Hallen Patrick, Schug David, Weissler Bjoern, Gebhardt Pierre, Salomon André, Kiessling Fabian, Schulz Volkmar
Department of Physics of Molecular Imaging Systems, Institute for Experimental Molecular Imaging, RWTH Aachen University, Aachen, Germany.
Department of Oncology Solutions, Philips Research, Eindhoven, Netherlands.
Biomed Phys Eng Express. 2018 Nov;4(6):065027. doi: 10.1088/2057-1976/aae6c2. Epub 2018 Oct 24.
The Hyperion II PET insert is the first scanner using fully digital silicon photomultipliers for simultaneous PET/MR imaging of small animals up to rabbit size. In this work, we evaluate the PET performance based on the National Eletrical Manufacturers Association (NEMA) NU 4-2008 standard, whose standardized measurement protocols allow comparison of different small-animal PET scanners. The Hyperion II small-animal PET/MR insert comprises three rings of 20 detector stacks with pixelated scintillator arrays with a crystal pitch of 1 mm, read out with digital silicon photomultipliers. The scanner has a large ring diameter of 209.6 mm and an axial field of view of 96.7 mm. We evaluated the spatial resolution, energy resolution, time resolution and sensitivity by scanning a Na point source. The count rates and scatter fractions were measured for a wide range of F activity inside a mouse-sized scatter phantom. We evaluated the image quality using the mouse-sized image quality phantom specified in the NEMA NU4 standard, filled with F. Additionally, we verified the imaging capabilities by performing a simultaneous PET/MRI scan of a mouse injected with F-FDG. We processed all measurement data with an energy window of 250 keV to 625 keV and a coincidence time window of 2 ns. The filtered-backprojection reconstruction of the point source has a full width at half maximum (FWHM) of 1.7 mm near the isocenter and degrades to 2.5 mm at a radial distance of 50 mm. The scanner's average energy resolution is 12.7% (Δ/ FWHM) and the coincidence resolution time is 609 ps. The peak absolute sensitivity is 4.0% and the true and noise-equivalent count rates reach their peak at an activity of 46 MBq with 483 kcps and 407 kcps, respectively, with a scatter fraction of 13%. The iterative reconstruction of the image quality phantom has a uniformity of 3.7%, and recovery coefficients from 0.29, 0.91 and 0.94 for rod diameters of 1 mm, 3 mm and 5 mm, respectively. After application of scatter and attenuation corrections, the air- and water-filled cold regions have spill-over ratios of 6.3% and 5.4%, respectively. The Hyperion II PET/MR insert provides state-of-the-art PET performance while enabling simultaneous PET/MRI acquisition of small animals up to rabbit size.
Hyperion II正电子发射断层扫描（PET）插入件是首款使用全数字硅光电倍增管的扫描仪，用于对兔大小及以下的小动物进行PET/磁共振成像（MRI）同步扫描。在本研究中，我们依据美国国家电气制造商协会（NEMA）NU 4 - 2008标准评估PET性能，该标准的标准化测量协议允许对不同的小动物PET扫描仪进行比较。Hyperion II小动物PET/MR插入件由三个环组成，每个环有20个探测器堆叠，配备像素化闪烁体阵列，晶体间距为1毫米，由数字硅光电倍增管读出信号。该扫描仪的大环直径为209.6毫米，轴向视野为96.7毫米。我们通过扫描一个钠点源来评估空间分辨率、能量分辨率、时间分辨率和灵敏度。在小鼠大小的散射体模内，针对广泛的氟活度范围测量计数率和散射分数。我们使用NEMA NU4标准中规定的小鼠大小的图像质量体模（填充氟）来评估图像质量。此外，我们通过对注射了氟代脱氧葡萄糖（F-FDG）的小鼠进行PET/MRI同步扫描来验证成像能力。我们使用250千电子伏特至625千电子伏特的能量窗和2纳秒的符合时间窗处理所有测量数据。点源的滤波反投影重建在等中心附近的半高宽（FWHM）为1.7毫米，在径向距离50毫米处降至2.5毫米。该扫描仪的平均能量分辨率为12.7%（Δ/FWHM），符合分辨率时间为609皮秒。峰值绝对灵敏度为4.0%，真计数率和噪声等效计数率分别在活度为46兆贝克勒尔（MBq）时达到峰值，分别为483千计数每秒（kcps）和407 kcps，散射分数为13%。图像质量体模的迭代重建均匀性为3.7%，对于直径为1毫米、3毫米和5毫米的棒，恢复系数分别为0.29、0.91和0.94。在应用散射和衰减校正后，空气填充和水填充的冷区溢出率分别为6.3%和5.4%。Hyperion II PET/MR插入件提供了先进的PET性能，同时能够对兔大小及以下的小动物进行PET/MRI同步采集。
