Representative contrast-enhanced T1-weighted (A, C, E and G) and fluid-attenuated inversion recovery (FLAIR) (B, D, F and H) images from two patients with glioblastomas (GBMs) at baseline (top row) and 1-month follow-up (bottom row). The images (A-D) are from a patient with pseudoprogression (PsP), showing increased tumor size at follow-up. The images (E-H) are from a patient with true progression (TP), showing decreased tumor size at follow-up, suggesting the limitation of conventional MR imaging in reliable distinction of TP from PsP in GBMs