Basic MRI image sequences include T1, T1 post-contrast, T2, and T2 FLAIR. A mnemonic to remember what is bright on T1 versus T2 MRI sequences is "FaT has one T, H2O is bright on T2." Another clue is that the gray matter on a T2 sequence is hyperintense compared with white matter, whereas gray matter is hypointense compared with white matter on a T1 sequence.
Compare the T1 post-contrast, T2, and T2 FLAIR images. FLAIR stands for "Fluid Attenuation Inversion Recovery." The T2 FLAIR sequence suppresses extracellular fluid signal. Hyperintense regions on T2 FLAIR indicate intracellular fluid accumulation/edema. This sequence is used to assess for intraparenchymal edema associated with a tumor.
Clinical pearl: In radiation treatment, the post-operative T2 FLAIR sequence is used to delineate target volumes for the initial 45-46 Gy of GBM treatment. The post-operative T1 post-contrast sequence is then used to delineate the boost volume.
