Extended cardiac reconstruction with large area detectors: a simulation study

Recently, three-dimensional cardiac cone beam reconstruction has been introduced for retrospectively gated volume CT imaging. In order to investigate the resulting image quality for large area detectors (LAD), a simulation study has been carried out: The FORBILD thorax phantom has been extended with a dynamic heart insert forming a 4D cardiac CT phantom. Cone beam projection data for 256. 128, 64 and 40-row systems at three different relative pitches (0.1, 0.2 and 0.3) have been simulated at a constant heart rate of 64 bpm. Images have been reconstructed employing the Extended Cardiac Reconstruction (ECR) algorithm. The temporal resolution has been calculated for 256, 128.64 and 40-row systems with different rotation times (0.33 s, 0.42 s, 0.50 s), relative pitches (0.05 up to 0.35) and heart rates (40 up to 120 bpm). With the increased volume coverage of LAD systems, scans with a low to intermediate relative pitch (0.1-0.2) become feasible without resulting in extensive scan times, inhibiting single breath hold acquisitions. With ECR, the image quality is excellent for systems with an increased cone-angle. Alternative reconstruction approaches such as iterative or exact schemes may further improve the image quality for detectors above 128 rows. The study shows that an intermediate relative pitch, e.g. 0.2, is feasible for cardiac data acquisition. It results in good temporal resolution at fast volume coverage.