Cranial surgery navigation aided by a compact intraoperative magnetic resonance imager

Object. In this article the authors report on a novel, compact device for m agnetic resonance (MR) imaging that has been developed for use in a standar d neurosurgical operating room. Methods. The device includes a permanent magnet with a field strength of 0. 12 tesla. The poles of the magnet are vertically aligned, with a gap of 25 cm. When not in use the magnet is stored in a shielded cage in a corner of the operating room; it is easily moved into position and attaches to a regu lar operating table. The magnet is raised for imaging when needed and may b e lowered to allow surgery to proceed unencumbered. Surgical navigation wit h optical and/or magnetic probes is incorporated into the system. Twenty-five patients have undergone removal of intracranial lesions with th e aid of this device. Operations included craniotomy for tumor or other les ion in 18 patients and transsphenoidal resection of tumor in seven. The num ber of scans ranged from two to five per surgery (average 3.4); image quali ty was excellent in 45%, adequate in 43%, and poor in 12%. In four patients MR imaging revealed additional tumor that was then resected; in five other s visual examination of the operative field was inconclusive but complete t umor removal was confirmed on MR imaging. In 21 patients early postoperativ e diagnostic MR studies corroborated the findings on the final intraoperati ve MR image. Using a water-covered phantom, the accuracy of the navigational tools was a ssessed; 120 data points were measured. The accuracy of the magnetic probe averaged 1.3 mm and 2.1 mm in the coronal and axial planes, respectively; t he optical probe accuracy was 2.1 mm and 1.8 mm in those planes. Conclusions. This device provides high-quality intraoperative imaging and a ccurate surgical navigation with minimal disruption in a standard neurosurg ical operating room.