Abstract
BackgroundMyocardial motion is an important observable for the assessment of heart condition. Accurate estimates of ventricular (LV) wall motion are required for quantifying myocardial deformation and assessing local tissue function and viability. Harmonic Phase (HARP) analysis was developed for measuring regional LV motion using tagged magnetic resonance imaging (tMRI) data. With current computer-aided postprocessing tools including HARP analysis, large motions experienced by myocardial tissue are, however, often intractable to measure. This paper addresses this issue and provides a solution to make such measurements possible.MethodsTo improve the estimation performance of large cardiac motions while analyzing tMRI data sets, we propose a two-step solution. The first step involves constructing a model to describe average systolic motion of the LV wall within a subject group. The second step involves time-reversal of the model applied as a spatial coordinate transformation to digitally relax the contracted LV wall in the experimental data of a single subject to the beginning of systole. Cardiac tMRI scans were performed on four healthy rats and used for developing the forward LV model. Algorithms were implemented for preprocessing the tMRI data, optimizing the model parameters and performing the HARP analysis. Slices from the midventricular level were then analyzed for all systolic phases.ResultsThe time-reversal operation derived from the LV model accounted for the bulk portion of the myocardial motion, which was the average motion experienced within the overall subject population. In analyzing the individual tMRI data sets, removing this average with the time-reversal operation left small magnitude residual motion unique to the case. This remaining residual portion of the motion was estimated robustly using the HARP analysis.ConclusionUtilizing a combination of the forward LV model and its time reversal improves the performance of motion estimation in evaluating the cardiac function.
Highlights
Cardiac dysfunction is associated with a variety of cardiovascular conditions that lead to heart failure
Preprocessing systolic frames with the time reversal operation prior to performing Harmonic Phase (HARP) analysis improves the performance of cardiac motion estimates from tagged magnetic resonance imaging (tMRI)
The simple prior time-reversal operation applied to a systolic image with the forward model of the left ventricular (LV) wall motion accounts for the large displacements experienced by the myocardial tissue in sequentially-acquired tMRI data
Summary
Cardiac dysfunction is associated with a variety of cardiovascular conditions that lead to heart failure. In the presence of large motions, the current analysis techniques including HARP fail to accurately describe the absolute displacement of the myocardial tissue. This paper addresses this issue and offers a solution – providing motion estimates with improved performance even when the tissue is subject to large movements. Harmonic Phase (HARP) analysis was developed for measuring regional LV motion using tagged magnetic resonance imaging (tMRI) data. With current computer-aided postprocessing tools including HARP analysis, large motions experienced by myocardial tissue are, often intractable to measure This paper addresses this issue and provides a solution to make such measurements possible.
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