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 (D(d-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 D(d-s) of approximately 4–6 mm. The average D(d-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 D(d-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 D(d-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.