Value of SPIO for MRI of the bone marrow before and after Total Body Irradiation (TBI) - Initial investigations in an animal model.

Purpose: Evaluation of the value of superparamagnetic iron oxides (SPIO; En dorem (R)) for MRI-derived quantifications of the permeability of the blood -bone marrow barrier and the phagocytic activity of reticuloendothelial sys tem (RES) bone marrow cells before and after TBI. Methods: 12 New Zealand w hite rabbits underwent MRI of the lumbar spine and os sacrum using T-1-weig hted spinecho (SE) and T-2-weighted Turbo-SE (TSE) sequences before and aft er injection of SPIO (Endorem (R)). Four animals each were examined without irradiation, after 4 Gy total body irradiation (TBI), and after 12 Gy TBI. Changes in bone marrow signal intensities (SI) after contrast agent inject ion were quantified as Delta SI(%) = / ((SIpost-SIpre)/SIpre) x 100% / I an d these data were correlated with bone marrow histopathology. Results: Hist opathology of the bone marrow revealed a radiation-induced decline of all h ematopoetic cell lines. SPIO were phagocytosed by bone marrow RES cells and caused a significant bone marrow signal decline on postcontrast T-2-weight ed images (p <0.05). Delta SI(%) data for T-2-weighted images were signific antly higher for the irradiated bone marrow as compared to non-irradiated c ontrols (p <0.05). Dynamic T-1-weighted images directly after contrast medi um injection were not able to characterize the permeability of the blood-bo ne marrow barrier. Conclusion: Hematopoetic bone marrow can be labelled wit h SPIO. Irradiation does not impair the phagocytic activity of bone marrow RES cells. However, the bone marrow enhancement with SPIO is smaller as com pared to previous results obtained by our group with USPIO.