Nonrigid registration of myocardial perfusion MRI using pseudo ground truth

In this paper we present a method for nonrigid registration of myocardial perfusion MR images. Instead of registering pairs of images within the observed sequence, we register the observed sequence to a pseudo ground truth, which is a motion/noise-free sequence estimated from the observed one. As the corresponding images of the two sequences have almost identical intensity distributions, our method overcomes the challenges arising from rapidly varying image intensity and contrast. The pseudo ground truth and the deformation fields for the observed sequence are obtained simultaneously by minimizing an energy functional integrating both the registration error and the spatiotemporal constraints on the pseudo ground truth in an expectation-maximization fashion. We have tested the proposed nonrigid registration method on real cardiac MR perfusion scans, both qualitatively and quantitatively. Experimental results show that the proposed method is able to successfully compensate for the heart motion during contrast enhancement.