Brain Shift Estimation in Image-Guided Neurosurgery Using 3-D Ultrasound

Intraoperative brain shift compensation: accounting for dural septa

Biomechanical models that describe soft tissue deformation provide a relatively inexpensive way to correct registration errors in image-guided neurosurgical systems caused by nonrigid brain shift. Quantifying the factors that cause this deformation to sufficient precision is a challenging task. To circumvent this difficulty, atlas-based methods have been developed recently that allow for uncertainty, yet still capture the first-order effects associated with deformation. The inverse solution is driven by sparse intraoperative surface measurements, which could bias the reconstruction and affect the subsurface accuracy of the model prediction. Studies using intraoperative MR have shown that the deformation in the midline, tentorium, and contralateral hemisphere is relatively small. The dural septa act as rigid membranes supporting the brain parenchyma and compartmentalizing the brain. Accounting for these structures in models may be an important key to improving subsurface shift accuracy. A novel method to segment the tentorium cerebelli will be described, along with the procedure for modeling the dural septa. Results in seven clinical cases show a qualitative improvement in subsurface shift accuracy making the predicted deformation more congruous with previous observations in the literature. The results also suggest a considerably more important role for hyperosmotic drug modeling for the intraoperative shift correction environment.

New prototype neuronavigation system based on preoperative imaging and intraoperative freehand ultrasound: system description and validation

PURPOSE

The aim of this report is to present IBIS (Interactive Brain Imaging System) NeuroNav, a new prototype neuronavigation system that has been developed in our research laboratory over the past decade that uses tracked intraoperative ultrasound to address surgical navigation issues related to brain shift. The unique feature of the system is its ability, when needed, to improve the initial patient-to-preoperative image alignment based on the intraoperative ultrasound data. Parts of IBIS Neuronav source code are now publicly available on-line.

METHODS

Four aspects of the system are characterized in this paper: the ultrasound probe calibration, the temporal calibration, the patient-to-image registration and the MRI-ultrasound registration. In order to characterize its real clinical precision and accuracy, the system was tested in a series of adult brain tumor cases.

RESULTS

Three metrics were computed to evaluate the precision and accuracy of the ultrasound calibration. 1) Reproducibility: 1.77 mm and 1.65 mm for the bottom corners of the ultrasound image, 2) point reconstruction precision 0.62-0.90 mm: and 3) point reconstruction accuracy: 0.49-0.74 mm. The temporal calibration error was estimated to be 0.82 ms. The mean fiducial registration error (FRE) of the homologous-point-based patient-to-MRI registration for our clinical data is 4.9 ± 1.1 mm. After the skin landmark-based registration, the mean misalignment between the ultrasound and MR images in the tumor region is 6.1 ± 3.4 mm.

CONCLUSIONS

The components and functionality of a new prototype system are described and its precision and accuracy evaluated. It was found to have an accuracy similar to other comparable systems in the literature.

Functional Magnetic Resonance Imaging and Diffusion Tensor Tractography Incorporated Into an Intraoperative 3-Dimensional Ultrasound-Based Neuronavigation System

BACKGROUND

Functional neuronavigation with intraoperative 3-dimensional (3D) ultrasound may facilitate safer brain lesion resections than conventional neuronavigation.

OBJECTIVE

In this study, functional magnetic resonance imaging (fMRI) and diffusion tensor tractography (DTT) were used to map eloquent areas. We assessed the use of fMRI and DTT for preoperative assessments and determined whether using these data together with 3D ultrasound during surgery enabled safer lesion resection.

METHODS

We reviewed 51 consecutive patients with intracranial lesions in whom fMRI with or without DTT was used to map eloquent areas. To assess a possible impact of fMRI/DTT, we reviewed and analyzed the quality of the fMRI/DTT data, any change in therapeutic strategies, lesion to eloquent area distance (LEAD), extent of resection, and clinical outcome.

RESULTS

As a result of the fMRI/DTT mapping, the therapeutic strategies were changed in 4 patients. The median tumor residue for glioma patients was 11% (n = 33) and 0% for nonglioma lesions (n = 12). For gliomas, there was a significant correlation between decreasing LEAD and increasing tumor residue. Of the glioma patients, 42% underwent gross total resection (≥ 95%) and 12% suffered neurological worsening after surgery as a result of complications. Of glioma patients with an LEAD of ≤ 5 mm, 24% underwent gross total resection and 10% experienced neurological deterioration.

CONCLUSION

This study demonstrates that preoperative fMRI and DTT had direct consequences for therapeutic strategies and indicates their impact on intraoperative strategies to spare eloquent cortex and tracts. Functional neuronavigation combined with intraoperative 3D ultrasound can, in most patients, enable resection of brain lesions with general anesthesia without jeopardizing neurological function.

A fast and efficient method to compensate for brain shift for tumor resection therapies measured between preoperative and postoperative tomograms

In this paper, an efficient paradigm is presented to correct for brain shift during tumor resection therapies. For this study, high resolution preoperative (pre-op) and postoperative (post-op) MR images were acquired for eight in vivo patients, and surface/subsurface shift was identified by manual identification of homologous points between the pre-op and immediate post-op tomograms. Cortical surface deformation data were then used to drive an inverse problem framework. The manually identified subsurface deformations served as a comparison toward validation. The proposed framework recaptured 85% of the mean subsurface shift. This translated to a subsurface shift error of 0.4 +/- 0.4 mm for a measured shift of 3.1 +/- 0.6 mm. The patient's pre-op tomograms were also deformed volumetrically using displacements predicted by the model. Results presented allow a preliminary evaluation of correction both quantitatively and visually. While intraoperative (intra-op) MR imaging data would be optimal, the extent of shift measured from pre- to post-op MR was comparable to clinical conditions. This study demonstrates the accuracy of the proposed framework in predicting full-volume displacements from sparse shift measurements. It also shows that the proposed framework can be extended and used to update pre-op images on a time scale that is compatible with surgery.

Image-guided intraoperative cortical deformation recovery using game theory: application to neocortical epilepsy surgery

During neurosurgery, nonrigid brain deformation prevents preoperatively-acquired images from accurately depicting the intraoperative brain. Stereo vision systems can be used to track intraoperative cortical surface deformation and update preoperative brain images in conjunction with a biomechanical model. However, these stereo systems are often plagued with calibration error, which can corrupt the deformation estimation. In order to decouple the effects of camera calibration from the surface deformation estimation, a framework that can solve for disparate and often competing variables is needed. Game theory, which was developed to handle decision making in this type of competitive environment, has been applied to various fields from economics to biology. In this paper, game theory is applied to cortical surface tracking during neocortical epilepsy surgery and used to infer information about the physical processes of brain surface deformation and image acquisition. The method is successfully applied to eight in vivo cases, resulting in an 81% decrease in mean surface displacement error. This includes a case in which some of the initial camera calibration parameters had errors of 70%. Additionally, the advantages of using a game theoretic approach in neocortical epilepsy surgery are clearly demonstrated in its robustness to initial conditions.

Comparative analysis of various brain imaging techniques

The bio-imaging techniques have widespread applications from diagnosing diseases to investigating the body tissues at the cells level. Traditionally, these techniques were used mainly in the orthopedic treatment. However, with the development of infrared cameras, ultrasound, and radio wave technology, they are used in different medical fields such as cardiovascular analysis, neurological treatment and infant care. This paper reviews the common bio-imaging techniques used in the brain imaging and compares them based on resolution, contrast, biological risks involved, and price.

Estimation of brain deformation for volumetric image updating in protoporphyrin IX fluorescence-guided resection

INTRODUCTION

Fluorescence-guided resection (FGR) of brain tumors is an intuitive, practical and emerging technology for visually delineating neoplastic tissue exposed intraoperatively. Image guidance is the standard technique for producing 3-dimensional spatially coregistered information for surgical decision making. Both technologies together are synergistic: the former detects surface fluorescence as a biomarker of the current surgical margin while the latter shows coregistered volumetric neuroanatomy but can be degraded by intraoperative brain shift. We present the implementation of deformation modeling for brain shift compensation in protoporphyrin IX FGR, integrating these two sources of information for maximum surgical benefit.

METHODS

Two patients underwent FGR coregistered with conventional image guidance. Histopathological analysis, intraoperative fluorescence and image space coordinates were recorded for biopsy specimens acquired during surgery. A biomechanical brain deformation model driven by intraoperative ultrasound data was used to generate updated MR images.

RESULTS

Combined use of fluorescence signatures and updated MR image information showed substantially improved accuracy compared to fluorescence or the original (i.e., nonupdated) MR images, detecting only true positives and true negatives, and no instances of false positives or false negatives.

CONCLUSION

Implementation of brain deformation modeling in FGR shows promise for increasing the accuracy of neurosurgical guidance in the delineation and resection of brain tumors.

A surface registration method for quantification of intraoperative brain deformations in image-guided neurosurgery

Intraoperative brain deformations decrease accuracy in image-guided neurosurgery. Approaches to quantify these deformations based on 3-D reconstruction of cortectomy surfaces have been described and have shown promising results regarding the extrapolation to the whole brain volume using additional prior knowledge or sparse volume modalities. Quantification of brain deformations from surface measurement requires the registration of surfaces at different times along the surgical procedure, with different challenges according to the patient and surgical step. In this paper, we propose a new flexible surface registration approach for any textured point cloud computed by stereoscopic or laser range approach. This method includes three terms: the first term is related to image intensities, the second to Euclidean distance, and the third to anatomical landmarks automatically extracted and continuously tracked in the 2-D video flow. Performance evaluation was performed on both phantom and clinical cases. The global method, including textured point cloud reconstruction, had accuracy within 2 mm, which is the usual rigid registration error of neuronavigation systems before deformations. Its main advantage is to consider all the available data, including the microscope video flow with higher temporal resolution than previously published methods.

An intraoperative brain shift monitor using shear mode transcranial ultrasound: preliminary results

OBJECTIVE

Various methods of intraoperative structural monitoring during neurosurgery are used to localize lesions after brain shift and to guide surgically introduced probes such as biopsy needles or stimulation electrodes. With its high temporal resolution, portability, and nonionizing mode of radiation, ultrasound has potential advantages over other existing imaging modalities for intraoperative monitoring, yet ultrasound is rarely used during neurosurgery largely because of the craniotomy requirement to achieve sufficiently useful signals.

METHODS

Prompted by results from recent studies on transcranial ultrasound, a prototype device that aims to use the shear mode of transcranial ultrasound transmission for intraoperative monitoring was designed, constructed, and tested with 10 human participants. Magnetic resonance images were then obtained with the device spatially registered to the magnetic resonance imaging (MRI) reference coordinates. Peaks in both the ultrasound and MRI signals were identified and analyzed for both spatial localization and signal-to-noise ratio (SNR).

RESULTS

The first results aimed toward validating the prototype device with MRI showed an excellent correlation (n = 38; R(2) = 0.9962) between the structural localization abilities of the two modalities. In addition, the overall SNR of the ultrasound backscatter signals (n = 38; SNR = 25.4 +/- 5.2 dB, mean +/- SD) was statistically equivalent to that of the MRI data (n = 38; SNR = 22.5 +/- 4.8 dB).

CONCLUSIONS

A statistically significant correlation of localized intracranial structures between intraoperative transcranial ultrasound monitoring and MRI data was achieved with 10 human participants. We have shown and validated a prototype device incorporating transcranial shear mode ultrasound for clinical monitoring applications.

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.

Deformable ultrasound registration without reconstruction

Ultrasound (US) imaging is often proposed as an interoperative imaging modality. This use nearly always requires that the collected data be registered to preoperative data of another modality. Existing intensity-based registration approaches all begin by reconstructing a 3D US volume from the collected 2D slices. We propose to directly register the set of 2D slices to the preoperative images. We argue this has a number of advantages, including the omission of the potentially complex reconstruction step, greater adaptability of the similarity measures, and easier parallelization. We describe a system for performing this task and present results on phantom data that show that our slice based method consistently outperforms a reconstruction based method in both speed and accuracy.

Sparse registration for three-dimensional stress echocardiography

Three-dimensional (3-D) stress echocardiography is a novel technique for diagnosing cardiac dysfunction. It involves evaluating wall motion of the left ventricle, by visually analyzing ultrasound images obtained in rest and in different stages of stress. Since the acquisitions are performed minutes apart, variabilities may exist in the visualized cross-sections. To improve anatomical correspondence between rest and stress, aligning the images is essential. We developed a new intensity-based, sparse registration method to retrieve standard anatomical views from 3-D stress images that were equivalent to the manually selected views in the rest images. Using sparse image planes, the influence of common image artifacts could be reduced. We investigated different similarity measures and different levels of sparsity. The registration was tested using data of 20 patients and quantitatively evaluated based on manually defined anatomical landmarks. Alignment was best using sparse registration with two long-axis and two short-axis views; registration errors were reduced significantly, to the range of interobserver variabilities. In 91% of the cases, the registration result was qualitatively assessed as better than or equal to the manual alignment. In conclusion, sparse registration improves the alignment of rest and stress images, with a performance similar to manual alignment. This is an important step towards objective quantification in 3-D stress echocardiography.

Semiautomatic registration of pre- and postbrain tumor resection laser range data: method and validation

This paper presents a semiautomatic method for the registration of images acquired during surgery with a tracked laser range scanner (LRS). This method, which relies on the registration of vessels that can be visualized in the pre- and the postresection images, is a component of a larger system designed to compute brain shift that occurs during tumor resection cases. Because very large differences between pre- and postresection images are typically observed, the development of fully automatic methods to register these images is difficult. The method presented herein is semiautomatic and requires only the identification of a number of points along the length of the vessels. Vessel segments joining these points are then automatically identified using an optimal path finding algorithm that relies on intensity features extracted from the images. Once vessels are identified, they are registered using a robust point-based nonrigid registration algorithm. The transformation computed with the vessels is then applied to the entire image. This permits establishment of a complete correspondence between the pre- and post-3-D LRS data. Experiments show that the method is robust to operator errors in localizing homologous points and a quantitative evaluation performed on ten surgical cases shows submillimetric registration accuracy.

Comparison of navigated 3D ultrasound findings with histopathology in subsequent phases of glioblastoma resection

OBJECTIVE

The purpose of the study was to compare the ability of navigated 3D ultrasound to distinguish tumour and normal brain tissue at the tumour border zone in subsequent phases of resection.

MATERIALS AND METHODS

Biopsies were sampled in the tumour border zone as seen in the US images before and during surgery. After resection, biopsies were sampled in the resection cavity wall. Histopathology was compared with the surgeon's image findings.

RESULTS

Before resection, the tumour border was delineated by ultrasound with high specificity and sensitivity (both 95%). During resection, ultrasound had acceptable sensitivity (87%), but poor specificity (42%), due to biopsies falsely classified as tumour by the surgeon. After resection, sensitivity was poor (26%), due to tumour or infiltrated tissue in several biopsies deemed normal by ultrasound, but the specificity was acceptable (88%).

CONCLUSIONS

Our study shows that although glioblastomas are well delineated prior to resection, there seem to be overestimation of tumour tissue during resection. After resection tumour remnants and infiltrated brain tissue in the resection cavity wall may be undetected. We believe that the benefits of intraoperative ultrasound outweigh the shortcomings, but users of intraoperative ultrasound should keep the limitations shown in our study in mind.

Utility of neuronavigation and neuromonitoring in epilepsy surgery

The management of medically refractory epilepsy poses both a valuable therapeutic opportunity and a formidable technical challenge to epilepsy surgeons. Recent decades have produced significant advancements in the capabilities and availability of adjunctive tools in epilepsy surgery. In particular, image-based neuronavigation and electrophysiological neuromonitoring represent versatile and informative modalities that can assist a surgeon in performing safe and effective resections. In the present article the authors discuss these 2 subjects with reference to how they can be applied and what evidence supports their use. As technologies evolve with demonstrated and potential utility, it is important for all clinicians who deal with epilepsy to understand where neuronavigation and neuromonitoring stand in the present and what avenues for improvement exist for the future.

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.

Simultaneous ultrasound and MRI system for breast biopsy: compatibility assessment and demonstration in a dual modality phantom

Simultaneous capturing of ultrasound (US) and magnetic resonance (MR) images allows fusion of information obtained from both modalities. We propose an MR-compatible US system where MR images are acquired in a known orientation with respect to the US imaging plane and concurrent real-time imaging can be achieved. Compatibility of the two imaging devices is a major issue in the physical setup. Tests were performed to quantify the radio frequency (RF) noise introduced in MR and US images, with the US system used in conjunction with MRI scanner of different field strengths (0.5 T and 3 T). Furthermore, simultaneous imaging was performed on a dual modality breast phantom in the 0.5 T open bore and 3 T close bore MRI systems to aid needle-guided breast biopsy. Fiducial based passive tracking and electromagnetic based active tracking were used in 3 T and 0.5 T, respectively, to establish the location and orientation of the US probe inside the magnet bore. Our results indicate that simultaneous US and MR imaging are feasible with properly-designed shielding, resulting in negligible broadband noise and minimal periodic RF noise in both modalities. US can be used for real time display of the needle trajectory, while MRI can be used to confirm needle placement.

[Evaluation of a DC pulsed magnetic tracking system in neurosurgical navigation: technique, accuracies, and influencing factors]

Navigation systems are useful instruments in cranial neurosurgery. For specification of position, so-called sensor-based navigation techniques use: (a) a signal emitter that generates a defined electromagnetic field in the area of the operation site; and (b) small sensors that detect the position of various operating instruments in the electromagnetic field. For a long time, owing to a lack of clinical data and long-term studies, electromagnetic systems have been regarded as error-prone and imprecise. With the development of a pulsed direct current (DC) technique, precision levels can now be reached that are comparable with those of established optical and mechanical measuring procedures. However, it must be noted that the influence on the measuring accuracy within the operating field increases with increasing susceptibility of the various metals used in the operating theatre (titanium<aluminium<high-alloy steels<low-alloy steels). The technique, accuracy, and influencing factors of a DC pulsed magnetic tracking system were investigated in more than 200 cases.

Is the image guidance of ultrasonography beneficial for neurosurgical routine?

BACKGROUND

Intraoperative US has been widely used in neurosurgical procedures. However, images are often difficult to read. In the present study, we evaluate whether the image guidance of ultrasonography is helpful for the interpretation of US scans.

METHODS

Twenty-nine patients with tumor were operated on with the aid of intraoperative US from January to June 2005. Image-guided sonography was used in 13 cases and nonnavigated US technology in the remaining cases. We compared the 2 technologies retrospectively.

RESULTS

Although image quality was good in most cases, orientation remained difficult in 8 of the 16 patients where conventional sonography was used. With the aid of image fusion for navigated sonography, the orientation was judged superior to nonnavigated US.

CONCLUSION

In our experience, integration of the US into the navigation system facilitates anatomical understanding. Thus, we feel that this technology is beneficial for neurosurgical routine.

COMPARISON OF TWO TECHNIQUES TO POSTOPERATIVELY LOCALIZE THE ELECTRODE CONTACTS USED FOR SUBTHALAMIC NUCLEUS STIMULATION

OBJECTIVE

Cerebral ventriculography (Vg) and magnetic resonance imaging (MRI) scanning are routine procedures to determine the implanted electrode placement into the subthalamic nucleus (STN) and are used in several centers that provide deep brain stimulation for Parkinson's disease patients. However, because of image distortion, MRI scan accuracy in determining electrode placement is still matter of debate. The objectives of this study were to verify the expected localization of the electrode contacts within the STN and to compare the stereotactic coordinates of these contacts determined intraoperatively by Vg with those calculated postoperatively by MRI scans. To our knowledge, this is the first study attempting to compare the "gold standard" of stereotactic accuracy (Vg) with the anatomic resolution provided by MRI scans.

METHODS

Images from 18 patients with Parkinson's disease who underwent bilateral operation were used in this study. Among the 36 chronically stimulated contacts, 28 contacts (78%) were localized in the dorsolateral part of the STN. The remaining eight contacts (22%) were located more dorsally in the zona incerta, close to the upper border of the STN.

RESULTS

Significant differences were found between Vg and MRI scans regarding the mediolateral x coordinate of the contacts for both left and right electrodes and regarding the right-sided anteroposterior y coordinate. No statistical difference was found for the left-sided y coordinate and the dorsoventral z coordinate for both sides.

CONCLUSION

If we assume that Vg is an imaging gold standard, our results suggest that postoperative MRI scanning may induce a slight image translation compared with Vg. However, MRI scans allowed localization of most of the contacts within the STN.

An atlas-based method to compensate for brain shift: preliminary results

Compensating for intraoperative brain shift using computational models has shown promising results. Since computational time is an important factor during neurosurgery, a priori knowledge of the possible sources of deformation can increase the accuracy of model-updated image-guided systems. In this paper, a strategy to compensate for distributed loading conditions in the brain such as brain sag, volume changes due to drug reactions, and brain swelling due to edema is presented. An atlas of model deformations based on these complex loading conditions is computed preoperatively and used with a constrained linear inverse model to predict the intraoperative distributed brain shift. This relatively simple inverse finite-element approach is investigated within the context of a series of phantom experiments, two in vivo cases, and a simulation study. Preliminary results indicate that the approach recaptured on average 93% of surface shift for the simulation, phantom, and in vivo experiments. With respect to subsurface shift, comparisons were only made with simulation and phantom experiments and demonstrated an ability to recapture 85% of the shift. This translates to a remaining surface and subsurface shift error of 0.7+/-0.3 mm, and 1.0+/-0.4 mm, respectively, for deformations on the order of 1cm.

Functional neuronavigation combined with intra-operative 3D ultrasound: initial experiences during surgical resections close to eloquent brain areas and future directions in automatic brain shift compensation of preoperative data

OBJECTIVE

The aims of this study were: 1) To develop protocols for, integration and assessment of the usefulness of high quality fMRI (functional magnetic resonance imaging) and DTI (diffusion tensor imaging) data in an ultrasound-based neuronavigation system. 2) To develop and demonstrate a co-registration method for automatic brain-shift correction of pre-operative MR data using intra-operative 3D ultrasound.

METHODS

Twelve patients undergoing brain surgery were scanned to obtain structural and fMRI data before the operation. In six of these patients, DTI data was also obtained. The preoperative data was imported into a commercial ultrasound-based navigation system and used for surgical planning and guidance. Intra-operative ultrasound volumes were acquired when needed during surgery and the multimodal data was used for guidance and resection control. The use of the available image information during planning and surgery was recorded. An automatic voxel-based registration method between preoperative MRA and intra-operative 3D ultrasound angiography (Power Doppler) was developed and tested postoperatively.

RESULTS

The study showed that it is possible to implement robust, high-quality protocols for fMRI and DTI and that the acquired data could be seamlessly integrated in an ultrasound-based neuronavigation system. Navigation based on fMRI data was found to be important for pre-operative planning in all twelve procedures. In five out of eleven cases the data was also found useful during the resection. DTI data was found to be useful for planning in all five cases where these data were imported into the navigation system. In two out of four cases DTI data was also considered important during the resection (in one case DTI data were acquired but not imported and in another case fMRI and DTI data could only be used for planning). Information regarding the location of important functional areas (fMRI) was more beneficial during the planning phase while DTI data was more helpful during the resection. Furthermore, the surgeon found it more user-friendly and efficient to interpret fMRI and DTI information when shown in a navigation system as compared to the traditional display on a light board or monitor. Updating MRI data for brain-shift using automatic co-registration of preoperative MRI with intra-operative ultrasound was feasible.

CONCLUSION

In the present study we have demonstrated how both fMRI and DTI data can be acquired and integrated into a neuronavigation system for improved surgical planning and guidance. The surgeons reported that the integration of fMRI and DTI data in the navigation system represented valuable additional information presented in a user-friendly way and functional neuronavigation is now in routine use at our hospital. Furthermore, the present study showed that automatic ultrasound-based updates of important pre-operative MRI data are feasible and hence can be used to compensate for brain shift.

Intraoperative navigated 3-dimensional ultrasound angiography in tumor surgery

BACKGROUND

Avoiding damage to blood vessels is often the concern of the neurosurgeon during tumor surgery. Using angiographic image data in neuronavigation may be useful in cases where vascular anatomy is of special interest. Since 2003, we have routinely used 3D ultrasound angiography in tumor surgery, and between January 2003 and May 2005, 62 patients with different tumors have been operated using intraoperative 3D ultrasound angiography in neuronavigation.

METHODS

An ultrasound-based neuronavigation system was used. In addition to 3D ultrasound tissue image data, 3D ultrasound angiography (power Doppler) image data were acquired at different stages of the operation. The value and role of navigated 3D ultrasound angiography as judged by the surgeon were recorded.

RESULTS

We found that intraoperative ultrasound angiography was easy to acquire and interpret, and that image quality was sufficient for neuronavigation. In 26 of 62 cases, ultrasound angiography was found to be helpful by visualizing hidden vessels adjacent to and inside the tumor, facilitating tailored approaches and safe biopsy sampling.

CONCLUSIONS

Intraoperative 3D ultrasound angiography is straightforward to use, image quality is sufficient for image guidance, and it adds valuable information about hidden vessels, increasing safety and facilitating tailored approaches. Furthermore, with updated 3D ultrasound angiography imaging, accuracy of neuronavigation may be maintained in cases of brain shift.

Patient-specific model of brain deformation: application to medical image registration

This contribution presents finite element computation of the deformation field within the brain during craniotomy-induced brain shift. The results were used to illustrate the capabilities of non-linear (i.e. accounting for both geometric and material non-linearities) finite element analysis in non-rigid registration of pre- and intra-operative magnetic resonance images of the brain. We used patient-specific hexahedron-dominant finite element mesh, together with realistic material properties for the brain tissue and appropriate contact conditions at boundaries. The model was loaded by the enforced motion of nodes (i.e. through prescribed motion of a boundary) at the brain surface in the craniotomy area. We suggest using explicit time-integration scheme for discretised equations of motion, as the computational times are much shorter and accuracy, for practical purposes, the same as in the case of implicit integration schemes. Application of the computed deformation field to register (i.e. align) the pre-operative images with the intra-operative ones indicated that the model very accurately predicts the displacements of the tumour and the lateral ventricles even for limited information about the brain surface deformation. The prediction accuracy improves when information about deformation of not only exposed (during craniotomy) but also unexposed parts of the brain surface is used when prescribing loading. However, it appears that the accuracy achieved using information only about the deformation of the exposed surface, that can be determined without intra-operative imaging, is acceptable. The presented results show that non-linear biomechanical models can complement medical image processing techniques when conducting non-rigid registration. Important advantage of such models over the previously used linear ones is that they do not require unrealistic assumptions that brain deformations are infinitesimally small and brain stress-strain relationship is linear.

A Novel Platform for Image-guided Ultrasound

OBJECTIVE:

The combination of classic neuronavigation and intraoperative ultrasound is a recent innovation in image guidance technology. However, this technique requires two hardware components (neuronavigation and an ultrasound system). It was the aim of the study to describe a new simplified technology of a so-called one-platform navigation system developed by our institution in collaboration with the industry and to demonstrate its range of various applications.

METHODS:

An ultrasound device (IGSonic; BrainLAB, Munich, Germany) is integrated into the VectorVision2 navigation system (BrainLAB, Munich, Germany). The IGSonic Probe 10V5 is connected to the VectorVision Navigation station via an IGSonic Device Box. Once the ultrasound probe is calibrated, the navigated ultrasound displays the sonographic image of the intracranial anatomy on the navigation screen in a composed overlay fashion. It might depict vascular structures within the ultrasound plane by a duplex mode. Ultrasound can also be operated independently from navigation.

RESULTS:

The VectorVision2 system combines intraoperative ultrasound data sets with preoperatively acquired neuronavigation data sets in plug and play fashion. The system provides a cost-effective intraoperative imaging modality that offers a good anatomic orientation by various composite images, including the display of the amount of brain shift. In our institution, the comprehensible interface led to a routine use of the technology by several neurosurgeons who had not been familiar with the ultrasound technology before.

CONCLUSION:

The integration of an ultrasound device into an existing navigation system has been successfully developed. The system offers a friendly user interface and cost-effective intraoperative imaging feedback. Although brain shift can be visualized by an image overlay technology as demonstrated by the present system, future developments should aim at fusion techniques of both intra- and preoperative image data sets.

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.

Computer-assisted 3D ultrasound-guided neurosurgery: technological contributions, including multimodal registration and advanced display, demonstrating future perspectives

BACKGROUND

Navigation systems are now frequently being used for guiding surgical procedures. Existing neuronavigation systems suffer from the lack of updated images when tissue changes during surgery as well as from user-friendly displays of all essential images for accurate and safe surgery guidance.

METHODS

We have developed various new technologies for improved neuronavigation. Using intraoperative 3D ultrasound (US) imaging, we have developed various registration algorithms for using and updating a complete multimodal and multivolume 3D map for navigation.

RESULTS

We experienced that advanced multimodal visualization makes it easy to interpret information from several image volumes and modalities simultaneously. Using high quality intraoperative 3D ultrasound, essential preoperative information could be corrected due to brain shift. fMRI and other important preoperative data could then be used together with intraoperative ultrasound imaging for more accurate, safer and improved guidance of therapy.

CONCLUSIONS

We claim that new features, as demonstrated in the present paper, using intraoperative 3D ultrasound in combination with advanced registration and display algorithms will represent important contributions towards more accurate, safer and more optimized future patient treatment.