Fanbeam准直器与平行孔准直器的性能比较

A Comparative Study of Fanbeam Collimator and Parallel-hole Collimator

目的 比较两种准直器的能峰响应、探测灵敏度、计数随采集窗宽变化的响应、计数随探测距离变化的响应等特性 ,评估 Fanbeam准直器性能特点 ,为临床更好地应用 Fanbeam准直器提供参考。方法 制作一个活度为 1.85× 10 8Bq(5 m Ci)的 99m Tc点源 ,分别用 Fanbeam准直器和平行孔准直器进行能峰检测、探测灵敏度检测、计数随采集窗宽变化和随探测距离变化的检测。结果 两种准直器的能谱响应无差异 ,与系统的固有能量响应曲线相一致。Fanbeam准直器的探测灵敏度高于平行孔准直器 ,最小探测距离条件下 ,灵敏度提高 10 0 %。采集计数随窗宽变化的响应特性 ,两种准直器相一致。配置平行孔准直器 (HPC- 4 5 ) ,计数随探测距离的变化不明显 ;配置Fanbeam准直器 (HU FB- 75 ) ,探测距离在 0～ 34cm的范围内 ,计数随探测距离的增加而增加 ,34cm处计数最大 ,探测距离大于 34cm ,计数随探测距离的增加而减少。结论 应用 Fanbeam准直器 ,系统的能量分辨率不受影响。Fanbeam准直器的探测灵敏度是平行孔准直器的 2倍以上。应用 Fanbeam准直器 ,其适宜的采集窗宽为 10 %～30 %。 Fanbeam准直器有一个特有的探测聚焦线 (Focal line) ,本文实测 HU FB- 75准直器的焦距为 34cm。

Objective This study was conducted to evaluate and compare the characters of HUFB 75 Fanbeam collimator and HPC 45 parallel hole collimator. Methods The response on energy was measured by PHA. The sensitivity was measured by static acquisition. The response on counts versus the change of acquisition windows (step=2%) and distance (step=1 cm) was measured by a series static acquisition. All of the above tests were performed with Fanbeam and parallel hole. Results The response on energy was identical. The sensitivity of Fanbeam collimator was over two times higher than that of parallel hole collimator. The response on counts versus the change of windows was identical. The counts had no significant difference with the change of distance for parallel hole collimator. For Fanbeam collimator, the counts increased with the increasing of distance in the range from 0 to 34 cm, the maximum counts occurred at the point of 34 cm, over this point, the counts decreased with the increasing of distance. Conclusion The energy resolution of SPECT was unchanged with Fanbeam collimator. The sensitivity of Fanbeam collimator was better than that of parallel hole collimator. The optimized acquisition windows for Fanbeam collimator ranged from 10% to 30%. Fanbeam collimator had a focal line, the focal distance of HUBF 75 was 34 cm.