Analysis of contrast agent induced interior structuring of tumours. (A): Transaxial NMR images of a mouse (face-down position) bearing two s.c. xenografts; left: HT29 colon carcinoma, right HCT8 colon carcinoma. Images were taken to the indicated time points after i.v. application of higher dosed Gd-BOPTA (0.1 mmol/kg). A time dependent alteration of contrast enhancement with initial enhancement of the tumor rim followed by a centripetal progression of the signal is observed in the HT29 tumor. The HCT8 tumor was too small for detailed analyses although a time dependent alteration of the signal could also be observed. (upper panel - grayscale, lower panel - pseudocolor) (B): Transaxial NMR images of a mouse (face-down position) bearing two s.c. HT29 xenografts 15 min and 30 min after i.v. application of Gd-BOPTA. One tumor showed strong contrast enhancement and an interior structuring could be observed (white arrow). (C): HE staining of the well structured left HT29 xenograft shown in (A). Depicted is a section at the side of the tumor to represent the whole structure composed of a large central necrotic/fibrotic area (white star) surrounded by peripherally arranged vital tumor cells (white arrow).