An Introduction to Neuronavigation
Over recent decades, a flexible Neuronavigation technique has been refined, know as frameless stereotaxy or image-guided surgery.
Instead of using a conventional stereotactic frame to define a reference coordinate system, an image data set, usually an anatomical CT or MRI, is used. A position sensor system is employed to track the location of the head as well as the surgical tools during the operation. Mapping the actual positioning on the reference image is usually done by identifying a series of anatomical landmarks on the images and then on the subject during surgery using a tracked hand-held pointer. Once registered, representations of the tools can be displayed on the images in real-time, and the display used to navigate the tools to the target. Frameless stereotaxy has revolutionised neurosurgery and led to the development of minimally invasive surgical techniques and the successful treatment of conditions that were previously deemed inoperable.
As the equipment and methods of frameless stereotaxy (now usually referred to as neuronavigation) became more common, other non-surgical applications evolved to take advantage of this image-guided methodology. Early adopters of image-guided TMS included Gugino and Pascual-Leone at Harvard and Paus at McGill; both had the ability to collaborate with researchers involved in image-guided neurosurgery. Today, several equipment manufacturers now offer TMS specific neuronavigation systems and almost 200 TMS research labs around the world now have neuronavigation systems for TMS localisation.
There are several advantages to using a neuronavigation system:
- The target for stimulation can be defined using the subject’s anatomy as seen on the images, functional data (e.g. fMRI or PET), as well as atlas coordinates using Talairach or MNI305 coordinates.
- The placement accuracy is high. The accuracy of a properly used neuronavigation systems is usually in the area of +/- 3mm.
- The position and orientation of the coil with regard to the target is monitored continuously so any movement can be detected and dealt with accordingly.
- The coil’s location and orientation can be recorded and later co-related with the stimulus results.
- By mapping the coil location to the image reference space, it can be correlated with any other data that can also be mapped to the image reference space, including fMRI, PET, EEG, MEG and NIRS-DOT.
Magstim is working to develop applications that will further advance the field of Neuronavigation, and supports ANT's Visor System.
Magstim has a worldwide network of distributors. To find out who your local distributor is, please call +44 (0)1994 24111 or e-mail sales@magstim.com.
