Estimation of the displacement of cardiac substructures and the motion of the coronary arteries using electrocardiographic gating

PURPOSE: The aim of this study was to quantify the displacement of cardiac substructures, including the anterior myocardial territory (AMT), left ventricle, and coronary arteries during a normal cardiac cycle. MATERIALS AND METHODS: Computed tomography (CT) images with retrospective electrocardiographic gating of 17 eligible patients were obtained. All images were reconstructed automatically for the end-diastolic and end-systolic phases. CT scanning without contrast at a random phase and a selected vertebral body were used as references to measure three-dimensionaldisplacements of the cardiac substructures. RESULTS: The displacement between the end-diastolic and end-systolic phases (Dd-s) was greater than that between the end-systolic and random phases and between the end-diastolic and random cardiac phases. The largest displacements for the heart were in the left, posterior, and inferior directions with an average Dd-s of approximately 4-6 mm. The average Dd-s for the AMT and left ventricle was 1.2-2.7 mm in the anterior and right directions, 4.3-7.8 mm in left and posterior directions, and 4.9-6.3 mm in superior and inferior directions. For the coronary arteries, the average Dd-s was 2.8-5.9 mm in the anterior-posterior direction, 3.5-6.6 mm in left-right direction, and 3.8-5.3 mm in the superior-inferior direction. Inter-observer agreement was excellent for the heart, AMT, and left ventricle (kappa coefficient, >0.75 for all) and good for most coronary arteries in three dimensions (kappa coefficient, 0.511-0.687). The Dd-s did not differ significantly between men and women. CONCLUSION: Most average displacements of the cardiac substructures and coronary arteries were 3-8 mm in three dimensions. These findings will be useful to accurately estimate the radiation dose to cardiac substructures during thoracic radiation and to evaluate the risk of radiation-related heart disease.