Design considerations in cardiac CT

In cardiac CT temporal resolution is directly related to the gantry rotation time of 3^rd generation CT scanners. This time cannot be substantially reduced below current standards of 0.33 s - 0.35 s due to mechanical limitations. As an alternative we present a dual source CT (DSCT) system. The system is equipped with two X-ray tubes and two corresponding detectors that are mounted onto the rotating gantry with an angular offset of 90°. Due to the simultaneous data acquisition and the angular offset, complementary quarter-scan data are measured at the same phase in the cardiac cycle. Hence, the exposure time of any image slice is reduced by a factor of two and the temporal resolution is improved by the same factor. In contrast to single source cardiac CT with multi-segment image reconstruction, the temporal resolution does not depend on the heart rate. Since multi-segment reconstruction techniques applied in single source cardiac CT, which limit the table speed, are no longer needed, faster volume coverage in cardiac spiral imaging can be achieved. As a consequence of these concepts, patient dose in cardiac CT can be significantly reduced. ECG correlated image reconstruction is based on 3D backprojection of the Feldkamp type. Data truncation coming from the fact that one detector (A) covers the entire scan field of view (50 cm in diameter), while the other detector (B) is restricted to a smaller, central field of view (26 cm in diameter), has to be treated. We evaluate temporal resolution and dose efficiency by means of phantom scans and computer simulations. We present first patient scans to illustrate the performance of DSCT for ECG correlated cardiac imaging.