Technical Specifications

The neuronavigation system is composed of a position sensor, made of an IR polarisoptical tracking unit which is available in two models: Polaris Vicra and Polaris Spectra. The only difference between these models is the dimension of their acquisition volume, that is the useful space for objects tracking; the Spectra unit has a volume much more bigger than the Vicra model.

Measurement volume in Polaris Spectra

Measurement volume in Polaris Vicra
Measurement volume in Polaris Spectra Measurement volume in Polaris Vicra

neuronavigation1The system can track the position of suitable passive wireless markers, for a total of 4 markers at the same time. The first marker is located on the head of the patient by means of a stretch band, which allows him/her to wear glasses and represents a non-invasive and user-friendly system for the patient, thanks to which MR images for TMS neuronavigation are co-recorded. The second marker, named stylus, is used to mark positions of interest on the patient’s scalp, in order to carry out the co-recording between the subject and MR. The co-recording between the subject and the marker is controlled through a proper best fit procedure, which allows to improve precision in the co-recording, lowering the error threshold to values < 2 mm.

During neuronavigation, the head of the subject is displayed in different modes:

  • 3D reconstruction of the scalp (either in standard colours or using the grey tones coming from MRS)

  • 3D reconstruction of the brain (either in standard colours or using the grey tones coming from MRS)

  • Axial view of magnetic resonance images

Next to each of these display modes, the coronal and sagittal views of MR images are displayed, which are constantly updated and lined up during neuronavigation to show the effective point reached by stimulation.


Two more markers are used to track the position of the stimulation coil(s). During the stimulation session, it is possible to track up to 2 coils at the same time and to store their respective position. The two markers positioned on coils are calibrated through a manual or automatic procedure, by means of suitable platforms for automatic calibration, to assure the best possible precision during the neuronavigation phase.

Both coils are tracked in 3D space according to the orthogonal axes of the spatial reference system of the position sensor. The markers positioned on coils can have 4 passive spheres (basic configuration) or they can have 6 spheres to assure a better visibility of the coil during stimulation.


brainIt is possible to store the coil position during the neuronavigation phase, in order to keep this data. Furthermore, it is possible to prearrange the target points manually identified on MRI, or to insert manually target points expressed in Talairach space, which are automatically located on the subject’s MRI. Later on, these points can be reached with the stimulation coil and displayed in 3D in the reconstruction of the scalp or brain. A new function to display target-coil distance enables to optimize the coil position in relation with the subject’s scalp, in order to obtain the maximum effect from the stimulation by reducing as much as possible the distance from the cortex. This function is called “Focus-Distance Map”.

neuronavigation2neuronavigation3Coil replacement on stimulation points already used before is carried out through a special re-targeting function. Here, once loaded the information on the desired stimulation point (recorded in previous sessions, even some time before), a sights is displayed to help the target centring, with a precision threshold set by the user, from 1 to 10 mm. This replacement function is also used to monitor the stability of stimulation and possible displacements of the coil or of the subject’s head during the stimulation session.

brain_homeAll the information related to the neuronavigation session are stored and it is possible to recall previous stimulation sessions, in order to elaborate data even in offline, to reconstruct EEG maps of potentials or maps of motor evoked potentials (MEP).

Moreover, the system estimates the potential of the induced electric field on a realistic model of the brain, using the Boundary Element Method (BEM). This mathematical method is based on the spatial position of the coil in relation with the subject, its inclination and the stimulation power used, but also on the coil’s geometry and on its construction features. This estimate is useful in order to evaluate the effects of the magnetic stimulation spread during neuronavigation.

In the system, it is also available a method for TMS neuronavigation on subjects who don’t have personal MR images. By means of a suitable procedure of probabilistic estimate, a model of MR is used and adapted to the scalp conformation of the subject. This procedure is able to preserve the anatomical correlation scalp-brain of the model and to obtain an extremely realistic reconstruction of the subject’s brain conformation.

MR images of the subject

reconstructured mr

MR Images of the subject Reconstructed MR Images