The predictive value of low–field strength magnetic resonance imaging for intraoperative residual tumor detection

Abstract

Neurosurgeons have been utilizing intraoperative MR (iMR) imaging to evaluate the extent of tumor resection since the 1990s. A low-field strength (0.12 T) MR imaging unit (PoleStar N20, Medtronic) is a practical and relatively inexpensive iMR imaging system that has found increased use in neurosurgery. The gold standard for post operative detection of residual tumor has been high-strength MR imaging performed within 48 hours of resection.The object of this study was to determine the predictive concordance of low-strength iMR imaging with standard high-strength MR imaging for detection of residual tumor. The authors retrospectively evaluated the MR images from 74 intracranial tumor resections, comparing the intraoperative images obtained using a 0.12-T iMR imaging unit to the immediate postoperative images obtained using a standard 1.5-T MR imaging unit within 48 hours after surgery. The sensitivity of low-field MR imaging for detection of residual tumor was 0.74 (95% CI 0.58-0.86),and its specificity was 0.97 (95% CI 0.83-1). When only glial tumors (42 of the 74 lesions) were analyzed, the sensitivity was 0.82 (95% CI 0.59-0.94) and the specificity was 0.95 (95% CI 0.73-1). These data could assist the neurosurgeon who has to decide intraoperatively whether the observed iMR images show residual tumor or not.