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

描述(申请人提供)：该项目的总体目标是开发一种新的核医学单光子发射计算机断层扫描(SPECT)准直技术。这种新型准直器融合了针孔准直在轴向的灵敏度和分辨率以及平行束(PB)和扇束(FB)的全采样特性。SPECT是一种常用的成像技术，它使用放射性标记的示踪剂来诊断疾病状态。在SPECT中，准直与位置敏感探测器(即伽马相机)一起使用。因此，SPECT测量一组线积分，通过重建软件将其倒置为示踪剂浓度的3D分布。PB和FB在轴向放大，是临床常用的准直器。针孔和锥束(CB)准直器也被用于研究和临床场景。CB的灵敏度在焦点附近增加，与FB类似，但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，在焦点(即光圈)附近的灵敏度和分辨率都较好，而CB和FB的最佳分辨率出现在它们的灵敏度最差的地方(即探测器附近)。然而，针孔和CB的一个问题是，它们不能从圆形轨道产生完整的数据，导致轴向模糊伪影。这些伪影不会出现在生成完整数据的PB和FB中。该项目提出的准直结合了针孔的良好的轴向灵敏度和分辨率特性与FB的完全采样特性。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；这一特性对于图像重建是有益的，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，后者具有大量的轴向切片混合。在本项目中，我们将设计并制作一个二维针孔准直器的样机。对灵敏度和分辨率的成像特性将进行解析和数值计算。这些计算将通过实验点源测量得到验证。灵敏度和分辨率将被合并到迭代重建算法中，该算法是3D的，但由于轴向重叠有限，因此只考虑附近的切片，这将有助于重建速度。实验模型的重建将用于测试该系统。在该项目的最后几年，将根据从原型获得的知识制造一套“生产型”准直器，每个准直器都可能包括多个狭缝以提高灵敏度。这套装置将使用拟人化的幻影来评估潜在的临床影响。当物体直径为中等大小(-11-27厘米)时，新的准直器将是有利的。因此，可能受益于这项新技术的临床和研究扫描包括大脑、乳房、四肢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.