Fukuda Atsushi, Ichikawa Nao, Fujita Yoshiharu, Lin Pei-Jan Paul, Matsubara Kosuke, Miyati Tosiaki
Division of PET Imaging, Shiga Medical Center Research Institute, 5-4-30 Moriyama, Moriyama, Shiga 524-8524, Japan.
Department of Radiology, Shiga Medical Center for Adults, 5-4-30 Moriyama, Moriyama, Shiga 524-0022, Japan.
Phys Med. 2017 May;37:43-48. doi: 10.1016/j.ejmp.2017.04.008. Epub 2017 Apr 19.
The purpose of this study was to develop a gantry overrun corrected CTDI (cCTDI) dosimetry and evaluate the differences between the displayed CTDI (dCTDI), measured CTDI (mCTDI), and the cCTDI.
The each 8 rotation times between 275 and 1000ms of two CT scanners were investigated. Rotation time (T) and the beam-on time (T) in axial scanning were measured accurately to determine the gantry overrun time (T) as T-T. Subsequently, mCTDI was measured by using a 100mm ionization chamber and CTDI phantoms. Furthermore, we introduced a gantry overrun correction factor (C=T/T) to obtain cCTDI. Upon completion of the data acquisition, the dCTDI and mCTDI were compared with the cCTDI.
The discrepancies of T were 0.2±0.2ms as compared to the preset rotation times, and T was machine-specific and almost constant (22.4±0.5ms or 45.1±0.3ms) irrespective of the preset rotation time. Both dCTDI and mCTDI were increasingly overestimated compared to cCTDI as the faster the preset rotation time was selected (1.7-23.5%).
The rotation time influences the accuracy of CTDI in modern CT, and should be taken into consideration when assessing the radiation output in modern CT.
本研究的目的是开发一种机架超程校正的CTDI（cCTDI）剂量测定法，并评估显示的CTDI（dCTDI）、测量的CTDI（mCTDI）和cCTDI之间的差异。
研究了两台CT扫描仪在275至1000毫秒之间的每8次旋转时间。精确测量轴向扫描中的旋转时间（T）和束流开启时间（T），以确定机架超程时间（T）为T - T。随后，使用100毫米电离室和CTDI体模测量mCTDI。此外，我们引入了机架超程校正因子（C = T/T）以获得cCTDI。数据采集完成后，将dCTDI和mCTDI与cCTDI进行比较。
与预设旋转时间相比，T的差异为0.2±0.2毫秒，并且T是特定于机器的，并且几乎恒定（22.4±0.5毫秒或45.1±0.3毫秒），与预设旋转时间无关。随着预设旋转时间选择得越快，dCTDI和mCTDI与cCTDI相比都越来越被高估（1.7 - 23.5%）。
旋转时间会影响现代CT中CTDI的准确性，在评估现代CT的辐射输出时应予以考虑。
