Original Research Article
Radiation dose reduction with increasing utilization of prospective gating in 64-multidetector cardiac computed tomography angiography

https://doi.org/10.1016/j.jcct.2011.06.005Get rights and content

Background

Medical radiation exposure is a major concern, and several methods have been proposed to reduce radiation doses in multidetector cardiac computed tomography (CT).

Objective

The purpose of this study was to review radiation doses of clinical cardiac CT performed at our center and to evaluate the effect of radiation dose reduction strategies on the median dose delivered to patients over time.

Methods

This study included 623 consecutive clinical patients (male, 58%) who were referred for imaging. The effective dose (mSv) was derived from the product of the dose-length-product (DLP) and a conversion coefficient for the chest (0.014).

Results

The median radiation dose of all patients was 3.0 mSv (interquartile range [IQR], 1.9–8.1 mSv). A significant difference was observed in radiation dose between the prospective (n = 384) and retrospective (n = 239) gating groups (2.0 vs 9.6 mSv; P < 0.0001). Compared with patients with coronary artery bypass grafting (CABG; n = 52), patients without CABG had significantly lower median radiation dose (prospective gating: 2.0 vs 3.4 mSv, P < 0.0001; retrospective gating: 9.3 vs 10.3 mSv, P < 0.0001). In patients with CABG, a significant difference was observed in radiation dose between prospective and retrospective gating (3.4 vs 10.3; P < 0.0001). The median radiation doses per month at our center decreased from 6.2 to 2.1 mSv over time with increasing use of prospective gating (≤91%).

Conclusion

Radiation reduction techniques have led to progressive decreases in radiation exposure over time, primarily because of prospective gating.

Introduction

Over the past decade, rapid developments were made in noninvasive coronary imaging modalities, including the evolution of multidetector computed tomography (CT) scanner technology from the initial 4-detector to the current 64-, 256-, and 320-detector models.1, 2, 3, 4, 5 Spatial and temporal resolutions have improved significantly along with diagnostic accuracy, and coronary CT angiography (CTA) has since become the preferred first-line test of a growing number of cardiologists in the evaluation of coronary artery disease (CAD), providing both plaque characteristics and stenosis severity.6 Coronary CTA is traditionally acquired with the use of retrospective electrocardiographic (ECG) gating, in which multiple phases of data are acquired throughout the cardiac cycle. This type of image acquisition offers the added advantage of ejection fraction and wall motion evaluation at the expense of increased radiation dose. Although this radiation exposure (13–18 mSv)2 is comparable to effective doses of standard myocardial perfusion imaging techniques,7 it is still 5–8 times the estimated value of worldwide average annual natural radiation exposure of 2.4 mSv.8

Multiple different methods have been reported to reduce the radiation dose of coronary CTA, including limiting craniocaudal scan length, reducing tube voltage (kV), minimizing the field of view (FOV), dose (mA) modulation (automatic tube current adjustment according to the baseline ECG or patient's body habitus), and the use of prospective ECG-triggered imaging.9, 10 Use of these techniques can result in dramatic reductions in total radiation exposure. The use of prospective ECG-triggered scanning techniques has increased over time with significant reductions in radiation exposure per scan compared with retrospective image acquisition protocols without compromise of image quality. Although lower radiation doses obtained with prospective triggering have been reported, little data are available on the effect of increasing utility and the reduction in mean doses delivered. The purpose of this study was to evaluate the actual mean monthly radiation dose reductions in a clinical practice for coronary CTA with increasing use of prospectively triggered study.

Section snippets

Study population

This was a prospective observational study that 623 patients (males, 58%) referred to our center for evaluation of CAD from April 2008 to June 2009. All patients were ≥18 years of age and referred for chest pain, abnormal stress test, shortness of breath, or syncope. Patients with known CAD (stents, coronary artery bypass grafting [CABG], myocardial infarction) were included. Exclusion criteria for the study included known allergy to iodine, atrial fibrillation, or renal failure (estimated

Results

Among 623 patients, 551(88%; 361 prospective gating, 190 retrospective gating) achieved a HR < 65 beats/min. The median coronary CTA radiation dose of all patients was 3.0 mSv (IQR, 1.9–8.1 mSv). A significant difference was observed in radiation dose between prospective gating (n = 384) and retrospective gating (n = 239) subjects (2.0 mSv [IQR, 1.8–2.9 mSv] vs 9.6 mSv [IQR, 7.7–12.6 mSv]; P < 0.0001). Patients without CABG (n = 571; male 56%) comprised 92% of total patients. Among 52 patients

Discussion

Critics of coronary CTA imaging cite the high radiation dose used, especially in retrospective gating acquisition mode, despite the modality's ability to provide high image quality and functional information, including wall motion and ejection fraction.13, 14 Although several studies have previously shown the radiation dose reduction of prospective triggering compared with retrospective imaging, no prior studies have documented the overall dose reduction of a clinical coronary CTA laboratory

Conclusion

The overall median radiation doses dropped by 66% over 14 months because of the increasing use of prospective imaging, along with other dose reduction strategies for 623 consecutive patients in our clinical laboratory. Routine application of currently available radiation dose-reduction techniques should reduce radiation exposure in coronary CTA.

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Conflict of interest: M.J.B. is on the Speaker's Bureau (modest) for GE Healthcare. The other authors report no conflicts of interest.

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