A proposal of an open PET geometry
A proposal of an open PET geometry
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DOI：
10.1088/0031-9155/53/3/015
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发表时间：
2008-02-07
影响因子：
3.5
通讯作者：
Murayama, Hideo
中科院分区：
文献类型：
--
作者：
Yamaya, Taiga;Inaniwa, Taku;Murayama, Hideo
PET扫描仪的长端口往往会给患者带来压力，尤其是幽闭恐惧症患者。它也阻止了医生和技术人员在扫描过程中照顾病人。在本文中，我们提出了一种“开放式PET”几何结构，它由两个轴向分离的探测器环组成。长而连续的视野（FOV），包括360度。可以对两个探测器环之间打开的间隙进行成像，从而可以对所有可能的响应线进行全3D图像重建。尽管开放PET的图像重建在分析上是一个不完全问题，但如果采用迭代图像重建方法，开放PET将变得可行。首先，我们实现了一个“掩模”3D有序子集期望最大化（OS-EM），其中系统矩阵通过对开放空间对应的检测器应用掩模从长“无间隙”扫描仪获得。接下来，为了评估所提出的开放式PET几何结构的成像性能，我们模拟了一个由可变间隙分隔的双HR+扫描仪（环直径D = 827 mm，轴长W = 154 mm x 2）。虽然中央切片的最大视场直径被限制在D/2，但间隙W是轴向连续视场3W的最大极限。当间隙超过W时，在开放空间两侧观察到伪影，通过将探测器部分插入不必要的开放空间，有效地减少了伪影。我们还使用jPET-D4获得的实验数据测试了开放PET的几何形状。jPET-D4是一个脑扫描仪的原型，它有5个环，24个检测器模块。我们从实验数据中剔除1个块环，模拟了66 mm间隙的开放jPET-D4。虽然在打开的间隙的两端可以看到一些伪影，但在有间隙和没有间隙的情况下获得的图像非常相似。提出的开放式PET几何形状有望实现束内PET，这是一种原位监测带电粒子治疗的方法，通过让光束穿过间隙。与传统的PET/CT不同，开放式PET几何结构还允许同时测量与CT相同的PET视场，而传统的PET/CT每个视场相隔几十厘米。
The long patient port of a PET scanner tends to put stress on patients, especially patients with claustrophobia. It also prevents doctors and technicians from taking care of patients during scanning. In this paper, we proposed an 'open PET' geometry, which consists of two axially separated detector rings. A long and continuous field-of-view (FOV) including a 360. opened gap between two detector rings can be imaged enabling a fully 3D image reconstruction of all the possible lines-of-response. The open PET will become practical if iterative image reconstruction methods are applied even though image reconstruction of the open PET is analytically an incomplete problem. First we implemented a 'masked' 3D ordered subset expectation maximization (OS-EM) in which the system matrix was obtained from a long 'gapless' scanner by applying a mask to detectors corresponding to the open space. Next, in order to evaluate imaging performance of the proposed open PET geometry, we simulated a dual HR+ scanner (ring diameter of D = 827 mm, axial length of W = 154 mm x 2) separated by a variable gap. The gap W was the maximum limit to have axially continuous FOV of 3W though the maximum diameter of FOV at the central slice was limited to D/2. Artifacts, observed on both sides of the open space when the gap exceeded W, were effectively reduced by inserting detectors partially into unnecessary open spaces. We also tested the open PET geometry using experimental data obtained by the jPET-D4. The jPET-D4 is a prototype brain scanner, which has 5 rings of 24 detector blocks. We simulated the open jPET-D4 with a gap of 66 mm by eliminating 1 block-ring from experimental data. Although some artifacts were seen at both ends of the opened gap, very similar images were obtained with and without the gap. The proposed open PET geometry is expected to lead to realization of in-beam PET, which is a method for an in situ monitoring of charged particle therapy, by letting the beams pass through the gap. The proposed open PET geometry will also allow simultaneous PET/CT measurements of the same PET FOV as the CT FOV, in contrast to the conventional PET/CT where each FOV is separated by several tens of centimeters.