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KMID : 1131320160180010047
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Journal of Korean Society of Computed Tomographic Technology
2016 Volume.18 No. 1 p.47 ~ p.56
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The Effect of Radiation Dose and Image Quality using AEC(Automatic Exposure Control) with Inappropriate Scout images: A Chest Phantom Experiment with Two Different AEC Modes
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Lee Ki-Baek
Kim Jung-Hoon
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Abstract
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Purpose : AEC is commonly used in most CT exams except for head CT. In order to use AEC properly, users have to acquire an ideal scout image. But, sometimes, this rule is broken. Thus, the purpose of this study was to evaluate the effect of automatic exposure control (AEC) with inappropriate scout image on radiation dose using a chest phantom with two different CT machines.
Materials and methods : Scout images of a Chest Phantom were obtained in three ways with two different AEC mode: First image included all chest parts of shoulder, lung field and liver(Normal scout), second image is cut in liver portion(Liver cut scout) and third image is cut in neck portion(Neck cut scout). And then, chest CT was done with same scan length. For chest CT, the difference of tube current (mA) and image noise within neck and liver portion was measured and compared.
Results : Tube currents (mA) of chest scan images were different according to acquired scout image. Compared Normal scout with Liver cut scout, mA within liver portion was decreased about 50% and with Neck cut scout, mA within neck portion was increased about two~three times. In comparison, image noise was inversely related.
Conclusion : Inappropriate scout image cause malfunction of AEC. Depending upon the location where scout image is cut off, AEC can increase or decrease the tube current at specific parts in CT examination. So, It is important to take a suitable scout image to give an ideal radiation dose on images.
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KEYWORD
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AEC, Normal scout , Liver cut scout, Neck cut scout, Dose, Image noise
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