Guérin Bastein, Fakhri Georges El
B. Guérin is with the University of Paris VI, 75006 Paris, France and also with Harvard University, Cambridge, MA 02138 USA. (e-mail:
IEEE Trans Nucl Sci. 2008;55(3):942-952. doi: 10.1109/TNS.2008.924064.
We have developed and validated a realistic simulation of random coincidences, pixelated block detectors, light sharing among crystal elements and dead-time in 2D and 3D positron emission tomography (PET) imaging based on the SimSET Monte Carlo simulation software. Our simulation was validated by comparison to a Monte Carlo transport code widely used for PET modeling, GATE, and to measurements made on a PET scanner. METHODS: We have modified the SimSET software to allow independent tracking of single photons in the object and septa while taking advantage of existing voxel based attenuation and activity distributions and validated importance sampling techniques implemented in SimSET. For each single photon interacting in the detector, the energy-weighted average of interaction points was computed, a blurring model applied to account for light sharing and the associated crystal identified. Detector dead-time was modeled in every block as a function of the local single rate using a variance reduction technique. Electronic dead-time was modeled for the whole scanner as a function of the prompt coincidences rate. Energy spectra predicted by our simulation were compared to GATE. NEMA NU-2 2001 performance tests were simulated with the new simulation as well as with SimSET and compared to measurements made on a Discovery ST (DST) camera. RESULTS: Errors in simulated spatial resolution (full width at half maximum, FWHM) were 5.5% (6.1%) in 2D (3D) with the new simulation, compared with 42.5% (38.2%) with SimSET. Simulated (measured) scatter fractions were 17.8% (21.3%) in 2D and 45.8% (45.2%) in 3D. Simulated and measured sensitivities agreed within 2.3 % in 2D and 3D for all planes and simulated and acquired count rate curves (including NEC) were within 12.7% in 2D in the [0: 80 kBq/cc] range and in 3D in the [0: 35 kBq/cc] range. The new simulation yielded significantly more realistic singles' and coincidences' spectra, spatial resolution, global sensitivity and lesion contrasts than the SimSET software.
我们基于SimSET蒙特卡罗模拟软件，开发并验证了一种用于二维和三维正电子发射断层扫描（PET）成像中随机符合、像素化块状探测器、晶体元件间光共享以及死时间的真实模拟。通过与广泛用于PET建模的蒙特卡罗传输代码GATE以及在PET扫描仪上进行的测量结果相比较，验证了我们的模拟。方法：我们修改了SimSET软件，以便在利用现有的基于体素的衰减和活度分布的同时，独立跟踪物体和隔板中的单个光子，并验证了SimSET中实现的重要性抽样技术。对于在探测器中相互作用的每个单个光子，计算相互作用点的能量加权平均值，应用模糊模型以考虑光共享并识别相关晶体。使用方差减少技术，将探测器死时间建模为每个块中局部单光子率的函数。将整个扫描仪的电子死时间建模为瞬发符合率的函数。将我们模拟预测的能谱与GATE进行比较。使用新模拟以及SimSET模拟了NEMA NU - 2 2001性能测试，并与在Discovery ST（DST）相机上进行的测量结果进行比较。结果：新模拟在二维（三维）中模拟空间分辨率（半高宽，FWHM）的误差为5.5%（6.1%），而SimSET为42.5%（38.2%）。模拟（测量）的散射分数在二维中为17.8%（21.3%），在三维中为45.8%（45.2%）。二维和三维中所有平面的模拟和测量灵敏度在2.3%以内一致，并且模拟和采集的计数率曲线（包括NEC）在二维的[0: 80 kBq/cc]范围内以及三维的[0: 35 kBq/cc]范围内在12.7%以内。与SimSET软件相比，新模拟产生的单光子和符合光子能谱、空间分辨率、整体灵敏度和病变对比度明显更逼真。
