Image Guided Surgery

Epilepsy Navigator (EpiNavTM) is an interactive neuronavigation system we are developing in conjunction with our clinical partners at the National Hospital for Neurosurgery and Neurology to assist in planning and guiding surgical interventions for epileptic patients.

 

Background

Epilepsy affects about 500,000 people in the UK. 20-30% of epilepsy patients continue to experience seizures after medication. Such patients are candidates for curative resection, where the brain region responsible for seizure onset is surgically removed in an attempt to eliminate seizures. Planning for curative resection involves identifying the brain region to be removed as well as eloquent regions (e.g. the motor cortex) which should be avoided during resection.

 

The goal of EpiNavTM is to develop a software platform to assist in planning and guiding surgical interventions for patients at every stage of the clinical process. EpiNavTM allows for the creation of multi-modal 3D maps of brain structures which can be used to direct neurosurgery. We are actively developing automated segmentation and planning tools in this platform to assist in electrode implantation and resection.  

 

Automated Vessel Segmentation

 Flowchart of vessel extraction algorithm

The ability to accurately identify and delineate structures to be avoided is essential to provide guidance for interventional neurosurgery. The most critical structures to be avoided are blood vessels, which may cause hemorrhage if punctured during surgery.

 

We have developed a novel multi-modal, multi-scale vessel segmentation algorithm for intracranial vessels [1]. Our method extracts a set of tensors for each input image over a range of scales. Tensors over images and scales are fused with a tensor voting scheme. A final segmentation is obtained using marching cubes on the fused image. Figure 1 illustrates a flowchart of our algorithm.

 Figure 1. Flowchart of the vessel extraction algorithm used for SEEG Electrode Planning.

 

 

 

Assisted SEEG Electrode Placement

 
        Figure 2. SEEG electrode trajectory determined via         assisted planning algorithm. Red and light blue         surfaces represent arteries and veins, respectively         while the white surface represents the scalp. The         colored patch represents the risk for potential entry         points and the pink object is the selected electrode         trajectory.

 

Stereoelectroencephalography (SEEG) depth electrodes are placed within the brain to help identify the brain region responsible for seizure onset. This invasive investigation carries the risk of hemorrhage, infection, and neurologic deficit. Careful planning of electrode placement can reduce risks by avoiding critical structures (e.g. blood vessels, cerebrospinal tract) within the brain.

 

We have developed assisted planning tools to aid in determining SEEG electrode placement [2]. Electrode trajectories, the path between entry on the scalp surface and the target in the cortex, are assessed via an automated entry point search and risk evaluation.

 

Entry point search first finds all points on the surface of the scalp. Potential entry points are removed from consideration if they meet one of three hard criteria: trajectories intersect critical structures, have too sharp an angle with respect to the skull surface, are longer than the SEEG electrode.

 

Risk evaluation is performed on the remaining trajectories by calculating a risk score that integrates the distance to critical structures along the entire trajectory. The lowest risk score trajectory is selected (pink line in Figure 2) and a risk map displays the relative risk score for the other potential entry points (colored patch in Figure 2 where red represents the highest risk and green represents the lowest risk).

 

EpiNavTM allows the user to interact with the selected trajectory, enabling manual modification of the trajectory to other low risk trajectories if the automatically defined trajectory is still unsuitable. Additionally EpiNavTM allows the user to navigate through the imagery along the path of the trajectory to identify the anatomic location of the trajectory throughout the cortex.

 

Publications

[1] M.A. Zuluaga, et al. “SEEG Trajectory Planning: Combining Stability, Structure and Scale in Vessel Extraction”. In: Medical Image Computing and Computer-Assisted Interventions - MICCAI 2014 (In press)

[2] Zombori, G., et al. "A computer assisted planning system for the placement of sEEG electrodes in the treatment of epilepsy." In: (Proceedings) Information Processing in Computer-Assisted Interventions. Fukuoka, Japan, 2014.

[3] Rodionov, R., Zombori, G., et al. "Feasibility of multimodal 3D neuroimaging to guide implantation of intracranial EEG electrodes." Epilepsy research 107.1 (2013): 91-100. 2013.