Early Radiation-induced Bone Marrow Injury: Serial MR Imaging During Initial 4 Weeks After Irradiation 1

Abstract

Magnetic resonance (MR) imaging has been widely used to detect bone marrow (BM) changes after radiotherapy. However, little information about the dynamic MR appearance of early radiation-induced BM injury is available. This experimental study was designed to determine the MR appearance of irradiated BM during the initial 4 weeks after irradiation. After focal BM irradiation (20 Gy, single dose, x-ray), 12 of 20 rabbits underwent serial MR studies weekly from days 7 to 28; eight rabbits were used for histologic investigation on days 7, 14, 21, and 28 after irradiation. Under microscopy, early BM changes after irradiation consisted of sinusoid dilatation and congestion, followed by a progressive decrease in cellularity and later fat degeneration. All irradiated BM showed relative hyperintensity on short-inversion time inversion recovery (STIR) imaging from days 7 to 21 after irradiation and increased enhancement with gadolinium diethylenetriamine pentaacetic acid (DTPA) administration from days 7 to 28 after irradiation. However, on STIR imaging and gadolinium DTPA enhancement, the relative signal intensity of irradiated BM appeared to decline in a time-dependent way. On fast spin-echo (FSE) T1-weighted imaging, relative hyperintensity was detected in irradiated BM from day 21 after irradiation. On fat-suppressed FSE T1-weighted imaging, a slight increase in signal intensity was shown in some irradiated BM (in five of 12 rabbits) on day 7 after irradiation. STIR imaging was sensitive to early BM congestion and sinusoidal dilatation, spin-echo T1-weighted imaging was effective in detecting later fatty degeneration in irradiated BM, and gadolinium DTPA enhancement may contribute to the evaluation of BM vascular injury in response to irradiation.