Sequential and Helical Scanning for Radiation Dose and Image Quality
Sequential and Helical Scanning for Radiation Dose and Image Quality
Objective. Concerns have been raised about the radiation exposure of coronary CT angiography (CTA). Recently, a prospective ECG-triggered sequential coronary CTA technique was developed to reduce exposure to ionizing radiation. The purpose of this analysis was to determine the impact of a sequential scanning technique on image quality and radiation dose in a prespecified subgroup analysis of the Prospective Multicenter Study on Radiation Dose Estimates of Cardiac CT Angiography I (PROTECTION I) Study when compared with a standard helical scanning technique.
Materials and methods. This analysis comprises 685 64-MDCT coronary angiography studies of 47 international study sites in which the image quality was assessed by an experienced coronary CTA investigator using a 4-point score (1 = nondiagnostic, 4 = excellent image quality). Image quality was analyzed in all patients studied with the sequential scanning mode (n = 99) and in randomly selected patients of the population studied with the helical acquisition mode (n = 586). Radiation dose estimates were derived from the dose–length product (DLP) and a conversion coefficient for the chest (0.014 mSv × mGy × cm).
Results. Although the sequential scanning mode significantly reduced radiation dose estimates by 68% from 11.2 mSv for the helical mode to 3.6 mSv for the sequential mode (p < 0.001), the median diagnostic image quality scores were comparable in both groups. The median diagnostic score for both scanning modes was 3.5 (interquartile range: sequential vs helical mode, 3.25–3.75 vs 3.0–3.75, respectively; p = 0.62).
Conclusion. The results of the PROTECTION I Study suggest that the prospective ECG-triggered sequential coronary CTA technique significantly reduces radiation dose without impairing image quality when compared with the standard retrospective helical data acquisition in patients with a low and stable heart rate.
With improvements in the temporal and spatial resolution of CT, coronary CT angiography (CTA) has become a common diagnostic technique in clinical practice, particularly for the examination of patients with an intermediate pretest probability for obstructive coronary artery disease. Nevertheless, there remains concern regarding the exposure to ionizing radiation and its potential hazards. The international Prospective Multicenter Study on Radiation Dose Estimates of Cardiac CT Angiography I (PROTECTION I) Study analyzed the extent of coronary CTA radiation dose estimates and the impact of different strategies to reduce dose in clinical practice. The study showed that effective radiation exposure usually adds up to doses between 8 and 18 mSv when performing 64-MDCT coronary angiography depending on the CT system, the scanning technique, and patient-dependent factors. For this reason, several dose-saving scanning techniques and algorithms have been developed.
Usually, coronary CTA is performed using the retrospective ECG-gated helical scanning technique. When compared with this helical image acquisition, the prospective ECG-triggered sequential scanning mode yields a considerable reduction of radiation dose. Originally, the prospective scanning algorithm was predominantly used for unenhanced calcium scoring. Recently, this scanning technique has been reintroduced into contrast-enhanced coronary CTA. When applying the prospective ECG-triggered sequential scanning algorithm, image acquisition is performed only during a short predefined time period in the R-R interval, requiring a low and stable heart rate. Small single-center studies have indicated that in comparison with retrospective ECG-gated helical scanning, sequential scanning allows a significant reduction of the radiation dose without impairing image quality in adequately selected patients. The aim of this analysis was to compare the sequential scanning mode and the standard helical image acquisition in a large prospective multicenter and multivendor study with respect to image quality and radiation dose.
Abstract and Introduction
Abstract
Objective. Concerns have been raised about the radiation exposure of coronary CT angiography (CTA). Recently, a prospective ECG-triggered sequential coronary CTA technique was developed to reduce exposure to ionizing radiation. The purpose of this analysis was to determine the impact of a sequential scanning technique on image quality and radiation dose in a prespecified subgroup analysis of the Prospective Multicenter Study on Radiation Dose Estimates of Cardiac CT Angiography I (PROTECTION I) Study when compared with a standard helical scanning technique.
Materials and methods. This analysis comprises 685 64-MDCT coronary angiography studies of 47 international study sites in which the image quality was assessed by an experienced coronary CTA investigator using a 4-point score (1 = nondiagnostic, 4 = excellent image quality). Image quality was analyzed in all patients studied with the sequential scanning mode (n = 99) and in randomly selected patients of the population studied with the helical acquisition mode (n = 586). Radiation dose estimates were derived from the dose–length product (DLP) and a conversion coefficient for the chest (0.014 mSv × mGy × cm).
Results. Although the sequential scanning mode significantly reduced radiation dose estimates by 68% from 11.2 mSv for the helical mode to 3.6 mSv for the sequential mode (p < 0.001), the median diagnostic image quality scores were comparable in both groups. The median diagnostic score for both scanning modes was 3.5 (interquartile range: sequential vs helical mode, 3.25–3.75 vs 3.0–3.75, respectively; p = 0.62).
Conclusion. The results of the PROTECTION I Study suggest that the prospective ECG-triggered sequential coronary CTA technique significantly reduces radiation dose without impairing image quality when compared with the standard retrospective helical data acquisition in patients with a low and stable heart rate.
Introduction
With improvements in the temporal and spatial resolution of CT, coronary CT angiography (CTA) has become a common diagnostic technique in clinical practice, particularly for the examination of patients with an intermediate pretest probability for obstructive coronary artery disease. Nevertheless, there remains concern regarding the exposure to ionizing radiation and its potential hazards. The international Prospective Multicenter Study on Radiation Dose Estimates of Cardiac CT Angiography I (PROTECTION I) Study analyzed the extent of coronary CTA radiation dose estimates and the impact of different strategies to reduce dose in clinical practice. The study showed that effective radiation exposure usually adds up to doses between 8 and 18 mSv when performing 64-MDCT coronary angiography depending on the CT system, the scanning technique, and patient-dependent factors. For this reason, several dose-saving scanning techniques and algorithms have been developed.
Usually, coronary CTA is performed using the retrospective ECG-gated helical scanning technique. When compared with this helical image acquisition, the prospective ECG-triggered sequential scanning mode yields a considerable reduction of radiation dose. Originally, the prospective scanning algorithm was predominantly used for unenhanced calcium scoring. Recently, this scanning technique has been reintroduced into contrast-enhanced coronary CTA. When applying the prospective ECG-triggered sequential scanning algorithm, image acquisition is performed only during a short predefined time period in the R-R interval, requiring a low and stable heart rate. Small single-center studies have indicated that in comparison with retrospective ECG-gated helical scanning, sequential scanning allows a significant reduction of the radiation dose without impairing image quality in adequately selected patients. The aim of this analysis was to compare the sequential scanning mode and the standard helical image acquisition in a large prospective multicenter and multivendor study with respect to image quality and radiation dose.
