Assessment of Myocardial Microvascular Function: New Opportunities in Fast Computed Tomography

A technical solution to avoid partial scan artifacts in cardiac MDCT

Quantitative evaluation of cardiac image data obtained using multidetector row computed tomography (CT) is compromised by partial scan reconstructions, which improve the temporal resolution but significantly increase image-to-image CT number variations for a fixed region of interest compared to full reconstruction images. The feasibility of a new approach to solve this problem is assessed. An anthropomorphic cardiac phantom and an anesthetized pig were scanned on a dual-source CT scanner using both full and partial scan acquisition modes under different conditions. Additional scans were conducted with the electrocardiogram (ECG) signal being in synchrony with the gantry rotation. In the animal study, a simple x-ray detector was used to generate a signal once per gantry rotation. This signal was then used to pace the pig's heart. Phantom studies demonstrated that partial scan artifacts are strongly dependent on the rotational symmetry of angular projections, which is determined by the object shape and composition and its position with respect to the isocenter. The degree of partial scan artifacts also depends on the location of the region of interest with respect to highly attenuating materials (bones, iodine, etc.) within the object. Single-source partial scan images (165 ms temporal resolution) were significantly less affected by partial scan artifacts compared to dual-source partial scan images (82 ms temporal resolution). When the ECG signal was in synchrony with the gantry rotation, the same cardiac phase always corresponded to the same positions of the x-ray tube(s) and, hence, the same scattering and beam hardening geometry. As a result, the range of image-to-image CT number variations for partial scan reconstruction images acquired in synchronized mode was decreased to that achieved using full reconstruction image data. The success of the new approach, which synchronizes the ECG signal with the position of the x-ray tube(s), was demonstrated both in the phantom and animal experiments.