GPS for the Brain

Neuronavigation Integrates Leica Surgical Microscopes

August 13, 2010

One of the challenges of neurosurgery is orientation at the surgical site. While treating cancers of the brain, surgeons often have to operate through healthy and functional tissue. The challenge is always trying to spare as much healthy tissue as possible, while removing as much of the tumor as possible. Neuronavigation technology facilitates both the planning and intraoperative orientation. The BRAINLAB AG company headquartered in Munich is one of the market leaders in the field of image-guided technology and became a pioneer in the market with the integration of its IGS software with Leica Microsystems’ surgical microscopes. Since then, all leading providers of IGS have integrated their software with surgical microscopes from Leica Microsystems.

At the base of the human skull there is a particularly high concentration of vital structures: blood vessels; nerves; centers for hormonal control of bodily functions; and centers for regulating breathing, blood pressure, and heart activity. Brain tissue cannot regenerate itself, so even the smallest injury can cause irreversible, profound brain damage, leaving  patients with a permanent handicap. This also makes the treatment of disease very difficult. Malignant gliomas, which account for 45 to 50 % of all brain tumors, infiltrate into tissue as they grow. Even under a surgical microscope, peripheral tumor regions are hard to differentiate from healthy tissue.

Wide application potential

Neuronavigation is a non-invasive imaging method and is mainly used for neurosurgical applications such as tumor resection or the treatment of aneurysms. As neurosurgeons do most of their work at the microscope, BRAINLAB has integrated the surgical microscope with the navigation, which enhances the microscope’s functionality.

Exact localization of brain structures

Neuronavigation works like a GPS system, enabling exact position tracking in the patient’s anatomy. Before surgery, reference point markers are adhered to the patient’s scalp, and MRI and CT scans are performed. The surgeon can pre-mark the tumor, the endangered areas, and the best access route to the tumor in these images and use it in the operating room as a digital treatment plan.

In the operation theater, a system consisting of two infrared cameras is directed at the surgical site. All instruments, including the surgical microscope, bear reflecting spherical markers. A reference star is attached to the patient’s head clamp to mark the position of the patient for the system. On the basis of infrared signals transmitted by the cameras, which are reflected back to the cameras from the markers, the positions of the instruments and the patient are localized and visualized for the camera or navigation system. Then the patient data prepared before surgery is loaded into the navigation system and reconstructed into 3D images on the monitor or image injection display. This gives the surgeon a continuous, real-time view of the exact position of the instruments in the brain structures on the preoperative anatomic data.

Enhancing the microscope’s functionality

The integration of the microscope with the navigation system significantly increases its functionality. With the Smart Auto-Focus, each navigated instrument can be focused, even outside of the image center. If a surgical instrument is not in the center of the microscope’s field of view, the Smart Auto-Tracking feature moves the microscope head to the correct x and y position until the instrument is seen in the field of view. All image information can be shown in the image-injection display, which enables the surgeon to overlay the navigation image onto the visual field of the microscope ocular.

The surgeon can then switch between two images, without interrupting the view through the microscope: When the image injection is activated, a computer generated transparent image is injected to the microscope’s field of view which allows the surgeon to see the focused region as well as the injected information. When activating the closed shutter mode, the ocular view closes. The surgeon can now see e.g. MR images in the ocular. "This is less tiring for the eyes because the eyes don’t have to keep adjusting. It also saves time", explains Valentin Elefteriu, project engineer at BRAINLAB.

Brainlab´s cranial navigation software shows the exact position of the microscope´s focal point and field of view in the brain structures on the preoperative data in different views. Planned objects, trajectories and labeled points can be displayed in all views and overlaid onto the microscope video.   

The Depthview feature also provides a continuous comparison of the real image and the preoperative data. Depthview shows the image level seen through the surgical microscope as a reconstruction in the anatomic images, which helps surgeons orientate themselves during surgery. "BRAINLAB provides us with improved imaging possibilities and control of the microscope", says Prof. Dr. Kai-Michael Scheufler, neurosurgery consultant at Hirslanden hospital in Switzerland. “By integrating real-time navigation with the field of view of the ocular, we can stay focused on the surgical task with more precision. Also, surgical procedures are enhanced because all of the relevant information can be remote controlled. This allows a fluid workflow while delivering the most advanced imaging possibilities at the touch of a button.” Prof. Scheufler uses BRAINLAB neuronavigation with the Leica M525 OH4 surgical microscope.

Taking the guesswork out of tumor resection

Every neurosurgical procedure demands a vast amount of surgeon experience, patience and competence. Although neuronavigation does not replace surgical skill, it effectively supports the surgeon in planning and performing a procedure and gives more precise information.

"The integration of the microscope with neuronavigation helps the surgeon to accurately identify questionable areas", explains Elefteriu. "For example, if he or she focuses on the edge of a tumor and can’t tell exactly where the tumor tissue ends, a look at the pre-planned anatomic data with microscope image overlay shows whether the focused area is part of the tumor or not." Precise planning can also minimize head shaving, skin incisions, and bone flap sawing and thus reduce stress for the patient.