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| Measurement studies on the CTDI of wide-beam multi-slice spiral CT |
| XU Hui1, WANG Jianchao1, HUANG Zhuo1, YUE Baorong1, FENG Zechen2 |
1. Key Laboratory of Radiological Protection and Nuclear Emergency, China CDC, National Institute for Radiological Protection, Chinese Center for Disease Control and Prevention, Beijing 100088 China;
2. Beijing Center for Disease Prevention and Control |
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Abstract Objective To study the relationship between the nominal beam width and CTDI measurement efficiency of wide beam multi-slice spiral CT to provide data support for improving the specification for quality control testing of CT in China.Methods Dose measurements were performed on a 128 detector row CT scanner. The effect of beam widths on CTDI100 and CTDI300 was assessed for acquisitions from 5 mm to 80 mm. The CTDI100 is based on application of the readily available 150 mm long CT dose body phantoms and the 100 mm pencil ionization chamber. CTDI300 is supported by measurements with extended 450 mm CT dose body phantom and a 300 mm long pencil CT ionization chamber. CTDI300 was used instead of CTDI∞ to calculate the CTDI measurement efficiency. An amended CTDI100,NT according to IEC and IAEA publications was calculated and compared with CTDI300.Results The CTDI100 measurement efficiency decreased with the increase of beam widths. The ratio of CTDI100 to CTDI300 was 0.62 from 5 mm, at a beam width of 80 mm, the measurement efficiency dropped to 0.56. Through the IEC and IAEA correction formula, the ratio of amended CTDI100,NT to CTDI∞ can be maintained at a relatively constant level.Conclusion The widely used CT dose index CTDI100 is lack of accuracy in evaluating the CT dose of wide-beam multi-slice spiral CT. The correction formula can characterize the dose level of wide beam multi-slice spiral CT to a constant ratio. On how to accurately express and measure the dose of wide beam CT by a simple way, the international community is still on the road.
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Received: 10 August 2017
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