One of the challenges associated with cardiac computed tomography (CT) imaging is resulting artifacts caused by the movement of the beating heart. To date, cardiac CT scanners utilize electrocardiogram (ECG) signals to gate the acquisition of scan data. With ECG cardiac gating, direct and consistent correlation between the phases of the ECG periodic signal and the physical position and shape of the heart is assumed such that if data is acquired only during a particular phase(s) of the periodic ECG signal, the heart will be in a particular position and shape when all the scan data is acquired. However, because this assumption may not always hold true, ideal gating process should be robust enough to be used in the presence of cardiac arrhythmias and over a large range of heartbeats.
University of Michigan researchers have developed a method to acquire images and reconstruct them in a way such that the resulting image is free of artifacts. This method takes advantage of x-ray projection views that are acquired at the same subject position, and reconstructs an image based on complete sets of projection views. In particular, as projection views are acquired during a CT scan, the correlation of a projection view and the projection view acquired at an adjacent view angle is calculated. A high correlation coefficient indicates that the view was acquired at the same subject position as the adjacent view, whereas a dip in the correlation coefficient indicates a movement. Once a desired subject reference position is established (e.g., a particular cardiac phase) projection views are acquired over the entire range of view angles and the correlation coefficients are monitored to ensure that the subject is captured in the same position in all views.
Applications and Advantages
- High resolution CT imaging of moving objects-nl-such as a beating heart
- CT image reconstruction for moving object with-nl-minimal artifacts
- Minimal time delay in image acquisition
- Gating at different parts of the heart may be-nl-achieved in a single acquisition cycle