Using Images To Safely Navigate Inside The Head: Cranial Navigation (Image Guided Surgery)
The use of live images for investigative and diagnostic purposes first became available in the mid-1980s. The next logical step was the use of those images to guide surgery and particularly craniotomies. Advances in the technology now allow images that were generated for diagnostic purposes to be used in concert with live images that are generated in the operating room and during an operation. These diagnostic images are used to “map” the operation using a computer and specialised applications. Increasing use is being made of robotics so the surgical instruments to be used in the surgery are connected to, and tracked by, computers.
High resolution images enable surgeons to conduct surgery more accurately and precisely especially inside the skull. Image guided or frameless surgeries were first used in craniotomies about ten years after the advent of the endoscopy. In addition to operations for brain tumours, examples of cranial investigations that utilise image guidance technologies include repair to damage after severe head trauma, vascular conditions (bleeding, blood clots, repairing abnormal blood vessels, aneurysms and inserting shunts), repairing the dura, i.e. the tissue that protects the brain, as well as for inserting deep brain stimulators for conditions like dystonia and Parkinson’s disease.
Technological advancement
The images used as part of the operating procedure are “collected” using a hand-held probe. They are generated by a range of equipment, from high resolution digital video cameras, computed and positron emission tomography (CT/PET scans) as well as magnetic resonance imaging (MRI). The last two techniques are used with caution because both the patient and the surgical team are exposed to forms of radiation. Together, these systems generate three dimensional images that enhance the neurosurgeon’s capability. Surgical teams’ work has consequently become more accurate especially as technological advances mean that images can be rendered at a micro and vascular level so that shapes, nerve tissues and blood vessels can be mapped and measured in real-time.
As already noted, integral to image guided surgery is the mechanism for tracking what happens during an operation. This information must, in turn, be conveyed to a display system so that the surgeon and team can follow the path of the probe, see the patient’s brain in three dimensions and monitor what they are doing. Again, computer applications are central to displaying and manipulating the images that are the surgeon’s eyes. They are becoming increasingly important as robotic surgery is becoming increasingly adopted.
Brain mapping
As with all humans, brains, like the rest of the body, share common features, but every person is unique. This can present significant challenges in brain surgery, particularly when the surgery is in a part of the brain that controls, for example, speech, vision and movement. Imagery enables surgeons to map patients’ brains during awake brain surgery using a functional MRI. During surgery, patients are woken up and asked to do certain things, and the surgeon can see what parts of the brain are active. Using this information, map the patients’ brain and s/he can complete the surgery in a way that does the least potential damage.
The advent of image guided surgery for cranial investigation has also meant that conditions previously considered inoperable because of their location in the brain, can now be treated. In addition to greater accuracy and the improved patient outcomes already mentioned, and because surgeons receive instant feedback on their actions during an operation, image guided surgery means that the surgeons have more control over their actions and outcomes.
Other benefits of cranial navigation using image guided surgery
These major technical advancements contribute to an overall reduction in the risk associated with cranial investigation. Frameless surgeries mean there is less likelihood of damaging healthy tissue and most importantly, vastly improves prognosis and potential patient outcomes. Consequently, in Europe, image-guided cranial navigation has become the standard of care in terms of its use pre- and post, as well as during operations. Using image guided surgery for intercranial navigation enables the neurosurgeon to accurately locate the point on the cranium through which the brain should be accessed. This significantly reduces the trauma and disruption associated with opening the skull to access the brain. In addition, intraoperative imaging is especially valuable because of the phenomenon of “brain shift” where the patient’s brain changes when the skull flap is removed, and the brain is exposed. This means that if the brain herniates, the pre-operative images may not reflect what is revealed in the operating room, making image guided surgery essential to a safe surgery and a good outcome.
A new way of working
Advances in image guided surgery now assist surgeons to develop highly personalised approaches to treatments. Surgical teams can develop patient-specific anatomical models which they can augment using information that they collect during clinical and diagnostic engagements with the patients. Augmented reality, often thought of as the prevue of gamers and aviation simulation training can be used by surgeons to plan their procedures, including the patient’s likely actual position in the operating theatre, because he can visualise the deep set tissue as it would be in the live patient.
