Original Research Article
Automatic Tube Potential Selection with Tube Current Modulation (APSCM) in coronary CT angiography: Comparison of image quality and radiation dose with conventional body mass index-based protocol

https://doi.org/10.1016/j.jcct.2012.04.002Get rights and content

Background

The use of Automatic Tube Potential Selection with Tube Current Modulation (APSCM) may lower radiation dose, but it is unknown whether image quality is maintained.

Objective

The aim of this study was to evaluate the radiation dose and image quality of APSCM application compared with conventional body mass index (BMI)–based examination protocol for coronary computed tomography angiography (CTA).

Methods

Consecutive patients (n = 487) were retrospectively enrolled: 239 patients who underwent coronary CTA with APSCM (APSCM group) and 248 patients who underwent coronary CTA with a BMI-based tube potential (in kV) and tube current-time product (in mAs) protocol (BMI-based group). Comparison of quantitative and qualitative image quality and radiation dose was performed.

Results

The use of APSCM found significant reduction in radiation dose compared with the BMI-based protocol, with a significantly more frequent use of 80 kV (P < 0.0001). Diagnostic image quality was maintained, with no significant difference between the 2 groups (P = 0.887).

Conclusion

The use of APSCM for coronary CTA significantly reduced radiation dose while maintaining image quality; therefore, it is feasible in daily practice which covers patients with various BMI values.

Introduction

Coronary CT angiography (CTA) is now widely acknowledged as a beneficial noninvasive imaging modality for the evaluation of coronary heart disease in the appropriate clinical scenario.1 However, with the increasing number of coronary CTA scans performed, there have also been increasing concerns on radiation dose safety, because coronary CTA has been shown to be associated with a nonnegligible lifetime attributable risk of cancer.2 Accordingly, remarkable advances have been made in both technology and coronary CTA protocols to achieve both high image quality and the lowest radiation dose possible.3

Until recently, tube potential (in kV) modulation has been a relatively uninvestigated area among strategies for radiation dose reduction. Generally, the radiation dose is proportional to the square of the tube potential in the setting of a constant tube current.4 Therefore, modulation of the tube potential holds promise in reducing radiation exposure.5, 6, 7 Furthermore, lower tube potential enhances iodine-induced contrast and thus is appropriate for high iodine contrast applications such as CTA. However, for larger patients higher noise levels are inevitable and thus may deteriorate image quality.8 Today, most institutions have a coronary CTA protocol that adapts tube potential and tube current-time product (in mAs) according to the patient’s body mass index (BMI; calculated as body weight in kg/height in m2) or other size-related parameters, and 80 kV is only applied to slim patients.

Automatic Tube Potential Selection with Tube Current Modulation (APSCM) is a recent software that automatically selects the tube potential and tube current-time product setting for each patient so that a user-chosen contrast-to-noise ratio (CNR) is maintained. Quality reference tube current-time product and reference tube potential are put in by the user to define and maintain image quality, and appropriate contrast gain settings are selected for each examination by choosing the examination type: noncontrast scans, soft tissue with contrast scans, and vascular scans. On the basis of attenuation information from a specific patient’s topogram, tube potential–specific tube current-time product curves for all tube potential levels (80 kV, 100 kV, 120 kV, or 140 kV) are calculated. The estimated dose is then obtained according to these tube potential–specific tube current-time product curves, and a dose-minimized tube potential is chosen. Although the tube potential is held constant, tube current-time product is automatically modulated throughout the examination by simultaneous application of a combined angular and z-axis modulation technique. In contrast, conventional examination protocols have used BMI or weight as a rough estimate of each patient’s attenuation profile for choosing tube potential and tube current-time product, and both are held constant throughout the examination.

The purpose of this study was to analyze the effects of APSCM in radiation dose reduction and image quality when applied to coronary CTA, in comparison with those of coronary CTA performed with conventional BMI-based examination protocols.

Section snippets

Study population

This study was approved by the institutional review board, and informed consent was obtained from all patients. Patients (n = 239) referred for coronary CTA from August to September 2011 were consecutively enrolled in this study and underwent coronary CTA with APSCM (hereafter referred to as the APSCM group). As a control group, 248 consecutive patients were included whom underwent coronary CTA by our institution’s previous BMI-based tube potential and tube current-time product protocol from

Patients and coronary CTA characteristics

The patient characteristics and coronary CTA parameters of both groups are summarized in Table 2. No significant difference was observed in sex, height, weight, and BMI between the 2 groups. In the APSCM group, the BMI range was between 16.32 and 34.17 (mean ± SD, 24.3 ± 3.27) and in the BMI-based group it was between 15.4 and 35.2 (mean ± SD, 24.3 ± 3.24). The APSCM group had a significantly lower HR, but the difference was <3 beats/min between the 2 groups. All scan modes were evenly

Discussion

This study shows that the application of APSCM to coronary CTA significantly reduces radiation dose while maintaining diagnostic image quality. We could show that the use of APSCM in an actual clinical setting of patients with various BMI values was feasible, which is of clinical significance because previous studies on low tube potential have only included patients below a designated BMI cutoff.6, 7, 10

In this study, the mean CT number and contrast enhancement of coronary arteries were

References (12)

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    As a result of the described differences in contrast and noise values between genders we found a significantly higher CNR in females. Park et al. and Layritz et al. analyzed CTCA data sets of 239 and 100 patients, respectively, who were examined using automated attenuation-based tube parameter selection [19,20]. Effective radiation dose was significantly lowered, while subjective image quality was maintained compared with data sets acquired using traditional BMI-based tube parameter selection.

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Conflict of interest: The authors report no conflicts of interest.

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