Intraoperative MR-guided neurosurgery.

For more than a decade neurosurgeons have become increasingly dependent on image guidance to perform safe, efficient, and cost-effective surgery. Neuronavigation is frame-based or frameless and requires obtaining computed tomography or magnetic resonance imaging (MRI) scans several days or immediately before surgery. Unfortunately, these systems do not allow the neurosurgeon to adjust for the brain shift that occurs once the cranium is open. This technical inability has led to the development of intraoperative MRI (ioMRI) systems ranging from 0.12-3.0T in strength. The advantages of ioMRI are the excellent soft tissue discrimination and the ability to view the operative site in three dimensions. Enhanced visualization of the intracranial lesion enables the neurosurgeon to choose a safe surgical trajectory that avoids critical structures, to maximize the extent of the tumor resection, and to exclude an intraoperative hemorrhage. All ioMRI systems provide basic T1- and T2-weighted imaging capabilities but high-field (1.5T) systems can also perform MR spectroscopy (MRS), MR venography (MRV), MR angiography (MRA), brain activation studies, chemical shift imaging, and diffusion-weighted imaging. Identifying vascular structures by MRA or MRV may prevent injury during surgery. Demonstrating elevated phosphocholine within a tumor may improve the diagnostic yield of brain biopsy. Mapping out neurologic function may influence the surgical approach to a tumor. The optimal strength for MR-guided neurosurgery is currently under investigation.