Schmitz Ruth E, Harrison Robert L, Stearns Charles W, Lewellen Thomas K, Kinahan Paul E
Department of Radiology, University of Washington, Seattle, WA 98195, USA.
IEEE Trans Med Imaging. 2007 Jul;26(7):935-44. doi: 10.1109/TMI.2007.895485.
We present a simulation study of the global count-rate performance of a positron emission tomography (PET) scanner with different levels of partial collimation to maximize the noise equivalent count rate for whole-body PET imaging. We achieve partial collimation by removing different numbers of septal rings from the standard 2-D septa set for the GE Advance PET scanner. System behavior is studied with a photon tracking simulation package, which we modify to enable the production of random coincidences. The simulations are validated with measured data taken in 2-D and fully 3-D acquisition mode on a GE Advance system using the National Electrical Manufacturers Association NU-2 count-rate phantom with two sets of annular sleeves to expand the diameter to 27 and 35 cm. For all diameters and in 2-D and fully 3-D mode, there is good agreement between measurements and simulations. All studies use the three phantom diameters to evaluate the effect of patient thickness for each amount of collimation. Optimized system parameters, such as maximum ring difference for single slice rebinning, are determined for the five partially collimated systems considered. The resulting global count rates for true, scattered, and random coincidences, the noise equivalent count (NEC) rates, and the scatter fractions for different levels of collimation are compared along with the results from the conventional 2-D and fully 3-D modes. Improved statistical data quality relative to both 2-D and fully 3-D data is found with the partially collimated systems, particularly when one-half or two-thirds of the septal rings are removed. An increase in NEC rates of as much as 50% is found for clinically relevant activities between 5-10 mCi (184-370 MBq). Scatter fractions for the partially collimated systems are intermediate between the 2-D and fully 3-D numbers. Many factors that affect image quality have not been considered in this paper. However, the significant increase in statistical data quality warrants further investigation of the impact of partial collimation on clinical whole-body PET imaging.
我们展示了一项针对正电子发射断层扫描（PET）扫描仪整体计数率性能的模拟研究，该扫描仪具有不同程度的部分准直，以最大化全身PET成像的噪声等效计数率。我们通过从GE Advance PET扫描仪的标准二维隔板组中移除不同数量的隔板环来实现部分准直。使用光子跟踪模拟软件包研究系统行为，我们对该软件包进行了修改，以使其能够产生随机符合事件。使用美国国家电气制造商协会（National Electrical Manufacturers Association）的NU - 2计数率体模以及两组环形套筒将直径扩展至27厘米和35厘米，在GE Advance系统上以二维和全三维采集模式获取测量数据，对模拟进行验证。对于所有直径以及二维和全三维模式，测量结果与模拟结果吻合良好。所有研究均使用三种体模直径来评估每种准直量下患者厚度的影响。针对所考虑的五个部分准直系统确定了优化的系统参数，例如单切片重排的最大环差。将不同准直水平下真符合、散射符合和随机符合的整体计数率、噪声等效计数（NEC）率以及散射分数的结果与传统二维和全三维模式的结果进行比较。发现部分准直系统相对于二维和全三维数据具有更高的统计数据质量，特别是当移除一半或三分之二的隔板环时。对于5 - 10毫居里（184 - 370兆贝可）之间的临床相关活度，发现NEC率提高了多达50%。部分准直系统的散射分数介于二维和全三维数据的散射分数之间。本文未考虑许多影响图像质量的因素。然而，统计数据质量的显著提高值得进一步研究部分准直对临床全身PET成像的影响。
