SPECT探头屏蔽性能的测量与评价

Measurement and evaluation of shielding effectiveness of SPECT detector

目的:探讨单光子发射断层扫描(SPECT)探头屏蔽性能的测量及评价,为SPECT性能评估提供参考。方法:按照美国电气制造商协会(NEMA)NU1-2007方法,对SPECT机型Ⅰ型和Ⅱ型2种机型的SPECT探头屏蔽性能进行测量,用特定位置点源的计数率与探头中心处点源的计数率百分比值,评价探头的屏蔽泄漏性能。结果:对患者体内成像视野外放射性活度的屏蔽性能,在距探头边缘10 cm、20 cm和30 cm位置处,机型Ⅰ的2个探头屏蔽泄漏平均值分别为0.663%、0.123%和0.033%,机型Ⅱ分别为0.683%、0.295%和0.143%。对探头附近患者之外放射性活度的屏蔽性能,在距探头中心50 cm、100 cm、150 cm和200 cm位置处,检查床机架前方(F方向)机型Ⅰ两个探头在各方向点位时屏蔽泄漏平均值分别为0.024%、0.025%、0.026%和0.024%,机型Ⅱ分别为0.095%、0.098%、0.096%和0.105%;垂直于检查床方向(S方向)机型Ⅰ两个探头在各个方向点位时屏蔽泄漏平均值分别为0.073%、0.073%、0.070%和0.075%,机型Ⅱ分别为0.180%、0.183%、0.187%和0.198%。结论:SPECT机型Ⅰ和机型Ⅱ的两个探头的屏蔽性能无明显差别;视野外患者体内放射性物质对图像质量的影响高于患者体外;机型Ⅰ的屏蔽性能明显优于机型Ⅱ。

Objective: To explore the measurement and evaluation of shielding effectiveness of SPECT detector so as to provide reference for performance assessment of SPECT. Methods: The shielding effectiveness of SPECT detector of two types of SPECT were measured according to the method of NEMA NU1-2007. And the shielding effectiveness of the detector was described as the percentage(%) of the count rate of point source of specific location and the count rate of point source of the center of detector. Results: For the shielding effectiveness of radioactivity outside visual field for in vivo imaging of patients, the average percentages of shielding leakage of two detectors of type I were 0.663%, 0.123% and 0.033% at 10 cm, 20 cm and 30 cm apart from the edge of detector, respectively, while that of type II were 0.683%,0.295% and 0.143%. For the shielding effectiveness of radioactivity besides the patients near the detector, at the locations of 50 cm,100 cm,150 cm and 200 cm apart from the center of detector, the average values of shielding leakage of point location of two detectors of type I at each direction were 0.024%, 0.025%, 0.026% and 0.024% on the front of rack of check bed(F direction), respectively, and that of type II were 0.095%, 0.098%, 0.096% and 0.105%. Besides, the average values of shielding leakage of point location of two detectors of type I at each direction were 0.073%,0.073%,0.070% and 0.075% on the direction that was vertical to the check bed(S direction), respectively, and that of type II were 0.180%, 0.183%, 0.187% and 0.198%. Conclusion: There is no significant difference in the shielding effectiveness of two detectors of each equipment type. The effect of radioactivity in vivo of patients outside the visual field on image quality is higher than that in vitro of patients. And the shielding effectiveness of type I is significantly better than that of type II.