SPECT with pinholes separated by slats for high-sensitivity complete imaging

描述（由申请人提供）：本项目的总体目标是开发一种用于核医学单光子发射计算机断层扫描（SPECT）的新准直技术。这种新型准直器将针孔准直在轴向方向上的灵敏度和分辨率特性与平行光束（PB）和扇光束（FB）的完全采样特性相结合。SPECT是一种常用的成像技术，其使用放射性标记的示踪剂来诊断疾病状态。准直在SPECT中与位置敏感检测器（即，伽马照相机）。因此，SPECT测量一组线积分，其通过重建软件被反转成示踪剂浓度的3D分布。PB和FB是临床常用的准直器，在横轴方向上放大。针孔和锥束（CB）准直器也用于研究和临床场景。CB的灵敏度在焦点附近增加，类似于FB的，然而CB和FB的分辨率在探测器附近更好。针孔准直的不同之处在于灵敏度和分辨率都在焦点附近更好（即，孔径），而CB和FB的最佳分辨率出现在它们的灵敏度最差的地方（即，在探测器附近）。然而，针孔和CB两者的问题在于它们不能从圆形轨道产生完整的数据，导致轴向模糊伪影。PB和FB不会出现这些伪影，它们会产生完整的数据。在这个项目中提出的准直结合了良好的轴向灵敏度和分辨率性能的针孔与FB的完整采样特性。准直是2D的，因为准直器可以轴向平移，但产生相同的投影图像;该属性有利于图像重建，因为除了探测器分辨率之外，切片彼此独立。这与针孔和CB形成鲜明对比，针孔和CB具有大量的轴向切片混合。在本计画中，我们将设计并制作一个二维针孔平行光管的原型。将解析和数值计算的灵敏度和分辨率的成像特性。这些计算将通过实验点源测量进行验证。灵敏度和分辨率将被纳入3D迭代重建算法中，但仅考虑附近切片，因为轴向重叠有限，这将有助于重建速度。重建的实验体模将用于测试系统。在该项目的后期，将根据从原型中获得的知识制造一套“生产”准直器，其中每个准直器都可能包含多个狭缝以提高灵敏度。将使用拟人体模评价该套件的潜在临床影响。当物体直径为中等尺寸（~ 11 - 27 cm）时，预期新的准直器是有利的。因此，可能受益于这种新技术的临床和研究扫描包括大脑，乳房，肢体以及一些儿科和动物应用。

DESCRIPTION (provided by applicant): The overall goal of this project is to develop a new collimation technique for single photon emission computed tomography (SPECT) in nuclear medicine. This new collimator merges the sensitivity and resolution properties of pinhole collimation in the transaxial direction with the complete-sampling properties of parallel-beam (PB) and fan-beam (FB). SPECT is a commonly used imaging technique that uses radiolabeled tracers for diagnosing disease states. Collimation is used in SPECT in conjunction with a position-sensitive detector (i.e., a gamma camera). Thus, SPECT measures a set of line integrals, which are inverted through reconstruction software into a 3D distribution of the tracer's concentration. PB and FB, which magnifies in the transaxial direction, are commonly used clinical collimators. Pinhole and cone-beam (CB) collimators are also used in research and clinical scenarios. CB's sensitivity increases near the focal point, analogously to FB's, yet CB's and FB's resolutions are better near the detector. Pinhole collimation is different in that sensitivity and resolution are both better near the focal point (i.e., the aperture), whereas CB's and FB's best resolutions occur where their sensitivities are worst (i.e., near the detector). However, a problem with both pinhole and CB is that they do not yield complete data from a circular orbit, leading to axial blurring artifacts. These artifacts do not occur for PB and FB, which yield complete data. The collimation proposed in this project combines the favorable transaxial sensitivity and resolution properties of a pinhole with the complete-sampling properties of FB. The collimation is 2D in that the collimator may be translated axially yet produce the same projection image; this property is beneficial for image reconstruction because slices are independent of each other, except for detector resolution. This contrasts sharply with pinhole and CB which have large mixing of axial slices. In this project, a prototype 2D-pinhole collimator will be designed and fabricated. The imaging properties of sensitivity and resolution will be calculated analytically and numerically. These calculations will be validated through experimental point-source measurements. The sensitivity and resolution will be incorporated into an iterative reconstruction algorithm that is 3D, but considers only nearby slices since there is limited axial overlap, which will aid reconstruction speed. Reconstruction of experimental phantoms will be used to test the system. In the later years of the project, a set of "production" collimators, each of which is likely to incorporate multiple slits for improved sensitivity, will be fabricated based on the knowledge gained from the prototype. This set will be evaluated for potential clinical impact using anthropomorphic phantoms. The new collimator is expected to be advantageous when the object diameter is mid-size (-11-27 cm). Thus, clinical and research scans that are likely to benefit from this new technique include brain, breast, limb, as well as some pediatric and animal applications.