Headset-Based AR Navigation System Improves EVD Placement

Traditional neuronavigation systems are limited to the operating room due to their large size and lack of portability. Additionally, these systems often require surgeons to mentally convert 2D information from remote displays into 3D actions, which divides attention between the two. On the other hand, augmented reality (AR) overlays 3D data onto the real world, potentially enhancing the surgeon’s view with relevant information. Now, a new clinical pilot study has shown that using AR to guide the placement of an external ventricular drain (EVD) at the bedside is more precise than freehand placement, resulting in fewer complications and reinterventions.

A team of neurosurgeons from Universitair Ziekenhuis Brussel (Brussels, Belgium) and Vrije Universiteit Brussel (Brussels, Belgium) tested a novel AR system that combines the Microsoft HoloLens II, a commercial AR headset, with custom-built surgical navigation software. This system integrates all necessary components for neuronavigation, such as high-accuracy tracking, image display, and a processing unit, into a standalone headset, eliminating the need for external cameras or computers. The process begins with preoperative imaging to create a 3D model of the patient's anatomy, which includes key coordinates for AR guidance, such as the foramen of Monro. An infrared-labeled reference frame is attached to the patient’s head using a clamping headband, allowing the AR system to track the head’s position and orientation.

The 3D model is transferred to the AR headset, where image-to-patient registration occurs through an infrared-tracked stylus. This process aligns the virtual anatomy with the patient’s actual anatomy. When planning the EVD trajectory, the system determines the shortest path from the skin surface to the ipsilateral frontal horn of the lateral ventricles, ensuring minimal disruption to brain tissue. The surgeon can adjust the trajectory as needed, considering the patient's unique anatomy or pathology. The trajectory and all relevant anatomical data are displayed as a 3D object on the patient, providing a depth perception that allows the surgeon to inspect the plan from all angles. A tracker is attached to the surgical drill, and the system continuously monitors the drill’s alignment, indicating any translational or angular errors. Once these errors are minimized below predefined thresholds (2 mm and 2°), the system turns the trajectory line green, signaling correct alignment. The system continues to provide feedback during the drilling process.

Following successful phantom studies, the neurosurgeons employed the AR navigation system in 11 critical care cases for EVD placement at the bedside. These patients required bedside intervention as their primary treatment. The team also recorded data from 11 patients who had EVD placed using the freehand technique during the same period. The first-in-human results, published in Neurosurgery, demonstrated that AR-guided placement led to better outcomes in all cases compared to freehand placement. Specifically, the AR-guided placements showed a statistically significant difference in terms of success (9 versus 5), optimal placement (8, including two slit ventricle cases, versus 3), and failure (0 versus 1). Additionally, no revisions were required for AR-guided placements, while four freehand placements needed revision. Building on these promising results, the researchers are preparing for a multicenter randomized controlled trial, set to launch at the end of 2025.

“The reinterventions, along with the implied multitude of attempts, constituted the primary cause of all procedure-related complications in the freehand group,” the authors report, “once more emphasizing the hazard related to multiple stick-and-poke attempts and the importance of first-attempt success.”

Related Links:
Universitair Ziekenhuis Brussel
Vrije Universiteit Brussel

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