Journal List > J Korean Soc Radiol > v.62(1) > 1086734

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Kim and Kim: Image Quality and Radiation Exposure in Coronary CT Angiography According to Tube Voltage and Body Mass Index
Interventional Radiology
Original Article

Journal of the Korean Society of Radiology 2010; 62(1): 29-35.

Published online: 31 January 2010

DOI: https://doi.org/10.3348/jksr.2010.62.1.29

Image Quality and Radiation Exposure in Coronary CT Angiography According to Tube Voltage and Body Mass Index

Yoon Kyung Kim, M.D., Yookyung Kim, M.D.2

1Department of Radiology, Korea University Guro Hospital, Korea University College of Medicine, Korea.

2Department of Radiology, Ewha Womans University MokDong Hospital, Korea.

Address reprint requests to: Yookyung Kim, M.D., Department of Radiology, Ewha Womans University MokDong Hospital, 911-1 MokDong YangCheon-ku, Seoul 158-710, Korea. Tel. 82-2-2650-5174, Fax. 82-2-2650-5071, yookkim@ewha.ac.kr

Received 26 April 2009       Accepted 26 July 2009

Copyright © 2010 The Korean Society of Radiology

Abstract

Purpose

To investigate the image quality and radiation dose of a coronary CT angiography (CCTA) according to tube voltage and body mass index (BMI).

Materials and Methods

This study included 139 patients who underwent CCTA using a retrospective electrocardiography-gating technique. A total of 48 patients (BMI <2 5, group A) were examined with 100 kVp, 45 patients (BMI > 25, group B) with 120 kVp, and 46 patients (BMI < 25, group C) with 120 kVp. Attenuation and image noise of the aorta and coronary arteries was measured. Moreover, the image quality of 9 coronary segments was graded on a scale of 1-5, where grade 4 or 5 was considered to be diagnostic. Image quality parameters and radiation dose were compared using a t-test or Chi-squared test.

Results

Vessel attenuation in group A was significantly higher than in groups B or C (group A, 592 ± 85 HU; group B, 437 ± 46 HU; group C, 469 ± 62 HU, p<0.001). Image noise was similar in group A and group B (23 ± 5 HU versus 22 ± 6 HU, p=0.427), but significantly higher in group A compared to group C (23 ± 5 HU versus 17 ± 4 HU, p<0.001). A significant difference was observed in the signal-to-noise ratio between the three groups (group A, 24 ± 6; group B, 19 ± 3; group C, 27 ± 5: p<0.05). Moreover, the contrast-to-noise ratio was significantly higher in group A than group B (group A 18 ± 5 versus group B 14 ± 3, p < 0.001) but not significantly different between group A and group C (group C 20 ± 4, p=0.127). The percentage of coronary segments with diagnostic image quality was 97.9% in group A, 96.0% in group B, and 99.0% in group C. The mean image quality score was 4.5 ± 0.5 in group A, 4.1 ± 0.4 in group B, and 4.2 ± 0,4 in group C (p<0.001). The effective radiation doses were 8.5 ± 0.8 mSv in group A, 14.3 ± 1.3 mSv in group B, and 14.9 ± 1.3 mSv in group C. A 42% reduction in mean effective radiation dose in group A was observed compared with groups B and C.

Conclusion

In patients with BMI less than 25 and a low-dose CCTA with 100 kVp leads to a significant reduction in radiation exposure without degradation of image quality.

Keywords: Coronary Angiography, Body mass index, Radiation Dosage

Figures and Tables

Fig. 1

Linear regression plot of mean vessel attenuation against body mass index shows significant negative dependency (r=-0.364, p<0.001). Solid line = mean; dashed lines = 95% confidence interval.

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Fig. 2

Linear regression plot of image noise against body mass index shows significant positive dependency (r=0.498, p<0.001). Solid line = mean; dashed lines = 95% confidence interval.

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Fig. 3

A-C. CT images in representative coronary CT angiography studies of group.

A. 44-year-old man from group A with BMI of 24.0 kg/m2. Axial CT image obtained at 100 kVp shows diagnostic image quality with vessel attenuation of 610 HU and image noise of 21 HU. Estimated radiation dose was 7.4 mSv.
B. 56-year-old woman from group B with BMI of 27.4 kg/m2. Axial CT image obtained at 120 kVp shows diagnostic image quality with vessel attenuation of 495 HU and image noise of 28 HU. Estimated radiation dose was 12.5 mSv.
C. 41-year-old man from group C with BMI of 23.5 kg/m2. Axial CT image obtained at 120 kVp shows diagnostic image quality with vessel attenuation of 518 HU and image noise of 14 HU. Estimated radiation dose was 14.6 mSv.
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Table 1

Patient Characteristics for the Three Groups

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Table 2

Objective Image Quality Parameters in Three Groups

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BMI=body mass index, HU=Hounsfield units, SNR=signal-to-noise ratio, CNR=contrast-to-noise ratio

Table 3

Subjective Image Quality Assessment in Three Groups

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Table 4

Radiation Dose Estimates in Three Groups

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