Towards Sub-Minute PET Examination Times
Towards Sub-Minute PET Examination Times
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DOI：
10.1109/tns.2010.2096542
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发表时间：
2011-02-01
影响因子：
1.8
通讯作者：
Bendriem, B.
中科院分区：
文献类型：
--
作者：
Eriksson, L.;Conti, M.;Bendriem, B.
正电子相机系统设计的主要性能参数是灵敏度和空间分辨率。本文涉及灵敏度，它是闪烁材料、探测器阵列所对的立体角和闪烁体填充分数的函数。通过延长圆柱形探测器系统的轴向范围可以增加立体角。大多数商用正电子相机系统都基于探测器块环，并使用正硅酸镥、LSO:Ce 或 LYSO:Ce 作为首选闪烁体。通过添加更多的环，立体角和绝对灵敏度都会增加，而假设晶体厚度相同，单个检测效率则保持相当恒定。研究表明，LSO:Ce 的 Ca 共掺杂可将闪烁衰减时间缩短至大约 30 ns，光输出超过 30000 ph/MeV。这一改进可能会带来飞行时间 (TOF) 优势，时间分辨率为 500 ps 或更小。如果大轴向视场 (AFOV) 系统的计数率灵敏度与 TOF 灵敏度的提高相结合，我们就有办法在亚分钟范围内创建检查时间，而不会影响图像质量。在本研究中，我们将现有的西门子分子 CT (mCT) 系统与未来带或不带 TOF 的 6、8、12、20 及更高块环系统进行了比较。 mCT 4 块环系统已用作参考。然后根据平面灵敏度将该系统达到可接受的图像质量的时间外推到其他系统。然而，平面灵敏度与立体角有关，并且对于大AFOV 来说达到饱和。这意味着存在计数率灵敏度上限。 20块环系统可以在一定的平面计数率下覆盖70厘米的检查范围，并且通过结合多环特征提供的高平面灵敏度计数率、LSO的高阻止能力以及由于改进的定时分辨率而带来的TOF增益，可以在大约10秒内提供可接受的质量图像。增加的灵敏度可用于减少患者剂量。
The main performance parameters in positron camera system design are sensitivity and spatial resolution. This paper concerns sensitivity, which is a function of the scintillation material, the solid angle subtended by the detector array, and the scintillator packing fraction. The solid angle can be increased by extending the axial extent of cylindrical detector systems. Most commercial positron camera systems are based on rings of detector blocks with lutetium oxyorthosilicate, LSO:Ce or LYSO:Ce, as the scintillator of choice. By adding more rings, the solid angle and thus the absolute sensitivity increases while the singles detection efficiency remains fairly constant assuming the same crystal thickness. It has been shown that Ca co-doping of LSO:Ce reduces the scintillation decay time to similar to 30 ns with a light output over 30000 ph/MeV. This improvement may give a time-of-flight (TOF) advantage with time resolution of 500 ps or less. If the count rate sensitivity of a large axial field-of-view (AFOV) system is combined with the TOF sensitivity increase, we have the means to create examination times in the sub-minute range with no compromise in image quality. In the present study we have compared the existing Siemens molecular CT (mCT) systems to future 6, 8, 12, 20 and higher block ring systems with and without TOF. The mCT 4 block ring system has been used as a reference. The time for acceptable image quality with this system is then extrapolated to other systems based on planar sensitivity. However, the planar sensitivity is related to the solid angle, and reaches saturation for large AFOVs. This implies that there is an upper count rate sensitivity limit. A 20 block ring system may cover a 70 cm examination range at a certain planar count rate and could provide acceptable quality images in approximately 10 seconds by combining the high planar sensitivity count rate provided by the multi-ring feature, the high stopping power of LSO and the TOF gain due to the improved timing resolution. The increased sensitivity may be used to reduce patient dose.