Pseudonormalization of diffusion weighted images: magnetic resonance imaging in an animal model (C6-glioma)

Purpose: Previous studies on intracranial tumors indicate that a high apparent diffusion coefficient (ADC) is due to low cellularity and that lower values indicate a dense, highly cellular tumor. Diffusion is affected by three major factors: cell density, existence and distribution of vasogenic edema, and hypoxic tissue. Therefore, we studied the characteristics of diffusion-weighted magnetic resonance imaging (DWI) in a rat brain C6 glioma during tumor progression. Materials and Methods: In male Wistar rats, C6 gliomas were implanted in the caudoputamen. At day 9, 11, 13 and 15 after tumor inoculation, conventional DWI was performed on a 2.35 Tesla small bore MRI unit (Biospec 24/40, BRUKER Medizintechnik, Ettlingen, Germany). Results: On conventional T2-weighted and contrast-enhanced T1-weighted images, all tumors could well be delineated from the surrounding brain tissue and showed significant progression. On DWI, the tumors were isointense or slightly hypointense compared to the surrounding brain. On the ADC maps, the tumors could be well visualized due to increasing ADC values from day 9 to 15. The mean ADC of brain tumor tissue was 0.76 +/- 0.4 x 10(-3) MM2/s at day 9 and 0.91 +/- 0.03 x 10(-3) MM2/S at day 15. The mean ADC of the normal contralateral caudoputamen was 0.59 +/- 0.007x 10(-3)MM(2/)s. Conclusion: T2 prolongation and increased water diffusion can be balanced on DWI in C6 gliomas, resulting in iso-intensity on DWI (T2 shine-through washout phenomenon). ADC maps are indispensable for the correct interpretation of tumor tissue diffusion behavior.