Optimization of helical pitch in cardiac MDCT acquisition in patients with arrhythmia requiring ECG-edit

The electrocardiogram (ECG)-edit is necessary in cardiac multidetector-row CT (MDCT) in arrhythmias [premature atrial contraction (PAC) or premature ventricular contraction (PVC)]; however, it sometimes results in a data deficit. Therefore, a thinner helical pitch (HP) should be set to avoid data deficits. The thinner helical pitch creates more radiation exposure. The purpose is to optimize HP in PAC or PVC. In a phantom study, an acrylic phantom (10 x 10 x 500 mm) was scanned by MDCT (Aquilion 64) using an artificial pacemaker at various gantry rotation speeds (r) and HP. We evaluated the relationships between HP and the maximal table moving length (Lmax) in the border of data deficit, and among r, HP, and the maximum data collection time interval (Tmax). In the clinical study, cardiac MDCT was performed in 44 cases (M/F: 26/18, 71.4±10.6 yrs) including 30 PAC and 14 PVC using the optimal HP derived from Tmax+10%. In the phantom study, there were significant correlations between HP and Lmax (Lmax=34.94-0.32 HP, r=0.999, P<0.0001), and Tmax [Tmax=(69.88/HP-0.64) x r] was calculated using formula. In 42/44 patients, high-quality images were obtained using the optimal HP; however, it resulted in data deficits in 2 patients, because of heart rate decreasing and a couple of PAC during scanning. Optimal HP significantly (P<0.0001) reduced radiation dose (-11.4%) compared with conventional HP. In conclusion, the optimal HP in PAC or PVC was calculated from the phantom study, provided fine images in 95% patients, and could reduce radiation dose. (author)