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Axial fluid-attenuated inversion recovery (FLAIR) images obtained from a patient with a grade III oligoastrocytoma. A, surgical planning images showing extent of FLAIR abnormality. B, intradissection images obtained when surgical goals were thought to have been achieved. The images show residual neoplasm and FLAIR abnormality. C, quality-assurance magnetic resonance images with further resection of neoplasm and dissection into the tumor/brain interface. Because of the dominant hemisphere location, the decision was made not to resect the FLAIR abnormality.
Source publication
This paper presents the development and implementation of an intra-operative magnetic resonance imaging (ioMRI) program using a moveable 3.0 T magnet with a large working aperture.
A previously established prototype 1.5 T ioMRI program based on a ceiling-mounted moveable magnet was upgraded to 3.0 T. The upgrade included a short, 1.73 m, magnet wit...
Context in source publication
Context 1
... these 40 patients, 30 underwent treatment for glioma, and the remainder had a variety of pathologies, including choroid plexus carcinoma, hemangioblastoma, ependymoma, medullo- blastoma, metastatic melanoma, olfactory groove meningioma (World Health Organization grade I), parasagittal meningioma (World Health Organization grade II), pituitary adenoma, and cavernoma. Of these 40 patients, unsuspected residual tumor was identified in 8 (20%), resulting in further surgical resection ( Figure 5). Of the 8 patients requiring additional resection, all were intra-axial lesions, including 5 high-grade gliomas, 1 low- grade glioma, 1 metastatic melanoma, and 1 pituitary adenoma. ...
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Citations
... Although low-field iMRI was first available in the United States in 1994 at Brigham and Women's Hospital in Boston, Massachusetts as a 0.5 Tesla (T) double donut scanner (23), experience with only a few 3T systems has been reported recently (9,17,(24)(25)(26)(27)(28). The main advantage of performing iMRI at higher field strength is generally superior image quality due to a higher signal-to-noise ratio (SNR). ...
Implementation of intraoperative magnetic resonance imaging (iMRI) has been shown to optimize the extent of resection and safety of brain tumor surgery. In addition, iMRI can help account for the phenomenon of brain shift and can help to detect complications earlier than routine postoperative imaging, which can potentially improve patient outcome. The higher signal-to-noise ratio offered by 3 Tesla (T) iMRI compared with lower field strength systems is particularly advantageous. The purpose of this article is to review the imaging protocols, imaging findings, and technical considerations related to 3T iMRI. To maximize efficiency, iMRI sequences can be tailored to particular types of tumors and procedures, including nonenhancing brain tumor surgery, enhancing brain tumor surgery, transsphenoidal pituitary tumor surgery, and laser ablation. Unique imaging findings on iMRI include the presence of surgically induced enhancement, which can be a potential confounder for residual enhancing tumor, and hyperacute hemorrhage, which tends to have intermediate signal on T1-weighted sequences and high signal on T2-weighted sequences due to the presence of oxyhemoglobin. MR compatibility and radiofrequency shielding pose particularly stringent technical constraints at 3T and influence the design and usage of the surgical suite with iMRI. J. Magn. Reson. Imaging 2014;39:1357–1365. © 2013 Wiley Periodicals, Inc.
Background
Intraoperative magnetic resonance imaging system (iMRIS) surgical theatre is a highly integrated operating room with an intraoperative magnetic resonance imaging (iMRI) designed originally for brain tumour surgery. Its use in neurointerventional procedures, particularly in the setting of endovascular coiling of intracranial aneurysms, has not been discussed in the literature to date. We present our initial experience about the safety and feasibility of iMRI to assess post operative complications and provide baseline imaging post coiling of intracranial aneurysms.
Methods
Consecutive patients who underwent iMRI between 2015 and 2018 were included in the study. Demographic, clinical details, endovascular technique and surgical outcomes were collected. Details of anesthesia during the procedure were also collected.
Results
Fifteen patients underwent iMRI with MRA to assess post coiling status of their elective endovascular coiling of intracranial aneurysms. The mean age in this cohort was 61 years and 46.7% were male. No immediate complications were seen either from the endovascular procedures or from the iMRI. All iMRI scans were performed as planned with no aborted or truncated scans. The image quality of the iMRI/MRA was adequate to detect the residual aneurysm, if present. There was no residual aneurysm on the angiogram that were not detected on the iMRIs. Of the 15 patients, 10 were safely discharged the following day and other 5 were discharged 2 days after their surgery.
Conclusions
The iMRI is an advantageous tool which can be integrated into neurointerventional workflow resulting in early post peri-procedural feedback and potentially reduced post-operative hospital stay.
Intracranial space-occupying lesions, particularly glial tumors in eloquent areas, may challenge the neurosurgeon who aims at preserving most relevant neuropsychological functions while removing as much of the lesion as possible. It has been repeatedly questioned whether radical resection of gliomas is the method of choice because of their invasive nature, but it has also been shown that patients can benefit from radical resection as much as possible both in primary and recurrent gliomas and in low-grade gliomas. Radical resection of glial tumors, however, is hampered by the risk of damaging neuronal functions, particularly of speech and motor functions. Therefore, early on in the development of modern neurosurgery, brain tumor surgery under local anesthesia (LA) was suggested in order to reduce the risk of immediate severe and nonreversible postoperative neurological deficit.
The concept of a mobile CT scanner was fi rst introduced by Klaus Fassbender, currently at Saarland University, Germany, and described in “Stroke” in 2003 (Fassbender et al. 2003, Fig. 10.2).
This chapter is based on the book How to Set Up an Acute Stroke Service by Grunwald, Fassbender and Wakhloo. Setting up an acute stroke service is a complex enterprise and necessitates background information on the medical condition stroke, current treatment options, reimbursement as well as the individual hospital environment. The chapter provides a general, comprehensive overview on each stage of the patient pathway. It explains what to consider when improving an existing service or when setting up a new service from scratch. In recent years, the creation of stroke centers has been a real asset to the management of acute ischemic stroke. The chapter identifies six important steps in the management of stroke, which helps to structure individual stroke pathway, tailored to specific institutional possibilities and constraints. Enabling the patient to keep up social contacts is perhaps the best opportunity to influence the patient's future quality of life.
This paper reviews the current intraoperative imaging tools that are available to assist neurosurgeons in the treatment of intracerebral hemorrhage (ICH). This review shares the authors' experience with each modality and discusses the advantages, potential limitations, and disadvantages of each.
Surgery for ICH is directed at blood clot removal, reduction of intracranial pressure, and minimization of secondary damage associated with hematoma breakdown products. For effective occlusion and safe obliteration of vascular anomalies associated with ICH, vascular neurosurgeons today require a thorough understanding of the various intraoperative imaging modalities available for obtaining real-time information. Use of one or more of these modalities may improve the surgeon's confidence during the procedure, the patient's safety during surgery, and surgical outcome.
The modern techniques discussed include 1) indocyanine green–based video angiography, which provides real-time information based on high-quality images showing the residual filling of vascular pathological entities and the patency of blood vessels of any size in the surgical field; and 2) intraoperative angiography, which remains the gold standard intraoperative diagnostic test in the surgical management of cerebral aneurysms and arteriovenous malformations. Hybrid procedures, providing multimodality image-guided surgeries and combining endovascular with microsurgical strategies within the same surgical session, have become feasible and safe. Microdoppler is a safe, noninvasive, and reliable technique for evaluation of hemodynamics of vessels in the surgical field, with the advantage of ease of use. Intraoperative MRI provides an effective navigation tool for cavernoma surgery, in addition to assessing the extent of resection during the procedure. Intraoperative CT scanning has the advantage of very high sensitivity to acute bleeding, thereby assisting in the confirmation of the extent of hematoma evacuation and the extent of vascular anomaly resection. Intraoperative ultrasound aids navigation and evacuation assessment during intracerebral hematoma evacuation surgeries. It supports the concept of minimally invasive surgery and has undergone extensive development in recent years, with the quality of ultrasound imaging having improved considerably.
Image-guided therapy, combined with modern intraoperative imaging modalities, has changed the fundamentals of conventional vascular neurosurgery by presenting real-time visualization of both normal tissue and pathological entities. These imaging techniques are important adjuncts to the surgeon's standard surgical armamentarium. Familiarity with these imaging modalities may help the surgeon complete procedures with improved safety, efficiency, and clinical outcome.
Intraoperative magnetic resonance imaging (iMRI) dates back to the 1990s and has been successfully applied in neurosurgery but they were low-field iMRI (< 1.0T). This paper reports the clinical experience with a 3T iMRI-integrated neurosurgical suite in Huashan Hospital, Shanghai, China.
From September 2010 through March 2012, 373 consecutive patients underwent neurological surgery under guidance with 3T iMRI. A retrospective analysis was conducted regarding clinical efficiency.
All surgery in the 373 patients was safe. The ratio of gross total resection for cerebral gliomas (n = 161) was increased from 55.90% to 87.58%. The ratio of benefit in extent of resection was 39.13%. One hundred and fifty eight of the 161 glioma patients accomplished follow-up at 3 months postoperatively. Twenty of 161 patients (12.42%) suffered from early motor deficit after surgery. Late motor deficit was however observed in five of 158 patients (3.16%). Twenty-one of 161 patients (13.04%) had early speech deficit and late speech deficit was only observed in six of 158 patients (3.80%). The ratio of gross total resection for pituitary adenomas (n = 49) was increased from 77.55% to 85.71%. The ratio of benefit in extent of resection was 10.2%. There were no iMRI-related adverse events even for patients who underwent awake craniotomy.
The 3T iMRI integrated neurosurgical suite provides high-quality intraoperative structural and functional imaging for real-time tumor resection control and accurate functional preservation, resulting in an improvement in maximal safe brain surgery.
This work investigates with simulation the effect of external stray magnetic fields on a recently reported MRI-linac hybrid, which by design will rotate about the patient axis during therapy. During rotation, interactions with magnetic fields from the earth or nearby ferromagnetic structures may cause unacceptable field distortions in the imaging field of view. Optimal approaches for passive shimming implementation, the degree and significance of residual distortion, and an analysis of the active shimming requirements for further correction are examined.
Finite element simulations were implemented on two representative types of biplanar magnet designs. Each of these magnet designs, consisting of a 0.2 T four-post and a 0.5 T C-type unit, was simulated with and without an external field on the order of the earth's field (0.5 G) over a range of rotated positions. Through subtraction, the field distribution resulting from the external field alone could be determined. These measured distributions were decomposed into spherical harmonic components, which were then used to investigate the effect of their selective removal to simulate the effects of passive and active shimming. Residual fields after different levels of shim treatment were measured and assessed in terms of their imaging consequence.
For both magnet types, the overall success of a passive shim implementation was highly dependent on the orientation for which it was based. If this orientation was chosen incorrectly, the passive shim would correct for the induced fields at that location, but the overall maximal distortion at other locations was exacerbated by up to a factor of two. The choice of passive shim orientation with the least negative consequence was found to be that where the magnet B(0) axis and transaxial component of the external field were aligned. Residual fields after passive shimming and frequency offset were found to be low in the simulated scenarios, contributing to <1 mm of distortion for most standard imaging sequences (based on a 0.5 G external field). However, extremely rapid single-shot sequences could be distorted by these residual fields to well over 5 mm. These residuals when analyzed were found to correspond primarily to second-order spherical harmonic terms. One term in particular was found to account for the vast majority of these residual fields, defined by the product of the two axes perpendicular to the axis of rotation. The implementation of this term would allow the resulting geometric distortion to fall to the order of 1 mm, even for single-shot sequences.
After appropriate passive shimming, the imaging distortion due to an external field of 0.5 G was found to be important only in rapid single-shot sequences, which are especially susceptible to field inhomogeneity. Should it be desirable to use these sequences for real-time tracking, made conceivable due to the lower susceptibility concerns at low field, these residual fields should be addressed. The ability to use only one second-order term for this correction will reduce the cost impact of this decision.
