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Abstract: Objective: Triple rule-out (TRO) computed tomographic angiography (CTA) is a protocol which allows evaluation of coronary arteries, aorta, pulmonary arteries and adjacent intrathoracic structures for patients with acute chest pain. Retrospective ECG-gated (RGH) is generally used for TRO CTA while the feasibility of using ECG-gated tube current modulation (ETCM) or prospective ECG-triggering (PGT) protocols have not been fully investigated. The objective of this study is to investigate the potential for dose reduction through the use of ETCM and PGT in TRO CTA examination as compared with routine RGH protocols. Material and methods: All TRO CTA examinations were performed on a 256-slice CT scanner using an anthropomorphic phantom. To determine equivalent doses for different organs, thermal-luminance dosimeters (TLDs) were placed in different positions in the organs during the scanning and effective doses were calculated based on ICRP-103 guidelines. Effective doses calculated from volume CT dose index (CTDIvol) were also compared with those obtained from TLD measurements. Results: From the study, the mean effective dose for RGH, ETCM and PGT scanning was 21.54 mSv, 15.52 mSv and 10.75 mSv respectively. The doses for ETCM and PGT techniques were significantly reduced by 27% and 50% (p < 0.01) as compared to that for RGH. Effective doses calculated from CTDI method for three protocols were no significantly difference compared with those obtained from TLD measurements. Conclusion: Radiation dose could be efficiently reduced by applying the ETCM and PGT protocols in the 256-slice TRO CTA examinations. [Copyright &y& Elsevier]

Abstract: Triple rule-out coronary CT angiography (TRO-CTA) is a new approach for providing noninvasive visualization of coronary arteries with simultaneous evaluation of pulmonary arteries, thoracic aorta and other intrathoracic structures. The increasing use of TRO-CTA examination with longer scan length is associated with the concerns about radiation dose and their corresponding cancer risk. The purpose of this study is to evaluate organ dose and effective dose for the TRO-CTA examination with 2 scan lengths: TROstd and TROext, using 256-slice CT. TRO-CTA examinations were performed on a 256-slice CT scanner without ECG-based tube current modulation. Absorbed organ doses were measured using an anthropomorphic phantom and thermal-luminance dosimeters (TLDs). Effective dose was determined by taking a sum of the measured absorbed organ doses multiplied with the tissue weighting factor based on ICRP-103, and compared to that calculated using the dose-length product (DLP) method. We obtained high organ doses in the thyroid, esophagus, breast, heart and lung in both TRO-CTA protocols. Effective doses of the TROstd and TROext protocols with the phantom method were 26.37 and 42.49mSv, while those with the DLP method were 19.68 and 38.96mSv, respectively. Our quantitative dose information establishes a relationship between radiation dose and scanning length, and can provide a practical guidance to best clinical practice. [Copyright &y& Elsevier]

Background: The aim of this study was to investigate patient doses in prospective electrocardiogram (ECG)-triggered CT coronary angiography (CTCA) combined with multi-segment reconstruction on a 320-detector-row CT. Methods: CTCA data acquired with prospective ECG (pECG) triggering at 0–100% (pECG100%), 30–80% (pECG50%), 70–80% (pECG10%) of the R–R interval and reconstructed using mono-, two- and three-segment reconstruction were investigated. Effective doses were estimated by using LiF-TLDs placed at several organ sites in an Alderson-Rando phantom. Results: With pECG100%, the estimation of effective dose of data reconstructed using mono-segment (pECG100%_1S) reconstruction was 10.01 ± 0.56 mSv. For data acquired using pECG50%, the effective doses were 6.16 ± 0.12, 9.92 ± 0.37 and 13.51 ± 0.17 mSv in mono-segment (pECG50%_1S), two-segment (pECG50%_2S) and three-segment (pECG50%_3S) reconstruction, respectively. The effective dose of data acquired with pECG10% and reconstructed using mono-segment (pECG10%_1S) reconstruction was 3.61 ± 0.07 mSv. We observed a difference of around 7.46% between effective doses estimated using TLD-phantom measurement and CT dose index (CTDI) obtained from the scanner. Conclusion: For patients with low and intermediate heart rate, radiation exposure could be reduced by 38.6% or more by narrowing pulsing window width. Although slightly higher radiation dose was observed in multi-segment reconstruction, this method can be used in high heart rate patients to provide data of high temporal resolution without increasing radiation exposure when it is combined with prospective ECG triggering. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this study is to assess radiation dose and the corresponding image quality from suggested CT protocols which depends on different mean heart rate and high heart rate variability by using 256-slice CT. Fifty consecutive patients referred for a cardiac CT examination were included in this study. All coronary computed tomographic angiography (CCTA) examinations were performed on a 256-slice CT scanner with one of five different protocols: retrospective ECG-gating (RGH) with full dose exposure in all R–R intervals (protocol A), RGH of 30–80% pulsing window with tube current modulation (B), RGH of 78±5% pulsing window with tube current modulation (C), prospective ECG-triggering (PGT) of 78% R–R interval with 5% padding window (D) and PGT of 78% R–R interval without padding window (E). Radiation dose parameters and image quality scoring were determined and compared. In this study, no significant differences were found in comparison on image quality of the five different protocols. Protocol A obtained the highest radiation dose comparing with those of protocols B, C, D and E by a factor of 1.6, 2.4, 2.5 and 4.3, respectively (p<0.001), which were ranged between 2.7 and 11.8mSv. The PGT could significantly reduce radiation dose delivered to patients, as compared to the RGH. However, the use of PGT has limitations and is only good in assessing cases with lower mean heart rate and stable heart rate variability. With higher mean heart rate and high heart rate variability circumstances, the RGH within 30–80% of R–R interval pulsing window is suggested as a feasible technique for assessing diagnostic performance. [Copyright &y& Elsevier]