Intraoperative MR imaging

Intraoperative MRI: A Review of Applications Across Neurosurgical Specialties

Intraoperative MRI (iMRI) made its debut to great fanfare in the mid-1990s. However, the enthusiasm for this technology with seemingly obvious benefits for neurosurgeons has waned. We review the benefits and utility of iMRI across the field of neurosurgery and present an overview of the evidence for iMRI for multiple neurosurgical disciplines: tumor, skull base, vascular, pediatric, functional, and spine. Publications on iMRI have steadily increased since 1996, plateauing with approximately 52 publications per year since 2011. Tumor surgery, especially glioma surgery, has the most evidence for the use of iMRI contributing more than 50% of all iMRI publications, with increased rates of gross total resection in both adults and children, providing a potential survival benefit. Across multiple neurosurgical disciplines, the ability to use a multitude of unique sequences (diffusion tract imaging, diffusion-weighted imaging, magnetic resonance angiography, blood oxygenation level-dependent) allows for specialization of imaging for various types of surgery. Generally, iMRI allows for consideration of anatomic changes and real-time feedback on surgical outcomes such as extent of resection and instrument (screw, lead, electrode) placement. However, implementation of iMRI is limited by cost and feasibility, including the need for installation, shielding, and compatible tools. Evidence for iMRI use varies greatly by specialty, with the most evidence for tumor, vascular, and pediatric neurosurgery. The benefits of real-time anatomic imaging, a lack of radiation, and evaluation of surgical outcomes are limited by the cost and difficulty of iMRI integration. Nonetheless, the ability to ensure patients are provided by a maximal yet safe treatment that specifically accounts for their own anatomy and highlights why iMRI is a valuable and underutilized tool across multiple neurosurgical subspecialties.

Intraoperative high-field resonance: How to optimize its use in our healthcare system

BACKGROUND AND AIMS

Intraoperative MRI (ioMRI) consists of performing a MRI during brain or spinal surgery. Although it is a safe and useful technique, it is available in a few hospitals. This means some aspects are not perfectly defined or standardized, forcing each center to develop its own solutions. Our goal is to describe the technique, evaluate the changes made to optimize its use and thus be able to facilitate the intraoperative resonance implementation in other neurosurgery departments.

METHODS

A prospective analysis of patients consecutively operated using high-field ioMRI guidance was carried out, describing the type of tumor, clinical data, time and sequences of ioMR, use of intraoperative neurophysiology, preoperative tumor volume, after ioMR, and postoperative, as well as complications.

RESULTS

ioMR was performed in 38 patients selected from among 425 brain tumors (9%) operated on in this interval. The tumor types were: 11 glioblastomas, 8 anaplastic astrocytomas, 5 diffuse astrocytomas, 4 meningiomas, 3 oligodendrogliomas, 2 metastases, 2 epidermoid cysts, 1 astroblastoma, 1 arachnoid cyst and 1 pituitary adenoma. The mean age was 45 years. The mean preoperative tumor volume was 45.22cc, after the ioMR 5.08cc and postoperative 1.28cc. Resection was extended after ioMR in 76%. Gross total resection was achieved in 15 patients and residual tumor of less than 1cc was observed in 8. An intentional tumor tissue was left in an eloquent brain region (mean volume 7cc) in 13 patients. Bleeding and ischemia complications were detected early on ioMR in 5%. MRI length was 47 min on average.

CONCLUSIONS

Intraoperative MRI was a useful and safe technique, and no associated complications were registered.

Is a modification of the radiotherapeutic target volume necessary after resection of glioblastomas with opening of the ventricles?

Extensive surgical resection of centrally localized, newly diagnosed glioblastoma can lead to opening ventricles and therefore carries a potential risk of spreading tumor cells into the cebrospinal fluid. However, whether ventricle opening consequently implies a greater frequency of distant tumor recurrence after radiation therapy-and, therefore, reduced survival-remains unknown. Therefore, is an adaption of target volumes in radiation therapy necessary to account for a potential tumor cell spread into the ventricle system? The present study assessed the resection statuses of 311 primary-glioblastoma patients who underwent radiation therapy. Overall, in 78 cases (25.1 %) the ventricle system was opened during surgical resection. This study assessed the connection between ventricle opening and progression-free survival, overall survival, and distant and multifocal recurrence. OS rates of patients that underwent gross total resection were superior to patients with subtotal resection (p = 0.002). PFS (p = 0.53) and OS (p = 0.18) did not differ due to ventricle opening during surgical resection. However, in a subsample of STR cases increased survival was observed when the ventricle system was opened (16.8 vs. 14.3 months; p = 0.03). The occurrence of distant (p = 0.75) and contralateral recurrence (p = 0.87) was not influenced by ventricle opening. Newly diagnosed glioblastoma patients whose ventricle systems were opened during microsurgical resection did not experience decreased survival or show increased likelihoods of distant and contralateral progressions following radiation therapy. In short, patients profit from surgical resections that are as extensive as reasonably possible, even if this entails ventricle opening. Thus, additional inclusion of the ventricles in the radiation therapy target volume after ventricle opening does not seem to be indicated.

Combining 5-Aminolevulinic Acid Fluorescence and Intraoperative Magnetic Resonance Imaging in Glioblastoma Surgery

BACKGROUND:

Glioblastoma resection guided by 5-aminolevulinic acid (5-ALA) fluorescence and intraoperative magnetic resonance imaging (iMRI) may improve surgical results and prolong survival.

OBJECTIVE:

To evaluate 5-ALA fluorescence combined with subsequent low-field iMRI for resection control in glioblastoma surgery.

METHODS:

Fourteen patients with suspected glioblastoma suitable for complete resection of contrast-enhancing portions were enrolled. The surgery was carried out using 5-ALA–induced fluorescence and frameless navigation. Areas suspicious for tumor underwent biopsy. After complete resection of fluorescent tissue, low-field iMRI was performed. Areas suspicious for tumor remnant underwent biopsy under navigation guidance and were resected. The histological analysis was blinded.

RESULTS:

In 13 of 14 cases, the diagnosis was glioblastoma multiforme. One lymphoma and 1 case without fluorescence were excluded. In 11 of 12 operations, residual contrast enhancement on iMRI was found after complete resection of 5-ALA fluorescent tissue. In 1 case, the iMRI enhancement was in an eloquent area and did not undergo a biopsy. The 28 biopsies of areas suspicious for tumor on iMRI in the remaining 10 cases showed tumor in 39.3%, infiltration zone in 25%, reactive central nervous system tissue in 32.1%, and normal brain in 3.6%. Ninety-three fluorescent and 24 non-fluorescent tissue samples collected before iMRI contained tumor in 95.7% and 87.5%, respectively.

CONCLUSION:

5-ALA fluorescence–guided resection may leave some glioblastoma tissue undetected. MRI might detect areas suspicious for tumor even after complete resection of all fluorescent tissue; however, due to the limited accuracy of iMRI in predicting tumor remnant (64.3%), resection of this tissue has to be considered with caution in eloquent regions.

Fluorescent nanoparticle uptake for brain tumor visualization

Accurate delineation of tumor margins is vital to the successful surgical resection of brain tumors. We have previously developed a multimodal nanoparticle CLIO-Cy5.5, which is detectable by both magnetic resonance imaging and fluorescence, to assist in intraoperatively visualizing tumor boundaries. Here we examined the accuracy of tumor margin determination of orthotopic tumors implanted in hosts with differing immune responses to the tumor. Using a nonuser-based signal intensity method applied to fluorescent micrographs of 9L gliosarcoma green fluorescent protein (GFP) tumors, mean overestimations of 2 and 24 microm were obtained using Cy5.5 fluorescence, compared to the true tumor margin determined by GFP fluorescence, in nude mice and rats, respectively. To resolve which cells internalized the nanoparticle and to quantitate degree of uptake, tumors were disaggregated and cells were analyzed by flow cytometry and fluorescence microscopy. Nanoparticle uptake was seen in both CD11b+ cells (representing activated microglia and macrophages) and tumor cells in both animal models by both methods. CD11b+ cells were predominantly found at the tumor margin in both hosts, but were more pronounced at the margin in the rat model. Additional metastatic (CT26 colon) and primary (Gli36 glioma) brain tumor models likewise demonstrated that the nanoparticle was internalized both by tumor cells and by host cells. Together, these observations suggest that fluorescent nanoparticles provide an accurate method of tumor margin estimation based on a combination of tumor cell and host cell uptake for primary and metastatic tumors in animal model systems and offer potential for clinical translation.

Intraoperative MR imaging: preliminary results with 3 tesla MR system

Aim of this study is to present the initial clinical experience with 3 tesla intraoperative MR (ioMR).

MATERIAL AND METHODS

The 3T MRI suite is built adjacent to the neurosurgical operation theatre. The magnet room and the operation theatre are interconnected by a door and both RF-shielded. Before the operation, the magnet (3T Trio, Siemens) and the console rooms are disinfected. Whenever imaging is needed during the operation, the door is opened and the patient is transferred from the operation table to the magnet cradle. Axial, sagittal and/or coronal TSE T2, SE T1 and 3D Flash T1 weighted images (4-6 mm section thickness, 1 mm interslice gap) are obtained according to the lesion. Total examination time is approximately 10 minutes.

RESULTS

Twenty-six patients were examined with ioMR. There were ten female and seven male patients. Lesions were pituitary adenoma in 10, low grade glial tumor in 9, meningioma and high grade glial tumor in 2 each and metastasis, haemangioblastoma and chordoma in one each. Follow-up time was 1 to 9 months. In 16 patients the first intraoperative examination revealed gross total tumor excision. However, in 10 patients due to tumor remnants surgical intervention was continued and a second examination revealed gross total tumor excision in all. Postoperative routine MR examinations confirmed total tumor excision in all patients. No complication occurred in this series.

CONCLUSION

This small group of patients examined with ioMR demonstrated that the procedure is simple, helpful in achieving gross total tumor excision without complications.

Apport de la résonance magnétique per-opératoire à bas champs dans la chirurgie de l’adénome hypophysaire

INTRODUCTION

Appropriate evaluation of resection remains one of the major difficulties of surgical treatment of pituitary adenoma. The transsphenoidal approach does not allow direct visual control. Endoscopy provides useful information but may no distinguish well residual adenoma from the pituitary gland. Intraoperative MRI offers new perspectives for assessing the quality of resection. We report our experience with low field intraoperative MRI in surgical treatment of pituitary adenoma.

POPULATION

Intraoperative MRI (Polestar N10, 30 patients and Polestar N20, 17 patients) was performed in 45 consecutive patients undergoing surgery for pituitary adenoma. Thirty-seven patients had a macroadenoma. Patients were in the prone position with the head fixed with a three-pin MRI-compatible headholder.

METHOD

Coronal T1 MRI scans with enhancement were acquired pre and per operatively. We compared scans and surgical filling (complete removal). If there was a difference, a surgical control was undertaken.

RESULTS

Intraoperative images were unavailable for two patients due to small size of the neck and the pituitary glands which were not in the middle in the field of view. For the others, the pituitary glands were in the field of view and the intraoperative scans could be used for comparison. For four patients, there was a discrepancy between surgeon filling and the intraoperative MRI. A control showed no residual adenoma but hemostatic tissue.

CONCLUSION

Low field intraoperative MRI is an excellent technique for controlling the size of pituitary adenoma resection.

MR-guided interventional procedures: a review

Magnetic resonance imaging (MRI) has emerged as a potential guidance tool for a variety of procedures. Diagnostic and therapeutic procedures using either open surgical or percutaneous access are performed. They span from simple lesion targeting and biopsy to complex applications requiring multiple tasks performed simultaneously or in rapid succession. These tasks include instrument guidance and therapy monitoring as well as procedural follow-up. The interventional use of MRI (IMRI) is increasing steadily. This article reviews the prerequisites, systems, and clinical interventional procedures of IMRI.

The Interventional MR Imaging Suite: Magnet Designs and Equipment Requirements

Soon after the introduction of MR imaging as an imaging tool, researchers began to investigate its capabilities to guide interventional minimally invasive procedures, such as biopsies. These early efforts have encouraged vendors and numerous research groups worldwide to identify clinical problems in the field of image-guided intervention, for which MR imaging is beneficial as an imaging modality, and to develop and refine soft-ware and hardware components to meet the specific requirements of interventional MR imaging. Over nearly 20 years, continuous advances in magnet and system design have accelerated the progress of MR-guided intervention.

Percutaneous Biopsy from Blinded to MR Guided: An Update on Current Techniques and Applications

The advent of interventional MR imaging techniques as well as their adoption to guide percutaneous biopsies and aspirations has served as a further step along a series of technical refinements that commenced with the implementation of image-guided approaches for tissue sampling. Nowadays, the practice of and the expectations from these procedures are quite different from those of the blind percutaneous thrusts performed in the late nineteenth and early twentieth centuries. As the field of interventional MR imaging continues to flourish and to attract more radiologists who realize the many opportunities that this technology can offer to their patients, there is a need for a full comprehension of the concepts, techniques, limitations, and cost-effectiveness of MR imaging guidance to present this service to clinical partners in the appropriate setting. Radiologists should also recognize the need for their significant involvement in the technical aspects of MR-guided procedures, because several user-defined parameters and trajectory decisions can alter device visualization in the MR imaging environment and hence affect procedure safety.

Interfering with cancer: a brief outline of advances in RNA interference in oncology

RNA interference (RNAi) is a potent and ubiquitous gene-silencing mechanism that is generating considerable excitement in the fields of molecular biology and gene therapy. It is now in widespread use for loss-of-function analysis in many diseases including cancer. Nevertheless, RNAi is still in its infancy, with new discoveries appearing on a monthly basis. This article presents a brief outline of the history and recent advances in RNAi with a specific focus on its potential in oncology.

Intracranial neuronavigation with intraoperative magnetic resonance imaging

PURPOSE OF REVIEW

This is an invited review regarding the use of intraoperative magnetic resonance imaging in the neurosurgical setting. The medical literature evaluating the intraoperative use of magnetic resonance imaging for neurosurgery has increased steadily since the implementation of this technique 10 years ago. The present review discusses recent findings and the current use of intraoperative magnetic resonance imaging in neurosurgery with special emphasis on the quality of available evidence.

RECENT FINDINGS

Intraoperative use of magnetic resonance imaging is a safe technique that enables the neurosurgeon to update data sets for navigational systems, to evaluate the extent of tumor resection and modify surgery if necessary, to guide instruments to the site of the lesion, and to evaluate the presence of intraoperative complications at the end of surgery. Although recent findings support the safety and efficacy of intraoperative magnetic resonance imaging for the above-mentioned purposes, there is no convincing evidence regarding its prognostic significance in the neurosurgical setting.

SUMMARY

Although the use of intraoperative magnetic resonance imaging in neurosurgery has increased significantly within the last 10 years, currently there are less than two dozen dedicated intraoperative units in the United States. The popularization of this technique depends on both economic justification and high-quality scientific evidence supporting its prognostic importance regarding patient outcome.