MULTIPLE FRACTIONATED AND SINGLE-DOSE IRRADIATION OF BONE-MARROW - EVALUATION BY MR AND CORRELATION WITH HISTOPATHOLOGICAL FINDINGS

Purpose. To evaluate the MR appearance of bone marrow during and after multiple fractionated and single-dose irradiation using SE sequences, with histopathological correlation. Material and Methods: The left hi nd limbs of Wistar rats were irradiated with doses of either 2 Gyx10 f ractions or 20 Gy as a single dose. MR images of the femora were taken on days 0, 1, 3, 5, 7, 10, 15, 20, 25, 30, 40, 50, 60, 90, 120, 150 a nd 180. T1-, proton-density- and T2-weighted images were obtained with SE sequences. The rats were sacrificed on days 3, 12, 40 and 180 for histological study. Results: No significant change in the T1 relaxatio n time was observed in the fractionated group during the first 15 days after irradiation. T2 did not change during the initial 7 days. There were significant differences in TI and T2 between nonirradiated and f ractionated, and between fractionated and single-dose irradiated marro ws (p<0.01). Sinusoidal dilatation, decrease in cellularity, and hemor rhage were observed on day 3. Fat increased on/after day 12. The fract ionated group showed mild changes compared to the single-dose irradiat ed group. Conclusion. The T1 and T2 relaxation times of bone marrow re ceiving multiple fractionated irradiation did not change significantly on SE sequences during the early phase. However, dilatation of sinuso ids, hemorrhage, decrease in cellularity, and increase in fat content were observed. Single-dose irradiation resulted in marked and early ch anges in T1 and T2 of the bone marrow.