Effect of bismuth breast shielding on radiation dose and image quality in coronary CT angiography

Cardiology Division, Department of Medicine, Columbia University Medical Center/New York-Presbyterian Hospital, 622 West 168th Street PH 10-203A, New York, NY 10032, USA.
Journal of Nuclear Cardiology (Impact Factor: 2.94). 11/2011; 19(1):100-8. DOI: 10.1007/s12350-011-9473-x
Source: PubMed


Coronary computed tomographic angiography (CCTA) is associated with high radiation dose to the female breasts. Bismuth breast shielding offers the potential to significantly reduce dose to the breasts and nearby organs, but the magnitude of this reduction and its impact on image quality and radiation dose have not been evaluated.
Radiation doses from CCTA to critical organs were determined using metal-oxide-semiconductor field-effect transistors positioned in a customized anthropomorphic whole-body dosimetry verification phantom. Image noise and signal were measured in regions of interest (ROIs) including the coronary arteries.
With bismuth shielding, breast radiation dose was reduced 46%-57% depending on breast size and scanning technique, with more moderate dose reduction to the heart, lungs, and esophagus. However, shielding significantly decreased image signal (by 14.6 HU) and contrast (by 28.4 HU), modestly but significantly increased image noise in ROIs in locations of coronary arteries, and decreased contrast-to-noise ratio by 20.9%.
While bismuth breast shielding can significantly decrease radiation dose to critical organs, it is associated with an increase in image noise, decrease in contrast-to-noise, and changes tissue attenuation characteristics in the location of the coronary arteries.

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Available from: Bin Cheng, Mar 17, 2015
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    ABSTRACT: Objective: The purposes of this essay are to describe the effects of bismuth breast shielding on radiation exposure of the breast and posterior chest wall and to present arguments for and against the use of breast shields. Conclusion: Breast tissue may receive substantial radiation doses during CT examinations. Bismuth shields effectively reduce breast exposure at the expense of increased noise and artifacts. Because bismuth shields reduce radiation transmission in all directions, posterior-to-anterior irradiation results in wasted exposure of posterior tissues. Similar breast radiation reductions can be achieved without shielding by globally reducing tube current. In general, more advanced methods of reducing exposure, including dose modulation and iterative reconstruction techniques, are superior if available.
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    ABSTRACT: The purpose of this study is to compare the image quality of coronary CT angiography performed with and without breast shields. This study involved a retrospective cohort of 72 women with possible angina who underwent 64-MDCT retrospective ECG-gated coronary CT angiography at a single academic tertiary medical center. Images of 36 women scanned while wearing bismuth-coated latex breast shields and 36 control subjects scanned without shields, matched by heart rate and body mass index, were graded on a standardized Likert scale for image quality, stenosis, and plaque by two independent board-certified readers blinded to breast shields. Seventy-two patients (mean [± SD] age, 53 ± 9 years) were included. The pre scan heart rate, body mass index, and Agatston score did not differ between groups. The median estimated radiation dose was 13.4 versus 16.1 mSv for those with and without breast shields (p = 0.003). For shielded versus unshielded scans, 86% versus 83% of coronary segments were rated excellent or above average (p = 0.4), median image quality was 2.0 for both groups, mean signal was 474 ± 75 and 452 ± 91 HU (p = 0.27), mean noise was 33.9 ± 8.5 and 29.8 ± 8.3 HU (p = 0.04), and median signal-to-noise ratio was 14.4 and 14.7 (p = 0.56), respectively. Breast shields for women undergoing coronary CT angiography slightly increased noise but did not negatively affect signal, signal-to-noise ratio, quality, or interpretability. Breast shield use warrants further study.
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