PET/CT显像中飞行时间技术对图像质量的评估

Study of Time-of-flight Influence on Image Quality by PET/CT Scanner

目的:研究飞行时间(TOF)技术对PET/CT图像质量的影响,并通过蒙特卡罗方法模拟验证TOF技术的优越性。方法:使用拥有TOF技术的飞利浦Gemini TF型号PET/CT,通过模体扫描分析不同采集计数下TOF重建和non-TOF重建图像的对比度变化。使用蒙特卡罗方法建立PET/CT仪器几何模型和物理过程,模拟PET/CT活度-计数特性曲线和不同时间分辨率下的信噪比(SNR)。结果:从模体实验所获得的图像比较中可以直观地看到,与non-TOF图像比较,TOF图像更加清晰,其均匀性、病灶轮廓区分度、鉴别小病灶的能力和病灶与本底的对比度等均明显优于non-TOF重建图像,特别是在低计数采集条件下,对比度可提高10%。蒙卡模拟PET的计数特性表明,符合计数和SNR随着活度的增大而增大,但在高活度区域随机符合计数过多并且SNR增长缓慢。SNR和时间分辨率成反比关系,时间分辨率越小,SNR越高,520 ps时间分辨率的SNR相较1 000 ps时间分辨率的SNR提高约50%。结论:使用TOF技术的PET/CT可以明显提高图像质量,减少扫描时间和注射用药剂量。

Objoollw To investigate the benefits of time-of-flight（TOF） technology on image quality in a PET/CT scanner, and to apply Monte Carlo method to simulating some performances of PET/CT with TOF capability, Methods Philips GEMI- NI TF PET/CT was used for phantom scan studies. The raw data were acquired and reconstructed using TOF and non-TOF methods. The contrast of TOF and non-TOF images were compared and analyzed in different experiment conditions. The PET/CT scanner＇s geometry and physics models were established using Monte Carlo method and the PET/CT counting per- formance and signal-to-noise（SNR） were simulated in different time resolutions. Results Research results stated that PET images quality was clear and contrasts were good with TOF technology. The contrast could be improved by 10%, especially in low counts and small lesion. Monte Carlo simulation showed shat coincidence counts and SNR increased with activity. However, in higher activity region there were much more random counts and the SNR increased slowly. The relation be- tween SNR and the time resolution was that the less the time resolution, the higher the SNR gained. The SNR of 520 ps time resolution was improved by 50% larger than that with 1 000 ps time resolution. C_,onduaion The PET/CT image quality can be improved using TOF technology, and short scan time and low dose can be gained at the same image quality.[Chinese Medical Equipment Journal,2013,34（1 ） ： 8-11]