FIG 4. In the animals in which C6-gliomas were (partially) resected, MIONs made it possible to determine the presence or absence of residual tumor, whereas the IV injection of a paramagnetic contrast agent produced confusing findings.

A, Two weeks after the stereotactic implantation of C6-glioma cells and 16 hours after the IV administration of MIONs, a preoperative T1-weighted image shows a right-hemispheric tumor hyperintense to brain.

B, Tumor was almost completely resected and postoperative MR image, obtained 30 min after the end of the operation, does not show hyperintense residual tumor. Because of brain shift, the resection cavity is almost completely filled with brain tissue. Also note the absence of surgically induced phenomena.

C, T1-weighted imaging was repeated after the IV administration of a paramagnetic contrast agent and shows intense surgically induced contrast enhancement (arrow), indistinguishable from residual enhancing tumor.

D, Histologic section shows multiple intraparenchymal bleeds due to surgery (arrowheads) but no residual tumor, except a small intraventricular tumor nodule (white arrow) that was too small for MR imaging detection.