Resection planning in extratemporal epilepsy surgery using 3D multimodality imaging and intraoperative MRI.

Surgical resection in non-lesional, extratemporal epilepsy, informed by stereoEEG recordings, is challenging. There are no clear borders of resection, and the surgeon is often operating in deep areas of the brain that are difficult to access. We present a technical note where 3D multimodality image integration in EpiNavTM is used to build a planned resection model, based on a previous intracranial EEG evaluation. Intraoperative MRI is then used to ensure a complete resection of the planned model. As stereoEEG becomes more common in the presurgical evaluation of epilepsy, these tools will become increasingly important to facilitate targeted cortical resections.

Automated multiple trajectory planning algorithm for the placement of stereo-electroencephalography (SEEG) electrodes in epilepsy treatment.

PURPOSE: About one-third of individuals with focal epilepsy continue to have seizures despite optimal medical management. These patients are potentially curable with neurosurgery if the epileptogenic zone (EZ) can be identified and resected. Stereo-electroencephalography (SEEG) to record epileptic activity with intracranial depth electrodes may be required to identify the EZ. Each SEEG electrode trajectory, the path between the entry on the skull and the cerebral target, must be planned carefully to avoid trauma to blood vessels and conflicts between electrodes. In current clinical practice trajectories are determined manually, typically taking 2-3 h per patient (15 min per electrode). Manual planning (MP) aims to achieve an implantation plan with good coverage of the putative EZ, an optimal spatial resolution, and 3D distribution of electrodes. Computer-assisted planning tools can reduce planning time by quantifying trajectory suitability. METHODS: We present an automated multiple trajectory planning (MTP) algorithm to compute implantation plans. MTP uses dynamic programming to determine a set of plans. From this set a depth-first search algorithm finds a suitable plan. We compared our MTP algorithm to (a) MP and (b) an automated single trajectory planning (STP) algorithm on 18 patient plans containing 165 electrodes. RESULTS: MTP changed all 165 trajectories compared to MP. Changes resulted in lower risk (122), increased grey matter sampling (99), shorter length (92), and surgically preferred entry angles (113). MTP changed 42 % (69/165) trajectories compared to STP. Every plan had between 1 to 8 (median 3.5) trajectories changed to resolve electrode conflicts, resulting in surgically preferred plans. CONCLUSION: MTP is computationally efficient, determining implantation plans containing 7-12 electrodes within 1 min, compared to 2-3 h for MP.

A Pipeline for 3D Multimodality Image Integration and Computer-assisted Planning in Epilepsy Surgery.

Epilepsy surgery is challenging and the use of 3D multimodality image integration (3DMMI) to aid presurgical planning is well-established. Multimodality image integration can be technically demanding, and is underutilised in clinical practice. We have developed a single software platform for image integration, 3D visualization and surgical planning. Here, our pipeline is described in step-by-step fashion, starting with image acquisition, proceeding through image co-registration, manual segmentation, brain and vessel extraction, 3D visualization and manual planning of stereoEEG (SEEG) implantations. With dissemination of the software this pipeline can be reproduced in other centres, allowing other groups to benefit from 3DMMI. We also describe the use of an automated, multi-trajectory planner to generate stereoEEG implantation plans. Preliminary studies suggest this is a rapid, safe and efficacious adjunct for planning SEEG implantations. Finally, a simple solution for the export of plans and models to commercial neuronavigation systems for implementation of plans in the operating theater is described. This software is a valuable tool that can support clinical decision making throughout the epilepsy surgery pathway.

Comparison of computer-assisted planning and manual planning for depth electrode implantations in epilepsy.

OBJECT The objective of this study was to evaluate the clinical utility of multitrajectory computer-assisted planning software (CAP) to plan stereoelectroencephalography (SEEG) electrode arrangements. METHODS A cohort of 18 patients underwent SEEG for evaluation of epilepsy at a single center between August 2013 and August 2014. Planning of electrodes was performed manually and stored using EpiNav software. CAP was developed as a planning tool in EpiNav. The user preselects a set of cerebral targets and optimized trajectory constraints, and then runs an automated search of potential scalp entry points and associated trajectories. Each trajectory is associated with metrics for a safety profile, derived from the minimal distance to vascular structures, and an efficacy profile, derived from the proportion of depth electrodes that are within or adjacent to gray matter. CAP was applied to the cerebral targets used in the cohort of 18 previous manually planned implantations to generate new multitrajectory implantation plans. A comparison was then undertaken for trajectory safety and efficacy. RESULTS CAP was applied to 166 electrode targets in 18 patients. There were significant improvements in both the safety profile and efficacy profile of trajectories generated by CAP compared with manual planning (p < 0.05). Three independent neurosurgeons assessed the feasibility of the trajectories generated by CAP, with 131 (78.9%) of 166 trajectories deemed suitable for implementation in clinical practice. CAP was performed in real time, with a median duration of 8 minutes for each patient, although this does not include the time taken for data preparation. CONCLUSIONS CAP is a promising tool to plan SEEG implantations. CAP provides feasible depth electrode arrangements, with quantitatively greater safety and efficacy profiles, and with a substantial reduction in duration of planning within the 3D multimodality framework.

Placental volume, vasculature and calcification in pregnancies complicated by pre-eclampsia and intra-uterine growth restriction.

OBJECTIVE: Pre-eclampsia (PET) and intrauterine growth restriction (IUGR), often associated with impaired placental function, are among the most common conditions contributing to increased perinatal mortality and morbidity. This study investigates if three dimensional power Doppler (3DPD) of the placenta and computerised analysis of placental calcification is different between PET/IUGR and normal pregnancies. STUDY DESIGN: This was a prospective cohort study involving 50 women with pre-eclampsia and/or IUGR, or with IUGR only from 24 to 40 weeks' gestation. 3DPD ultrasound was used to calculate placental volume, vascularisation index (VI), flow index (FI) and vascularisation-flow index (VFI). Following each scan the percentage of placental calcification was also calculated, by computer analysis. Results were compared with normal (control) values, and findings correlated with maternal and fetal Doppler parameters and placental histology. RESULTS: Volume, VI, and VFI are not influenced by gestational age in PET/IUGR pregnancies. FI was found to increase with gestational age (p=0.009) and was lower than normal in the total study group from 24 to 30 weeks (p=0.006). In the pregnancies affected by PET, whether or not IUGR was present, all three indices were lower than normal values between 24 and 30 weeks (VI: p=0.038, FI: p=0.004, VFI: p=0.015). Vascularisation and flow indices were less than the normal 50th centile in the majority of cases of utero-placental insufficiency (p=0.047), and vascularisation and vascularisation flow indices were lower in cases of accelerated placental maturation (p=0.016 and 0.041 respectively). Placental volume greater than the 50th centile between 24 and 30 weeks was associated with the presence of infarction on histology (p=0.021). Flow index (p=0.002) and vascularisation flow index (p=0.036) were lower in the presence of bilateral uterine artery notches. Calcification, similar to the control group, was related to an increasing UAPI (p=0.041) and MCA PI <5th centile (p=0.010). CONCLUSIONS: The study findings suggest that there may be a role for 3DPD placental assessment of volume, vascularisation and blood flow and computer analysis of placental calcification in the identification and management of PET/IUGR pregnancy.

Stability, structure and scale: improvements in multi-modal vessel extraction for SEEG trajectory planning.

PURPOSE: Brain vessels are among the most critical landmarks that need to be assessed for mitigating surgical risks in stereo-electroencephalography (SEEG) implantation. Intracranial haemorrhage is the most common complication associated with implantation, carrying significantly associated morbidity. SEEG planning is done pre-operatively to identify avascular trajectories for the electrodes. In current practice, neurosurgeons have no assistance in the planning of electrode trajectories. There is great interest in developing computer-assisted planning systems that can optimise the safety profile of electrode trajectories, maximising the distance to critical structures. This paper presents a method that integrates the concepts of scale, neighbourhood structure and feature stability with the aim of improving robustness and accuracy of vessel extraction within a SEEG planning system. METHODS: The developed method accounts for scale and vicinity of a voxel by formulating the problem within a multi-scale tensor voting framework. Feature stability is achieved through a similarity measure that evaluates the multi-modal consistency in vesselness responses. The proposed measurement allows the combination of multiple images modalities into a single image that is used within the planning system to visualise critical vessels. RESULTS: Twelve paired data sets from two image modalities available within the planning system were used for evaluation. The mean Dice similarity coefficient was 0.89 ± 0.04, representing a statistically significantly improvement when compared to a semi-automated single human rater, single-modality segmentation protocol used in clinical practice (0.80 ± 0.03). CONCLUSIONS: Multi-modal vessel extraction is superior to semi-automated single-modality segmentation, indicating the possibility of safer SEEG planning, with reduced patient morbidity.

Utility of 3D multimodality imaging in the implantation of intracranial electrodes in epilepsy.

OBJECTIVE: We present a single-center prospective study, validating the use of 3D multimodality imaging (3 DMMI) in patients undergoing intracranial electroencephalography (IC-EEG). METHODS: IC-EEG implantation preparation entails first designing of the overall strategy of implantation (strategy) and second the precise details of implantation (planning). For each case, the multidisciplinary team made decisions on strategy and planning before the disclosure of multimodal brain imaging models. Any changes to decisions, following disclosure of the multimodal models, were recorded. RESULTS: Disclosure of 3 DMMI led to a change in strategy in 15 (34%) of 44 individuals. The changes included addition and subtraction of electrodes, addition of grids, and going directly to resection. For the detailed surgical planning, 3 DMMI led to a change in 35 (81%) of 43 individuals. Twenty-five (100%) of 25 patients undergoing stereo-EEG (SEEG) underwent a change in electrode placement, with 158 (75%) of 212 electrode trajectories being altered. SIGNIFICANCE: The use of 3 DMMI makes substantial changes in clinical decision making.

The NifTK software platform for image-guided interventions: platform overview and NiftyLink messaging.

PURPOSE: To perform research in image-guided interventions, researchers need a wide variety of software components, and assembling these components into a flexible and reliable system can be a challenging task. In this paper, the NifTK software platform is presented. A key focus has been high-performance streaming of stereo laparoscopic video data, ultrasound data and tracking data simultaneously. METHODS: A new messaging library called NiftyLink is introduced that uses the OpenIGTLink protocol and provides the user with easy-to-use asynchronous two-way messaging, high reliability and comprehensive error reporting. A small suite of applications called NiftyGuide has been developed, containing lightweight applications for grabbing data, currently from position trackers and ultrasound scanners. These applications use NiftyLink to stream data into NiftyIGI, which is a workstation-based application, built on top of MITK, for visualisation and user interaction. Design decisions, performance characteristics and initial applications are described in detail. NiftyLink was tested for latency when transmitting images, tracking data, and interleaved imaging and tracking data. RESULTS: NiftyLink can transmit tracking data at 1,024 frames per second (fps) with latency of 0.31 milliseconds, and 512 KB images with latency of 6.06 milliseconds at 32 fps. NiftyIGI was tested, receiving stereo high-definition laparoscopic video at 30 fps, tracking data from 4 rigid bodies at 20-30 fps and ultrasound data at 20 fps with rendering refresh rates between 2 and 20 Hz with no loss of user interaction. CONCLUSION: These packages form part of the NifTK platform and have proven to be successful in a variety of image-guided surgery projects. Code and documentation for the NifTK platform are available from http://www.niftk.org . NiftyLink is provided open-source under a BSD license and available from http://github.com/NifTK/NiftyLink . The code for this paper is tagged IJCARS-2014.

A novel method for implementation of frameless StereoEEG in epilepsy surgery.

BACKGROUND: Stereoelectroencephalography (SEEG) is an invasive diagnostic procedure in epilepsy surgery that is usually implemented with frame-based methods. OBJECTIVE: To describe a new technique of frameless SEEG and report a prospective case series at a single center. METHODS: Image integration and planning of electrode trajectories were performed preoperatively on specialized software and exported to a Medtronic S7 StealthStation. Trajectories were implemented by frameless stereotaxy using percutaneous drilling and bolt insertion. RESULTS: Twenty-two patients went this technique, with the insertion of 187 intracerebral electrodes. Of 187 electrodes, 175 accurately reached their neurophysiological target, as measured by postoperative computed tomography reconstruction and multimodal image integration with preoperative magnetic resonance imaging. Four electrodes failed to hit their target due to extradural deflection, and 3 were subsequently resited satisfactorily. Eight electrodes were off target by a mean of 3.6 mm (range, 0.9-6.8 mm) due to a combination of errors in bolt trajectory implementation and bending of the electrode. There was 1 postoperative hemorrhage that was clinically asymptomatic and no postoperative infections. Sixteen patients were offered definitive cortical resections, and 6 patients were excluded from resective surgery. CONCLUSION: Frameless SEEG is a novel and safe method for implementing SEEG and is easily translated into clinical practice.

Internal or in-scan validation: a method to assess CBCT and MSCT gray scales using a human cadaver.

OBJECTIVE: This study aimed to explore whether cone beam computed tomography (CBCT) and multislice computed tomography (MSCT) can be used to quantify tissue density and to determine if the Hounsfield unit scale is applicable. STUDY DESIGN: A clinical MSCT scanner and effective energy adjusted photon beam attenuation references were used to compare the gray scale of CBCT images of the mandible region. A phantom was scanned using axial cadaver slices and 4 different homogeneous reference objects. The consistency of the references' gray values and 12 linear profile lines from both scanner data sets were compared. RESULTS: The gray values of the 2 scans showed strong correlation with quantified position-dependent differences as an outcome of the validation process. CONCLUSIONS: The introduced internal, in-scan validation is able to estimate and has a potential to compensate for the differences between MSCT and CBCT protocols. This validation serves as a guide in situations where the users can expect deviations.

Feasibility of multimodal 3D neuroimaging to guide implantation of intracranial EEG electrodes.

BACKGROUND: Since intracranial electrode implantation has limited spatial sampling and carries significant risk, placement has to be effective and efficient. Structural and functional imaging of several different modalities contributes to localising the seizure onset zone (SoZ) and eloquent cortex. There is a need to summarise and present this information throughout the pre/intra/post-surgical course. METHODS: We developed and implemented a multimodal 3D neuroimaging (M3N) pipeline to guide implantation of intracranial EEG (icEEG) electrodes. We report the implementation of the pipeline for operative planning and a description of its use in clinical decision-making. RESULTS: The results of intraoperative application of the M3N pipeline demonstrated clinical benefits in all 15 implantation surgeries assessed. The M3N software was used to simulate placement of intracranial electrodes in 2 cases. The key benefits of using the M3N pipeline are illustrated in 3 representative case reports. CONCLUSION: We have demonstrated feasibility of the developed intraoperative M3N pipeline which serves as a prototype for clinical implementation. Further validity studies with larger sample groups are required to determine the utility of M3N in routine surgical practice.