Recovery of slice rotations with the stack alignment transform in cardiac MR series

Abstract

Generic solutions for misalignment correction in image stacks are based on slice-byslice registration to a reference volume. Slice misalignment in cardiac Magnetic Resonance cine series typically includes translational and rotational components. Recovery of rotation in medial down to apical slices with the basic slice-to-volume registration may provide unreliable results because of rotational symmetry of the short-axis view of the left ventricle. This paper describes a novel method for correction of stack misalignment in cardiac cine series with recovery of the rotational component. The core of the presented method is a custom spatial transform which parametrises a set of independent centred rigid transforms, one per slice in a stack. The stack alignment transform was designed to circumvent the weaknesses associated with slice-to-volume registration and improve the reliability of misalignment correction over the slice-by-slice registration approach. The image similarity metric for every iteration during the stack alignment transform optimisation is calculated on the whole image stack with all slice correction parameters contributing to the result. The presented method was evaluated on 50 clinical datasets and the results demonstrate an improvement of misalignment correction with the proposed transform. The study also provides evidence of the importance of recovery of slice rotations in this application; the presented method is general enough to be applied to similar problems in other image modalities.