Radiation dose in 320-slice multidetector cardiac CT: A single center experience of evolving dose minimization

BackgroundMinimization of radiation exposure remains an important subject that occurs in parallel with advances in scanner technology.ObjectiveWe report our experience of evolving radiation dose and its determinants after the introduction of 320-multidetector row cardiac CT within a single tertiary cardiology referral service.MethodsFour cohorts of consecutive patients (total 525 scans), who underwent cardiac CT at defined time points as early as 2008, are described. These include a cohort just after scanner installation, after 2 upgrades of the operating system, and after introduction of an adaptive iterative image reconstruction algorithm. The proportions of nondiagnostic coronary artery segments and studies with nondiagnostic segments were compared between cohorts.ResultsSignificant reductions were observed in median radiation doses in all cohorts compared with the initial cohort (P < .001). Median dose-length product fell from 944 mGy · cm (interquartile range [IQR], 567.3–1426.5 mGy · cm) to 156 mGy · cm (IQR, 99.2–265.0 mGy · cm). Although the proportion of prospectively triggered scans has increased, reductions in radiation dose have occurred independently of distribution of scan formats. In multiple regression that combined all groups, determinants of dose-length product were tube output, the number of cardiac cycles scanned, tube voltage, scan length, scan format, body mass index, phase width, and heart rate (adjusted R2 = 0.85, P < .001). The proportion of nondiagnostic coronary artery segments was slightly increased in group 4 (2.9%; P < .01).ConclusionWhile maintaining diagnostic quality in 320-multidetector row cardiac CT, the radiation dose has decreased substantially because of a combination of dose-reduction protocols and technical improvements. Continued minimization of radiation dose will increase the potential for cardiac CT to expand as a cardiac imaging modality.