MR-Directed Stereotactic Resections and Per-Operative Screening using Low-Field MRI

Precision resection of stereotactically defined volume presents one of the current applications of “volumetric stereotaxis”. Computer-assisted reconstruction of serial outlines of the volume for resection obtained with modern computerised neuroimaging methods defines the spatial coordinates of that volume and allows its interpolation in a three-dimensional matrix (Kelly et al., 1984). Information derived from stereotactically performed computerised imaging allows the suspension of the given volume into a stereotactic three-dimensional space and its precise resection using a stereotactic technique. Experience with CT-directed volumetric resections indicates that the method is satisfactory. The ability of magnetic resonance imaging (MRI) to define the boundaries of most intracranial structures more accurately and its superior diagnostic image sensitivity make its use in stereotactic volumetric resections highly desirable. The use of MRI, however, in computerised volumetric stereotactic surgery presents considerable difficulties. Problems concerning the construction of stereotactic hardware materials such as fiducials, frame and stabilising devises have now been successfully addressed. Computer software compatible with current imaging and stereotactic hardware has also been developed and used in clinical practice and although the problem of linear distortion still remains, especially in the periphery of the image, it is now possible to use MRI-derived information in volumetric stereotactic resections either indirectly by registration of the stereotactic coordinates or directly through specially developed software (Kelly et al, 1987).