Monocrystalline iron oxide nanoparticles: Possible solution to the problemof surgically induced intracranial contrast enhancement in intraoperative MR imaging

BACKGROUND AND PURPOSE: Intraoperative MR imaging is increasingly being use d to control the extent of surgical resection; however, surgical manipulati on itself causes intracranial contrast enhancement, which is a source of er ror. Our purpose was to investigate the potential of monocrystalline iron o xide nanoparticles (MIONs) to solve this problem in an animal model. METHODS: In male Wistar rats, surgical lesions of the brain were produced. The animals underwent MR examination immediately afterward. In the first gr oup, a paramagnetic contrast agent was administered, whereas the second gro up of animals received MIONs 1 day before surgery. In a third group of anim als, malignant glioma cells were stereotactically implanted in the caudoput amen, Two weeks later, MIONs were IV injected and the tumor was (partially) resected. Immediately after resection, MR examination was performed to det ermine the extent of residual tumor. RESULTS: Surgically induced intracranial contrast enhancement was seen in a ll animals in which a paramagnetic contrast agent was used. Conversely, whe n MIONs had been injected, no signal changes that could be confused with re sidual tumor were detected. In the animals that had undergone (partial) res ection of experimental gliomas, MR assessment of residual tumor was possibl e without any interfering surgically induced phenomena. CONCLUSION: Because MIONs are stored in malignant brain tumor cells longer than they circulate in the blood, their use offers a promising strategy to avoid surgically induced intracranial contrast enhancement, which is known to be a potential source of error in intraoperative MR imaging.