水模体摆放方式对CT性能测试结果的影响研究

目的 比较悬挂放置和床上放置两种模体摆放方式对CT值（水）、噪声、均匀性测试结果的影响，明确哪一种摆放方式更为合理。方法 按照GB 17589-2011中的方法进行实验。实验中分别采用两种模体摆放方式，一种是利用CATPHAN500模体箱将CTWV17型悬挂式水模体放置于碳纤维板床外；一种是直接将CTWV17型悬挂式水模体放置于碳纤维板床上。采用同一扫描条件，分别扫描5次并获取CT影像5幅，在影像上测量CT值（水）、噪声、均匀性。结果 CT值（水）测试中，采用水模体悬挂放置的测试方法，结果为（0.39±1.49）HU；采用水模体放置床上的测试方法，结果为（1.00±1.83）HU；采用配对的t检验进行均数的比较，t=-2.55，P=0.022。噪声测试中，采用水模体悬挂放置的测试方法，结果为0.23±0.06；采用水模体放置床上的测试方法，结果为0.25±0.08；采用配对的t检验进行均数的比较，t=-3.38，P=0.004。均匀性测试中，采用水模体悬挂放置的测试方法，结果为（0.47±0.66）HU；采用水模体放置床上的测试方法，结果为（-0.06±1.82）HU；采用配对的t检验进行均数的比较，t=4.25，P=0.001。两种放置方法CT值（水）、噪声和均匀性的实验结果均存在差异。结论 碳纤维床板对CT值（水）、噪声、均匀性有潜在影响，在测试CT值（水）、噪声和均匀性时，应当采用模体悬挂放置的方式。

Study of the effect of water phantom setting patterns on CT

Objective To compare the effects of two types of phantom setting methods (suspension and place-on-couch) on the CT value (water), noise and uniformity of performance test results, and to find out which mehtod is more reasonable.Methods According to the method in GB 17589-2011, two kinds of phantom place patterns were tested:suspend the CT-WV17 phantom on-the phantom box or directly place the CT-WV17 on couch. With the same scanning parameters, the phantom was scanned for 5 times at each setting patterns, and the CT value (water), noise and uniformity on the images were measured.Results For the CT value (water), the results were averaged to be (0.39±1.49) HU and (1.00±1.83) HU for different phantom setting patterns, respectively, and the difference was significant (t=-2.55, P=0.022). In noise test, the results were averaged to be (0.23±0.06) and (0.25±0.08) for the two methods, respectively, and the difference was also significant (t=-3.38,P=0.004). In the unifomity test, the averaged results were (0.47±0.66) HU and (-0.06±1.82) HU for the two setting patterns, respectively, the significant difference (t=4.25,P=0.001) was also observed.Conclusion Carbon fiber couch has a potential impact on CT value (water), noise and uniformity. When testing CT value (water), noise and uniformity, the phantom-suspension should be used.