SU-G-TeP3-12: Retrospective Assessment of R2star Using Ultra-High Field MRI in a Rodent Model of Radiation Necrosis




To establish a quantitative MRI method that would be capable of predicting radiation necrosis without using a contrast agent.


Healthy male Fischer 344 rats were irradiated using an animal irradiator capable of delivering 2.3 Gy/min with a kVp of 225 V. A dose of 40 Gy was given to half the brain in a single session. Rats were scanned using a 9.4 T animal MRI before irradiation and every two weeks following radiation until either necrosis developed or they were sacrificed for health reasons. A multi-echo gradient-echo sequence was acquired at every time point and the apparent transverse relaxation rate R2* was calculated based on the measured signal decay. At the last time point, an ROI mask with an R2* value of greater than 45 s−1 was applied in the area of the external and internal capsule where radiation necrosis was confirmed. A retrospective analysis was performed to determine whether R2* values would be able to predict where radiation necrosis would occur.


Radiation necrosis was morphologically visible between weeks 22–24 following treatment. Gadolinium MRI and histology confirmed radiation necrosis in the area of MRI enhancement. Our data suggests that there is a trend towards significance in the lesion as early as 12 weeks prior to morphological changes on MRI with significance occurring 6 weeks prior (p≤0.05, p≤0.01 at week 24). Measurements of the R2* in the hippocampus did not show any significant difference; however, there are areas of visible R2* change within sub-hippocampal regions.


R2* is a promising method that could be able to predict an underlying disease process that occurs prior to radiation necrosis. The constant increase in R2* values suggests a possible neuroinflammatory mechanism rather than an acute vascular event where R2* would tend to decrease in the area.