A 48-year-old man with Moyamoya disease.

(A). A true noncontrast (TNC) image shows a large lobar haematoma in the right fronto-parietal lobe. (B). A virtual noncontrast image clearly shows a haematoma with image quality similar to the TNC image. (C–E). Monoenergetic (MonoE) images at 40 keV (C), 80 keV (D), and 140 keV (E). A small, dot-like enhancement (arrow) is noted in the medial aspect of the haematoma, suggesting active extravasation at 40 keV, and this lesion has similar attenuation to the haematoma as the keV values increase. (F). On a spectral plot from a MonoE image at 40 keV, active extravasation reveals a gradual decrease in HU values with a steep slope (ROI 3), suggesting iodine. (G). An iodine overlay fusion image based on 80 keV MonoE image also shows conspicuous delineation of a small, active extravasation (arrow).