FIGURE 5.

Axial postcontrast T1 (PC-T1)-weighted image from a patient with true progression (TP) (top row), demonstrating a neoplasm in the right parietal region infiltrating into the lateral ventricles. The regions of interest are overlaid on the image, with the colors indicating the following defined regions: white, contrast-enhancing region; yellow, central core; orange, immediate peritumoral region; and brown, distal peritumoral region. Fractional anisotropy (FA), cerebral blood volume (CBV), volume transfer constant (K^trans), and volume fraction of plasma space in tissues (Vp) values from the enhancing regions (arrows) in TP are higher than those of pseudoprogression (PsP) (bottom row). A photomicrograph of hematoxylin–eosin (H & E) stain from the TP case demonstrates areas of high tumor cellularity, pseudopalisading necrosis, endothelial proliferation, and increased mitotic activity, whereas PsP shows predominant treatment-related changes, including extensive geographic necrosis and vascular fibrinoid necrosis