Rationale and Objectives
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.
Materials and Methods
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.
Results
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.
Conclusion
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.
As the main hematogenic organ in the human body, bone marrow (BM) is sensitive to radiation . In medical practice, BM may be exposed to radiation for radiotherapy of malignancies, leading to resultant radiation-induced injury to varying degrees . Generally, BM changes in response to radiation are dose and time dependent, which is characterized in histologic structure by early marrow edema, sinusoids disruption, hypocellularity with vasculature destruction, and late fatty replacement and endosteal fibrosis . Magnetic resonance (MR) imaging (MRI) has been considered an accurate and integral technique in the detection of radiation-induced effects on BM . Studies using short-inversion time inversion recovery (STIR) imaging reported that early BM edema attributable to radiation was presented as hyperintensity . Fatty transformation in irradiated BM appeared as bright signal intensity (SI) in spin-echo (SE) T1-weighted imaging or opposed-phase chemical-shift imaging . A prospectively study by Otake et al described transient enhancement in irradiated BM early after the initiation of radiotherapy.
To our knowledge, the majority of previous MR studies in radiation-induced BM injury detection were performed in patients undergoing radiotherapy for malignancies, who were irradiated to different bones and with varied fractionated doses . Little information about the dynamic MR appearance of early radiation-induced BM injury is available. In this MR study using STIR imaging, routine SE sequences, and gadolinium diethylenetriamine pentaacetic acid (DTPA) enhancement, we prospectively performed a serial evaluation of early radiation-induced BM changes in a rabbit model. Our purposes were to determine the MR appearance of irradiated BM during the initial 4 weeks after irradiation and to reassess the role of different MR techniques in early radiation-induced BM injury detection.
Materials and methods
Animals
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X-Irradiation
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MR Investigation
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Histologic Examination
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Results
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Table 1
Relative Signal Intensity of Irradiated Bone Marrow on Magnetic Resonance Imaging on Days 7, 14, 21, and 28 After Irradiation
Modality Day 7 Day 14 Day 21 Day 28 STIR imaging 58.3 ± 8.7% 57.1 ± 9.0% 37.7 ± 10.3% 21.2 ± 6.6% T1WI 5.1 ± 3.0% 8.1 ± 2.8% 21.8 ± 11.3% 37.2 ± 15.3% FS T1WI 15.5 ± 4.6% 12.0 ± 4.3% 9.5 ± 2.0% 8.4 ± 1.9% CE 36.9 ± 15.4% 32.0 ± 9.6% 24.9 ± 10.8% 16.4 ± 8.3%
CE, gadolinium diethylenetriamine pentaacetic acid enhancement; FS, fat-suppressed; T1WI, T1-weighted imaging.
Data are expressed as mean ± standard error.
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Discussion
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Conclusion
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