Fig 2. T1-weighted MR imaging in a patient with recurrence of a low-grade astrocytoma. The patient had stable disease after previous craniotomy (A) but showed recurrence on gadolinium images in March 2005 (B). The patient received ferumoxtran-10, and 24 hours later underwent preoperative MR imaging (C) as well as MR imaging with the 0.15T intraoperative scanner before (D) and during (E) craniotomy. Postoperative MR imaging (F) correlated with the residual areas of enhancing tumor seen on intraoperative MR imaging. High signal intensity in the tumor cavity, not present on intraoperative MR imaging, demonstrates the problem of differentiating residual enhancing tumor from blood products. Because the ferumoxtran-10 persists for 4–7 days, the postoperative MR images were exactly the same with or without the addition of gadolinium.