Space-time segmentation using level set active contours applied to myocardial gated SPECT

This paper presents a new variational method for the segmentation of a movi ng object against a still background, over a sequence of [two-dimensional o r three-dimensional (3-D)] image frames. The method is illustrated in appli cation to myocardial gated single photon emission computed tomography (SPEC T) data, and incorporates a level set framework to handle topological chang es while providing closed boundaries. The key innovation is the introduction of a geometrical constraint into the derivation of the Euler-Lagrange equations, such that the segmentation of each individual frame can be interpreted as a closed boundary of an object (an isolevel of a set of hyper-surfaces) while integrating information over the entire sequence. This results in the definition of an evolution veloci ty normal to the object boundary. Applying this method to 3-D myocardial ga ted SPECT sequences, the left ventricle endocardial and epicardial limits c an be computed in each frame. This space-time segmentation method was tested on simulated and clinical 3- D myocardial gated SPECT sequences and the corresponding ejection fractions were computed.