Expandable grid, a simple, readily available and precise technique for intraoperative stereotactic real-time imaging

Pre- and postoperative imaging constitutes a firm brick in planning and steering accurate stereotactic procedures. The availability of intraoperative control measures, e.g., CT, MRI, and microelectrode recording (MER), is often limited to a minority of centers. Our approach utilizes fluoroscopy for target planning and coordinates validation as control.

This technique was primarily conceived for the RM (Riechert Mundinger) stereotactic system, but it also applies to the ZD (Zamorano-Dujovny) system. In the present study, we shifted the zero of the Z-value (axis of the patient) to + 60 mm. This corresponds to the center of the Angio/X-ray localizing plates. By assigning a radiopaque marker to the center of each plate, aligning these centers produced orthogonal and non-distorted stereotactic space. In this space, the magnification variable matters to us the most. Using available viewer software, we printed a millimetric grid on translucent foils with the corresponding magnification factor, which can easily be superimposed on the fluoroscopic image. This allows the precise validation of the coordinates of points of interest, including typical stereotactic landmarks. This technique can be used in both views, AP and lateral.

We have validated this technique under non-clinical (phantom) conditions and with intraoperative images obtained during routine stereotactic procedures. The latter were acquired using our classical stereotactic fixedly-mounted X-ray system. We found identical results, with an accuracy margin of error lower than 1 mm.

This simple geometrical adaptation proved to be an accurate, accessible, mobile, and manageable technique providing immediate access to stereotactic coordinates during surgery. The accuracy proved to be non-inferior to other more complex and time-consuming imaging modalities.