A new nonrigid registration framework for improved visualization of transmural perfusion gradients on cardiac first-pass perfusion MRI

A new framework for accurate registration of the segmented left ventricle (LV) on cardiac first-pass magnetic resonance imaging (FP-MRI) to precisely analyze the myocardial transit of contrast agent, especially in the ischemically damaged heart, is proposed. Due to the continuous physiological motion of the heart that causes the LV wall to change shape significantly, within the same scan, at the same cross section, we propose a new registration methodology that involves three steps: (i) global target-to-reference frame-to-frame alignment based on maximizing normalized mutual information (NMI); (ii) local alignment based on using a B-splines transformation model that maximizes a new similarity function that accounts for the 1^st- and 2^nd-order NMI between the globally aligned frames followed by (iii) a refinement step which is based on deforming each pixel of the target wall over evolving closed equi-spaced contours (iso-contours) to closely match the reference wall. Respective iso-contours in both reference and target frames are matched based on solving the Laplace equation. We have tested our framework on 20 FP-MRI datasets that have been collected from patients with ischemic damage resulting from heart attacks and who are undergoing experimental therapy, and have documented an improvement in the visualization and display of perfusion-related indexes.