Bae Seungbin, Chun Jaehee, Cha Hyemi, Yeom Jung Yeol, Lee Kisung, Lee Hakjae
Bio-convergence Engineering, College of Health Science, Korea University, Seoul, 02841, Republic of Korea.
School of Biomedical Engineering, College of Health Science, Korea University, Seoul, 02841, Republic of Korea.
Med Phys. 2017 Feb;44(2):470-478. doi: 10.1002/mp.12075.
In the past decade, demands for organ specific (target oriented) single-photon emission computed tomography (SPECT) is increasing, and several groups have conducted studies on developing clinical dedicated SPECT with pinhole collimator to improve the spatial resolution. However, acceptance angle of the collimator cannot be adjusted to fit the different ROIs of target objects because the shape of pinhole could not be changed, and the magnifying factor cannot be maximized as the collimator-to-detector distance is fixed. Furthermore, those dedicated pinhole SPECTs are typically made for a single purpose and therefore possess a drawback in that it cannot be utilized for any other purpose. In this study, we propose a novel SPECT system using variable pinhole collimator (VP SPECT) whose parameters are flexible.
The proposed variable pinhole collimator is modeled on conventional pinhole by piling several tungsten layers of different apertures. Depending on the combination of the holes in each layer, a variety of hole diameters and acceptance angles of the pinhole can be made. In addition, VP SPECT system allows attaching the collimator to the object as close as possible to maximize the sensitivity and adjust the distance of the pinhole from the scintillation detector to optimize the system resolution for each rotation angle, automatically. For quantitative measurement, we compared the sensitivity and spatial resolution of VP SPECT with those of conventional pinhole SPECT. To determine the possibility of the clinical and preclinical use of proposed system, a digital mouse whole-body (MOBY) phantom is used for simulating the live mouse model.
The result of simulation using ultra-micro hot spot phantom shows that the sensitivity of the proposed VP SPECT system is about 297% of that of the conventional system. While hot rods of diameter 0.6 mm can be distinguished in the image with the proposed VP SPECT system, 1.2-mm hot rods are barely discernible in the conventional pinhole SPECT image. According to the result of MOBY phantom simulation, heart walls separated by 3 mm were not distinguished in conventional pinhole SPECT images, but were clearly discerned in VP SPECT images.
In this study, we designed a novel pinhole collimator for SPECT and presented preliminary results of target oriented imaging with a simulation study. Currently, we are pursuing strategies to realize the proposed system, with the goal to apply the technology into a high-sensitivity and high-resolution preclinical SPECT. Should VP SPECT be applied to the clinical setting, we anticipate a high-sensitivity, high-resolution system for applications such as heart dedicated SPECT or related fields.
在过去十年中，对器官特异性（靶向）单光子发射计算机断层扫描（SPECT）的需求不断增加，一些研究团队开展了关于开发带有针孔准直器的临床专用SPECT以提高空间分辨率的研究。然而，由于针孔形状无法改变，准直器的接受角不能调整以适应目标物体的不同感兴趣区域（ROI），并且由于准直器到探测器的距离固定，放大倍数无法最大化。此外，那些专用针孔SPECT通常是为单一目的制造的，因此存在无法用于其他目的的缺点。在本研究中，我们提出了一种使用可变针孔准直器（VP SPECT）的新型SPECT系统，其参数具有灵活性。
所提出的可变针孔准直器是通过堆叠几层不同孔径的钨层，以传统针孔为模型。根据每层孔的组合，可以制造出各种针孔直径和接受角。此外，VP SPECT系统允许将准直器尽可能靠近物体安装，以最大化灵敏度，并自动调整针孔到闪烁探测器的距离，为每个旋转角度优化系统分辨率。为了进行定量测量，我们将VP SPECT的灵敏度和空间分辨率与传统针孔SPECT的进行了比较。为了确定所提出系统临床和临床前应用的可能性，使用数字小鼠全身（MOBY）模型来模拟活体小鼠模型。
使用超微热点模型的模拟结果表明，所提出的VP SPECT系统的灵敏度约为传统系统的297%。在所提出的VP SPECT系统的图像中可以分辨出直径0.6毫米的热棒，而在传统针孔SPECT图像中几乎无法分辨出1.2毫米的热棒。根据MOBY模型模拟的结果，在传统针孔SPECT图像中无法分辨出相隔3毫米的心脏壁，但在VP SPECT图像中清晰可辨。
在本研究中，我们设计了一种用于SPECT的新型针孔准直器，并通过模拟研究给出了靶向成像的初步结果。目前，我们正在寻求实现所提出系统的策略，目标是将该技术应用于高灵敏度和高分辨率的临床前SPECT。如果VP SPECT应用于临床环境，我们预计它将成为一种用于心脏专用SPECT或相关领域的高灵敏度、高分辨率系统。
