/cylindrical iMRI systems, and minimal access open surgery with electromyographic guidance in a standard operating room. For more than 2500 percutaneous open iMRI procedures, 25 incisional surgery open iMRI cases, 3 incisional surgery closed/cylindrical iMRI cases, 25 computed tomography-guided percutaneous procedures, and more than 1000 minimal access incisional surgery cases in the standard operating room with electromyographic guidance, cycle time for intraoperative data collection and numbers of guidance events per case were assessed. Cycle time varied greatly. The minimum was for open surgery in the standard operating room with direct nerve stimulation for electromyography, requiring 10 to 15 seconds, which was applicable for dozens of assessments during the surgery and had negligible effects on total surgical time. Percutaneous procedures in the open iMRI environment allowed for 20 or 30 imaging events during a procedure, with cycle times of between 10 and 20 seconds. Incisional surgery in the open iMRI system had a cycle time of about 1 to 5 minutes for "in-magnet" procedures and about 5 to 10 minutes for "magnet-adjacent" procedures. Incisional surgery in closed/cylindrical iMRI procedures had a cycle time of 45 to 60 minutes, and the technique proved awkward to use more than once or twice per surgical case. Percutaneous open-configuration iMRI provides clear benefits over computed tomography or ultrasound. Minimal access surgery and incisional open-configuration iMRI are useful and effective in some situations. Closed/cylindrical iMRI systems pose challenges for patient safety, add greatly to surgical time, and provide limited useful intraoperative benefits.

Anesthesia for brain tumor resection using intraoperative magnetic resonance imaging (iMRI) with the Polestar N-20 system: experience and challenges

The Polestar N-20 Scanner (Medtronic Navigation, Louisville, CO) is an intraoperative magnetic resonance image (iMRI) guidance system designed for neurosurgery. Sixty-five patients underwent craniotomy for tumor resection using the iMRI during the period from April 2005 to December 2006. Anesthesiologists used an iMRI-compatible patient monitoring system (Veris MR, MEDRAD, Indianola, PA), anesthesia machine (Aestiva/5 MRI, Datex-Ohmeda, Madison, WI), and infusion pumps (Continuum; MEDRAD). Average setup time for each case (from intubation to incision) was one hour, 33 minutes and showed learning improvement over the 21-month period. The challenges facing the anesthesiologists in these cases included the need to use longer intravenous (IV) catheters and gas delivery and sampling lines, which increased dead space. Electrocardiographic signals became contaminated with electrical noise during iMRI scan procedures, which made it difficult to distinguish rhythm changes. None of our iMRI patients underwent a repeat resection, whereas the repeat resection rate for conventional tumor resection is reported to be as high as 30%. The use of a small, low-field iMRI system provided adequate imaging for resection of lesions without the need of repeat resections in the weeks following the initial procedure, and did not significantly alter the anesthetic procedure. A team effort between the anesthesiologists, surgeons, nurses, and MRI technicians is paramount for the practical and efficient use of these iMRI systems.