Rasouli Mahmoud, Takavar Abbas, Ay Mohammad Reza, Saber Sasan, Loudos George
Medical Physics and Biomedical Engineering Department, School of Medicine, Tehran University of Medical Sciences, Tehran, Iran.
J Nucl Med Technol. 2010 Dec;38(4):199-204. doi: 10.2967/jnmt.109.073072. Epub 2010 Nov 15.
Dedicated γ-cameras based on pixelated scintillators have long been used for breast tumor imaging. Intercrystal scattering (ICS) increases the background counting rate and degrades the image quality when small crystal pixels are used. Because of the small size of applied collimators, scattered radiation and septal penetration are high, and therefore collimator characteristics must be carefully considered. In our study, we investigated the influence of ICS events on position-detection accuracy (PDA) for pixelated crystals and the effects of different geometries of hexagonal-hole collimators on the performance of these cameras, using Monte Carlo simulation to optimize camera design. The arrays of thallium-doped cesium iodide detectors with different pixel dimensions that had been exposed to 140-keV photons of isotropic point source, 50 mm from the collimator surface, were simulated. Hexagonal-hole collimators were 10.5, 15, and 21 mm long. The septal thickness varied from 0.1 to 0.5 mm, with 3 different hole diameters. The results confirmed that by increasing the crystal pixel size, ICS was decreased and change of detection efficiency was negligible, but PDA, contrast-to-noise ratio, and spatial resolution (full width at half maximum) were increased. Our experiences confirmed that 2 × 2 mm was an optimum crystal pixel size, especially for a lower ICS fraction and an appropriate full width at half maximum. Because collimators are the limiting factor for spatial resolution and sensitivity, careful collimator design is of great importance.
基于像素化闪烁体的专用γ相机长期以来一直用于乳腺肿瘤成像。当使用小晶体像素时，晶体间散射（ICS）会增加背景计数率并降低图像质量。由于所应用准直器尺寸较小，散射辐射和隔板穿透率较高，因此必须仔细考虑准直器特性。在我们的研究中，我们使用蒙特卡罗模拟来优化相机设计，研究了ICS事件对像素化晶体位置检测精度（PDA）的影响以及六边形孔准直器不同几何形状对这些相机性能的影响。模拟了不同像素尺寸的铊掺杂碘化铯探测器阵列，这些探测器阵列距离准直器表面50毫米，暴露于各向同性点源的140 keV光子下。六边形孔准直器的长度分别为10.5、15和21毫米。隔板厚度从0.1到0.5毫米不等，有3种不同的孔径。结果证实，通过增加晶体像素尺寸，ICS降低，检测效率的变化可忽略不计，但PDA、对比度噪声比和空间分辨率（半高宽）增加。我们的经验证实，2×2毫米是最佳晶体像素尺寸，特别是对于较低的ICS分数和合适的半高宽。由于准直器是空间分辨率和灵敏度的限制因素，仔细的准直器设计非常重要。
