Cardiac image registration of the left atrium and pulmonary veins.

Cardiac image registration, in the context of the left atrium, is intermodal, with the acquired image and the real-time reference image residing in different image spaces, and involves optimization, where one image space is transformed into the other. Geometry-based methods, which include using fiducial points and/or surface-based techniques, are usually used for cardiac image registration. During fiducial point registration, fiducial points are either external skin markers or manually determined by marking anatomical landmarks using mapping catheters. Usually, a minimum of three noncollinear points is needed for optimal registration. During surface registration, each of the images' surfaces are characterized to determine the best transformation between them. Unlike the rigid body registration used extensively in the study of the brain, cardiac image registration is unique and challenging. In addition to the errors inherent in intermodal registration, errors due to respiration and cardiac motion during the cardiac cycle are specific to cardiac image registration. This review addresses the basic principles of registration and the inherent registration errors as they relate to cardiac imaging and registration.