Abstracts

The Responsive Neurostimulator System (RNS^TM; NeuroPace, Inc.) is currently under investigation as a neurosurgical option for medically refractory epilepsy. Following surgical positioning within a craniectomy, this pacemaker-like device allows for chronic cortical EEG monitoring (via two intracranial electrodes) and the delivery of focused electrical pulses with the goal of terminating seizure activity. Patients with implanted RNS^TM devices may require post-operative imaging, either for the assessment of lead placement or, more importantly, for the purpose of emergent radiographic evaluation in cases of perioperative neurological decline. As MRI is currently contraindicated in implanted patients, CT remains the imaging modality of choice. Unfortunately, the metallic nature, large surface area, and proximity of the device to the underlying cortex produce overwhelming artifact on conventional axial CT images, resulting in limited diagnostic utility. We sought to develop a strategy that would overcome this technical difficulty and allow for the generation of diagnostically useful CT images in patients with implanted RNS^TM devices., Two individuals with previously implanted RNS^TM devices, admitted for battery replacement, were included in the study. Following acquisition of conventional CT scans oriented in the standard axial plane, the patients were repositioned in the lateral decubitus position with their heads rotated and extended away from the side of the device. The scanner gantry was then appropriately angled to allow for the acquisition of images in the parasagittal plane parallel to the device axis. Contiguous fine-cut images were obtained and subsequently reconstructed using commercially available imaging software (Siemens). The resulting data were rendered in the true axial plane, for comparison to corresponding images from the conventional protocol, and were also used to generate three-dimensional reconstructions., Significant decreases were noted in the severity of device-related artifact on reconstructed axial images when compared to conventionally acquired images. The minimization of artifact allowed for diagnostic visualization of the subdural space and underlying cortex immediately adjacent to the device. In addition, artifact-free fine-cut imaging data were successfully used to generate detailed three-dimensional reconstructions of the cranial vault, providing for visualization of the stimulator and the intracranial position of attached electrodes., This technique provides a straightforward method for the acquisition of diagnostic-quality CT images in patients with the implanted RNS^TM device. We predict that similar strategies may be employed to optimize post-operative imaging in patients harboring a broad spectrum of intracranial hardware.,