Instituto de Instrumentación para Imagen Molecular (I3M), Centro mixto CSIC - Universitat Politècnica de València - CIEMAT, camino de Vera s∕n, 46022 Valencia, Spain.
Med Phys. 2013 May;40(5):051906. doi: 10.1118/1.4800798.
The authors have developed a trimodal PET∕SPECT∕CT scanner for small animal imaging. The gamma ray subsystems are based on monolithic crystals coupled to multianode photomultiplier tubes (MA-PMTs), while computed tomography (CT) comprises a commercially available microfocus x-ray tube and a CsI scintillator 2D pixelated flat panel x-ray detector. In this study the authors will report on the design and performance evaluation of the multimodal system.
X-ray transmission measurements are performed based on cone-beam geometry. Individual projections were acquired by rotating the x-ray tube and the 2D flat panel detector, thus making possible a transaxial field of view (FOV) of roughly 80 mm in diameter and an axial FOV of 65 mm for the CT system. The single photon emission computed tomography (SPECT) component has a dual head detector geometry mounted on a rotating gantry. The distance between the SPECT module detectors can be varied in order to optimize specific user requirements, including variable FOV. The positron emission tomography (PET) system is made up of eight compact modules forming an octagon with an axial FOV of 40 mm and a transaxial FOV of 80 mm in diameter. The main CT image quality parameters (spatial resolution and uniformity) have been determined. In the case of the SPECT, the tomographic spatial resolution and system sensitivity have been evaluated with a (99m)Tc solution using single-pinhole and multi-pinhole collimators. PET and SPECT images were reconstructed using three-dimensional (3D) maximum likelihood and ordered subset expectation maximization (MLEM and OSEM) algorithms developed by the authors, whereas the CT images were obtained using a 3D based FBP algorithm.
CT spatial resolution was 85 μm while a uniformity of 2.7% was obtained for a water filled phantom at 45 kV. The SPECT spatial resolution was better than 0.8 mm measured with a Derenzo-like phantom for a FOV of 20 mm using a 1-mm pinhole aperture collimator. The full width at half-maximum PET radial spatial resolution at the center of the field of view was 1.55 mm. The SPECT system sensitivity for a FOV of 20 mm and 15% energy window was 700 cps∕MBq (7.8 × 10(-2)%) using a multi-pinhole equipped with five apertures 1 mm in diameter, whereas the PET absolute sensitivity was 2% for a 350-650 keV energy window and a 5 ns timing window. Several animal images are also presented.
The new small animal PET∕SPECT∕CT proposed here exhibits high performance, producing high-quality images suitable for studies with small animals. Monolithic design for PET and SPECT scintillator crystals reduces cost and complexity without significant performance degradation.
作者开发了一种用于小动物成像的三模态正电子发射断层扫描/单光子发射计算机断层扫描/计算机断层扫描扫描仪。伽马射线子系统基于与多阳极光电倍增管（MA-PMT）耦合的单片晶体，而计算机断层扫描（CT）包括一个商用微焦点 X 射线管和一个 CsI 闪烁体 2D 像素化平板 X 射线探测器。在这项研究中，作者将报告多模态系统的设计和性能评估。
基于锥形束几何形状进行 X 射线透射测量。通过旋转 X 射线管和 2D 平板探测器来获取单个投影，从而使 CT 系统的横向视野（FOV）大致为 80mm 直径，轴向 FOV 为 65mm。单光子发射计算机断层扫描（SPECT）组件具有安装在旋转架上的双探头探测器几何形状。为了优化特定用户的要求，包括可变 FOV，可以改变 SPECT 模块探测器之间的距离。正电子发射断层扫描（PET）系统由八个紧凑模块组成，形成一个八边形，轴向 FOV 为 40mm，横向 FOV 为 80mm 直径。已经确定了主要 CT 图像质量参数（空间分辨率和均匀性）。在 SPECT 的情况下，使用（99m）Tc 溶液使用单孔和多孔准直器评估了层析空间分辨率和系统灵敏度。使用作者开发的三维（3D）最大似然和有序子集期望最大化（MLEM 和 OSEM）算法重建 PET 和 SPECT 图像，而 CT 图像则使用基于 3D 的 FBP 算法获得。
CT 空间分辨率为 85μm，在 45kV 下充满水的体模中均匀性为 2.7%。使用直径为 1mm 的小孔准直器，在 FOV 为 20mm 的情况下，使用类似 Derenzo 的体模测量的 SPECT 空间分辨率优于 0.8mm。在视场中心，PET 径向空间分辨率的半最大值全宽为 1.55mm。使用配备五个直径为 1mm 孔的多孔准直器，对于 FOV 为 20mm 和 15%能量窗口，SPECT 系统灵敏度为 700cps∕MBq（7.8×10(-2)%），而 PET 绝对灵敏度为 350-650keV 能量窗口和 5ns 定时窗口的 2%。还呈现了一些动物图像。
这里提出的新型小动物 PET∕SPECT∕CT 具有高性能，可生成适合小动物研究的高质量图像。用于 PET 和 SPECT 闪烁晶体的单片设计降低了成本和复杂性，而不会显著降低性能。
