Background: Magnetic Resonance Imaging (MRI) is a safe modality and useful in characterizing normal and abnormal bone marrow (BM). MRI also presents a more global view of BM than biopsy therefore, it may provide a better understanding of hematologic disorders. The purpose of this study was to monitor radiation-induced alterations of BM in acute phase of irradiation (1-10 day after total body irradiation (TBI)) with conventional MRI.

Materials and Methods: Twelve New Zealand adult male white rabbits (10 for TBI and 2 as controls) were irradiated to 6 Gy gamma rays. MRI was performed for each rabbit femoral
marrow and marginal muscles around femur region (as internal control) using T1- weighted (W) and SPIR (TR/TE 631/15) techniques before and after (24h, 48h, 72h, 5d, 10d) post TBI.

Results: The results were expressed as MR signal ratio (mean MR signal of femur/mean MR signal of muscle). The BM MR –signal intensity (SI) values were subsequently compared to the histologic values of BM cellularity, edema and hemorrhage. Values of T1-SI of BM for 1 to 5 days after irradiation was smaller than those the values for before irradiation data (P < 0.006). SPIR-SI values of BM in 3, 5 and 10 days were less than values for before irradiation
(P < 0.001). Since SI depends to edema and hemorrhage the high correlation between cellularity and T1-SI (r = 0.725, P = 0.018) or SPIR-SI(r = 0.814, P = 0.004) was not found.