Fig 1. Imaging intratumor injection. Nude rats with 7-day intracerebral small cell lung carcinoma xenografts were scanned by MR imaging 1 day before and 1 hour after intratumor injection of either gadolinium (top) or ferumoxtran-10 (bottom) contrast agents. Axial T1-weighted MR images were obtained at 3T by using a custom rat head coil.9 One day after contrast injection, coronal 100-µm rat brain sections were evaluated for histology by hematoxylin staining. Delivery of the USPIO is highly heterogeneous throughout the tumor and brain around the tumor, in contrast to the more homogeneous distribution of gadolinium.