Impact of Image Resolution and Resampling on Motion Tracking of the Left Chambers from Cardiac Scans

Abstract

Cardiac magnetic resonance (CMR) is an important diagnostic imaging modality in cardiovascular medicine. Estimation of myocardium motion derived from CMR scans is routinely used to measure the cardiac mechanics. However, tracking a rapidly moving organ can be compromised by artefacts or impaired image quality. To assess how in-plane image resolution and slice sampling in short and long axis scans impact errors in motion tracking, we utilised retrospective gated cardiac computed tomography (CCT) imaging as a surrogate groundtruth for motion estimation across 10 clinical datasets, since these scans have a higher isotropic resolution than CMR and the ability to capture full 3D motion. In our work, the left atrial (LA) and ventricular (LV) cavities were first delineated, and then reconstructed short and long axis images were used in a non-rigid registration method with optimised hyperparameters to track endocardial motion. Finally, global and regional functions in the form of area, circumferential, and longitudinal strains were computed. Our findings showed that tracking LA was more sensitive than LV to changes in the in-plane resolution and magnitude of strain was robust to resolution changes in short axis images, when correlated with the groundtruth (r: 0.87–0.99, $R^2$: 0.75–0.98). We also found that 9 short axis slices could capture the motion of LV almost as accurately as 36 slices captured in long axis (r: 0.89 vs. 0.90, $R^2$: 0.80 vs. 0.80), illustrating that the cardiac mechanics measured by short axis scans are more likely to be robust to image artefacts and reconstruction parameters.