Published online Nov 28, 2014.
https://doi.org/10.3348/jksr.2014.71.6.278
Radiation Dose and Imaging Quality of Abdominal Computed Tomography before and after Scan Protocol Adjustment: Single-Institution Experience in Three Years
Abstract
Purpose
To compare radiation dose and image quality of abdominal CT for patients who underwent repeated CT examinations before and after adjustment of scan protocol.
Materials and Methods
We compared radiation dose and image quality of repeated abdominal CT scans (at three-year-interval) of 50 patients with chronic liver disease, 50 patients with early gastric cancer, and 50 patients with uterine cancer. To reduce radiation dose, we optimized CT protocols by omitting unnecessary pre-contrast phase, reducing kVp, and setting higher noise index. Data of dose reports were collected. Objective image quality was evaluated for noise level, signal to noise ratio (SNR), and contrast noise ratio (CNR). For subjective image quality, we evaluated image noise, contrast, and overall diagnostic acceptability.
Results
The mean values of dose length product of 2011 CT scans compared to those of 2008 CT scans were 27.6% to 45.7%. The image noise level, SNR, and CNR were significantly (p < 0.05) worse in 2011 CT scans compared to 2008 CT scans. For subjective image quality, image noise was also significantly (p < 0.05) worse in 2011. However, CNR and diagnostic acceptability showed variable results. No CT scans were considered as unacceptable image.
Conclusion
We modified abdominal CT protocols to reduce radiation exposure while trying to maintain diagnostic acceptability.
Fig. 1
A. A CT image was obtained in 2008. Measured image noise, signal to noise ratio, contrast to noise ratio were 11.30, 12.01, and 5.21, respectively. Overall diagnostic acceptability by two radiologists was 4. Volume CT dose index (CTDIvol) and dose length product (DLP) were 12.58 and 642.74, respectively. B. A CT image was obtained in 2011. Comparing to 2008 CT scan, 2011 CT scan shows substantially decreased quality with much more granular and noise image. Measured image noise, signal to noise ratio, contrast to noise ratio were 15.12, 10.14, and 4.64, respectively. Overall diagnostic acceptability by two radiologists was 3 (which means slightly degraded image quality, but acceptable). However, radiation exposure of 2011 CT is less than the half of 2008 CT (CTDIvol: 4.8; DLP: 241.67).
Axial CT images acquired in a 59-year-old female with known uterine cervical cancer.
Table 1
A Comparison of the General Characteristics of the Patients between the Groups of Liver CT, Uterus CT, and Stomach CT
Table 2
Scan Protocol Changes of Liver, Stomach, and Uterus CT
Table 3
A Comparison of the Radiation Dose Parameters
Table 4
A Comparison of the Quantitative Measuring Attenuation Parameters
Table 5
Mode and Minimum of the Subjective Image Quality
This study was supported by a grant from the Medical Device Safety Bureau, the Ministry of Food and Drug Safety.