Korean J Radiol.  2015 Feb;16(1):13-20. 10.3348/kjr.2015.16.1.13.

Evaluation of a Chest Circumference-Adapted Protocol for Low-Dose 128-Slice Coronary CT Angiography with Prospective Electrocardiogram Triggering

• Lu C
• Wang Z
• Ji J
• Wang H
• Hu X
• Chen C

• KMID: 2069981
• DOI: http://doi.org/10.3348/kjr.2015.16.1.13

Abstract

OBJECTIVE
To assess the effect of chest circumference-adapted scanning protocol on radiation exposure and image quality in patients undergoing prospective electrocardiogram (ECG)-triggered coronary CT angiography (CCTA).
MATERIALS AND METHODS
One hundred-eighty-five consecutive patients, who had undergone prospective ECG triggering CCTA with a 128-slice CT, were included in the present study. Nipple-level chest circumference, body weight and height were measured before CT examinations. Patients were divided into four groups based on kV/ref.mAs = 100/200, 100/250, 120/200, and 120/250, when patient's chest circumference was < or = 85.0 (n = 56), 85.0-90.0 (n = 53), 90.0-95.0 (n = 44), and > 95.0 (n = 32), respectively. Image quality per-segment was independently assessed by two experienced observers. Image noise and attenuation were also measured. Signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) were calculated. The effective radiation dose was calculated using CT dose volume index and the dose-length product.
RESULTS
A significant correlation was observed between patients' chest circumference and body mass index (r = 0.762, p < 0.001). Chest circumference ranged from 74 to 105 cm, and the mean effective radiation dose was 1.9-3.8 mSv. Diagnostic image quality was obtained in 98.5% (2440/2478) of all evaluated coronary segments without any significant differences among the four groups (p = 0.650). No significant difference in image noise was observed among the four groups (p = 0.439), thus supporting the validity of the chest circumference-adapted scanning protocol. However, vessel attenuation, SNR and CNR were significantly higher in the 100 kV groups than in the 120 kV groups (p < 0.05).
CONCLUSION
A measure of chest circumference can be used to adapt tube voltage and current for individualized radiation dose control, with resultant similar image noise and sustained diagnostic image quality.

Keyword

Chest circumference; Computed tomography; Coronary angiography; Radiation dose; Image quality

MeSH Terms

Adult
Aged
Body Mass Index
Contrast Media/diagnostic use
Electrocardiography
Female
Heart/*radiography
Heart Rate
Humans
Male
Middle Aged
Prospective Studies
Radiation Dosage
Signal-To-Noise Ratio
Tomography, X-Ray Computed/*methods
*Waist Circumference
Contrast Media

Figure

• 

  Fig. 1 Linear regression plot showing significant correlation between chest circumference and body mass index (r = 0.762, p < 0.001).

• 

  Fig. 2 Curved-planar reconstruction of right coronary artery and volume-rendered trees demonstrating image quality of four CCTA protocols. A. Tube voltage 100 kV, tube current 200 mAs. B. Tube voltage 100 kV, tube current 250 mAs. C. Tube voltage 120 kV, tube current 200 mAs. D. Tube voltage 120 kV, tube current 250 mAs. ROI was placed at root of ascending aorta and image noise was similar in four groups, while image quality of coronary segments remained diagnostic. CCTA = coronary CT angiography, ROI = region of interest

• 

  Fig. 3 77-year-old man with BMI of 23.0 and chest circumference of 84.0 cm. Axial CT images obtained at 100 kV and 200 mAs show ascending aorta with image noise of 36 HU and vessel attenuation of 611 HU. BMI = body mass index, HU = Hounsfield unit

• 

  Fig. 4 45-year-old woman with BMI of 23.1 and chest circumference of 94.0 cm. Axial CT images obtained at 120 kV and 200 mAs show ascending aorta with image noise of 36.4 HU and vessel attenuation of 509.3 HU. This female patient had same BMI, but larger chest circumference, than male patient represented in Figure 3. Image noise was similar when chest circumference-adapted scanning protocol was used. BMI = body mass index, HU = Hounsfield unit

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