FIG 3. Surgically induced, delayed (time-dependent) enhancement at the resection margins. Preoperative MR image (top) (674/20/2) shows a left occipital, contrast-enhancing tumor. Intraoperative T1-weighted images (middle [from left to right], unenhanced and 5, 10, and 20 minutes postcontrast) (532/15/3) show linear enhancement at the resection margin, which is more pronounced the more time has elapsed since the administration of the contrast agent (arrows). Also note the diffusion of the contrast agent into the fluid-filled resection cavity, leading to increased signal intensity of the fluid on the delayed images. The probable cause of this type of surgically induced contrast enhancement is leakage of contrast agent out of surgically opened blood vessels. The enhancement is not present on the preoperative (top) or postoperative (bottom) MR images (674/20/2).