Akagi Noriaki, Ohkawa Y, Kadohisa S, Nakagiri Y, Hiraki Y
Central Division of Radiology, Okayama University Hospital.
Nihon Hoshasen Gijutsu Gakkai Zasshi. 2004 Dec;60(12):1664-5. doi: 10.6009/jjrt.kj00003560626.
It is for a purpose of this study to measure radiation dose by analyzing a dose profile of multi-slice computed tomography varying with helical pitch and a row slice thickness difference complicatedly.
We used multi-slice computed tomography, and helical pitch and row slice thickness change and scanned the helical scan. I used CTDI phantom of a diameter of 25 cm and I inserted roentgen diagnosis use film UR-2(new) which I put between my own phantom in center and 1 cm away from the outer surface and scanned it. And the provided level profile was converted into a dose profile with the dose-density curve which I made beforehand. I analyzed radiation dose than the dose profile.
In multi-slice computed tomography, radiation dose varied with assembly of row slice thickness and helical pitch. The change of a dose profile changed in a phantom surface part complicatedly. The maximum dose by the measurement of this time was 29 mGy in row slice thickness 0.5 mm, assembly of helical pitch 2.5. In addition, the minimum dose was 6.8 mGy in row slice thickness 3.0 mm, assembly of helical pitch 5.5. And, as for the difference of maximum dose in the same dose profile and the smallest dose, there were about 20 % in row slice thickness 1.0 mm, assembly of helical pitch 5.5.
The dosimetry of multi-slice computed tomography by a film method enabled it to measure a change of a dose profile by a difference of a scan parameter by high interest solution ability. In addition, it is a method more superior in dosimetry of multi-slice computed tomography spreading through a Z-axis direction broadly than determination by computed tomography use ionization chamber dosimeter. Because radiation dose increases by a scan in thin row slice thickness and small helical pitch, care is necessary.
本研究旨在通过分析多层螺旋计算机断层扫描随螺距和排层厚差异而复杂变化的剂量分布来测量辐射剂量。
我们使用多层螺旋计算机断层扫描，改变螺距和排层厚并进行螺旋扫描。我使用了直径为25 cm的CTDI体模，在体模中心与距外表面1 cm处放置了用于X线诊断的UR - 2（新型）胶片并进行扫描。然后将得到的层面分布用我预先制作的剂量 - 密度曲线转换为剂量分布。我根据剂量分布分析辐射剂量。
在多层螺旋计算机断层扫描中，辐射剂量随排层厚和螺距的组合而变化。剂量分布的变化在体模表面部分复杂地改变。此次测量的最大剂量在排层厚0.5 mm、螺距组合为2.5时为29 mGy。此外，最小剂量在排层厚3.0 mm、螺距组合为5.5时为6.8 mGy。并且，在排层厚1.0 mm、螺距组合为5.5时，同一剂量分布中最大剂量与最小剂量的差值约为20%。
通过胶片法对多层螺旋计算机断层扫描进行剂量测定，凭借高分辨率能力能够测量因扫描参数差异导致的剂量分布变化。此外，与使用计算机断层扫描电离室剂量仪进行测定相比，这是一种在沿Z轴方向广泛扩展的多层螺旋计算机断层扫描剂量测定中更优越的方法。由于在薄排层厚和小螺距扫描时辐射剂量会增加，所以需要谨慎。
