Khateri Parisa, Lustermann Werner, Ritzer Christian, Tsoumpas Charalampos, Dissertori Günther
Institute for Particle Physics and Astrophysics, ETH Zürich, Zürich, Switzerland.
Department of Nuclear Medicine and Molecular Imaging, University of Groningen, Groningen, The Netherlands.
EJNMMI Phys. 2022 Jun 13;9(1):42. doi: 10.1186/s40658-022-00454-2.
The SAFIR prototype insert is a preclinical Positron Emission Tomography (PET) scanner built to acquire dynamic images simultaneously with a 7 T Bruker Magnetic Resonance Imaging (MRI) scanner. The insert is designed to perform with an excellent coincidence resolving time of 194 ps Full Width Half Maximum (FWHM) and an energy resolution of 13.8% FWHM. These properties enable it to acquire precise quantitative images at activities as high as 500 MBq suitable for studying fast biological processes within short time frames (< 5 s). In this study, the performance of the SAFIR prototype insert is evaluated according to the NEMA NU 4-2008 standard while the insert is inside the MRI without acquiring MRI data.
Applying an energy window of 391-601 keV and a coincidence time window of 500 ps the following results are achieved. The average spatial resolution at 5 mm radial offset is 2.6 mm FWHM when using the Filtered Backprojection 3D Reprojection (FBP3DRP) reconstruction method, improving to 1.2 mm when using the Maximum Likelihood Expectation Maximization (MLEM) method. The peak sensitivity at the center of the scanner is 1.06%. The Noise Equivalent count Rate (NECR) is 799 kcps at the highest measured activity of 537 MBq for the mouse phantom and 121 kcps at the highest measured activity of 624 MBq for the rat phantom. The NECR peak is not yet reached for any of the measurements. The scatter fractions are 10.9% and 17.8% for the mouse and rat phantoms, respectively. The uniform region of the image quality phantom has a 3.0% STD, with a 4.6% deviation from the expected number of counts per voxel. The spill-over ratios for the water and air chambers are 0.18 and 0.17, respectively.
The results satisfy all the requirements initially considered for the insert, proving that the SAFIR prototype insert can obtain dynamic images of small rodents at high activities ([Formula: see text] 500 MBq) with a high sensitivity and an excellent count-rate performance.
SAFIR原型插入式正电子发射断层扫描（PET）扫描仪是一款临床前设备，旨在与7T布鲁克磁共振成像（MRI）扫描仪同时采集动态图像。该插入式扫描仪的设计使其具有194皮秒半高宽（FWHM）的出色符合分辨时间以及13.8% FWHM的能量分辨率。这些特性使其能够在高达500 MBq的活度下采集精确的定量图像，适用于在短时间框架（<5秒）内研究快速生物过程。在本研究中，在插入式扫描仪置于MRI内部且不采集MRI数据的情况下，根据NEMA NU 4 - 2008标准对SAFIR原型插入式扫描仪的性能进行评估。
应用391 - 601 keV的能量窗和500皮秒的符合时间窗，取得了以下结果。使用滤波反投影三维重投影（FBP3DRP）重建方法时，在5毫米径向偏移处的平均空间分辨率为2.6毫米FWHM，使用最大似然期望最大化（MLEM）方法时提高到1.2毫米。扫描仪中心处的峰值灵敏度为1.06%。对于小鼠模型，在最高测量活度537 MBq时，噪声等效计数率（NECR）为799千计数每秒；对于大鼠模型，在最高测量活度624 MBq时，NECR为121千计数每秒。所有测量均未达到NECR峰值。小鼠和大鼠模型的散射分数分别为10.9%和17.8%。图像质量模型的均匀区域标准差为3.0%，与每个体素预期计数数量的偏差为4.6%。水腔和空气腔的溢出率分别为0.18和0.17。
结果满足了最初对插入式扫描仪设定的所有要求，证明SAFIR原型插入式扫描仪能够在高活度（≥500 MBq）下以高灵敏度和出色的计数率性能获取小型啮齿动物的动态图像。
