- 期刊
A Practical Method to Test Computed Tomography Automatic Tube Current Modulation Function
測試電腦斷層掃描儀自動管電流調控功能的方法
摘要
本研究提出一個測試電腦斷層掃描儀自動管電流調控功能的實用方法，利用常見的標準16及32公分直徑圓柱型均勻壓克力假體及10公分筆型空氣游離腔，量測電腦斷層體積劑量指標(修正值)，並紀錄每張切面的電流值及指定區域內的電腦斷層值之標準差。透過特殊的擺放設置，產生不均質假體的效果，可用以測試體型變化或受照體的材質變化，開啟自動管電流調控功能後，輻射劑量的調降效果及相對應的影像雜訊變化，第一組模擬厚度的變化，在10公分螺旋掃描範圍內，由直徑32公分實心圓柱假體變成16公分，當自動管電流調控功能開啟時，螢幕顯示每張切面的管電流降低比率在10.33%到65.67 %之間，指定區域內的電腦斷層值之標準差的差異分佈為+4.3至-1.0；第二組模擬不均質的變化，由32公分直徑實心變成32公分外徑16公分內徑空心圓柱假體，當自動管電流調控功能開啟時，螢幕所顯示的管電流由269降為244，又升高至283，再降至235，指定區域內的電腦斷層值之標準差的差異分佈為+3.3至-1.0，兩組測試均顯示開啟自動管電流調控功能可調降輻射劑量，而且不會造成影像中電腦斷層值之標準差的變化有大幅度增加。
並列摘要
This study provides a practical method for the test of automatic tube current modulation function on computed tomography(CT). Measuring modify volume CT dose index(CTDIvol-modify) and recording tube current of every slice standard deviation(S.D.) of CT numbers in selected regions with the use of standard 16 cm and 32 cm diameter cylindrical homogeneous acrylic phantom and 10 cm long pen-shape ionization chamber. Phantoms generate non-homogeneous effects with special set-up which can be used to test shape or material change. Radiation dose reduction and corresponding image noise change can be measured after automatic tube current modulation is turned on. The first set simulates thickness change within 10 cm helical scanning region when diameter decreased from 32 cm cylinder to 16 cm. Screen shows the tube current reduction rate is between 10.33% and 65.67 % while the difference distribution S.D. of CT numbers is between +4.3 and -1.0. Second set simulates non-homogeneous change where a 32 cm diameter cylinder phantom is changed to a 32 cm cylinder with 16 cm diameter hollow inside. Screen shows the tube current reduced from 269 to 244 then rise to 283 and drop to 235 while the difference distribution S.D. of CT numbers is between +3.3 and -1.0. Both tests demonstrate the automatic tube current modulation function may reduce radiation dose and dose not caused drastic increase on S.D. of CT numbers change of these images.