en Radiation Biology Radiation Biology تحقيق بديع Original Research <p><strong>Background: </strong>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. </p><p><strong>Materials and Methods: </strong>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 <br>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. </p><p><strong>Results: </strong>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 <br>(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. </p><strong>Conclusion: </strong>This study indicated that radiation-induced modification of BM-SI is tightly linked to the parameters like decline of all hematopoietic cell lines, edema and hemorrhage. It was <br>concluded that MRI can distinguish normal from irradiated BM so that radiation-induced <br>alterations in BM could be assessed with MRI. <i>Iran </i><i>. J. Radiat. Res., 2004 2 (3): 117-126 </i> ,Acute irradiation,BM cellularity,BM edema & hemorrhage,MR -SI 117 126 http://ijrr.com/browse.php?a_code=A-10-1-67&slc_lang=en&sid=1 Sh. Akhlaghpoor shahram_ak@yahoo.com 79003194753284600192 79003194753284600192 Yes H. Khani 79003194753284600193 79003194753284600193 No F. Kossari 79003194753284600194 79003194753284600194 No M. H. Zahmatkesh 79003194753284600195 79003194753284600195 No