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KMID : 1103720100620010029
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Journal of the Korean Society of Radiology
2010 Volume.62 No. 1 p.29 ~ p.35
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Image Quality and Radiation Exposure in Coronary CT Angiography According to Tube Voltage and Body Mass Index
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Kim Yoon-Kyung
Kim Yoo-Kyung
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Abstract
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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.
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KEYWORD
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Coronary Angiography, Body mass index, Radiation Dosage
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