CT剂量指数的研究

Study of the Computed Tomography Dose Index.

目的 研究用不同积分区间 (± 7T和± 5 0mm)计算CT剂量指数 (CTDI)时对结果的影响。方法 用热释光剂量计 (TLD)在标准的CT剂量监测模体上 ,测量日立W -10 0 0型CT机的单层扫描的剂量分布曲线 ,根据分布曲线计算不同积分区所对应的CTDI值。结果 对层厚大于 7mm(10mm)的单层扫描 ,± 5 0mm积分长度所得的CTDI10 0 小于± 7T积分长度所得的CTDIF;对层厚小于 7mm(5mm)的单层扫描 ,则CTDI10 0 大于CTDIF。结论 当扫描层厚不是 7mm时 ,用 10 0mm活性长度的笔形电离室测得的CTDI10 0 与CTDIF 有差异 ,为了便于统一比较 。

Objective The impact on the computed tomography dose index(CTDI)value of varying integrating lengths(±7 T and±50 mm)is analyged.Methods A Hitachi W-1000 scanner was used with thermoluminescent dosimeters and computed tomography dosimetry phantoms.The dose profiles are measured for single scan and the corresponding CTDI calculated for varying integrating lengths.Results For slice thickness over 7 mm(10 mm),the CTDI 100 value obtained with ±50 mm of integrating length will underestimate the CTDI F.By contrast,for the slice thickness below 7 mm(5 mm),the CTDI 100 will overestimate the CTDI F.Conclusion The differences between CTDI 100 value and CTDI F are presented for varying slice thickness.The measured CTDI 100 value should be corrected for different slice thickness when using a pencil ionization chamber.