J Korean Soc Radiol.  2016 Oct;75(4):285-295. 10.3348/jksr.2016.75.4.285.

100 kVp Low-Tube Voltage Abdominal CT in Adults: Radiation Dose Reduction and Image Quality Comparison of 120 kVp Abdominal CT

• Ha HI
• Hong SS
• Kim MJ
• Lee K

• KMID: 2353679
• DOI: http://doi.org/10.3348/jksr.2016.75.4.285

Abstract

PURPOSE
To compare image quality and the effect of radiation dose reduction after decreasing tube voltage from 120 kVp to 100 kVp for abdominal CT in adults.
MATERIALS AND METHODS
A total of 200 patients who underwent abdominal CT at 120 kVp (n = 100) or 100 kVp (n = 100) were enrolled. Automatic tube current modulation was applied with other scan parameters being constant. Radiation dose was calculated based on CT dosimetry index. The image quality of abdominal organs and image noise were assessed quantitatively and qualitatively.
RESULTS
A radiation dose reduction of 13.3% was found in the 100 kVp group. On quantitative analysis, image noise was increased up to 47% in the 100 kVp group. CT numbers of liver, pancreas, renal cortex, aorta, portal vein, and psoas muscle in the 100 kVp group were significantly (p < 0.05) higher than those in the 120 kVp group. Signal-to-noise ratio was significantly higher (p < 0.05) in the 120 kVp group. Contrast-to-noise ratio (CNR) of the liver was higher in the 120 kVp group. However, no significant (p > 0.05) difference was observed in the CNR of other organs between the two groups. On qualitative analysis, noise texture of abdominal organs, artifact, and diagnostic acceptability were not significantly (p > 0.05) different.
CONCLUSION
100 kVp abdominal CT reduced radiation dose by 13.3% without sacrificing image quality compared to 120 kVp abdominal CT.

MeSH Terms

Abdomen
Adult*
Aorta
Artifacts
Diagnostic Imaging
Humans
Liver
Noise
Pancreas
Portal Vein
Psoas Muscles
Signal-To-Noise Ratio
Technology, Radiologic
Tomography, X-Ray Computed*

Figure

• 

  Fig. 1 Body mass index distribution showing no significant difference between 120 kVp and 100 kVp groups (p = 0.9477).

• 

  Fig. 2 Quantitative analysis of image noise (mean ± SD). Image noise in the 100 kVp group (10.6 ± 3.8) was higher (p < 0.0001) that that (7.2 ± 1.5) in the 120 kVp group. SD = standard deviation

• 

  Fig. 3 Qualitative analysis of noise texture (mean ± SD). A. Hepatic noise texture is significantly (p = 0.0001) different between the two groups. B-D. Mean noise texture of pancreas, renal cortex, and psoas muscle is more than 2.8. There is no significant (p > 0.05) difference between the groups. CI = confidence interval, SD = standard deviation, k =interrater agreement

• 

  Fig. 4 Qualitative analysis of the artifact (mean ± SD). There is no significant (p = 0.192) difference in artifact rated by two readers between 120 kVp and 100 kVp groups. CI = confidence interval, SD = standard deviation, k = interrater agreement

• 

  Fig. 5 Qualitative analysis of diagnostic acceptability (mean ± SD). There is no significant (p = 0.216) difference in diagnostic acceptability scored by two readers between 120 kVp and 100 kVp groups. CI = confidence interval, SD = standard deviation, k = interrater agreement

• 

  Fig. 6 A 59-year-old male patient underwent gastrectomy of the gastric cancer with post-operative follow-up CT scans using 120 kVp (DLP, 631 mGy·cm) and 100 kVp (DLP, 567 mGy·cm) (window width/level, 45/400) tube voltage at 6-month intervals. A. Hepatic and pancreatic noise texture is rated at 3 points by both readers. SNR and CNR of liver are 19.9 and 8.6 on 120 kVp, respectively, versus 14.5 and 6.8 on 100 kVp. SNR and CNR of pancreas are 17.4 and 6.9 on 120 kVp, respectively, versus 13.2 and 6.0 on 100 kVp. B. SNR and CNR of renal cortex are 30.1 and 19.8 on 120 kVp, respectively, versus 25.9 and 17.8 on 100 kVp. CNR = contrast-to-noise ratio, DLP = dose length product, SNR = signal-to-noise ratio C. On magnification images, hepatic noise texture on 100 kVp shows more pixelated texture (dot-line circle) compared to that of 120 kVp. However, this difference can be hardly detected on normal scale image. The diagnostic acceptability is scored at 3 points by both readers. Estimated DLP reduction is 10.2%. DLP = dose length product

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