J Korean Soc Radiol.  2017 Oct;77(4):211-216. 10.3348/jksr.2017.77.4.211.

Windows Setting for Low kVp Abdominal CT: Comparison to 120-kVp CT Images

• Kim JS
• Choi JI
• Choi MH
• Park MY
• Rha SE
• Oh SN
• Jung SE
• Byun JY

• KMID: 2392116
• DOI: http://doi.org/10.3348/jksr.2017.77.4.211

Abstract

PURPOSE
The purpose of the study is to identify the optimal window level (WL) and window width (WW) to maximize visualization of the findings for low kVp abdominal CT images utilizing the automated tube voltage selection (ATVS) (which produces-brightness and contrast very similar to that produced by a 120-kVp CT scanner).
MATERIALS AND METHODS
We enrolled 61 patients who underwent: 1) dynamic abdominal CT scanning using ATVS technique (in 2015) and 2) a second CT scan, on this occasion implementing a 120-kVp protocol (in 2014). With ATVS, all scans were performed using 80-kVp for the arterial phase. For the portal phase, 80-kVp and 100-kVp were applied in 27 and 34 patients, respectively. Two radiologists then over-read and compared the ATVS images to the 120-kVp images, assessing brightness and contrast. After the over-read and comparison, they selected the WL and WW for ATVS because they produced brightness and contrast very similar to that appreciated in the 120-kVp images.
RESULTS
The WL and the WW for the arterial phase (mode/mean) were 130 Hounsfield unit (HU)/120.7 HU and 230 HU/259.6 HU, respectively. For the portal phase, the WL and the WW (mode/mean) were 90 HU/109.6 HU and 450 HU/450.0 HU for 80-kVp, and 40 HU/63.5 HU and 400 HU/382.4 HU for 100-kVp, respectively. The mean values of WL and WW for 80-kVp were significantly higher than those for 100-kVp (p < 0.001).
CONCLUSION
Based upon the findings, it was determined that WL and WW with ATVS should be higher than those used for 120-kVp protocol in order to obtain comparable brightness and contrast in the images produced by abdominal CT scanning.

MeSH Terms

Body Image
Humans
Radiation Dosage
Radiology Information Systems
Tomography, X-Ray Computed*

Figure

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  Fig. 1 An 81-year-old male with hepatocellular carcinoma, treated by right hemi-hepatectomy. A, B. The arterial phase images acquired using (A) 120-kVp and (B) 80-kVp at the same window width of 180 HU and window level of 80 HU. The 80-kVp image is too bright compared to the 120-kVp image. HU = Hounsfield unit

• 

  Fig. 2 A 47-year-old male with hepato-cellular carcinoma, treated by transarterial chemoembolization. A. The arterial phase image acquired using 120-kVp in 2014 with a window width of 180 HU and a window level of 80 HU shows multiple lipiodolized lesions in the left hemi-liver. B. The arterial phase image acquired using 80-kVp in 2015 with the same window setting as (A) shows too much contrast and brightness. Lipiodol uptake is not clearly visible. C. The same image of (B) with a window width of 350 HU and a window level of 130 HU shows similar brightness and contrast as (A). HU = Hounsfield unit

• 

  Fig. 3 A 52-year-old female with hepato-cellular carcinoma treated by transarterial chemoembolization. A. The portal venous phase image, acquired using 120-kVp in 2014 with a window width of 350 HU and a window level of 40 HU shows, appropriate brightness and contrast. B. The portal venous phase image, acquired using 80-kVp in 2015 with the same window setting as (A), is considered too bright for optimal visualization. C. The same image of (B), with a window width of 450 HU and a window level of 90 HU, demonstrates brightness and contrast similar to (A). HU = Hounsfield unit

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