Brain shift compensation and neurosurgical image fusion using intraoperative MRI: current status and future challenges

Application accuracy of a frameless optical neuronavigation system as a guide for craniotomies in dogs

BACKGROUND

Optical neuronavigation systems using infrared light to create a virtual reality image of the brain allow the surgeon to track instruments in real time. Due to the high vulnerability of the brain, neurosurgical interventions must be performed with a high precision. The aim of the experimental cadaveric study was to determine the application accuracy of a frameless optical neuronavigation system as guide for craniotomies by determining the target point deviation of predefined target points at the skull surface in the area of access to the cerebrum, cerebellum and the pituitary fossa. On each of the five canine cadaver heads ten target points were marked in a preoperative computed tomography (CT) scan. These target points were found on the cadaver skulls using the optical neuronavigation system. Then a small drill hole (1.5 mm) was drilled at these points. Subsequently, another CT scan was made. Both CT data sets were fused into the neuronavigation software, and the actual target point coordinates were identified. The target point deviation was determined as the difference between the planned and drilled target point coordinates. The calculated deviation was compared between two observers.

RESULTS

The analysis of the target point accuracies of all dogs in both observers taken together showed a median target point deviation of 1.57 mm (range: 0.42 to 5.14 mm). No significant differences were found between the observers or the different areas of target regions.

CONCLUSION

The application accuracy of the described system is similar to the accuracy of other optical neuronavigation systems previously described in veterinary medicine, in which mean values of 1.79 to 4.3 mm and median target point deviations of 0.79 to 3.53 mm were determined.

Learning Expected Appearances for Intraoperative Registration during Neurosurgery

We present a novel method for intraoperative patient-to-image registration by learning Expected Appearances. Our method uses preoperative imaging to synthesize patient-specific expected views through a surgical microscope for a predicted range of transformations. Our method estimates the camera pose by minimizing the dissimilarity between the intraoperative 2D view through the optical microscope and the synthesized expected texture. In contrast to conventional methods, our approach transfers the processing tasks to the preoperative stage, reducing thereby the impact of low-resolution, distorted, and noisy intraoperative images, that often degrade the registration accuracy. We applied our method in the context of neuronavigation during brain surgery. We evaluated our approach on synthetic data and on retrospective data from 6 clinical cases. Our method outperformed state-of-the-art methods and achieved accuracies that met current clinical standards.

Advances in the intraoperative delineation of malignant glioma margin

Surgery plays a critical role in the treatment of malignant glioma. However, due to the infiltrative growth and brain shift, it is difficult for neurosurgeons to distinguish malignant glioma margins with the naked eye and with preoperative examinations. Therefore, several technologies were developed to determine precise tumor margins intraoperatively. Here, we introduced four intraoperative technologies to delineate malignant glioma margin, namely, magnetic resonance imaging, fluorescence-guided surgery, Raman histology, and mass spectrometry. By tracing their detecting principles and developments, we reviewed their advantages and disadvantages respectively and imagined future trends.

Augmented and virtual reality usage in awake craniotomy: a systematic review

Augmented and virtual reality (AR, VR) are becoming promising tools in neurosurgery. AR and VR can reduce challenges associated with conventional approaches via the simulation and mimicry of specific environments of choice for surgeons. Awake craniotomy (AC) enables the resection of lesions from eloquent brain areas while monitoring higher cortical and subcortical functions. Evidence suggests that both surgeons and patients benefit from the various applications of AR and VR in AC. This paper investigates the application of AR and VR in AC and assesses its prospective utility in neurosurgery. A systematic review of the literature was performed using PubMed, Scopus, and Web of Science databases in accordance with the PRISMA guidelines. Our search results yielded 220 articles. A total of six articles consisting of 118 patients have been included in this review. VR was used in four papers, and the other two used AR. Tumour was the most common pathology in 108 patients, followed by vascular lesions in eight patients. VR was used for intraoperative mapping of language, vision, and social cognition, while AR was incorporated in preoperative training of white matter dissection and intraoperative visualisation and navigation. Overall, patients and surgeons were satisfied with the applications of AR and VR in their cases. AR and VR can be safely incorporated during AC to supplement, augment, or even replace conventional approaches in neurosurgery. Future investigations are required to assess the feasibility of AR and VR in various phases of AC.

Tracking motor and language eloquent white matter pathways with intraoperative fiber tracking versus preoperative tractography adjusted by intraoperative MRI-based elastic fusion

OBJECTIVE

Preoperative fiber tracking (FT) enables visualization of white matter pathways. However, the intraoperative accuracy of preoperative image registration is reduced due to brain shift. Intraoperative FT is currently considered the standard of anatomical accuracy, while intraoperative imaging can also be used to correct and update preoperative data by intraoperative MRI (ioMRI)-based elastic fusion (IBEF). However, the use of intraoperative tractography is restricted due to the need for additional acquisition of diffusion imaging in addition to scanner limitations, quality factors, and setup time. Since IBEF enables compensation for brain shift and updating of preoperative FT, the aim of this study was to compare intraoperative FT with IBEF of preoperative FT.

METHODS

Preoperative MRI (pMRI) and ioMRI, both including diffusion tensor imaging (DTI) data, were acquired between February and November 2018. Anatomy-based DTI FT of the corticospinal tract (CST) and the arcuate fascicle (AF) was reconstructed at various fractional anisotropy (FA) values on pMRI and ioMRI, respectively. The intraoperative DTI FT, as a baseline tractography, was fused with original preoperative FT and IBEF-compensated FT, processes referred to as rigid fusion (RF) and elastic fusion (EF), respectively. The spatial overlap index (Dice coefficient [DICE]) and distances of surface points (average surface distance [ASD]) of fused FT before and after IBEF were analyzed and compared in operated and nonoperated hemispheres.

RESULTS

Seventeen patients with supratentorial brain tumors were analyzed. On the operated hemisphere, the overlap index of pre- and intraoperative FT of the CST by DICE significantly increased by 0.09 maximally after IBEF. A significant decrease by 0.5 mm maximally in the fused FT presented by ASD was observed. Similar improvements were found in IBEF-compensated FT, for which AF tractography on the tumor hemispheres increased by 0.03 maximally in DICE and decreased by 1.0 mm in ASD.

CONCLUSIONS

Preoperative tractography after IBEF is comparable to intraoperative tractography and can be a reliable alternative to intraoperative FT.

Use of virtual magnetic resonance imaging to compensate for brain shift during image-guided surgery: illustrative case

BACKGROUND

Maximal safe resection is the paramount objective in the surgical management of malignant brain tumors. It is facilitated through use of image-guided neuronavigation. Intraoperative image guidance systems use preoperative magnetic resonance imaging (MRI) as the navigational map. The accuracy of neuronavigation is limited by intraoperative brain shift and can become less accurate over the course of the procedure. Intraoperative MRI can compensate for dynamic brain shift but requires significant space and capital investment, often unavailable at many centers.

OBSERVATIONS

The authors described a case in which an image fusion algorithm was used in conjunction with an intraoperative computed tomography (CT) system to compensate for brain shift during resection of a brainstem hemorrhagic melanoma metastasis. Following initial debulking of the hemorrhagic metastasis, intraoperative CT was performed to ascertain extent of resection. An elastic image fusion (EIF) algorithm was used to create virtual MRI relative to both the intraoperative CT scan and preoperative MRI, which facilitated complete resection of the tumor while preserving critical brainstem anatomy.

LESSONS

EIF algorithms can be used with multimodal images (preoperative MRI and intraoperative CT) and create an updated virtual MRI data set to compensate for brain shift in neurosurgery and aid in maximum safe resection of malignant brain tumors.

Pose Estimation and Non-Rigid Registration for Augmented Reality During Neurosurgery

OBJECTIVE

A craniotomy is the removal of a part of the skull to allow surgeons to have access to the brain and treat tumors. When accessing the brain, a tissue deformation occurs and can negatively influence the surgical procedure outcome. In this work, we present a novel Augmented Reality neurosurgical system to superimpose pre-operative 3D meshes derived from MRI onto a view of the brain surface acquired during surgery.

METHODS

Our method uses cortical vessels as main features to drive a rigid then non-rigid 3D/2D registration. We first use a feature extractor network to produce probability maps that are fed to a pose estimator network to infer the 6-DoF rigid pose. Then, to account for brain deformation, we add a non-rigid refinement step formulated as a Shape-from-Template problem using physics-based constraints that helps propagate the deformation to sub-cortical level and update tumor location.

RESULTS

We tested our method retrospectively on 6 clinical datasets and obtained low pose error, and showed using synthetic dataset that considerable brain shift compensation and low TRE can be achieved at cortical and sub-cortical levels.

CONCLUSION

The results show that our solution achieved accuracy below the actual clinical errors demonstrating the feasibility of practical use of our system.

SIGNIFICANCE

This work shows that we can provide coherent Augmented Reality visualization of 3D cortical vessels observed through the craniotomy using a single camera view and that cortical vessels provide strong features for performing both rigid and non-rigid registration.

Photoacoustic-MR Image Registration Based on a Co-Sparse Analysis Model to Compensate for Brain Shift

Brain shift is an important obstacle to the application of image guidance during neurosurgical interventions. There has been a growing interest in intra-operative imaging to update the image-guided surgery systems. However, due to the innate limitations of the current imaging modalities, accurate brain shift compensation continues to be a challenging task. In this study, the application of intra-operative photoacoustic imaging and registration of the intra-operative photoacoustic with pre-operative MR images are proposed to compensate for brain deformation. Finding a satisfactory registration method is challenging due to the unpredictable nature of brain deformation. In this study, the co-sparse analysis model is proposed for photoacoustic-MR image registration, which can capture the interdependency of the two modalities. The proposed algorithm works based on the minimization of mapping transform via a pair of analysis operators that are learned by the alternating direction method of multipliers. The method was evaluated using an experimental phantom and ex vivo data obtained from a mouse brain. The results of the phantom data show about 63% improvement in target registration error in comparison with the commonly used normalized mutual information method. The results proved that intra-operative photoacoustic images could become a promising tool when the brain shift invalidates pre-operative MRI.

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.

Advanced Imaging Techniques for Newly Diagnosed and Recurrent Gliomas

Management of gliomas following initial diagnosis requires thoughtful presurgical planning followed by regular imaging to monitor treatment response and survey for new tumor growth. Traditional MR imaging modalities such as T1 post-contrast and T2-weighted sequences have long been a staple of tumor diagnosis, surgical planning, and post-treatment surveillance. While these sequences remain integral in the management of gliomas, advances in imaging techniques have allowed for a more detailed characterization of tumor characteristics. Advanced MR sequences such as perfusion, diffusion, and susceptibility weighted imaging, as well as PET scans have emerged as valuable tools to inform clinical decision making and provide a non-invasive way to help distinguish between tumor recurrence and pseudoprogression. Furthermore, these advances in imaging have extended to the operating room and assist in making surgical resections safer. Nevertheless, surgery, chemotherapy, and radiation treatment continue to make the interpretation of MR changes difficult for glioma patients. As analytics and machine learning techniques improve, radiomics offers the potential to be more quantitative and personalized in the interpretation of imaging data for gliomas. In this review, we describe the role of these newer imaging modalities during the different stages of management for patients with gliomas, focusing on the pre-operative, post-operative, and surveillance periods. Finally, we discuss radiomics as a means of promoting personalized patient care in the future.

Viscoelastic biomechanical models to predict inward brain-shift using public benchmark data

Brain-shift during neurosurgery compromises the accuracy of tracking the boundaries of the tumor to be resected. Although several studies have used various finite element models (FEMs) to predict inward brain-shift, evaluation of their accuracy and efficiency based on public benchmark data has been limited. This study evaluates several FEMs proposed in the literature (various boundary conditions, mesh sizes, and material properties) by using intraoperative imaging data (the public REtroSpective Evaluation of Cerebral Tumors [RESECT] database). Four patients with low-grade gliomas were identified as having inward brain-shifts. We computed the accuracy (using target registration error) of several FEM-based brain-shift predictions and compared our findings. Since information on head orientation during craniotomy is not included in this database, we tested various plausible angles of head rotation. We analyzed the effects of brain tissue viscoelastic properties, mesh size, craniotomy position, CSF drainage level, and rigidity of meninges and then quantitatively evaluated the trade-off between accuracy and central processing unit time in predicting inward brain-shift across all models with second-order tetrahedral FEMs. The mean initial target registration error (TRE) was 5.78 ± 3.78 mm with rigid registration. FEM prediction (edge-length, 5 mm) with non-rigid meninges led to a mean TRE correction of 1.84 ± 0.83 mm assuming heterogeneous material. Results show that, for the low-grade glioma patients in the study, including non-rigid modeling of the meninges was significant statistically. In contrast including heterogeneity was not significant. To estimate the optimal head orientation and CSF drainage, an angle step of 5° and an CSF height step of 5 mm were enough leading to <0.26 mm TRE fluctuation.

Utilizing Intraoperative Navigated 3D Color Doppler Ultrasound in Glioma Surgery

Background

In glioma surgery, the patient’s outcome is dramatically influenced by the extent of resection and residual tumor volume. To facilitate safe resection, neuronavigational systems are routinely used. However, due to brain shift, accuracy decreases with the course of the surgery. Intraoperative ultrasound has proved to provide excellent live imaging, which may be integrated into the navigational procedure. Here we describe the visualization of vascular landmarks and their shift during tumor resection using intraoperative navigated 3D color Doppler ultrasound (3D iUS color Doppler).

Methods

Six patients suffering from glial tumors located in the temporal lobe were included in this study. Intraoperative computed tomography was used for registration. Datasets of 3D iUS color Doppler were generated before dural opening and after tumor resection, and the vascular tree was segmented manually. In each dataset, one to four landmarks were identified, compared to the preoperative MRI, and the Euclidean distance was calculated.

Results

Pre-resectional mean Euclidean distance of the marked points was 4.1 ± 1.3 mm (mean ± SD), ranging from 2.6 to 6.0 mm. Post-resectional mean Euclidean distance was 4.7. ± 1.0 mm, ranging from 2.9 to 6.0 mm.

Conclusion

3D iUS color Doppler allows estimation of brain shift intraoperatively, thus increasing patient safety. Future implementation of the reconstructed vessel tree into the navigational setup might allow navigational updating with further consecutive increasement of accuracy.

Applications of augmented reality in the neurosurgical operating room: A systematic review of the literature

Advancements in imaging techniques are key forces of progress in neurosurgery. The importance of accurate visualization of intraoperative anatomy cannot be overemphasized and is commonly delivered through traditional neuronavigation. Augmented Reality (AR) technology has been tested and applied widely in various neurosurgical subspecialties in intraoperative, clinical use and shows promise for the future. This systematic review of the literature explores the ways in which AR technology has been successfully brought into the operating room (OR) and incorporated into clinical practice. A comprehensive literature search was performed in the following databases from inception-April 2020: Ovid MEDLINE, Ovid EMBASE, and The Cochrane Library. Studies retrieved were then screened for eligibility against predefined inclusion/exclusion criteria. A total of 54 articles were included in this systematic review. The studies were sub- grouped into brain and spine subspecialties and analyzed for their incorporation of AR in the neurosurgical clinical setting. AR technology has the potential to greatly enhance intraoperative visualization and guidance in neurosurgery beyond the traditional neuronavigation systems. However, there are several key challenges to scaling the use of this technology and bringing it into standard operative practice including accurate and efficient brain segmentation of magnetic resonance imaging (MRI) scans, accounting for brain shift, reducing coregistration errors, and improving the AR device hardware. There is also an exciting potential for future work combining AR with multimodal imaging techniques and artificial intelligence to further enhance its impact in neurosurgery.

Impact of 3-Dimensional Versus 2-Dimensional Image Distortion Correction on Stereotactic Neurosurgical Navigation Image Fusion Reliability for Images Acquired With Intraoperative Magnetic Resonance Imaging

BACKGROUND

Fusion of preoperative and intraoperative magnetic resonance imaging (iMRI) studies during stereotactic navigation may be very useful for procedures such as tumor resections but can be subject to error because of image distortion.

OBJECTIVE

To assess the impact of 3-dimensional (3D) vs 2-dimensional (2D) image distortion correction on the accuracy of auto-merge image fusion for stereotactic neurosurgical images acquired with iMRI using a head phantom in different surgical positions.

METHODS

T1-weighted intraoperative images of the head phantom were obtained using 1.5T iMRI. Images were postprocessed with 2D and 3D image distortion correction. These studies were fused to T1-weighted preoperative MRI studies performed on a 1.5T diagnostic MRI. The reliability of the auto-merge fusion of these images for 2D and 3D correction techniques was assessed both manually using the stereotactic navigation system and via image analysis software.

RESULTS

Eight surgical positions of the head phantom were imaged with iMRI. Greater image distortion occurred with increased distance from isocenter in all 3 axes, reducing accuracy of image fusion to preoperative images. Visually reliable image fusions were accomplished in 2/8 surgical positions using 2D distortion correction and 5/8 using 3D correction. Three-dimensional correction yielded superior image registration quality as defined by higher maximum mutual information values, with improvements ranging between 2.3% and 14.3% over 2D correction.

CONCLUSION

Using 3D distortion correction enhanced the reliability of surgical navigation auto-merge fusion of phantom images acquired with iMRI across a wider range of head positions and may improve the accuracy of stereotactic navigation using iMRI images.

Deformation Aware Augmented Reality for Craniotomy using 3D/2D Non-rigid Registration of Cortical Vessels

Intra-operative brain shift is a well-known phenomenon that describes non-rigid deformation of brain tissues due to gravity and loss of cerebrospinal fluid among other phenomena. This has a negative influence on surgical outcome that is often based on pre-operative planning where the brain shift is not considered. We present a novel brain-shift aware Augmented Reality method to align pre-operative 3D data onto the deformed brain surface viewed through a surgical microscope. We formulate our non-rigid registration as a Shape-from-Template problem. A pre-operative 3D wire-like deformable model is registered onto a single 2D image of the cortical vessels, which is automatically segmented. This 3D/2D registration drives the underlying brain structures, such as tumors, and compensates for the brain shift in sub-cortical regions. We evaluated our approach on simulated and real data composed of 6 patients. It achieved good quantitative and qualitative results making it suitable for neurosurgical guidance.

High-quality photoacoustic image reconstruction based on deep convolutional neural network: towards intra-operative photoacoustic imaging

The use of intra-operative imaging system as an intervention solution to provide more accurate localization of complicated structures has become a necessity during the neurosurgery. However, due to the limitations of conventional imaging systems, high-quality real-time intra-operative imaging remains as a challenging problem. Meanwhile, photoacoustic imaging has appeared so promising to provide images of crucial structures such as blood vessels and microvasculature of tumors. To achieve high-quality photoacoustic images of vessels regarding the artifacts caused by the incomplete data, we proposed an approach based on the combination of time-reversal (TR) and deep learning methods. The proposed method applies a TR method in the first layer of the network which is followed by the convolutional neural network with weights adjusted to a set of simulated training data for the other layers to estimate artifact-free photoacoustic images. It was evaluated using a generated synthetic database of vessels. The mean of signal to noise ratio (SNR), peak SNR, structural similarity index, and edge preservation index for the test data were reached 14.6 dB, 35.3 dB, 0.97 and 0.90, respectively. As our results proved, by using the lower number of detectors and consequently the lower data acquisition time, our approach outperforms the TR algorithm in all criteria in a computational time compatible with clinical use.

A novel three-dimensional template combined with MR-guided 125I brachytherapy for recurrent glioblastoma

Background

At present, the treatment of recurrent glioblastoma is extremely challenging. In this study, we used a novel three-dimensional non-coplanar template (3DNPT) combined with open MR to guide ¹²⁵I seed implantation for recurrent glioblastoma. The aim of this study was to evaluate the feasibility, accuracy, and effectiveness of this technique.

Methods

Twenty-four patients of recurrent glioblastoma underwent 3DNPT with open MR-guided ¹²⁵I brachytherapy from August 2017 to January 2019. Preoperative treatment plan and 3DNPT were made according to enhanced isovoxel T1-weighted MR images. ¹²⁵I seeds were implanted using 3DNPT and 1.0-T open MR imaging guidance. Dosimetry verification was performed after brachytherapy based on postoperative CT/MR fusion images. Preoperative and postoperative dosimetry parameters of D90, V100, V200, conformity index (CI), external index (EI) were compared. The objective response rate (ORR) at 6 months and 1-year survival rate were calculated. Median overall survival (OS) measured from the date of brachytherapy was estimated by Kaplan-Meier method.

Results

There were no significant differences between preoperative and postoperative dosimetry parameters of D90, V100, V200, CI, EI (P > 0.05). The ORR at 6 months was 75.0%. The 1-year survival rate was 58.3%. Median OS was 12.9 months. One case of small amount of epidural hemorrhage occurred during the procedure. There were 3 cases of symptomatic brain edema after brachytherapy treatment, including grade three toxicity in 1 case and grade two toxicity in 2 cases. The three patients were treated with corticosteroid for 2 to 4 weeks. The clinical symptoms related to brain edema were significantly alleviated thereafter.

Conclusions

3DNPT combined with open MR-guided ¹²⁵I brachytherapy for circumscribed recurrent glioblastoma is feasible, effective, and with low risk of complications. Postoperative dosimetry matched the preoperative treatment plan. The described method can be used as a novel implantation technique for ¹²⁵I brachytherapy in the treatment of recurrent gliomas.

Trial registration

The study was approved by the Institutional Review Board of Shandong Provincial Hospital Affiliated to Shandong University (NSFC:NO.2017–058), registered 1st July 2017.

Onscreen-guided resection of extra-axial and intra-axial forebrain masses through registration of a variable-suction tissue resection device with a neuronavigation system

OBJECTIVES

To describe a novel surgical technique in which neuronavigation is used to guide a tissue resection device during excision of forebrain masses in locations difficult to visualize optically.

STUDY DESIGN

Short case series.

ANIMALS

Six dogs and one cat with forebrain masses (five neoplastic, two nonneoplastic) undergoing excision with a novel tissue resection device and veterinary neuronavigation system.

METHODS

The animals and resection instrument were coregistered to the neuronavigation system. Surgery was guided by real-time onscreen visualization of the resection instrument position relative to the preoperative MR images. Surgical outcome was evaluated by calculating residual tumor volume according to postoperative MRI.

RESULTS

The technique was technically simple and led to the collection of diagnostic tissue samples in all cases. Postoperative MRI was available in six cases, two with gross-total resection, three with near-total resection, and one with subtotal resection.

CONCLUSION

Neuronavigation-guided resection of intra-axial and extra-axial brain masses with the resection device resulted in gross-total or near-total resection in five of six animals with tumors otherwise difficult to visualize. Risk of brain shift limited absolute reliance on navigation images.

CLINICAL SIGNIFICANCE

Real-time neuronavigation assistance is a feasible method for guidance and successful resection of brain masses that are poorly visualized because of intra-axial or deep location, tumor appearance, or hemorrhage.

Alignment of Cortical Vessels viewed through the Surgical Microscope with Preoperative Imaging to Compensate for Brain Shift

Brain shift is a non-rigid deformation of brain tissue that is affected by loss of cerebrospinal fluid, tissue manipulation and gravity among other phenomena. This deformation can negatively influence the outcome of a surgical procedure since surgical planning based on pre-operative image becomes less valid. We present a novel method to compensate for brain shift that maps preoperative image data to the deformed brain during intra-operative neurosurgical procedures and thus increases the likelihood of achieving a gross total resection while decreasing the risk to healthy tissue surrounding the tumor. Through a 3D/2D non-rigid registration process, a 3D articulated model derived from pre-operative imaging is aligned onto 2D images of the vessels viewed through the surgical miscroscopic intra-operatively. The articulated 3D vessels constrain a volumetric biomechanical model of the brain to propagate cortical vessel deformation to the parenchyma and in turn to the tumor. The 3D/2D non-rigid registration is performed using an energy minimization approach that satisfies both projective and physical constraints. Our method is evaluated on real and synthetic data of human brain showing both quantitative and qualitative results and exhibiting its particular suitability for real-time surgical guidance.

Application of diffusion tensor tractography in the surgical treatment of brain tumors located in functional areas

The present study aimed to explore the application of diffusion tensor tractography (DTT) in the preoperative planning and prognostic evaluation of tumors located in the functional areas of the brain. A total of 42 patients diagnosed with intracranial tumors were randomly assigned to either the trial or the control group. DT imaging (DTI) was performed on the basis of preoperative conventional magnetic resonance imaging (MRI) and analyzed for patients in the trial group. Patients in the control group underwent only routine MRI scans. The effect of DTT on the prognosis of patients was evaluated by tumor resection rate and quality of life evaluation using Karnofsky performance score (KPS) comparison between the trial and control groups. There were no significant differences for total tumor removal rate in the trial group (85.71%) compared with that in the control group (71.43%) (P>0.05). The rate of postoperative symptom improvement in the trial group (85.71%) was significantly higher compared with that in the control group (47.62%) (P<0.05). The KPS value of the trial group was significantly higher postoperatively (78.57±17.40) compared with that preoperatively (66.67±16.23) (P<0.05). The KPS value of the control group postoperatively (72.38±19.21) was significantly higher compared with that preoperatively (66.67±16.00) (P<0.05). The postoperative KPS improvement rate [postoperative value-preoperative value)/preoperative value] of the trial group was significantly higher compared with that in the control group. In conclusion, the use of DTT is an effective supplement to traditional MRI, with particular relevance in preoperative planning, particularly for tumors in the functional area of the brain, and can significantly improve the prognostic function of patients.

Predicted Microscopic Cortical Brain Images for Optimal Craniotomy Positioning and Visualization

During a craniotomy, the skull is opened to allow surgeons to have access to the brain and perform the procedure. The position and size of this opening are chosen in a way to avoid critical structures, such as vessels, and facilitate the access to tumors. Planning the operation is done based on pre-operative images and does not account for intra-operative surgical events. We present a novel image-guided neurosurgical system to optimize the craniotomy opening. Using physics-based modeling we define a cortical deformation map that estimates the displacement field at candidate craniotomy locations. This deformation map is coupled with an image analogy algorithm that produces realistic synthetic images that can be used to predict both the geometry and the appearance of the brain surface before opening the skull. These images account for cortical vessel deformations that may occur after opening the skull and is rendered in a way that increases the surgeon's understanding and assimilation. Our method was tested retrospectively on patients data showing good results and demonstrating the feasibility of practical use of our system.

Intraoperative Use of Functional MRI for Surgical Decision Making after Limited or Infeasible Electrocortical Stimulation Mapping

BACKGROUND AND PURPOSE

Functional magnetic resonance imaging (fMRI) is becoming widely recognized as a key component of preoperative neurosurgical planning, although intraoperative electrocortical stimulation (ECS) is considered the gold standard surgical brain mapping method. However, acquiring and interpreting ECS results can sometimes be challenging. This retrospective study assesses whether intraoperative availability of fMRI impacted surgical decision-making when ECS was problematic or unobtainable.

METHODS

Records were reviewed for 191 patients who underwent presurgical fMRI with fMRI loaded into the neuronavigation system. Four patients were excluded as a bur-hole biopsy was performed. Imaging was acquired at 3 Tesla and analyzed using the general linear model with significantly activated pixels determined via individually determined thresholds. fMRI maps were displayed intraoperatively via commercial neuronavigation systems.

RESULTS

Seventy-one cases were planned ECS; however, 18 (25.35%) of these procedures were either not attempted or aborted/limited due to: seizure (10), patient difficulty cooperating with the ECS mapping (4), scarring/limited dural opening (3), or dural bleeding (1). In all aborted/limited ECS cases, the surgeon continued surgery using fMRI to guide surgical decision-making. There was no significant difference in the incidence of postoperative deficits between cases with completed ECS and those with limited/aborted ECS.

CONCLUSIONS

Preoperative fMRI allowed for continuation of surgery in over one-fourth of patients in which planned ECS was incomplete or impossible, without a significantly different incidence of postoperative deficits compared to the patients with completed ECS. This demonstrates additional value of fMRI beyond presurgical planning, as fMRI data served as a backup method to ECS.

Extent of Glioma Resection on Intraoperative Ultrasound Correlates Well with Postoperative MRI Results

Background: Maximal surgical resection is thought to confer survival benefit for both high- and low-grade gliomas. Intraoperative imaging assists with achieving maximal surgical resection. Different intraoperative imaging modalities have been implemented, but intra-operative MRI has a high cost that may limit its uptake in resource scarce healthcare systems. Objectives: This study aims to evaluate intraoperative ultrasound as a surrogate for intra and post-operative MRI for assessing the extent of resection of glioma. Methods: A partially prospective comparative study, which compares a prospective cohort group with a historical control group. We evaluated 74 glioma patients, who all underwent surgery in a regional UK Neurosurgical centre between October 2013 and October 2017. The study population was divided into 2 groups based on the use of ultrasound to guide the resection. We compared the size of the lesion prior and after excision to evaluate the extent of resection and undertook comparison with post-operative MRI. Results: The mean extent of resection on the ultrasound images was 96.1 % and 97.7 % on the postoperative MR. Using Spearman’s correlation; extent of resection on the ultrasound images was strongly correlated with the extent of resection on the postoperative MR images (P=value <0.001). The use of intraoperative ultrasound was associated with a significant increase in the number of patients in whom 95% or greater extent of resection was achieved (Fisher’s exact test P= value 0.033). Conclusion: Intra-operative ultrasonography could provide a reliable and cheaper alternative to intraoperative MRI to improve the extent of resection in glioma surgery.

Application of multi-wavelength technique for photoacoustic imaging to delineate tumor margins during maximum-safe resection of glioma: A preliminary simulation study

Accurate margin delineation and safe maximal resection of glioma is one of the most challenging problems of neurosurgery, due to its close resemblance to normal brain parenchyma. However, different intraoperative visualization methods have been used for real-time intraoperative investigation of the borders of the resection cavity, each having advantages and limitations. This preliminary study was designed to simulate multi-wavelength photoacoustic imaging for brain tumor margin delineation for maximum safe resection of glioma. Since the photoacoustic signal is directly related to the amount of optical energy absorption by the endogenous tissue chromophores such as hemoglobin; it may be able to illustrate the critical structures such as tumor vessels during surgery. The simulation of the optical and acoustic part was done by using Monte-Carlo and k-wave toolbox, respectively. As our simulation results proved, at different wavelengths and depths, the amount of optical absorption for the blood layer is significantly different from others such as normal and tumoral tissues. Furthermore, experimental validation of our approach confirms that, by using multi-wavelengths proportional to the depth of the tumor margin during surgery, tumor margin can be differented using photoacoustic imaging at various depths. Photoacoustic imaging may be considered as a promising imaging modality which combines the spectral contrast of optical imaging as well as the spatial resolution of ultrasound imaging, and may be able to delineate the vascular-rich glioma margins at different depths of the resection cavity during surgery.

No time for drifting: Comparing performance and applicability of signal detrending algorithms for real-time fMRI

As a consequence of recent technological advances in the field of functional magnetic resonance imaging (fMRI), results can now be made available in real-time. This allows for novel applications such as online quality assurance of the acquisition, intra-operative fMRI, brain-computer-interfaces, and neurofeedback. To that aim, signal processing algorithms for real-time fMRI must reliably correct signal contaminations due to physiological noise, head motion, and scanner drift. The aim of this study was to compare performance of the commonly used online detrending algorithms exponential moving average (EMA), incremental general linear model (iGLM) and sliding window iGLM (iGLM^window). For comparison, we also included offline detrending algorithms (i.e., MATLAB's and SPM8's native detrending functions). Additionally, we optimized the EMA control parameter, by assessing the algorithm's performance on a simulated data set with an exhaustive set of realistic experimental design parameters. First, we optimized the free parameters of the online and offline detrending algorithms. Next, using simulated data, we systematically compared the performance of the algorithms with respect to varying levels of Gaussian and colored noise, linear and non-linear drifts, spikes, and step function artifacts. Additionally, using in vivo data from an actual rt-fMRI experiment, we validated our results in a post hoc offline comparison of the different detrending algorithms. Quantitative measures show that all algorithms perform well, even though they are differently affected by the different artifact types. The iGLM approach outperforms the other online algorithms and achieves online detrending performance that is as good as that of offline procedures. These results may guide developers and users of real-time fMRI analyses tools to best account for the problem of signal drifts in real-time fMRI.

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fMRI time series are almost always affected by signal drifts.

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Signal drifts can be reduced in real-time using different correction methods.

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Robustness of these methods was tested in the presence of different artifacts.

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Incremental GLM (iGLM, iGLM^window) were found optimal in most cases.

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.

Tractography for Surgical Neuro-Oncology Planning: Towards a Gold Standard

Magnetic resonance imaging tractography permits in vivo visualization of white matter structures. Aside from its academic value, tractography has been proven particularly useful to neurosurgeons for preoperative planning. Preoperative tractography permits both qualitative and quantitative analyses of tumor effects upon surrounding white matter, allowing the surgeon to specifically tailor their operative approach. Despite its benefits, there is controversy pertaining to methodology, implementation, and interpretation of results in this context. High-definition fiber tractography (HDFT) is one of several non-tensor tractography approaches permitting visualization of crossing white matter trajectories at high resolutions, dispensing with the well-known shortcomings of diffusion tensor imaging (DTI) tractography. In this article, we provide an overview of the advantages of HDFT in a neurosurgical context, derived from our considerable experience implementing the technique for academic and clinical purposes. We highlight nuances of qualitative and quantitative approaches to using HDFT for brain tumor surgery planning, and integration of tractography with complementary operative adjuncts, and consider areas requiring further research.

Application of fluorescein sodium in breast cancer brain-metastasis surgery

Objective

Surgical resection serves an important role in the multidisciplinary treatment of cerebral metastases (CMs). Conventional white-light, microsurgical, and circumferential stripping of CMs is standard neurosurgical procedure, but is associated with a high recurrence rate. Based on this outcome, there is an urgent need for a new surgical strategy, such as fluorescence-guided resection, for CMs, in order to achieve total removal.

Methods

A retrospective study was carried out in 38 patients clinically and pathologically diagnosed with breast cancer brain metastasis at three medical centers from May 2012 to June 2016. The study comprised group 1 (fluorescein-guided surgery) and group 2 (standard microsurgery). In group 1, 5 mg/kg of fluorescein sodium was injected intravenously after an allergy test and before general anesthesia for 17 patients. A yellow 560 filter was employed for microsurgical tumor resection. Group 2 consisted of 21 patients for whom fluorescein was not administered.

Results

Surgical outcomes were assessed concerning the extent of resection and Karnofsky performance status. Gross total resection was achieved in these patients, with high fluorescence markedly enhancing tumor visibility. The extent of resection had a powerful influence on performance status. Overall survival after CM was 24.1 months in patients given fluorescein and was 22.8 months in the nonfluorescein group.

Conclusion

Fluorescein-guided surgery is a simple, safe, and practical method to resect breast cancer brain metastasis, and leads to a higher proportion of resection compared to common microsurgery. This offers a tremendous advantage when navigating a tiny tumor, and improves the quality of life of patients with CM.

Tactile sensor-based real-time clustering for tissue differentiation

PURPOSE

Reliable intraoperative delineation of tumor from healthy brain tissue is essentially based on the neurosurgeon's visual aspect and tactile impression of the considered tissue, which is-due to inherent low brain consistency contrast-a challenging task. Development of an intelligent artificial intraoperative tactile perception will be a relevant task to improve the safety during surgery, especially when-as for neuroendoscopy-tactile perception will be damped or-as for surgical robotic applications-will not be a priori existent. Here, we present the enhancements and the evaluation of a tactile sensor based on the use of a piezoelectric tactile sensor.

METHODS

A robotic-driven piezoelectric bimorph sensor was excited using multisine to obtain the frequency response function of the contact between the sensor and fresh ex vivo porcine tissue probes. Based on load-depth, relaxation and creep response tests, viscoelastic parameters E₁ and E₂ for the elastic moduli and η for the viscosity coefficient have been obtained allowing tissue classification. Data analysis was performed by a multivariate cluster algorithm.

RESULTS

Cluster algorithm assigned five clusters for the assignment of white matter, basal ganglia and thalamus probes. Basal ganglia and white matter have been assigned to a common cluster, revealing a less discriminatory power for these tissue types, whereas thalamus was exclusively delineated; gray matter could even be separated in subclusters.

CONCLUSIONS

Bimorph-based, multisine-excited tactile sensors reveal a high sensitivity in ex vivo tissue-type differentiation. Although, the sensor principle has to be further evaluated, these data are promising.

Non-rigid registration of 3D ultrasound for neurosurgery using automatic feature detection and matching

PURPOSE

The brain undergoes significant structural change over the course of neurosurgery, including highly nonlinear deformation and resection. It can be informative to recover the spatial mapping between structures identified in preoperative surgical planning and the intraoperative state of the brain. We present a novel feature-based method for achieving robust, fully automatic deformable registration of intraoperative neurosurgical ultrasound images.

METHODS

A sparse set of local image feature correspondences is first estimated between ultrasound image pairs, after which rigid, affine and thin-plate spline models are used to estimate dense mappings throughout the image. Correspondences are derived from 3D features, distinctive generic image patterns that are automatically extracted from 3D ultrasound images and characterized in terms of their geometry (i.e., location, scale, and orientation) and a descriptor of local image appearance. Feature correspondences between ultrasound images are achieved based on a nearest-neighbor descriptor matching and probabilistic voting model similar to the Hough transform.

RESULTS

Experiments demonstrate our method on intraoperative ultrasound images acquired before and after opening of the dura mater, during resection and after resection in nine clinical cases. A total of 1620 automatically extracted 3D feature correspondences were manually validated by eleven experts and used to guide the registration. Then, using manually labeled corresponding landmarks in the pre- and post-resection ultrasound images, we show that our feature-based registration reduces the mean target registration error from an initial value of 3.3 to 1.5 mm.

CONCLUSIONS

This result demonstrates that the 3D features promise to offer a robust and accurate solution for 3D ultrasound registration and to correct for brain shift in image-guided neurosurgery.

The usefulness of fibrin glue as a support in the dissection of malignant cystic brain tumors

BACKGROUND

If the complete microsurgical resection of a brain tumor is a logical oncologic goal, the surgical strategy for the cystic component remains controversial secondary to the risk of morbidity. The objective of this study was to analyze the interest of using fibrin glue in the resection of malignant cystic brain tumors (MCBT).

METHODS

Seven patients (median: 60-years-old (range [52-72]/sex ratio M/F: 2.5) were analyzed prospectively in the Neurosurgery Department at Strasbourg University Hospital, from October 2014 to November 2016. The surgical technique consisted of injecting fibrin glue into the tumor cyst after partial drainage. After the solidification of the glue, the cysts walls were removal by following the dissection plan around the fibrin glue. The primary objective was to evaluate the quality of surgical resection on brain MRI scans postoperatively with the use of ITK-SNAP software for precise measurements of tumor volume.

RESULTS

Four metastases and 3 glial lesions were operated on with this technique. An average reduction in cystic volume of 64.6% (P=0.016) and 82.1% (P=0.016) for contrast enhancement volume were observed. If two cases (#2 and #7) were excluded, the average contrast enhancement reduction was respectively 94% and 72% for the cystic volume. In addition, there were no complications, tumor recurrence or difference between gliomas and metastases and the Karnofsky score increased by at least 10% in all patients.

CONCLUSION

This procedure allowed to extend the resection to the cystic component of MCBT without increasing the risk of morbidity related to injury on the underlying parenchyma.

Awake Craniotomy for Tumor Resection: Further Optimizing Therapy of Brain Tumors

In recent years more and more data have emerged linking the most radical resection to prolonged survival in patients harboring brain tumors. Since total tumor resection could increase postoperative morbidity, many methods have been suggested to reduce the risk of postoperative neurological deficits: awake craniotomy with the possibility of continuous patient-surgeon communication is one of the possibilities of finding out how radical a tumor resection can possibly be without causing permanent harm to the patient.In 1994 we started to perform awake craniotomy for glioma resection. In 2005 the use of intraoperative high-field magnetic resonance imaging (MRI) was included in the standard tumor therapy protocol. Here we review our experience in performing awake surgery for gliomas, gained in 219 patients.Patient selection by the operating surgeon and a neuropsychologist is of primary importance: the patient should feel as if they are part of the surgical team fighting against the tumor. The patient will undergo extensive neuropsychological testing, functional MRI, and fiber tractography in order to define the relationship between the tumor and the functionally relevant brain areas. Attention needs to be given at which particular time during surgery the intraoperative MRI is performed. Results from part of our series (without and with ioMRI scan) are presented.

Novel imaging approaches to cerebrovascular disease

Imaging techniques available to the physician treating neurovascular disease have substantially grown over the past several decades. New techniques as well as advances in imaging modalities continuously develop and provide an extensive array of modalities to diagnose, characterize, and understand neurovascular pathology. Modern noninvasive neurovascular imaging is generally based on computed tomography (CT), magnetic resonance (MR) imaging, or nuclear imaging and includes CT angiography, CT perfusion, xenon-enhanced CT, single-photon emission CT, positron emission tomography, magnetic resonance angiography, MR perfusion, functional magnetic resonance imaging with global and regional blood oxygen level dependent imaging, and magnetic resonance angiography with the use of the noninvasive optional vessel analysis software (River Forest, Ill). In addition to a brief overview of the technique, this review article discusses the clinical indications, advantages, and disadvantages of each of those modalities.

Brain shift in neuronavigation of brain tumors: A review

PURPOSE

Neuronavigation based on preoperative imaging data is a ubiquitous tool for image guidance in neurosurgery. However, it is rendered unreliable when brain shift invalidates the patient-to-image registration. Many investigators have tried to explain, quantify, and compensate for this phenomenon to allow extended use of neuronavigation systems for the duration of surgery. The purpose of this paper is to present an overview of the work that has been done investigating brain shift.

METHODS

A review of the literature dealing with the explanation, quantification and compensation of brain shift is presented. The review is based on a systematic search using relevant keywords and phrases in PubMed. The review is organized based on a developed taxonomy that classifies brain shift as occurring due to physical, surgical or biological factors.

RESULTS

This paper gives an overview of the work investigating, quantifying, and compensating for brain shift in neuronavigation while describing the successes, setbacks, and additional needs in the field. An analysis of the literature demonstrates a high variability in the methods used to quantify brain shift as well as a wide range in the measured magnitude of the brain shift, depending on the specifics of the intervention. The analysis indicates the need for additional research to be done in quantifying independent effects of brain shift in order for some of the state of the art compensation methods to become useful.

CONCLUSION

This review allows for a thorough understanding of the work investigating brain shift and introduces the needs for future avenues of investigation of the phenomenon.

Minimally invasive surgery of the anterior skull base: transorbital approaches

Minimally invasive approaches are becoming increasingly popular to access the anterior skull base. With interdisciplinary cooperation, in particular endonasal endoscopic approaches have seen an impressive expansion of indications over the past decades. The more recently described transorbital approaches represent minimally invasive alternatives with a differing spectrum of access corridors. The purpose of the present paper is to discuss transorbital approaches to the anterior skull base in the light of the current literature. The transorbital approaches allow excellent exposure of areas that are difficult to reach like the anterior and posterior wall of the frontal sinus; working angles may be more favorable and the paranasal sinus system can be preserved while exposing the skull base. Because of their minimal morbidity and the cosmetically excellent results, the transorbital approaches represent an important addition to established endonasal endoscopic and open approaches to the anterior skull base. Their execution requires an interdisciplinary team approach.

Feasibility of the Combined Application of Navigated Probabilistic Fiber Tracking and Navigated Ultrasonography in Brain Tumor Surgery

BACKGROUND

Surgical resection of intra-axial tumors is a challenging procedure because of indistinct tumor margins, infiltration, and displacement of white matter tracts surrounding the lesion. Hence, gross total tumor resection without causing new neurologic deficits is demanding, especially in tumor sites adjoining eloquent structures. Feasibility of the combination of navigated probabilistic fiber tracking to identify eloquent fiber pathways and navigated ultrasonography to control brain shift was tested.

METHODS

Eleven patients with lesions adjacent to eloquent white matter structures (pyramidal tract, optic radiation and arcuate fascicle) were preoperatively subjected to magnetic resonance imaging including diffusion-weighted imaging on a 3-T magnetic resonance system (Trio [Siemens, Erlangen, Germany]). Probabilistic fiber tracking was performed using the tools of the FMRIB Software Library (FSL). Results of probabilistic fiber tracking and high-resolution anatomic images were integrated into the neuronavigation system Stealth Station (Medtronic, Minneapolis, Minnesota, USA) together with the navigated ultrasonography (SonoNav [Medtronic]).

RESULTS

FSL-based probabilistic fiber tracking depicted the pyramidal tract, the optic radiation, and arcuate fascicle anatomically plausibly. Integration of the probabilistic fiber tracking into neuronavigation was technically feasible and allowed visualization of the reconstructed fiber pathways. Navigated ultrasonography controlled brain shift.

CONCLUSIONS

Integration of probabilistic fiber tracking and navigated ultrasonography into intraoperative neuronavigation facilitated anatomic orientation during glioma resection. FSL-based probabilistic fiber tracking integrated sophisticated fiber tracking algorithms, including modeling of crossing fibers. Combination with navigated ultrasonography provided a three-dimensional estimation of intraoperative brain shift and, therefore, improved the reliability of neuronavigation.

Fluorescein sodium-guided surgery in cerebral lymphoma

OBJECTIVES

Growth and progress of primary central nervous lymphoma (PCNSL) severely disrupt the blood brain barrier (BBB). Such disruptions can be intraoperatively visualized by injecting fluorescein sodium (FL) and applying a YELLOW 560 nm surgical microscope filter. Here, we report a small cohort of patients with PCNSL that mimicked high grade gliomas (HGG) or cerebral metastases (CM), who had been operated on with the use of FL.

PATIENTS AND METHODS

Retrospectively, seven patients with PCNSL were identified, who had been operated on by means of microsurgery after intravenous FL injection. The surgical reports were screened for statements on the grade of fluorescent staining in the tumor area. One representative case was chosen to show the staining under white light as well as under filtered light at different distances to the tumor area.

RESULTS

All patients had shown bright and homogenous fluorescent staining of the tumor (n=7. 100%). No adverse effects had been observed.

CONCLUSION

Similar to patients with HGG or CM, patients with PCNSL may benefit from use of FL and the dedicated YELLOW 560 nm filter in open surgery.

Resection of cerebral gangliogliomas causing drug-resistant epilepsy: short- and long-term outcomes using intraoperative MRI and neuronavigation

OBJECT Cerebral gangliogliomas (GGs) are highly associated with intractable epilepsy. Incomplete resection due to proximity to eloquent brain regions or misinterpretation of the resection amount is a strong negative predictor for local tumor recurrence and persisting seizures. A potential method for dealing with this obstacle could be the application of intraoperative high-field MRI (iopMRI) combined with neuronavigation. METHODS Sixty-nine patients (31 female, 38 male; median age 28.5 ± 15.4 years) suffering from cerebral GGs were included in this retrospective study. Five patients received surgery twice in the observation period. In 48 of the 69 patients, 1.5-T iopMRI combined with neuronavigational guidance was used. Lesions close to eloquent brain areas were resected with the implementation of preoperative diffusion tensor imaging tractography and blood oxygenation level-dependent functional MRI (15 patients). RESULTS Overall, complete resection was accomplished in 60 of 69 surgical procedures (87%). Two patients underwent biopsy only, and in 7 patients, subtotal resection was accomplished because of proximity to critical brain areas. Excluding the 2 biopsies, complete resection using neuronavigation/iopMRI was documented in 33 of 46 cases (72%) by intraoperative imaging. Remnant tumor mass was identified intraoperatively in 13 of 46 patients (28%). After intraoperative second-look surgery, the authors improved the total resection rate by 9 patients (up to 91% [42 of 46]). Of 21 patients undergoing conventional surgery, 14 (67%) had complete resection without the use of iopMRI. Regarding epilepsy outcome, 42 of 60 patients with seizures (70%) became completely seizure free (Engel Class IA) after a median follow-up time of 55.5 ± 36.2 months. Neurological deficits were found temporarily in 1 (1.4%) patient and permanently in 4 (5.8%) patients. CONCLUSIONS Using iopMRI combined with neuronavigation in cerebral GG surgery, the authors raised the rate of complete resection in this series by 19%. Given the fact that total resection is a strong predictor of long-term seizure control, this technique may contribute to improved seizure outcome and reduced neurological morbidity.

Robotics in the neurosurgical treatment of glioma

Background:

The treatment of glioma remains a significant challenge with high recurrence rates, morbidity, and mortality. Merging image guided robotic technology with microsurgery adds a new dimension as they relate to surgical ergonomics, patient safety, precision, and accuracy.

Methods:

An image-guided robot, called neuroArm, has been integrated into the neurosurgical operating room, and used to augment the surgical treatment of glioma in 18 patients. A case study illustrates the specialized technical features of a teleoperated robotic system that could well enhance the performance of surgery. Furthermore, unique positional and force information of the bipolar forceps during surgery were recorded and analyzed.

Results:

The workspace of the bipolar forceps in this robot-assisted glioma resection was found to be 25 × 50 × 50 mm. Maximum values of the force components were 1.37, 1.84, and 2.01 N along x, y, and z axes, respectively. The maximum total force was 2.45 N. The results indicate that the majority of the applied forces were less than 0.6 N.

Conclusion:

Robotic surgical systems can potentially increase safety and performance of surgical operation via novel features such as virtual fixtures, augmented force feedback, and haptic high-force warning system. The case study using neuroArm robot to resect a glioma, for the first time, showed the positional information of surgeon's hand movement and tool-tissue interaction forces.

Deformable registration of preoperative MR, pre-resection ultrasound, and post-resection ultrasound images of neurosurgery

PURPOSE

Sites that use ultrasound (US) in image-guided neurosurgery (IGNS) of brain tumors generally have three sets of imaging data: preoperative magnetic resonance (MR) image, pre-resection US, and post-resection US. The MR image is usually acquired days before the surgery, the pre-resection US is obtained after the craniotomy but before the resection, and finally, the post-resection US scan is performed after the resection of the tumor. The craniotomy and tumor resection both cause brain deformation, which significantly reduces the accuracy of the MR-US alignment.

METHOD

Three unknown transformations exist between the three sets of imaging data: MR to pre-resection US, pre- to post-resection US, and MR to post-resection US. We use two algorithms that we have recently developed to perform the first two registrations (i.e., MR to pre-resection US and pre- to post-resection US). Regarding the third registration (MR to post-resection US), we evaluate three strategies. The first method performs a registration between the MR and pre-resection US, and another registration between the pre- and post-resection US. It then composes the two transformations to register MR and post-resection US; we call this method compositional registration. The second method ignores the pre-resection US and directly registers the MR and post-resection US; we refer to this method as direct registration. The third method is a combination of the first and second: it uses the solution of the compositional registration as an initial solution for the direct registration method. We call this method group-wise registration.

RESULTS

We use data from 13 patients provided in the MNI BITE database for all of our analysis. Registration of MR and pre-resection US reduces the average of the mean target registration error (mTRE) from 4.1 to 2.4 mm. Registration of pre- and post-resection US reduces the average mTRE from 3.7 to 1.5 mm. Regarding the registration of MR and post-resection US, all three strategies reduce the mTRE. The initial average mTRE is 5.9 mm, which reduces to 3.3 mm with the compositional method, 2.9 mm with the direct technique, and 2.8 mm with the group-wise method.

CONCLUSION

Deformable registration of MR and pre- and post-resection US images significantly improves their alignment. Among the three methods proposed for registering the MR to post-resection US, the group-wise method gives the lowest TRE values. Since the running time of all registration algorithms is less than 2 min on one core of a CPU, they can be integrated into IGNS systems for interactive use during surgery.

Neuronavigation in small animals: development, techniques, and applications

A persistent obstacle to accurate diagnosis and treatment of brain disease has been the difficulties in safely obtaining representative biopsy material in a live patient. Major problems are the variability in the anatomy between individuals and the inability to reliably locate deep structures through reliance on surface anatomic features. Although stereotaxic devices have been available for many years, they have now been supplanted by frameless systems, which are more accurate and less cumbersome and allow good surgical access and provision of intraoperative feedback of instrument location.

The evolving role of neurological imaging in neuro-oncology

Neuroimaging has played a critical role in the management of patients with neurological disease, since the first ventriculogram was performed in 1918 by Walter Dandy (Mezger et al. Langenbecks Arch Surg 398(4):501-514, 2013). Over the last century, technology has evolved significantly, and within the last decade, the role of imaging in the management of patients with neuro-oncologic disease has shifted from a tool for gross identification of intracranial pathology, to an integral part of real-time neurological surgery. Current neurological imaging provides detailed information about anatomical structure, neurological function, and metabolic and metabolism-important characteristics that help clinicians and surgeons non-invasively manage patients with brain tumors. It is valuable to review the evolution of neurological imaging over the past several decades, focusing on its role in the management of patients with intracranial tumors. Novel neuro-imaging tools and developing technology with the potential to further transform clinical practice will be discussed, as will the key role neurological imaging plays in neurosurgical planning and intraoperative navigation. With increasingly complex imaging modalities creating growing amounts of raw data, validation of techniques, data analysis, and integrating various pieces of imaging data into individual patient management plans, remain significant challenges for clinicians. We thus suggest mechanisms that might ultimately allow for evidence based integration of imaging in the management of patients with neuro-oncologic disease.

Co-registration of intra-operative brain surface photographs and pre-operative MR images

PURPOSE

Brain shift, the change in configuration of the brain after opening the dura mater, is a significant problem for neuronavigation. Brain structures at intra-operative deformed positions must be matched with corresponding structures in the pre-operative 3D planning data. A method to co-register the cortical surface from intra-operative microscope images with pre-operative MRI-segmented data was developed and tested.

METHODS

Automated classification of sulci on MRI-extracted cortical surfaces was tested by comparison with user guided marking of prominent sulci on an intra-operative photography. A variational registration method with a fidelity energy for 3D deformations of the cortical surface in conjunction with a higher-order, linear elastic prior energy was used for the actual registration. The minimization of this energy was performed with a regularized gradient descent scheme using finite elements for spatial discretization. The sulcal classification method was tested on eight different clinical MRI data sets by comparison of the deformed MRI scans with intra-operative photographs of the brain surface.

RESULTS

User intervention was required for marking sulci on the photographs demonstrating the potential for incorporating an automatic classifier. The actual registration was validated first on an artificial testbed. The complete algorithm for the co-registration of actual clinical MRI data was successful for eight different patients.

CONCLUSIONS

Pre-operative MRI scans can be registered to intra-operative brain surface photographs using a surface-to-surface registration method. This co-registration method has potential applications in neurosurgery, particularly during functional procedures.

Relative survival of patients with non-malignant central nervous system tumours: a descriptive study by the Austrian Brain Tumour Registry

BACKGROUND

Unlike malignant primary central nervous system (CNS) tumours outcome data on non-malignant CNS tumours are scarce. For patients diagnosed from 1996 to 2002 5-year relative survival of only 85.0% has been reported. We investigated this rate in a contemporary patient cohort to update information on survival.

METHODS

We followed a cohort of 3983 cases within the Austrian Brain Tumour Registry. All patients were newly diagnosed from 2005 to 2010 with a histologically confirmed non-malignant CNS tumour. Vital status, cause of death, and population life tables were obtained by 31 December 2011 to calculate relative survival.

RESULTS

Overall 5-year relative survival was 96.1% (95% CI 95.1-97.1%), being significantly lower in tumours of borderline (90.2%, 87.2-92.7%) than benign behaviour (97.4%, 96.3-98.3%). Benign tumour survival ranged from 86.8 for neurofibroma to 99.7% for Schwannoma; for borderline tumours survival rates varied from 83.2 for haemangiopericytoma to 98.4% for myxopapillary ependymoma. Cause of death was directly attributed to the CNS tumour in 39.6%, followed by other cancer (20.4%) and cardiovascular disease (15.8%).

CONCLUSION

The overall excess mortality in patients with non-malignant CNS tumours is 5.5%, indicating a significant improvement in survival over the last decade. Still, the remaining adverse impact on survival underpins the importance of systematic registration of these tumours.

Frameless stereotactic functional neuronavigation combined with intraoperative magnetic resonance imaging as a strategy in highly eloquent located tumors causing epilepsy

BACKGROUND

Intractable epilepsy due to tumors located in highly eloquent brain regions is often considered surgically inaccessible because of a high risk of postoperative neurological deterioration. Intraoperative MRI and functional navigation contribute to overcome this problem.

OBJECTIVES

To retrospectively investigate the long-term results and impact of functional neuronavigation and 1.5-tesla intraoperative MRI on patients who underwent surgery of tumors associated with epilepsy located close to or within eloquent brain areas.

METHODS

Nineteen patients (9 female, 10 male, mean age 41.4 ± 13.4 years, 11 low-grade and 8 high-grade glial tumors) were evaluated preoperatively using BOLD imaging, diffusion-tensor imaging tractography and magnetoencephalography. Functional data were implemented into neuronavigation in this multimodal approach.

RESULTS

In 14 of 19 patients (74%), complete resection was achieved, and in 5 patients significant tumor volume reduction was accomplished. Eight of 14 (57%) complete resections were achieved only by performing an intraoperative image update. Neurological deterioration was found permanently in 2 patients. After a mean follow-up of 43.8 ± 23.8 months, 15 patients (79%) became seizure free (Engel class Ia).

CONCLUSIONS

Despite the highly eloquent location of tumors causing intractable epilepsy, our multimodal approach led to complete resection in more than two-thirds of patients with an acceptable neurological morbidity and excellent long-term seizure control.

5-Aminolevulinic acid induced fluorescence is a powerful intraoperative marker for precise histopathological grading of gliomas with non-significant contrast-enhancement

BACKGROUND

Intraoperative identification of anaplastic foci in diffusely infiltrating gliomas (DIG) with non-significant contrast-enhancement on MRI is indispensible to avoid histopathological undergrading and subsequent treatment failure. Recently, we found that 5-aminolevulinic acid (5-ALA) induced protoporphyrin IX (PpIX) fluorescence can visualize areas with increased proliferative and metabolic activity in such gliomas intraoperatively. As treatment of DIG is predominantely based on histopathological World Health Organisation (WHO) parameters, we analyzed whether PpIX fluorescence can detect anaplastic foci according to these criteria.

METHODS

We prospectively included DIG patients with non-significant contrast-enhancement that received 5-ALA prior to resection. Intraoperatively, multiple samples from PpIX positive and negative intratumoral areas were collected using a modified neurosurgical microscope. In all samples, histopathological WHO criteria and proliferation rate were assessed and correlated to the PpIX fluorescence status.

RESULTS

A total of 215 tumor specimens were collected in 59 patients. Of 26 WHO grade III gliomas, 23 cases (85%) showed focal PpIX fluorescence, whereas 29 (91%) of 33 WHO grade II gliomas were PpIX negative. In intratumoral areas with focal PpIX fluorescence, mitotic rate, cell density, nuclear pleomorphism, and proliferation rate were significantly higher than in non-fluorescing areas. The positive predictive value of focal PpIX fluorescence for WHO grade III histology was 85%.

CONCLUSIONS

Our study indicates that 5-ALA induced PpIX fluorescence is a powerful marker for intraoperative identification of anaplastic foci according to the histopathological WHO criteria in DIG with non-significant contrast-enhancement. Therefore, application of 5-ALA optimizes tissue sampling for precise histopathological diagnosis independent of brain-shift.