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KMID : 1149020170190020027
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Journal of Korean Society of Computed Tomographic Technology
2017 Volume.19 No. 2 p.27 ~ p.36
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Comparative study on optimal noise index and radiation dose according to body weight versus body mass index (BMI) in abdomen pelvis CT
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Kim Eun-Ji
Lee Ki-Baek
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Abstract
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Purpose : Although Automatic Exposure Control (AEC) function in CT is known to modulate radiation dose according to patient's thickness, it does not run fully automatically. As the CT machine used in this study sets noise index (NI) and the range of tube currents before CT scanning, AEC cannot be flexibly applied to thin or obese patients. The purpose of this study was to investigate how AEC will be applied to various patients' size in practice and to find out the adequate parameter- weight (kg) or BMI (kg/m2)- for AEC application by assessing radiation dose and image quality.
Materials and Methods : 50 patients who underwent abdomen and pelvis (AP) CT with Lightspeed VCT XTe (GE Healthcare, Waukesha, USA) were enrolled in this study. Firstly, these patients were divided into three groups by NI: A (control group, NI=10.5), B (experimental group, NI=12.81), and C (experimental group, NI=14.8). Scan parameters were set equally in all groups. Secondly, patients were divided by weight classes (40-90kg; 5-kg interval scale) and each group included 15 cases. Then, obtained cases were divided into weights (5 groups; 10- kg interval scale) and the Asia-Pacific BMI. These data were evaluated by measuring noise, SNR, and radiation dose. For the evaluation of Iterative Reconstruction (IR) applied CT images, CT images were reconstructed as follows: only filtered back projection (FBP) for A group (control), FBP, ASIR 30%, and ASIR 50% for B and C group (experimental).
Results : Patients were divided into thin (<55kg or BMI<25), normal (40-55 kg or BMI 25-29.9), and obese (>80kg or BMI>30) groups by radiation dose. When setting NI 12.8 with ASIR 30% in thin group and NI 14.8 with ASIR 50% in obese group showed similar image quality at NI 10.5 with dose reduction.
Conclusion : Weight could be better than BMI when applying AEC in APCT. Good-quality CT image can be obtained even in thin or obese patients by applying adequate NI and AEC.
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KEYWORD
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BODY WEIGHT, BMI, AEC, ASIR, APCT
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