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Keywords:
Abdomen, CT, Radiation safety
Authors:
J. I. Choi, S. B. Park, J. Hur, J. B. Lee, H. J. Park, Y. S. Kim; Seoul/KR
DOI:
10.1594/ecr2015/C-0782
Aims and objectives
PURPOSE: To compare radiation dose and image quality in regular,
low,
and ultralow dose CT protocols,
and to evaluate diagnostic performance of low dose CT for urolithiasis.
Introduction
Urolithiasis is a common health problem,
and its estimated lifetime risk is 5-10% in Europe and the United States [1-3].
An increase in incidence and prevalence of the disease has been reported worldwide in both children and adults [4-7].
For these patients,
multi-detector computed tomography (MDCT) provides a rapid and accurate examination with high sensitivity,
specificity and accuracy (100%,
96% and 98%,
respectively) [8].
Furthermore,
because of the low detection rate of other modalities including intravenous pyelography or ultrasonography,
MDCT has emerged as the frontline diagnostic modality [9,
10].
As MDCT usage becomes more widespread,
the importance of radiation exposure is becoming a concern.
There were considerable increases of total effective radiation doses and the proportion of medical sources in the past decades.
Among the man-made sources,
MDCT is the largest proportion,
accounting for about one-half [11].
Although debatable,
there are increasing concerns that even a single typical abdomen CT examination may increase the risk of carcinogenesis [12].
Because of multiple MDCT examinations during treatment and the relatively high recurrence rate of urolithiasis,
the patient’s lifetime cumulative radiation exposure can be higher,
especially in young patients.
For these reasons,
many investigators have made an effort to decrease the effective dose of MDCT for urolithiasis,
using a low-dose approach that results in an estimated dose from 0.7 to 4.2 millisieverts (mSv) [13].
Lowering the effective dose decreases the quality of the image due to the excessive image noise,
potentially causing a decrease in diagnostic performance and confidence.
Therefore,
the as low as reasonably achievable (ALARA) principle is used to achieve the lowest radiation dose possible while maintaining an optimal image quality in MDCT examinations [14].
The iterative reconstruction (IR) algorithms have been introduced and many studies have reported improved image quality and radiation dose reduction while maintaining diagnostic performance compared to filtered back-projection (FBP) [15].
There are several statistical IR algorithms commercially available and a few knowledge or model-based IR algorithms have investigated and introduced more recently.
Due to the differences in each algorithm and the reconstructed images,
there are different advantages and disadvantages.
The purpose of this study was to compare the radiation dose,
and the objective and subjective image qualities in regular dose,
low dose,
and ultralow dose MDCT protocols reconstructed by FBP,
statistical IR and knowledge-based IR.
We also evaluated the differences in diagnostic performance between regular dose and low dose protocols for urolithiasis.