Intraoperative Magnetic Resonance Imaging to Update Interactive Navigation in Neurosurgery: Method and Preliminary Experience

Raman spectroscopy: A prospective intraoperative visualization technique for gliomas

The infiltrative growth and malignant biological behavior of glioma make it one of the most challenging malignant tumors in the brain, and how to maximize the extent of resection (EOR) while minimizing the impact on normal brain tissue is the pursuit of neurosurgeons. The current intraoperative visualization assistance techniques applied in clinical practice suffer from low specificity, slow detection speed and low accuracy, while Raman spectroscopy (RS) is a novel spectroscopy technique gradually developed and applied to clinical practice in recent years, which has the advantages of being non-destructive, rapid and accurate at the same time, allowing excellent intraoperative identification of gliomas. In the present work, the latest research on Raman spectroscopy in glioma is summarized to explore the prospect of Raman spectroscopy in glioma surgery.

The impact of 1.5-T intraoperative magnetic resonance imaging in pediatric tumor surgery: Safety, utility, and challenges

Objective

In this study, we present our experience with 1.5-T high-field intraoperative magnetic resonance imaging (ioMRI) for different neuro-oncological procedures in a pediatric population, and we discuss the safety, utility, and challenges of this intraoperative imaging technology.

Methods

A pediatric consecutive-case series of neuro-oncological surgeries performed between February 2020 and May 2022 was analyzed from a prospective ioMRI registry. Patients were divided into four groups according to the surgical procedure: intracranial tumors (group 1), intraspinal tumors (group 2), stereotactic biopsy for unresectable tumors (group 3), and catheter placement for cystic tumors (group 4). The goal of surgery, the volume of residual tumor, preoperative and discharge neurological status, and postoperative complications related to ioMRI were evaluated.

Results

A total of 146 procedures with ioMRI were performed during this period. Of these, 62 were oncology surgeries: 45 in group 1, two in group 2, 10 in group 3, and five in group 4. The mean age of our patients was 8.91 years, with the youngest being 12 months. ioMRI identified residual tumors and prompted further resection in 14% of the cases. The mean time for intraoperative image processing was 54 ± 6 min. There were no intra- or postoperative security incidents related to the use of ioMRI. The reoperation rate in the early postoperative period was 0%.

Conclusion

ioMRI in pediatric neuro-oncology surgery is a safe and reliable tool. Its routine use maximized the extent of tumor resection and did not result in increased neurological deficits or complications in our series. The main limitations included the need for strict safety protocols in a highly complex surgical environment as well as the inherent limitations on certain patient positions with available MR-compatible headrests.

Navigated Intraoperative 3D Ultrasound in Glioblastoma Surgery: Analysis of Imaging Features and Impact on Extent of Resection

Background

Neuronavigation is routinely used in glioblastoma surgery, but its accuracy decreases during the operative procedure due to brain shift, which can be addressed utilizing intraoperative imaging. Intraoperative ultrasound (iUS) is widely available, offers excellent live imaging, and can be fully integrated into modern navigational systems. Here, we analyze the imaging features of navigated i3D US and its impact on the extent of resection (EOR) in glioblastoma surgery.

Methods

Datasets of 31 glioblastoma resection procedures were evaluated. Patient registration was established using intraoperative computed tomography (iCT). Pre-operative MRI (pre-MRI) and pre-resectional ultrasound (pre-US) datasets were compared regarding segmented tumor volume, spatial overlap (Dice coefficient), the Euclidean distance of the geometric center of gravity (CoG), and the Hausdorff distance. Post-resectional ultrasound (post-US) and post-operative MRI (post-MRI) tumor volumes were analyzed and categorized into subtotal resection (STR) or gross total resection (GTR) cases.

Results

The mean patient age was 59.3 ± 11.9 years. There was no significant difference in pre-resectional segmented tumor volumes (pre-MRI: 24.2 ± 22.3 cm³; pre-US: 24.0 ± 21.8 cm³). The Dice coefficient was 0.71 ± 0.21, the Euclidean distance of the CoG was 3.9 ± 3.0 mm, and the Hausdorff distance was 12.2 ± 6.9 mm. A total of 18 cases were categorized as GTR, 10 cases were concordantly classified as STR on MRI and ultrasound, and 3 cases had to be excluded from post-resectional analysis. In four cases, i3D US triggered further resection.

Conclusion

Navigated i3D US is reliably adjunct in a multimodal navigational setup for glioblastoma resection. Tumor segmentations revealed similar results in i3D US and MRI, demonstrating the capability of i3D US to delineate tumor boundaries. Additionally, i3D US has a positive influence on the EOR, allows live imaging, and depicts brain shift.

Combining Pre-operative Diffusion Tensor Images and Intraoperative Magnetic Resonance Images in the Navigation Is Useful for Detecting White Matter Tracts During Glioma Surgery

Purpose

We developed a navigation system that superimposes the fractional anisotropy (FA) color map of pre-operative diffusion tensor imaging (DTI) and intraoperative magnetic resonance imaging (MRI). The current study aimed to investigate the usefulness of this system for neurophysiological monitoring and examination under awake craniotomy during tumor removal.

Method

A total of 10 glioma patients (4 patients with right-side tumors; 5 men and 5 women; average age, 34 years) were evaluated. Among them, the tumor was localized to the frontal lobe, insular cortex, and parietal lobe in 8, 1, and 1 patient, respectively. There were 3 patients who underwent surgery on general anesthesia, while 7 patients underwent awake craniotomy. The index of DTI anisotropy taken pre-operatively (magnetic field: 3 tesla, 6 motion probing gradient directions) was analyzed as a color map (FA color map) and concurrently co-registered in the intraoperative MRI within the navigation. In addition to localization of the bipolar coagulator and the cortical stimulator for brain mapping on intraoperative MRI, the pre-operative FA color map was also concurrently integrated and displayed on the navigation monitor. This white matter nerve functional information was confirmed directly by using neurological examination and referring to the electrophysiological monitoring.

Results

Intraoperative MRI, integrated pre-operative FA color map, and microscopic surgical view were displayed on one screen in all 10 patients, and white matter fibers including the pyramidal tract were displayed as a reference in blue. Regarding motor function, motor-evoked potential was monitored as appropriate in all cases, and removal was possible while directly confirming motor symptoms under awake craniotomy. Furthermore, the white matter fibers including the superior longitudinal fasciculus were displayed in green. Importantly, it was useful not only to localize the resection site, but to identify language-related, eye movement-related, and motor fibers at the electrical stimulation site. All motor and/or language white matter tracts were identified and visualized with the co-registration and then with an acceptable post-operative neurological outcome.

Conclusion

Co-registering an intraoperative MR images and a pre-operative FA color map is a practical and useful method to predict the localization of critical white matter nerve functions intraoperatively in glioma surgery.

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

BACKGROUND AND AIMS

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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.

The Neurosurgeon's Armamentarium for Gliomas: An Update on Intraoperative Technologies to Improve Extent of Resection

Maximal safe resection is the standard of care in the neurosurgical treatment of high-grade gliomas. To aid surgeons in the operating room, adjuvant techniques and technologies centered around improving intraoperative visualization of tumor tissue have been developed. In this review, we will discuss the most advanced technologies, specifically fluorescence-guided surgery, intraoperative imaging, neuromonitoring modalities, and microscopic imaging techniques. The goal of these technologies is to improve detection of tumor tissue beyond what conventional microsurgery has permitted. We describe the various advances, the current state of the literature that have tested the utility of the different adjuvants in clinical practice, and future directions for improving intraoperative technologies.

Fluorescence Guidance and Intraoperative Adjuvants to Maximize Extent of Resection

Safely maximizing extent of resection has become the central goal in glioma surgery. Especially in eloquent cortex, the goal of maximal resection is balanced with neurological risk. As new technologies emerge in the field of neurosurgery, the standards for maximal safe resection have been elevated. Fluorescence-guided surgery, intraoperative magnetic resonance imaging, and microscopic imaging methods are among the most well-validated tools available to enhance the level of accuracy and safety in glioma surgery. Each technology uses a different characteristic of glioma tissue to identify and differentiate tumor tissue from normal brain and is most effective in the context of anatomic, connectomic, and neurophysiologic context. While each tool is able to enhance resection, multiple modalities are often used in conjunction to achieve maximal safe resection. This paper reviews the mechanism and utility of the major adjuncts available for use in glioma surgery, especially in tumors within eloquent areas, and puts forth the foundation for a unified approach to how leverage currently available technology to ensure maximal safe resection.

Navigated 3D Ultrasound in Brain Metastasis Surgery: Analyzing the Differences in Object Appearances in Ultrasound and Magnetic Resonance Imaging

Background: Implementation of intraoperative 3D ultrasound (i3D US) into modern neuronavigational systems offers the possibility of live imaging and subsequent imaging updates. However, different modalities, image acquisition strategies, and timing of imaging influence object appearances. We analyzed the differences in object appearances in ultrasound (US) and magnetic resonance imaging (MRI) in 35 cases of brain metastasis, which were operated in a multimodal navigational setup after intraoperative computed tomography based (iCT) registration. Method: Registration accuracy was determined using the target registration error (TRE). Lesions segmented in preoperative magnetic resonance imaging (preMRI) and i3D US were compared focusing on object size, location, and similarity. Results: The mean and standard deviation (SD) of the TRE was 0.84 ± 0.36 mm. Objects were similar in size (mean ± SD in preMRI: 13.6 ± 16.0 cm3 vs. i3D US: 13.5 ± 16.0 cm3). The Dice coefficient was 0.68 ± 0.22 (mean ± SD), the Hausdorff distance 8.1 ± 2.9 mm (mean ± SD), and the Euclidean distance of the centers of gravity 3.7 ± 2.5 mm (mean ± SD). Conclusion: i3D US clearly delineates tumor boundaries and allows live updating of imaging for compensation of brain shift, which can already be identified to a significant amount before dural opening.

A Micro Saddle Coil with Switchable Sensitivity for Local High-Resolution Imaging of Luminal Tissue

This paper reports on a micro saddle coil for local high-resolution magnetic resonance imaging (MRI) fabricated by embedding a flexible coil pattern into a polydimethyilsiloxane (PDMS) tube. We can change the sensitivity of the micro coil by deforming the shape of the coil from a saddle-shaped mode to a planar-shaped mode. The inductance, the resistance, and the Q-factor of the coil in the saddle-shaped mode were 2.45 μH, 3.31 Ω, and 39.9, respectively. Those of the planar-shaped mode were 3.07 μH, 3.92 Ω, and 42.9, respectively. In MRI acquired in saddle-shaped mode, a large visible area existed around the coil. Although the sensitive area was considerably reduced in the planar-shaped mode, clear MRI images were obtained. The signal-to-noise ratios (SNR) of the saddle-shaped and planar-shaped modes were 194.9 and 505.9, respectively, at voxel size of 2.0 × 2.0 × 2.0 mm³ and 11.7 and 37.4, respectively, at voxel size of 0.5 × 0.5 × 1.0 mm³. The sensitivity of the saddle-shaped and the planar-shaped modes were about 3 times and 10 times higher, respectively, than those of the medical head coil at both voxel sizes. Thus, the micro saddle coil enabled large-area imaging and highly sensitive imaging by switching the shape of the coil.

Factors triggering an additional resection and determining residual tumor volume on intraoperative MRI: analysis from a prospective single-center registry of supratentorial gliomas

OBJECTIVE

In this analysis, the authors sought to identify variables triggering an additional resection (AR) and determining residual intraoperative tumor volume in 1.5-T intraoperative MRI (iMRI)-guided glioma resections.

METHODS

A consecutive case series of 224 supratentorial glioma resections (WHO Grades I–IV) from a prospective iMRI registry (inclusion dates January 2011–April 2013) was examined with univariate and multiple regression models including volumetric data, tumor-related, and surgeon-related factors. The surgeon's expectation of an AR, in response to a questionnaire completed prior to iMRI, was evaluated using contingency analysis. A machine-learning prediction model was applied to consider if anticipation of intraoperative findings permits preoperative identification of ideal iMRI cases.

RESULTS

An AR was performed in 70% of cases after iMRI, but did not translate into an accumulated risk for neurological morbidity after surgery (p = 0.77 for deficits in cases with AR vs no AR). New severe persistent deficits occurred in 6.7% of patients. Initial tumor volume determined frequency of ARs and was independently correlated with larger tumor remnants delineated on iMRI (p < 0.0001). Larger iMRI volume was further associated with eloquent location (p = 0.010) and recurrent tumors (p < 0.0001), and with WHO grade (p = 0.0113). Greater surgical experience had no significant influence on the course of surgery. The surgeon's capability of ruling out an AR prior to iMRI turned out to incorporate guesswork (negative predictive value 43.6%). In a prediction model, AR could only be anticipated with 65% accuracy after integration of confounding variables.

CONCLUSIONS

Routine use of iMRI in glioma surgery is a safe and reliable method for resection guidance and is characterized by frequent ARs after scanning. Tumor-related factors were identified that influenced the course of surgery and intraoperative decision-making, and iMRI had a common value for surgeons of all experience levels. Commonly, the subjective intraoperative impression of the extent of resection had to be revised after iMRI review, which underscores the manifold potential of iMRI guidance. In combination with the failure to identify ideal iMRI cases preoperatively, this study supports a generous, tumor-oriented rather than surgeon-oriented indication for iMRI in glioma surgery.

Surgical management of high-grade glioma: a standard of care

Neurosurgical oncology for intrinsic glioma is evolving rapidly. It must be patient-centered, consultant-led and research-orientated. The value of specialist neurosurgical engagement is becoming more widely recognized. Detailed evaluation tailored to each patient is essential before the surgical admission, in conjunction with clinical oncology input. Medical optimization, collation of magnetic resonance datasets for preoperative planning and providing an informed explanation of the proposed management and its alternatives are all part of the neurosurgeon's remit. Meticulous microsurgical technique during surgery utilizing modern neuronavigation and physiological monitoring are integral components of the specialist armamentarium. A clear understanding of the rationale for surgical intervention, including its place alongside radiotherapy and chemotherapy, informs surgical decision-making. Recognition and understanding of these issues are driving the evolution of neurosurgical management of high-grade glioma. New challenges are emerging and need to be critically evaluated in robustly designed clinical trials.

Cortical surface shift estimation using stereovision and optical flow motion tracking via projection image registration

Stereovision is an important intraoperative imaging technique that captures the exposed parenchymal surface noninvasively during open cranial surgery. Estimating cortical surface shift efficiently and accurately is critical to compensate for brain deformation in the operating room (OR). In this study, we present an automatic and robust registration technique based on optical flow (OF) motion tracking to compensate for cortical surface displacement throughout surgery. Stereo images of the cortical surface were acquired at multiple time points after dural opening to reconstruct three-dimensional (3D) texture intensity-encoded cortical surfaces. A local coordinate system was established with its z-axis parallel to the average surface normal direction of the reconstructed cortical surface immediately after dural opening in order to produce two-dimensional (2D) projection images. A dense displacement field between the two projection images was determined directly from OF motion tracking without the need for feature identification or tracking. The starting and end points of the displacement vectors on the two cortical surfaces were then obtained following spatial mapping inversion to produce the full 3D displacement of the exposed cortical surface. We evaluated the technique with images obtained from digital phantoms and 18 surgical cases - 10 of which involved independent measurements of feature locations acquired with a tracked stylus for accuracy comparisons, and 8 others of which 4 involved stereo image acquisitions at three or more time points during surgery to illustrate utility throughout a procedure. Results from the digital phantom images were very accurate (0.05 pixels). In the 10 surgical cases with independently digitized point locations, the average agreement between feature coordinates derived from the cortical surface reconstructions was 1.7-2.1mm relative to those determined with the tracked stylus probe. The agreement in feature displacement tracking was also comparable to tracked probe data (difference in displacement magnitude was <1mm on average). The average magnitude of cortical surface displacement was 7.9 ± 5.7 mm (range 0.3-24.4 mm) in all patient cases with the displacement components along gravity being 5.2 ± 6.0 mm relative to the lateral movement of 2.4 ± 1.6 mm. Thus, our technique appears to be sufficiently accurate and computationally efficiency (typically ∼15 s), for applications in the OR.

Current concepts in the surgical management of glioma patients

The scientific basis for the surgical management of patients with glioma is rapidly evolving. The infiltrative nature of these cancers precludes a surgical cure, but despite this, cytoreductive surgery remains central to high-quality patient care. In addition to tissue sampling for accurate histopathological diagnosis and molecular genetic characterisation, clinical benefit from decompression of space-occupying lesions and microsurgical cytoreduction has been reported in patients with different grades of glioma. By integrating advanced surgical techniques with molecular genetic characterisation of the disease and targeted radiotherapy and chemotherapy, it is possible to construct a programme of personalised surgical therapy throughout the patient journey. The goal of therapeutic packages tailored to each patient is to optimise patient safety and clinical outcome and must be delivered in a multidisciplinary setting. Here we review the current concepts that underlie surgical subspecialisation in the management of patients with glioma.

Awake craniotomy may further improve neurological outcome of intraoperative MRI-guided brain tumor surgery

BACKGROUND

Results of awake craniotomy are compared to results of resections done under general anesthesia in patients operated with IMRI control. We hypothesized that stimulation of the cortex and white matter during awake surgery supplements IMRI control allowing for safer resection of eloquent brain area tumors.

METHODS

The study group consisted of 20 consecutive patients undergoing awake craniotomy with IMRI control. Resection outcome of these patients was compared to a control group of 20 patients operated in the same IMRI suite but under general anesthesia without cortical stimulation. The control group was composed of those patients whose age, sex, tumor location, recurrence and histology best matched to patients in study group.

RESULTS

Cortical stimulation identified functional cortex in eight patients (40 %). Postoperatively the neurological condition in 16 patients (80 %) in the study group was unchanged or improved compared with 13 patients (65 %) in the control group. In both groups, three patients (15 %) had transient impairment symptoms. There was one patient (5 %) with permanent neurological impairment in the study group compared to four patients (20 %) in the control group. These differences between groups were not statistically significant. There was no surgical mortality in either group and the overall infection rate was 5 %. Mean operation time was 4 h 45 min in the study group and 3 h 15 min in the control group.

CONCLUSIONS

The study consisted of a limited patient series, but it implies that awake craniotomy with bipolar cortical stimulation may help to reduce the risk of postoperative impairment following resection of tumors located in or near speech and motor areas also under IMRI control.

Combined intraoperative magnetic resonance imaging and navigated neuroendoscopy in children with multicompartmental hydrocephalus and complex cysts: a feasibility study

OBJECT

The rationale for using endoscopy to treat complex cysts and multiloculated hydrocephalus is to combine several CSF compartments into a minimum number, establish a connection to functioning CSF compartments (that is, ventricles), and decrease shunt dependency. The aim is to decrease the number of proximal shunt catheters, the number of shunt revisions, and in selected cases even to avoid a shunt. In cases of distorted anatomy and multiloculated cysts, endoscopy may be problematic because of orientation issues. Standard navigation becomes useless soon after CSF loss due to brain shift. Therefore, the concept of "real-time" navigation and intraoperative imaging in combination with endoscopic surgery has been previously suggested. The goal of the present study was to assess the feasibility and efficacy of combining intraoperative MR (iMR) imaging and navigated neuroendoscopy in infants.

METHODS

The authors report their experience in treating 5 infants (aged 6-14 months), who underwent surgery for multicystic hydrocephalus presenting with shunt malfunction (4 patients) and a quadrigeminal fetal arachnoid cyst (1 patient). In all infants, a low-field portable iMR imaging system (0.12-T PoleStar N-10/0.15-Tesla PoleStar N-20) was used in conjunction with navigated endoscopy. The authors used e-steady, T1-weighted, and T2-weighted sequences (acquisition time 24 seconds to 3.5 minutes).

RESULTS

The iMR imaging system provided clear images that correlated with the endoscopic appearance of the cystic membranes in all patients, and the images were helpful in determining trajectories and redefining targets. The iMR images documented brain shift and changes in CSF spaces during surgery. There were no intraoperative complications or technical difficulties of visualization. No infection or any other immediate postoperative complication occurred. Patients were followed up for 9 months to 7 years. The infant presenting with the quadrigeminal cyst remains shunt free since surgery, and the patients with multicystic hydrocephalus have 1-2 shunts each. Following endoscopic, iMR imaging-guided surgery, shunt catheter positioning was found to be optimal and as planned according to the postoperative imaging.

CONCLUSIONS

Navigated neuroendoscopy and iMR imaging may complement each other, offering an advantage over other modalities in complicated cases of hydrocephalus. Whenever targets and trajectories need to be redefined, the iMR images provided an updated navigation data set, allowing accurate navigation of the endoscope and minimizing the number of CSF compartments. Direct vision through the endoscope provides microanatomical details for the optimization of fenestration and catheter positioning. The combined usage of the two modalities may transform a conventional procedure into a visually controlled real-time navigated process.

Intraoperative acquisition of fMRI and DTI

Multimodal functional navigation enables removing a tumor close to eloquent brain areas with low postoperative deficits, whereas additional intraoperative imaging ensures that the maximum extent of the resection can be achieved and updates the image data compensating for the effects of brain shift. Intraoperative imaging beyond standard anatomic imaging, that is, intraoperative functional magnetic resonance imaging (fMRI) and especially intraoperative diffusion tensor imaging (DTI), add further safety for complex tumor resections. This article discusses the acquisition of intraoperative fMRI, DTI, and imaging.

Multimodal navigation integrated with imaging

Intraoperative high-field MRI in combination and close integration with microscope-based navigation serving as a common interface for the presentation of multimodal data in the surgical field seems to be one of the most promising surgical setups allowing avoiding unwanted tumor remnants while preserving neurological function. Multimodal navigation integrates standard anatomical, structural, functional, and metabolic data. Navigation achieves visualizing the initial extent of a lesion with the concomitant identification of neighboring eloquent brain structures, as well as, providing a tool for a direct correlation of histology and multimodal data. With the help of intraoperative imaging navigation data can be updated, so that brain shift can be compensated for and initially missed tumor remnants can be localized reliably.

Lows and highs: 15 years of development in intraoperative magnetic resonance imaging

Intraoperative magnetic resonance imaging (ioMRI) during neurosurgical procedures was first implemented in 1995. In the following decade ioMRI and image guided surgery has evolved from an experimental stage into a safe and routinely clinically applied technique. The development of ioMRI has led to a variety of differently designed systems which can be basically classified in one- or two-room concepts and low- and high-field installations. Nowadays ioMRI allows neurosurgeons not only to increase the extent of tumor resection and to preserve eloquent areas or white matter tracts but it also provides physiological and biological data of the brain and tumor tissue. This article tries to give a comprehensive review of the milestones in the development of ioMRI and neuronavigation over the last 15 years and describes the personal experience in intraoperative low and high-field MRI.

Advanced imaging in brain tumor surgery

The advanced imaging techniques outlined in this article are only slowly establishing their place in surgical practice. Even a low risk of false information is unacceptable in neurosurgery, thus decision-making is necessarily conservative. As more validation studies and greater experience accrue, surgeons are becoming more comfortable weighing the quality of information from functional imaging studies. Advanced imaging information is highly complementary to established surgical "good practice" such as anatomic planning, awake craniotomy, and electrocortical stimulation; its greatest impact is perhaps on how neurosurgery is planned and discussed before the patient is ever brought to the operating room. Access to functional magnetic resonance (MR) imaging, diffusion tractography, and intraoperative MR imaging can influence neurosurgical decisions before, during, and after surgery. However, the widespread adoption of these techniques in neurosurgical practice remains limited by the lack of standardized methods, the need for validation across institutions, and the unclear cost-effectiveness particularly for intraoperative MR imaging. Before advanced imaging results can be used therapeutically, it is incumbent on the neurosurgeon and neuroradiologist to develop a working understanding of each technique's strengths and weaknesses, positive and negative predictive values, and modes of failure. This content presents several imaging methods that are increasingly used in neurosurgical planning. As these techniques are progressively applied to surgery, radiologists, medical physicists, neuroscientists, and engineers will be necessary partners with the treating neurosurgeon to bridge the gap between the experimental and the therapeutic.

A sparse intraoperative data-driven biomechanical model to compensate for brain shift during neuronavigation

BACKGROUND AND PURPOSE

Intraoperative brain deformation is an important factor compromising the accuracy of image-guided neurosurgery. The purpose of this study was to elucidate the role of a model-updated image in the compensation of intraoperative brain shift.

MATERIALS AND METHODS

An FE linear elastic model was built and evaluated in 11 patients with craniotomies. To build this model, we provided a novel model-guided segmentation algorithm. After craniotomy, the sparse intraoperative data (the deformed cortical surface) were tracked by a 3D LRS. The surface deformation, calculated by an extended RPM algorithm, was applied on the FE model as a boundary condition to estimate the entire brain shift. The compensation accuracy of this model was validated by the real-time image data of brain deformation acquired by intraoperative MR imaging.

RESULTS

The prediction error of this model ranged from 1.29 to 1.91 mm (mean, 1.62 ± 0.22 mm), and the compensation accuracy ranged from 62.8% to 81.4% (mean, 69.2 ± 5.3%). The compensation accuracy on the displacement of subcortical structures was higher than that of deep structures (71.3 ± 6.1%:66.8 ± 5.0%, P < .01). In addition, the compensation accuracy in the group with a horizontal bone window was higher than that in the group with a nonhorizontal bone window (72.0 ± 5.3%:65.7 ± 2.9%, P < .05).

CONCLUSIONS

Combined with our novel model-guided segmentation and extended RPM algorithms, this sparse data-driven biomechanical model is expected to be a reliable, efficient, and convenient approach for compensation of intraoperative brain shift in image-guided surgery.

Automatic non-linear MRI-ultrasound registration for the correction of intra-operative brain deformations

OBJECTIVE

Movements of brain tissue during neurosurgical procedures reduce the effectiveness of using pre-operative images for intra-operative surgical guidance. In this paper, we explore the use of acquiring intra-operative ultrasound (US) images for the quantification of and correction for non-linear brain deformations.

MATERIALS AND METHODS

We will present a multi-modal registration strategy that automatically matches pre-operative images (e.g., MRI) to intra-operative US to correct for these deformations. The strategy involves using the predicted appearance of neuroanatomical structures in US images to build "pseudo ultrasound" images based on pre-operative segmented MRI. These images can then be non-linearly registered to intra-operative US using cross-correlation measurements within the ANIMAL package. The feasibility of the theory is demonstrated through its application to clinical patient data acquired during 12 neurosurgical procedures.

RESULTS

Results of applying the method to 12 surgical cases, including those with brain tumors and selective amygdalo-hippocampectomies, indicate that our strategy significantly recovers from non-linear brain deformations occurring during surgery. Quantitative results at tumor boundaries indicate up to 87% correction for brain shift.

CONCLUSIONS

Qualitative and quantitative examination of the results indicate that the system is able to correct for non-linear brain deformations in clinical patient data.

Intraoperative computed tomography and automated registration for image-guided cranial surgery

OBJECTIVES

Two key problems for the use of navigation systems in image-guided surgery are accurate patient-to-image registration and the fact that with ongoing surgery the patient's anatomy is altered while the image data remains unchanged. A system for intraoperative CT imaging and fully automated registration of this image addresses both problems. It had been evaluated successfully in phantom studies. In this clinical study, we assessed the impact of the system on intraoperative workflow and registration accuracy in everyday patient care.

METHODS

In ten patients who underwent image-guided surgery, CT image data were acquired intraoperatively and were automatically registered in the navigation system. Registration accuracy and surgical outcome were assessed clinically. In six of these patients, a maxillary splint with markers had been inserted to cross-check registration accuracy. The target registration error of these markers was measured.

RESULTS

In all cases, registration accuracy was clinically sufficient and the surgical task could be performed successfully. In those cases where a maxillary template with target markers was attached for additional control of the registration accuracy, the target registration error was always better than 2 mm. Automated registration reduced the intraoperative registration time considerably and partially compensated for the time needed to perform the image data acquisition.

CONCLUSIONS

Intraoperative CT imaging and automated registration successfully address the two key problems of image-guided surgery. The method is robust and accurate and proved its usability in everyday patient care.

Updating navigation with intraoperative image data

OBJECTIVES

To localize overlooked tumor remnants by updating navigation with intraoperative magnetic resonance imaging compensating for the effects of brain shift.

METHODS

In 112 patients among 805 patients that were investigated by combined use of intraoperative high-field (1.5 T) magnetic resonance imaging and navigation, mostly glioma cases (n = 85), an update of the navigation was performed. Intraoperative image data were rigidly registered with the preoperative image data, the tumor remnant was segmented, and then the initial patient registration was restored so that the registration coordinate system of the preoperative image data was applied on the intraoperative images, allowing navigation updating without intraoperative patient re-registration.

RESULTS

Navigation could be updated reliably in all cases. Potential positional shifting impairing the initial update strategy was observed only in 2 cases so that a patient re-registration was necessary. The target registration error of the initial patient registration was 1.33 +/- 0.63 mm, and registration of preoperative and intraoperative images could be performed with high accuracy, as proven by landmark checks. Updating of navigation resulted in increased resections or correction of a catheter position or biopsy sampling site in 94%. In the remaining 7 patients, the intraoperative images were used for correlation with the surgical site but without changing the surgical strategy.

CONCLUSIONS

Navigation can be reliably updated with intraoperative image data without repeated patient registration, facilitating the update procedure. Updated navigation allows achieving enlarged resections and compensates for the effects of brain shift.

A comparative analysis of coregistered ultrasound and magnetic resonance imaging in neurosurgery

OBJECTIVE

This work presents qualitative and quantitative side-by-side comparisons of oblique coregistered magnetic resonance imaging (MRI) scans and ultrasound images obtained during 35 neurosurgical procedures.

METHODS

Spatially registered series of ultrasound images were recorded for subsequent off-line evaluation and comparison with corresponding preoperative MRI studies. The degree of misalignment was reduced by reregistering the target volume directly with segmented features.

RESULTS

The initial apparent spatial misalignment of the target volume after craniotomy ranged from 0.11 to 8.73 mm (mean, 4.01 mm). After reregistration, the mutual information in overlapping segmented features was increased, presumably evidence of a better alignment locally. Additionally, the degree of feature congruence, which was assessed quantitatively through a convex hull approximation, demonstrated that the ultrasound volume was consistently smaller than its MRI counterpart.

CONCLUSION

Although intraoperative ultrasound tends to be difficult to interpret by itself, when accurately coregistered with preoperative MRI scans, its potential utility as a navigational guide is enhanced.

SURGERY OF INTRINSIC CEREBRAL TUMORS

TUMORS AND OTHER structural lesions located with and adjacent to the cerebral cortex present certain challenges in terms of the overall management and design of surgical strategies. This comprehensive analysis attempts to define the current understanding of cerebral localization and function and includes the latest advances in functional imaging, as well as surgical technique, including localization of tumors and neurophysiological mapping to maximize extent of resection while minimizing morbidity. Finally, it remains to be seen whether or not stimulation mapping will be the most useful way to identify function within the cortex in the future. Another potential paradigm would be to actually record baseline oscillatory rhythms within the cortex and, following presentation of a given task, determine if those rhythms are disturbed enough to identify eloquent cortex as a means of functional localization. This would be a paradigm shift away from stimulation mapping, which currently deactivates the cortex, as opposed to identifying an activation function which identifies functional cortex.

Optically neuronavigated ultrasonography in an intraoperative magnetic resonance imaging environment

OBJECTIVE

To develop a clinically useful method that shows the corresponding planes of intraoperative two-dimensional ultrasonography and intraoperative magnetic resonance imaging (MRI) scans determined with an optical neuronavigator from an intraoperative three-dimensional MRI scan data set, and to determine the qualitative and the quantitative spatial correspondence between the ultrasonography and MRI scans.

METHODS

An ultrasound probe was interlinked with an ergonomic and MRI scan-compatible ultrasonography probe tracker to the optical neuronavigator used in a low-field intraoperative MRI scan environment for brain surgery. Spatial correspondence measurements were performed using a custom-made ultrasonography/MRI scan phantom. In this work, instruments to combine intraoperatively collected ultrasonography and MRI scan data with an optical localization method in a magnetic environment were developed. The ultrasonography transducer tracker played an important role. Furthermore, a phantom for ultrasonography and MRI scanning was produced. This is the first report, to our knowledge, regarding the possibility of combining the two most important intraoperative imaging modalities used in neurosurgery, ultrasonography and MRI scanning, to guide brain tumor surgery.

RESULTS

The method was feasible and, as shown in an illustrative surgical case, has direct clinical impact on image-guided brain surgery. The spatial deviation between the ultrasonography and the MRI scans was, on average, 1.90 +/- 1.30 mm at depths of 0 to 120 mm from the ultrasonography probe.

CONCLUSION

The overall result of this work is a unique method to guide the neurosurgical operation with neuronavigated ultrasonography imaging in an intraoperative MRI scanning environment. The relevance of the method is emphasized in minimally invasive neurosurgery.

Surgical anatomy of microneurosurgical sulcal key points

OBJECTIVE

The brain sulci constitute the main microanatomic delimiting landmarks and surgical corridors of modern microneurosurgery. Because of the frequent difficulty in intraoperatively localizing and visually identifying the brain sulci with assurance, the main purpose of this study was to establish cortical/sulcal key points of primary microneurosurgical importance to provide a sulcal anatomic framework for the placement of craniotomies and to facilitate the main sulci intraoperative identification.

METHODS

The study was performed through the evaluation of 32 formalin-fixed cerebral hemispheres of 16 adult cadavers, which had been removed from the skulls after the introduction of plastic catheters through properly positioned burr holes necessary for the evaluation of cranial-cerebral relationships. Three-dimensional anatomic and surgical images are displayed to illustrate the use of sulcal key points.

RESULTS

The points studied were the anterior sylvian point, the inferior rolandic point, the intersection of the inferior frontal sulcus with the precentral sulcus, the intersection of the superior frontal sulcus with the precentral sulcus, the superior rolandic point, the intersection of the intraparietal sulcus with the postcentral sulcus, the superior point of the parieto-occipital sulcus, the euryon (the craniometric point that corresponds to the center of the parietal tuberosity), the posterior point of the superior temporal sulcus, and the opisthocranion, which corresponds to the most prominent point of the occipital bossa. These points presented regular neural and cranial-cerebral relationships and can be considered consistent microsurgical cortical key points.

CONCLUSION

These sulcal and gyral key points can be particularly useful for initial intraoperative sulci identification and dissection. Together, they compose a framework that can help in the understanding of hemispheric lesion localization, in the placement of supratentorial craniotomies, as landmarks for the transsulcal approaches to periventricular and intraventricular lesions, and in orienting the anatomic removal of gyral sectors that contain infiltrative tumors.

AN INTEGRATED RADIO FREQUENCY PROBE AND CRANIAL CLAMP FOR INTRAOPERATIVE MAGNETIC RESONANCE IMAGING

OBJECTIVE

To design an integrated radio frequency (RF) head probe and cranial clamp for intraoperative magnetic resonance imaging (MRI) that do not interfere with the operating procedures.

METHODS

A concept based on four inductively coupled rings was developed and applied for an intraoperative RF probe. The probe was integrated with a specially designed cranial clamp and incorporated into the intraoperative MRI system.

RESULTS

The design of the RF probe allows splitting the probe into two separate parts; the lower two rings and matching ring are permanently incorporated into the patient table, and the two upper rings can be removed to expose the patient's head during neurosurgery. The probe produces a homogeneous B1 field over the entire region of interest with sufficient sensitivity to obtain high quality images. The cranial clamp, made of MRI compatible materials, is asymmetrical to allow variable head positioning.

CONCLUSION

The described RF head probe and cranial clamp have been used successfully in more than 400 brain surgeries without compromising sterility of the operating area. Pre-, intra-, and postsurgical MRI scans have been obtained without a need to move a patient or reposition the head for imaging sessions. The images were of high quality and free of susceptibility or eddy currents artifacts. With minor modifications, the integrated RF probe and cranial clamp can be used successfully in other intraoperative MRI systems.

Image-guided ultrasonography for recurrent cystic gliomas

BACKGROUND

Long-term survival of patients with recurrent gliomas depends on the extent of resection. Thus, the desirability of an intra-operative imaging modality that can augment the resection extension without affecting vital surrounding structures is more than obvious. It was the aim of the present study to evaluate a possible benefit of image-guided intra-operative ultrasonography for the surgery of recurrent gliomas.

METHOD

The authors performed ultrasonography-assisted image-guided resection of recurrent gliomas in 16 patients. An ultrasound device (IGSonic) was integrated into the VectorVision2 navigation system (BrainLAB, Heimstetten, Germany). The IGSonic Probe 10V5 was connected to the VectorVision Navigation station via an IGSonic Device Box. Following patient registration, MRI based neuronavigation was used to determine the skin incision and the bone flap. Before opening the dura, the underlying structures were explored by ultrasound combined with the corresponding MR images. The navigated ultrasound displayed the sonographic image of the intracranial anatomy on the navigation screen in a composed overlay fashion.

FINDINGS

The integration of intra-operative ultrasound into neuronavigation system offered quick and helpful intra-operative images in all 16 procedures. Due to the specific ultrasonic characteristics of the solid and the cystic parts, our technique created highly useful images in 10 patients with cystic recurrences. In these, user friendly images were obtained that were easy to understand even for neurosurgeons without major experience in intra-operative ultrasound.

CONCLUSIONS

Neurosonography is a time- and cost-effective technology offering intra-operative imaging. The improved orientation and visualization of tumour remnants, adjacent ventricles, and the enhanced intra- and peri-tumoural vasculature is one of the main advantages of ultrasonography-assisted image-guided surgery, which is most obvious during surgery for cystic gliomas.

Intra-operative 3D ultrasound in neurosurgery

In recent years there has been a considerable improvement in the quality of ultrasound (US) imaging. The integration of 3D US with neuronavigation technology has created an efficient and inexpensive tool for intra-operative imaging in neurosurgery. In this review we present the technological background and an overview of the wide range of different applications. The technology has so far mostly been applied to improve surgery of tumours in brain tissue, but it has also been found to be useful in other procedures such as operations for cavernous haemangiomas, skull base tumours, syringomyelia, medulla tumours, aneurysms, AVMs and endoscopy guidance.

Nonrigid 3D brain registration using intensity/feature information

The brain deforms non-rigidly during neurosurgery, preventing preoperatively acquired images from accurately depicting the intraoperative brain. If the deformed brain surface can be detected, biomechanical models can be applied to calculate the resulting volumetric deformation. The reliability of this volumetric calculation is dependent on the accuracy of the surface detection. This work presents a surface tracking algorithm which relies on Bayesian analysis to track cortical surface movement. The inputs to the model are 3D preoperative brain images and intraoperative stereo camera images. The addition of a camera calibration optimization term creates a more robust model, capable of tracking the cortical surface in the presence of camera calibration error.

Comparing 0.2 tesla with 1.5 tesla intraoperative magnetic resonance imaging analysis of setup, workflow, and efficiency

RATIONALE AND OBJECTIVES

To compare low-field with high-field intraoperative magnetic resonance imaging (MRI) in respect to setup, workflow, and efficiency.

MATERIALS AND METHODS

A total of 750 patients were investigated either with a 0.2 T (March 1996-July 2001) or a 1.5 T (April 2002-August 2004) MRI system adapted for intraoperative use.

RESULTS

With the low-field setup, 330 patients were examined in 65 months; with the high-field setup, 420 patients were examined in 29 months, which is a 2.8-fold increase in cases per month (14.5 versus 5.1) reflecting improved ease of use. Concerning intraoperative workflow, the time for preparation to start intraoperative imaging decreased fivefold (2 minutes instead of 10 minutes); navigation was applied more often with 57% versus 51% (240/420 versus 167/330), whereas functional data were integrated in 35% versus 39% (84/240 versus 65/167). Application of navigation updates was doubled (22% versus 11%; 53/240 versus 18/167). Image acquisition time was reduced by a factor of two, allowing a more detailed imaging protocol, whereas the image quality is clearly improved in the high-field setup, where there was no difference between the standard preoperative image quality compared with the intraoperative quality. This contributed to an increased detection of tumor remnants and extended resections in pituitary (36% versus 29%; 47/129 versus 17/59) and glioma surgery (41% versus 26%; 38/93 versus 28/106).

CONCLUSION

Compared with the low-field setup, the high-field setup results not only in clearly superior image quality and increased imaging armamentarium, contributing to increased rates of detected tumor remnants, but also in a distinct improvement of intraoperative workflow. Furthermore, intraoperative high-field MRI offers various modalities beyond standard anatomic imaging, such as magnetic resonance spectroscopy, diffusion tensor imaging, and functional MRI.

Intraoperative functional MRI: Implementation and preliminary experience

For a non-invasive identification of eloquent brain areas in neurosurgical procedures up to now only preoperative functional brain mapping techniques are available. These are based, e.g., on preoperative functional magnetic resonance imaging (fMRI) investigations in awake patients. The aim of this study was to investigate the feasibility to perform fMRI during neurosurgical procedures in anesthetized patients. For that purpose, a passive stimulation paradigm with peripheral nerve stimulation was applied. A 1.5-T MR scanner placed in a radiofrequency-shielded operating room with an adapted operating table was used for intraoperative fMRI. The fMRI data were analyzed during acquisition by an online statistical evaluation package installed on the MR scanner console. In addition, phase reversal of somatosensory evoked potentials was used for verification of intraoperative fMRI. In four anesthetized patients with lesions in the vicinity of the central region a total of 11 fMRI measurements were successfully acquired and analyzed online. Activation was found in the somatosensory cortex, which could be confirmed by intraoperative phase reversal for each measurement. Furthermore, statistical parametric mapping (SPM) was employed for an extensive offline data analysis. We did not observe any neurological deterioration or complications due to the stimulation technique. Intraoperative fMRI is technically feasible allowing a real-time identification of eloquent brain areas despite brain shift.

In touch with robotics: neurosurgery for the future

The introduction of multiple front-end technologies during the past quarter century has generated an emerging futurism for the discipline of neurological surgery. Driven primarily by synergistic developments in science and engineering, neurosurgery has always managed to harness the potential of the latest technical developments. Robotics represents one such technology. Progress in development of this technology has resulted in new uses for robotic devices in our discipline, which are accompanied by new potential dangers and inherent risks. The recent surge in robot-assisted interventions in other disciplines suggests that this technology may be considered one of a spectrum of frontier technologies poised to fuel the development of neurosurgery and consolidate the era of minimalism. On a more practical level, if the introduction of robotics in neurosurgery proves beneficial, neurosurgeons will need to become facile with this technology and learn to harness its potential so that the best surgical results may be achieved in the least invasive manner. This article reviews the role of robotic technology in the context of neurosurgery.

1.5 T: intraoperative imaging beyond standard anatomic imaging

Intraoperative high-field MRI with integrated microscope-based neuronavigation is a safe and reliable technique providing immediate intraoperative quality control. Major indications are pituitary tumor, glioma, and epilepsy surgery. Intraoperative high-field MRI provides intraoperative anatomic images at high quality that are up to the standard of pre- and postoperative neuroradiologic imaging. Compared with previous low-field MRI systems used for intraoperative imaging, not only is the image quality is clearly superior but the imaging spectrum is much wider and the intraoperative work flow is improved. Furthermore, high-field MRI offers various modalities beyond standard anatomic imaging, such as magnetic resonance spectroscopy, diffusion tensor imaging, and functional MRI.

Intraoperative three-dimensional imaging with a motorized mobile C-arm (SIREMOBIL ISO-C-3D) in foot and ankle trauma care: a preliminary report

OBJECTIVE

The aim of the study was to assess the feasibility and benefit of the intraoperative use of a mobile C-arm with 3-dimensional imaging (ISO-C-3D).

DESIGN

Prospective consecutive clinical study.

SETTING

University hospital, level I trauma center.

METHODS

The ISO-C-3D was used for intraoperative visualization in foot and ankle trauma care. Conventional C-arms were used to judge the reduction and implant position before the ISO-C-3D was used. Time spent, changes resulting from use of the ISO-C-3D, and surgeons' ratings (visual analogue scale, 0-10 points) were recorded.

PATIENTS

Between January 1, 2003 and March 15, 2004, the ISO-C-3D was used in 62 cases (factures: pilon, n = 1; Weber-C ankles, n = 7; isolated dorsal Volkmann, n = 1; talus, n = 3; calcaneus, n = 20; navicular, n = 1; cuboid, n = 1; Lisfranc fracture-dislocation, n = 6; hindfoot arthrodesis with or without correction, n = 12).

RESULTS

On average, the operation was interrupted for 440 seconds (range 330-700); 120 seconds, on average, for the ISO-C-3D scan and 210 seconds, on average, for evaluation of the images by the surgeon. In 39% of the cases (24 of 62), the reduction and/or implant position was corrected during the same procedure after the ISO-C-3D scan. The ratings of the 8 surgeons who used the ISO-C-3D were 9.2(5.2-10) for feasibility, 9.5 (6.1-10) for accuracy, and 8.2 (4.5-10) for clinical benefit.

CONCLUSION

Intraoperative 3-dimensional visualization with the ISO-C-3D can provide useful information in foot and ankle trauma care that cannot be obtained from plain films or conventional C-arms. During the same procedure, after conventional C-arm scans judged the positioning to be correct and an ISO-C-3D scan was done, the reduction and/or implant position was corrected in 39% of the cases in this study, although not unnecessarily prolonging the operation. The ISO-C-3D appears to be most helpful in procedures with a closed reduction and internal fixation, and/or when axial reformations provide information that is not possible to obtain with a conventional C-arm and/or direct visualization during open reduction and internal fixation.

Cortical Surface Tracking Using a Stereoscopic Operating Microscope

OBJECTIVE:

To measure and compensate for soft tissue deformation during image-guided neurosurgery, we have developed a novel approach to estimate the three-dimensional (3-D) topology of the cortical surface and track its motion over time.

METHODS:

We use stereopsis to estimate the 3-D cortical topology during neurosurgical procedures. To facilitate this process, two charge-coupled device cameras have been attached to the binocular optics of a stereoscopic operating microscope. Before surgery, this stereo imaging system is calibrated to obtain the extrinsic and intrinsic camera parameters. During surgery, the 3-D shape of the cortical surface is automatically estimated from a stereo pair of images and registered to the preoperative image volume to provide navigational guidance. This estimation requires robust matching of features between the images, which, when combined with the camera calibration, yields the desired 3-D coordinates. After the 3-D cortical surface has been estimated from stereo pairs, its motion is tracked by comparing the current surface with its previous locations.

RESULTS:

We are able to estimate the 3-D topology of the cortical surface with an average error of less than 1.2 mm. Executing on a 1.1-GHz Pentium machine, the 3-D estimation from a stereo pair of 1024 × 768 resolution images requires approximately 60 seconds of computation. By applying stereopsis over time, we are able to track the motion of the cortical surface, including the pulsatile movement of the cortical surface, gravitational sag, tissue bulge as a result of increased intracranial pressure, and the parenchymal shape changes associated with tissue resection. The results from 10 surgical patients are reported.

CONCLUSION:

We have demonstrated that a stereo vision system coupled to the operating microscope can be used to efficiently estimate the dynamic topology of the cortical surface during surgery. The 3-D surface can be coregistered to the preoperative image volume. This unique intraoperative imaging technique expands the capability of the current navigational system in the operating room and increases the accuracy of anatomic correspondence with preoperative images through compensation for brain deformation.