Intraoperative magnetic resonance imaging in neurosurgery: the Brigham concept

Intraoperative MR Imaging during Glioma Resection

One of the major issues in the surgical treatment of gliomas is the concern about maximizing the extent of resection while minimizing neurological impairment. Thus, surgical planning by carefully observing the relationship between the glioma infiltration area and eloquent area of the connecting fibers is crucial. Neurosurgeons usually detect an eloquent area by functional MRI and identify a connecting fiber by diffusion tensor imaging. However, during surgery, the accuracy of neuronavigation can be decreased due to brain shift, but the positional information may be updated by intraoperative MRI and the next steps can be planned accordingly. In addition, various intraoperative modalities may be used to guide surgery, including neurophysiological monitoring that provides real-time information (e.g., awake surgery, motor-evoked potentials, and sensory evoked potential); photodynamic diagnosis, which can identify high-grade glioma cells; and other imaging techniques that provide anatomical information during the surgery. In this review, we present the historical and current context of the intraoperative MRI and some related approaches for an audience active in the technical, clinical, and research areas of radiology, as well as mention important aspects regarding safety and types of devices.

Bone Wax as an Intra-Cavitary Fiducial for Intra-Operative Magnetic Resonance Imaging Guided Resections of Eloquent Cortex Glioma

Background

The extent of resection of eloquent cortex low-grade glioma is improved by intraoperative magnetic resonance imaging (IOMRI) which is faced with challenges such as difficulty in automated registration after the MRI and prolongation of operative time.

Objective

We describe an easier and foolproof method of resection using bone wax as fiducial.

Surgical Procedure

A young male with right-frontal low-grade glioma anterior and superficial to the motor fibers was operated using IOMRI and awake craniotomy under neuromonitoring. Motor cortex mapping using phase reversal and continuous motor evoked potential (MEP) monitoring was used initially followed by continuous sub-cortical suction stimulation for deeper decompression until stimulation was seen. Bone wax in a triangular shape was placed at the suspicious margin and IOMRI was done.

Results

The tumor residue was seen anterior and deeper to the bone wax and removed subsequently.

Conclusion

The use of bone wax as a fiducial can aid in IOMRI-guided resection of eloquent cortex glioma in awake patients.

Enhanced registration of ultrasound volumes by segmentation of resection cavity in neurosurgical procedures

PURPOSE

Neurosurgeons can have a better understanding of surgical procedures by comparing ultrasound images obtained at different phases of the tumor resection. However, establishing a direct mapping between subsequent acquisitions is challenging due to the anatomical changes happening during surgery. We propose here a method to improve the registration of ultrasound volumes, by excluding the resection cavity from the registration process.

METHODS

The first step of our approach includes the automatic segmentation of the resection cavities in ultrasound volumes, acquired during and after resection. We used a convolution neural network inspired by the 3D U-Net. Then, subsequent ultrasound volumes are registered by excluding the contribution of resection cavity.

RESULTS

Regarding the segmentation of the resection cavity, the proposed method achieved a mean DICE index of 0.84 on 27 volumes. Concerning the registration of the subsequent ultrasound acquisitions, we reduced the mTRE of the volumes acquired before and during resection from 3.49 to 1.22 mm. For the set of volumes acquired before and after removal, the mTRE improved from 3.55 to 1.21 mm.

CONCLUSIONS

We proposed an innovative registration algorithm to compensate the brain shift affecting ultrasound volumes obtained at subsequent phases of neurosurgical procedures. To the best of our knowledge, our method is the first to exclude automatically segmented resection cavities in the registration of ultrasound volumes in neurosurgery.

Ultrasonographic features of focal cortical dysplasia and their relevance for epilepsy surgery

OBJECTIVE Surgery has proven to be the best therapeutic option for drug-refractory cases of focal cortical dysplasia (FCD)-associated epilepsy. Seizure outcome primarily depends on the completeness of resection, rendering the intraoperative FCD identification and delineation particularly important. This study aims to assess the diagnostic yield of intraoperative ultrasound (IOUS) in surgery for FCD-associated drug-refractory epilepsy. METHODS The authors prospectively enrolled 15 consecutive patients with drug-refractory epilepsy who underwent an IOUS-assisted microsurgical resection of a radiologically suspected FCD between January 2013 and July 2016. The findings of IOUS were compared with those of presurgical MRI postprocessing and the sonographic characteristics were analyzed in relation to the histopathological findings. The authors investigated the added value of IOUS in achieving completeness of resection and improving postsurgical seizure outcome. RESULTS The neurosurgeon was able to identify the dysplastic tissue by IOUS in all cases. The visualization of FCD type I was more challenging compared to FCD II and the demarcation of its borders was less clear. Postsurgical MRI showed residual dysplasia in 2 of the 3 patients with FCD type I. In all FCD type II cases, IOUS allowed for a clear intraoperative visualization and demarcation, strongly correlating with presurgical MRI postprocessing. Postsurgical MRI confirmed complete resection in all FCD type II cases. Sonographic features correlated with the histopathological classification of dysplasia (sonographic abnormalities increase continuously in the following order: FCD IA/IB, FCD IC, FCD IIA, FCD IIB). In 1 patient with IOUS features atypical for FCD, histopathological investigation showed nonspecific gliosis. CONCLUSIONS Morphological features of FCD, as identified by IOUS, correlate well with advanced presurgical imaging. The resolution of IOUS was superior to MRI in all FCD types. The appreciation of distinct sonographic features on IOUS allows the intraoperative differentiation between FCD and non-FCD lesions as well as the discrimination of different histological subtypes of FCD. Sonographic demarcation depends on the underlying degree of dysplasia. IOUS allows for more tailored resections by facilitating the delineation of the dysplastic tissue.

Segmentation-based registration of ultrasound volumes for glioma resection in image-guided neurosurgery

PURPOSE

In image-guided surgery for glioma removal, neurosurgeons usually plan the resection on images acquired before surgery and use them for guidance during the subsequent intervention. However, after the surgical procedure has begun, the preplanning images become unreliable due to the brain shift phenomenon, caused by modifications of anatomical structures and imprecisions in the neuronavigation system. To obtain an updated view of the resection cavity, a solution is to collect intraoperative data, which can be additionally acquired at different stages of the procedure in order to provide a better understanding of the resection. A spatial mapping between structures identified in subsequent acquisitions would be beneficial. We propose here a fully automated segmentation-based registration method to register ultrasound (US) volumes acquired at multiple stages of neurosurgery.

METHODS

We chose to segment sulci and falx cerebri in US volumes, which remain visible during resection. To automatically segment these elements, first we trained a convolutional neural network on manually annotated structures in volumes acquired before the opening of the dura mater and then we applied it to segment corresponding structures in different surgical phases. Finally, the obtained masks are used to register US volumes acquired at multiple resection stages.

RESULTS

Our method reduces the mean target registration error (mTRE) between volumes acquired before the opening of the dura mater and during resection from 3.49 mm (± 1.55 mm) to 1.36 mm (± 0.61 mm). Moreover, the mTRE between volumes acquired before opening the dura mater and at the end of the resection is reduced from 3.54 mm (± 1.75 mm) to 2.05 mm (± 1.12 mm).

CONCLUSION

The segmented structures demonstrated to be good candidates to register US volumes acquired at different neurosurgical phases. Therefore, our solution can compensate brain shift in neurosurgical procedures involving intraoperative US data.

An experimental and numerical study on tactile neuroimaging: A novel minimally invasive technique for intraoperative brain imaging

BACKGROUND

The success of tumour neurosurgery is highly dependent on the ability to accurately localize the operative target, which may shift during the operation. Performing intraoperative brain imaging is crucial in minimally invasive neurosurgery to detect the effect of brain shift on the tumour's location, and to maximize the efficiency of tumour resection.

METHOD

The major objective of this research is to introduce tactile neuroimaging as a novel minimally invasive technique for intraoperative brain imaging. To investigate the feasibility of the proposed method, an experimental and numerical study was first performed on silicone phantoms mimicking the brain tissue with a tumour. Then the study was extended to a clinical model with the meningioma tumour.

RESULTS

The stress distribution on the brain surface has high potential to intraoperatively localize the tumour.

CONCLUSION

Results suggest that tactile neuroimaging can be used to provide non-invasive and real-time intraoperative data on a tumour's features.

Finite element modeling of haptic thermography: A novel approach for brain tumor detection during minimally invasive neurosurgery

Intraoperative Thermal Imaging (ITI) is a novel neuroimaging method that can potentially locate tissue abnormalities and hence improves surgeon's diagnostic ability. In the present study, thermography technique coupled with artificial tactile sensing method called "haptic thermography" is utilized to investigate the presence of an abnormal object as a tumor with an elevated temperature relative to the normal tissue in the brain. The brain tissue is characterized as a hyper-viscoelastic material to be descriptive of mechanical behavior of the brain tissue during tactile palpation. Based on a finite element approach, Magnetic Resonance Imaging (MRI) data of a patient diagnosed to have a brain tumor is utilized to simulate and analyze the capability of haptic thermography in detection and localization of brain tumor. Steady-state thermal results prove that temperature distribution is an appropriate outcome of haptic thermography for the superficial tumors while heat flux distribution can be used as an extra thermal result for deeply located tumors.

Real time 3D visualization of intraoperative organ deformations using structured dictionary

Restricted visualization of the surgical field is one of the most critical challenges for minimally invasive surgery (MIS). Current intraoperative visualization systems are promising. However, they can hardly meet the requirements of high resolution and real time 3D visualization of the surgical scene to support the recognition of anatomic structures for safe MIS procedures. In this paper, we present a new approach for real time 3D visualization of organ deformations based on optical imaging patches with limited field-of-view and a single preoperative scan of magnetic resonance imaging (MRI) or computed tomography (CT). The idea for reconstruction is motivated by our empirical observation that the spherical harmonic coefficients corresponding to distorted surfaces of a given organ lie in lower dimensional subspaces in a structured dictionary that can be learned from a set of representative training surfaces. We provide both theoretical and practical designs for achieving these goals. Specifically, we discuss details about the selection of limited optical views and the registration of partial optical images with a single preoperative MRI/CT scan. The design proposed in this paper is evaluated with both finite element modeling data and ex vivo experiments. The ex vivo test is conducted on fresh porcine kidneys using 3D MRI scans with 1.2 mm resolution and a portable laser scanner with an accuracy of 0.13 mm. Results show that the proposed method achieves a sub-3 mm spatial resolution in terms of Hausdorff distance when using only one preoperative MRI scan and the optical patch from the single-sided view of the kidney. The reconstruction frame rate is between 10 frames/s and 39 frames/s depending on the complexity of the test model.

Anesthetic concerns for pediatric patients in an intraoperative MRI suite

PURPOSE OF REVIEW

Intraoperative magnetic resonance imaging (iMRI) is an evolving technology used to provide precise intraoperative navigation during a variety of neurosurgical and other types of surgical procedures. Anesthesiologists need to be aware of the unique challenges created by this environment. Failure to recognize the differences between the diagnostic MRI environment and the iMRI environment can compromise the safety of the patient and operating room staff and present logistical problems.

RECENT FINDINGS

Recent surgical reports herald the uses and benefits of iMRI. However, there are a few in the anesthesia literature addressing the significant benefits and the anesthesia-specific issues this technology creates. We will review recent reports describing anesthetic care of patients in this environment as well as examine the recent surgical and radiologic literature as they relate to issues faced by anesthesiologists.

SUMMARY

We describe the design of different iMRI suites as well as provide a breakdown of both patient and equipment issues encountered by anesthesiologists practicing in this environment. Finally, we offer our ongoing experience in this environment and provide suggestions to optimize patient outcomes.

Implementation and preliminary clinical experience with the use of ceiling mounted mobile high field intraoperative magnetic resonance imaging between two operating rooms

OBJECTIVE

Intraoperative magnetic resonance imaging (ioMRI) provides immediate feedback and quality assurance enabling the neurosurgeon to improve the quality of a range of neurosurgical procedures. Implementation of ioMRI is a complex and costly process. We describe our preliminary 16 months experience with the integration of an IMRIS movable ceiling mounted high field (1.5 T) ioMRI setup with two operating rooms.

METHODS

Aspects of implementation of our ioMRI and our initial 16 months of clinical experience in 180 consecutive patients were reviewed.

RESULTS

The installation of a ceiling mounted movable ioMRI between two operating rooms was completed in April 2008 at Barnes-Jewish Hospital in St. Louis. Experience with 180 neurosurgical cases (M:F-100:80, age range 1-79 years, 71 gliomas, 57 pituitary adenomas, 9 metastases, 11 other tumor cases, 4 Chiari decompressions, 6 epilepsy resections and 22 other miscellaneous procedures) demonstrated that this device effectively provided high quality real-time intraoperative imaging. In 74 of all 180 cases (41%) and in 54% of glioma resections, the surgeon modified the procedure based upon the ioMRI. Ninety-three percent of ioMRI glioma cases achieved gross/near total resection compared to 65% of non ioMRI glioma cases in this time frame.

CONCLUSION

A movable high field strength ioMRI can be safely integrated between two neurosurgical operating rooms. This strategy leads to modification of the surgical procedure in a significant number of cases, particularly for glioma surgery. Long-term follow up is needed to evaluate the clinical and financial impact of this technology in the field of neurosurgery.

Intraoperative imaging in neurosurgery: where will the future take us?

Intraoperative MRI (ioMRI) dates back to the 1990s and since then has been successfully applied in neurosurgery for three primary reasons with the last one becoming the most significant today: (1) brain shift-corrected navigation, (2) monitoring/controlling thermal ablations, and (3) identifying residual tumor for resection. IoMRI, which today is moving into other applications, including treatment of vasculature and the spine, requires advanced 3T MRI platforms for faster and more flexible image acquisitions, higher image quality, and better spatial and temporal resolution; functional capabilities including fMRI and DTI; non-rigid registration algorithms to register pre- and intraoperative images; non-MRI imaging improvements to continuously monitor brain shift to identify when a new 3D MRI data set is needed intraoperatively; more integration of imaging and MRI-compatible navigational and robot-assisted systems; and greater computational capabilities to handle the processing of data. The Brigham and Women's Hospital's "AMIGO" suite is described as a setting for progress to continue in ioMRI by incorporating other modalities including molecular imaging. A call to action is made to have other researchers and clinicians in the field of image guided therapy to work together to integrate imaging with therapy delivery systems (such as laser, MRgFUS, endoscopic, and robotic surgery devices).

Present day's standards in microsurgery of low-grade gliomas

Low-grade gliomas are slow growing intrinsic lesions that induces a progressive functional reshaping of the brain. Surgical removal of these lesions requires the combined efforts of a multidiscipinary team of neurosurgeon, neuroradiologist, neuropsychologist, neurophysiologist, and neurooncologists that all together contribute in the definition of the location, extension, and extent of functional involvement that a specific lesion has induced in a particular patient. Each tumor has induced particular and specific changes of the functional network, that varies among patients. This requires that each treatment plan should be tailored to the tumor and to the patient. When this is reached, surgery should be accomplished according to functional and anatomical boundaries, and has to aim to the maximal resection with the maximal patient functional preservation. This can be reached at the time of the initial surgery, depending on the functional organization of the brain, or may require additional surgeries, eventually intermingled with adjuvant treatments. The use of so called brain mapping techniques extend surgical indications, improve extent of resection with greater oncological impact, minimization of morbidity and increase in quality of life. To achieve the goal of a satisfactory tumor resection associated with the full preservation of the patients abilities, a series of neuropsychological, neurophysiological, neuroradiological and intraoperative investigations have to be performed. In this chapter, we will describe the rationale, the indications and the modality for performing a safe and rewarding surgical removal of low-grade gliomas by using these techniques, as well as the functional and oncological results.

Infrared thermal imaging: a review of the literature and case report

Intraoperative Thermal Imaging (ITI) is a novel neuroimaging technique that can potentially locate the margins of primary and metastatic brain tumors. As a result, the additional real-time anatomical and pathophysiological information may significantly contribute to an improved extent of tumor resection. Our objectives in this article are i) to briefly discuss the current status of intraoperative imaging modalities including ITI and ii) to present a case report that evaluates the usefulness of ITI in detection of brain tumor and its margins. In this case report, ITI was used in a patient with a metastatic intracortical melanoma. The thermal profile of the tumor and surrounding normal cerebral cortex were mapped with a ThermaCAM P60 (TCP60) infrared camera by FLIR Systems. The data obtained by TCP60, intra-operatively, revealed a clear demarcation of tumor with significant temperature differences, up to 3.3 degrees C, between the tumor core (36.4 degrees C) and the surrounding normal tissue (33.1 degrees C). Ultrasound and pre-resection MR and CT confirmed the position and size of the metastasis. The volume of the tumor was preoperatively calculated using the CyberKnife software and postoperative volumetric measurement of the tumor residual was calculated by the Gamma Knife software. Our result, along with previously published results of others, suggests that thermal imaging could be used to provide a rapid, non-invasive, and real-time intra-operative imaging.

Intraoperative ultrasound to define focal cortical dysplasia in epilepsy surgery

Focal cortical dyplasia (FCD) is a frequent cause of medication-resistant focal epilepsy. Patients with FCD may benefit from epilepsy surgery. However, it is difficult to intraoperatively define lesion boundaries. In this case report we present a novel tool to identify FCD intraoperatively. A patient with frontal lobe epilepsy underwent resection of a left frontomesial FCD. Image guidance was achieved by intraoperative ultrasound, which depicted the lesion with a higher resolution than preoperative MRI. Postoperatively the patient remained seizure free. Intraoperative ultrasound may be helpful in identifying and targeting subtle epileptogenic lesions, which are difficult to visualize.

MRI-guided laparoscopic and robotic surgery for malignancies

Endoscopic surgery has some clear benefits, but it also has some disadvantages in reducing surgeons' normal dexterity and limiting their ability to deal with difficult situations. Computer-aided surgery has been proposed to overcome some of the drawbacks of traditional minimally invasive surgery. The proposed systems make possible a secure, precise procedure with no limitations on the operator's freedom of movement. Image-guided surgery is a new technical tool in surgical oncology. Interventional magnetic resonance imaging (MRI) has entered a new stage in which computer-based techniques play an expanding role in planning, monitoring, and controlling procedures. MRI-guided surgery not only represents a technical challenge but is a transformation from conventional hand-eye coordination to interactive navigational operations. We have recently developed an MRI-guided robot-assisted interventional surgical system as well as an MRI-compatible endoscope. They allow the performance of precise image-guided interventional therapy and endoscopic surgery. MRI-guided laparoscopic surgery is now feasible for malignancies and will play an important part in the development of minimally invasive therapy.