Dynamic contrast-enhanced (DCE) imaging is a method for acquiring a series of MR images in rapid succession following the administration of contrast. Similar to CT, viewing the "wash-in" and "wash-out" of contrast on MRI may improve the detection and delineation of tumors and vascular lesions. The technique is also called "keyhole" imaging, deriving from the k-space representation of the sequence, which resembles a slot or keyhole. The middle portion of k-space (the keyhole) contains low spatial frequency information - overall brightness or darkness and general shapes within the image. The peripheral portions of k-space contain high spatial frequency information (edges and details). When gadolinium contrast passes through the anatomy of interest, only the general brightness or darkness change significantly. This dynamic information can be obtained from sampling the center of k-space only. In the basic keyhole method, an initial pre-contrast reference image is obtained at full resolution using the complete set of k-space data. Following contrast injection, the center of k-space is repeatedly sampled every few seconds while the periphery is only sampled occasionally. Because only the central keyhole data changes during a dynamic acquisition, an appreciable savings in scan time can be achieved by not rescanning the periphery. Final images at full resolution are then reconstructed using the peripheral k-space data from the reference data set and central k-space data from the keyhole sets. A variety of more sophisticated DCE techniques exist including modeling of perfusion and permeability. Image shows a contrast-enhanced pituitary MRI using keyhole technique. Note left sided microadenoma (arrow) seen on dynamic portion of study, invisible at 5 min. #MRI #DCE #keyhole_imaging
