An Adapted Optical Flow Algorithm for Robust Quantification of Cardiac Wall Motion From Standard Cine-MR Examinations

This paper presents a method for local myocardial motion estimation from a conventional steady-state free precession cine-MRI sequence using a modified phase-based optical flow (OF) technique. Initially, the technique was tested on synthetic images to evaluate its robustness with regards to Rician noise and to brightness variations. The method was then applied to cardiac images acquired on 11 healthy subjects. Myocardial velocity is measured in centimeter per second in each studied pixel and visualized as colored vectors superimposed on MRI images. The estimated phase-based OF results were compared with a reference OF method and gave similar results on synthetic images, i.e., without a significant difference of the mean angular error. Applied on cine-MRI of normal hearts, the calculated velocities from short-axis images concord with values obtained in the literature. The advantage of the presented method is its robustness with respect to Rician noise and to brightness changes often observed in cine-MRI sequences, and especially with the through-plane movement of the heart. Motion assessment using our method on cine-MR images gives promising results on motion estimation on a pixel-by-pixel basis, leading to a regional measurement of the time-velocity course of myocardial displacement in different segments of the heart wall.

I. Introduction

Cardiac MRI is a noninvasive technique allowing the study of the cardiac function. ECG-gated steady-state free precession (SSFP) cine-MRI sequences have the advantage of providing detailed morphological information coupled with an adequate temporal resolution and an excellent contrast between structures. These sequences are widely used in clinical practice for the study of myocardial function [1] through the estimation of ejection fraction (EF) and myocardial thickness.