Interventional Brain Procedures Performed with Interactive MR-Guidance in the Open MR System

We aimed to develop a pre-procedural imaging protocol which provides functional and anatomic information for lesion characterisation and procedural planning and to determine appropriate sequence parameters for “real-time” intra-procedural tracking of interventional devices. 34 patients underwent MRI guided procedures using a 0.5 T open-bore magnet. Interactive “real time” imaging was accomplished with a 3D optical tracking system and specialised image guidance software implemented on an interactive workstation. Pre-procedural planning in a 1.5 T magnet included standard T1- and T2-weighted images, 3D target volume determination and segmentation analysis, 3D time-of-flight MRA, cerebral blood volume mapping, and functional cortical mapping. Intra-procedure imaging included baseline and final T1- and T2-weighted imaging and interactive T1-weighted RF-spoiled GE images acquired every 4 sec for contrast enhancing lesions; or T2-weighted SSFSE images acquired every 3 sec, for nonenhancing lesions. Pre-procedural imaging offered precise anatomic, functional and volumetric definition of the target, eloquent brain, skull surface and surrounding vessels for appropriate burr hole placement and trajectory planning. MR perfusion offered tissue characterisation and margin definition not evident with conventional MRI. Real time imaging helped avoid vascular structures and eloquent brain without complications, always yielded diagnostic biopsy tissue and showed progressive collapse of necrotic tumors, abscesses, and hematomas with relief from mass effect. On-line imaging during excision of an infiltrating glioma allowed more confident tumor margin estimation. Improved pre-procedural image acquisition and processing and on-line imaging in an accessible MR system allows real time procedural monitoring increasing its accuracy, safety and diagnostic and therapeutic yield.