Weng Fenghua, Bagchi Srijeeta, Zan Yunlong, Huang Qiu, Seo Youngho
School of Biomedical Engineering, Shanghai Jiao Tong University, Shanghai, China.
Physics Research Laboratory, Department of Radiology and Biomedical Imaging, University of California, San Francisco, CA, USA.
Nucl Instrum Methods Phys Res A. 2016 Jan 11;806:330-339. doi: 10.1016/j.nima.2015.09.115.
In single photon emission computed tomography, it is a challenging task to maintain reasonable performance using only one specific collimator for radio-tracers over a broad spectrum of diagnostic photon energies, since photon scatter and penetration in a collimator differ with the photon energy. Frequent collimator exchanges are inevitable in daily clinical SPECT imaging, which hinders throughput while subjecting the camera to operational errors and damage. Our objective is to design a collimator, which independent of the photon energy performs reasonably well for commonly used radiotracers with low- to medium-energy levels of gamma emissions. Using the Geant4 simulation toolkit, we simulated and evaluated a parallel-hole collimator mounted to a CZT detector. With the pixel-geometry-matching collimation, the pitch of the collimator hole was fixed to match the pixel size of the CZT detector throughout this work. Four variables, hole shape, hole length, hole radius/width and the source-to-collimator distance were carefully studied. Scatter and penetration of the collimator, sensitivity and spatial resolution of the system were assessed for four radionuclides including Co, Tc, I and In, with respect to the aforementioned four variables. An optimal collimator was then decided upon such that it maximized the total relative sensitivity () for the four considered radionuclides while other performance parameters, such as scatter, penetration and spatial resolution, were benchmarked to prevalent commercial scanners and collimators. Digital phantom studies were also performed to validate the system with the optimal square-hole collimator (23 mm hole length, 1.28 mm hole width, 0.32 mm septal thickness) in terms of contrast, contrast-to-noise ratio and recovery ratio. This study demonstrates promise of our proposed energy-optimized collimator to be used in a CZT-based gamma camera, with comparable or even better imaging performance versus commercial collimators such as low-energy high resolution (LEHR) and medium energy general purpose (MEGP) collimators.
在单光子发射计算机断层扫描中，仅使用一种特定准直器针对广泛诊断光子能量范围内的放射性示踪剂维持合理性能是一项具有挑战性的任务，因为准直器中的光子散射和穿透会因光子能量而异。在日常临床单光子发射计算机断层扫描成像中，频繁更换准直器是不可避免的，这会阻碍通量，同时使相机容易出现操作错误和损坏。我们的目标是设计一种准直器，其对于具有低至中能水平伽马发射的常用放射性示踪剂，能在与光子能量无关的情况下表现良好。使用Geant4模拟工具包，我们对安装在碲锌镉（CZT）探测器上的平行孔准直器进行了模拟和评估。在整个工作过程中，通过像素几何匹配准直，准直器孔的间距固定为与CZT探测器的像素尺寸相匹配。仔细研究了四个变量，即孔的形状、孔的长度、孔的半径/宽度以及源到准直器的距离。针对包括钴（Co）、锝（Tc）、碘（I）和铟（In）在内的四种放射性核素，就上述四个变量评估了准直器的散射和穿透、系统的灵敏度和空间分辨率。然后确定了一种最佳准直器，使其在最大化所考虑的四种放射性核素的总相对灵敏度（）的同时，将诸如散射、穿透和空间分辨率等其他性能参数与普遍使用的商业扫描仪和准直器进行对比。还进行了数字体模研究，以在对比度、对比噪声比和恢复率方面验证具有最佳方孔准直器（孔长23毫米、孔宽1.28毫米、隔板厚度0.32毫米）的系统。这项研究表明，我们提出的能量优化准直器有望用于基于CZT的伽马相机，与低能高分辨率（LEHR）和中能通用（MEGP）准直器等商业准直器相比，具有相当甚至更好的成像性能。
