- 學位論文
利用SPC方法對CT球管性能進行評估之研究
Evaluation the Performance of CT X-Ray Tube by Statistical Process Control Method
摘要
背景與目的：電腦斷層造影儀器對於影像品質的要求是最高的並且為法規明文規定品保項目。因此對電腦斷層球管性能進行評估實為重要課題。 研究方法：本研究利用水假體影像實驗。使用直徑21公分、高20公分原廠水假體，資料收集時間為2014年5月2日至2015年5月4日，每日進行一次共367筆資料。每筆資料各有五種不同切面厚度，並且各自記錄五個不同位置的平均值。最後利用利用統計製程控制(statistical process control, SPC)方法繪製管制圖及其能力指標，對電腦斷層掃描儀球管性能進行評估。 研究結果：經由SPC管制圖發現水假體五種不同切面厚度影像之五點感興趣區域(ROI)平均值管制圖，在球管失效前即監測到異常。球管失效當日五種不同切面厚度影像之五點ROI平均值管制圖，都超過正常管制限值。更換球管以後，所有ROI平均值其值都在管制界限內。球管失效前切面厚度為1.25 mm影像之五點ROI平均值Cpk指標均低於1.67，表示X光球管性能已不穩定可能隨時失效。更換球管後水假體影像，五點ROI平均值Cpk指標均高於1.67代表X光球管性能穩定。 結論：利用SPC方法之管製圖與能力指標，應用於水假體切面厚度為1.25 mm影像ROI平均值，能提早發現球管失效或異常；其餘各切面厚度並無法提早發現異常。背景與目的：電腦斷層造影儀器對於影像品質的要求是最高的並且為法規明文規定品保項目。因此對電腦斷層球管性能進行評估實為重要課題。 研究方法：本研究利用水假體影像實驗。使用直徑21公分、高20公分原廠水假體，資料收集時間為2014年5月2日至2015年5月4日，每日進行一次共367筆資料。每筆資料各有五種不同切面厚度，並且各自記錄五個不同位置的平均值。最後利用利用統計製程控制(statistical process control, SPC)方法繪製管制圖及其能力指標，對電腦斷層掃描儀球管性能進行評估。 研究結果：經由SPC管制圖發現水假體五種不同切面厚度影像之五點感興趣區域(ROI)平均值管制圖，在球管失效前即監測到異常。球管失效當日五種不同切面厚度影像之五點ROI平均值管制圖，都超過正常管制限值。更換球管以後，所有ROI平均值其值都在管制界限內。球管失效前切面厚度為1.25 mm影像之五點ROI平均值Cpk指標均低於1.67，表示X光球管性能已不穩定可能隨時失效。更換球管後水假體影像，五點ROI平均值Cpk指標均高於1.67代表X光球管性能穩定。 結論：利用SPC方法之管製圖與能力指標，應用於水假體切面厚度為1.25 mm影像ROI平均值，能提早發現球管失效或異常；其餘各切面厚度並無法提早發現異常。
並列摘要
Background and purpose: It is important to obtain high quality of images by computed tomography (CT) according to the quality assurance with legal provision. Hence, it is crucial issue to evaluate the performance of X-ray tube for CT scanner. Research method: A water phantom with diameter 21 cm and height 20 cm were designed in this study during May 2, 2014 to May 4, 2015. The experiment was performed each day by CT scanner. Total 367 images were obtained for analysis. There were five different slicing thickness and five regions of interest (ROI) were designed for each image. The mean values of ROI were computed to perform statistical processing control (SPC) with control chart and capacity of SPC. Meanwhile, the control chart of mean and capacity of SPC (i.e., Cpk) were applied to monitor and detect the failure or hazard of X-ray tube on CT scanner. Research result: The control charts of mean of five ROI on five different slicing thickness images were shown abnormality. Especially, all of the control charts of mean on all images were immediately pointed out of control spec on the day that X-ray tube out of work. Meanwhile, all of the control charts of mean were returned to normality as change new x-ray tube. Moreover, the obtained Cpk by five means of ROI under slicing thickness 1.25 mm of water phantom was lower than 1.67. It represents instability of x-ray tube. Once x-ray tube was replaced by new one, the Cpk is over 1.67. It is demonstrated the stationary of x-ray tube. Conclusion: The control chart of mean computed from 1.25 mm slicing thickness of water phantom could early 47 days highlight the abnormality of x-ray tube as well as its Cpk. The images obtained from other slicing thickness could not early detect the instability of x-ray tube on CT scanner.