Radiation effects in the rat spinal cord: evaluation with apparent diffusion coefficient versus T2 at serial MR imaging.
OBJECTIVE
To prospectively determine whether apparent diffusion coefficients (ADCs) are more sensitive to radiation-induced changes in the rat spinal cord than T2 relaxation times.


METHODS
The study was approved by the institutional ethical committee on animal welfare. One centimeter of the thoracolumbar spinal cord of six rats was irradiated with 36 Gy. For 3-6 months after irradiation, five 7.0-T magnetic resonance (MR) imaging measurements were performed in each rat until motor impairment developed. Six age-matched rats were examined as controls. Measurements were performed by using diffusion-weighted imaging with five b values and a spin-echo sequence with 20 echoes. ADC and T2 values were calculated, and the spatiotemporal evolution of the radiation-induced lesions was determined semiautomatically. The final MR measurements were compared with the histologic findings.


RESULTS
Shortly before the neurologic signs appeared, the first radiation effects manifested as well-circumscribed white matter (WM) lesions with a low longitudinal ADC and normal or high T2. WM lesions with high T2 correlated with confluent necrosis at histologic analysis, whereas WM lesions with normal T2 correlated with focal necrosis and demyelination. In the gray matter (GM), lesions with diffusely high T2 were present and were attributed to edema. T2 changes in the GM preceded T2 and ADC changes in the WM.


CONCLUSIONS
In the WM, longitudinal ADC was more sensitive for the detection of radiation damage than T2, but in the GM, T2 was more sensitive.
Philippens
Marielle E P
ME
Department of Radiation Oncology , Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands. m.philippens@umcutrecht.nl
Gambarota
Giulio
G
van der Kogel
Albert J
AJ
Heerschap
Arend
A
D000465:Algorithms; D000818:Animals; D038524:Diffusion Magnetic Resonance Imaging; D007091:Image Processing, Computer-Assisted; D016018:Least-Squares Analysis; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D011446:Prospective Studies; D011832:Radiation Injuries / Q000473:pathology*; D051381:Rats; D017208:Rats, Wistar; D012680:Sensitivity and Specificity; D013116:Spinal Cord / Q000528:radiation effects*; D018709:Statistics, Nonparametric