CT值-相对电子密度转换曲线的影响因素分析

目的 探讨本院使用不同扫描参数、电子密度体模和CT机对CT值-相对电子密度(CT-RED)转换曲线的影响因素。方法 在不同扫描电压、层厚下测量TM164CT性能模体和CIRS-062电子密度模体不同电子密度插件在东芝AQUILION^TM型、西门子SOMATOM^TMSENSATION^TM 64型CT和西门子SOMATOM^TMSENSATION^TM OPEN型CT机扫描的CT值,建立相应的CT-RED转换曲线并进行比较。结果 1、2、3 mm扫描层厚及不同扫描电流对CT值影响可忽略,低原子序数材料在不同型号CT、不同扫描电压下的CT值差异可忽略;不同扫描电压对高原子序数材料CT值有明显差异,同台CT机出现的最大差异约为400 HU;两种模体在软组织-致密骨范围内所提供的CT值有明显差异,最大可达约500 HU。结论 不同电子密度模体、CT机及扫描电压对CT-RED转换曲线高原子序数材料部分有影响,因此在治疗计划系统使用前必须根据临床使用条件选用合适的电子密度模体对该曲线进行测量,以保证治疗计划剂量计算的精确度。

Impact factor of relationships between CT value and relative electron density for treatment planning system

Objective To study the CT values of certain phantoms scanned by various CT scanners with dissimilar parameters. Methods The CT values of tissue equivalent inserts was measured in the TM164 and CIRS-062 phantom scanned by TOSHIBA AQUILION^TM, SIEMENS SOMATOM^TMSENSATION^TM 64 and SIEMENS SOMATOM^TMSENSATION^TM OPEN with different voltages, currents and slice thicknesses and then the corresponding CT-to-density curves was compared. Results There are no significant differences of CT values with various currents and slice thicknesses and also for low atom number materials scanned by different scanners with various tube voltages. The CT values of high atom number materials have obvious differences scanned with tube voltage, the maximum is about 400 HU. There are also significant differences between CT-density curves of two phantoms in the range from soft tissues to dense bone, the maximum is up to 500 HU. Conclusions CT-density curves were highly affected by materials of phantoms, scanners and tube voltages. It is necessary to measure the curve with a comfortable phantom and certain scanner to assure the accuracy for dose calculation for treatment planning system.