Massoumzadeh P, Rudin S, Bednarek D R
University at Buffalo (SUNY), School of Medicine and Biomedical Sciences, Department of Radiology, USA.
Med Phys. 1998 Feb;25(2):161-71. doi: 10.1118/1.598191.
Region of interest (ROI) fluoroscopic techniques have the potential for improving image quality and greatly reducing radiation dose. The utility of ROI imaging depends on the material used for the filter. Various materials for x-ray beam shaping ROI filters are evaluated using a computer simulation to determine their transmission and effect on radiographic image quality as a function of kVp. Selected measurements were also performed to verify the results of the simulation. Rare earth materials such as gadolinium (Gd) showed distinct advantages over conventional filter materials such as copper (Cu). The effects of Gd and Cu filters on transmission, contrast, and contrast to noise ratio using a CsI image receptor were investigated for beams of 40 to 100 kVp for a broad range of thicknesses of iodine, barium, bone, fat, and for a range of phantom thicknesses. The results were the following: (1) Gd generally increases image contrast while Cu substantially decreases contrast for all materials at all kVp's; (2) Gd has much less variation in transmission with kVp than Cu; and (3) for the same signal in the ROI and with thicknesses of filters which provides the same entrance phantom kerma, Gd provides higher contrast to noise ratio than Cu for lower kVp values while Cu provides higher contrast to noise ratio at higher kVp values. Analytical results of transmission and contrast improvement as a function of iodine concentration, filter thickness, and kVp compared favorably with experimental values. In conclusion, Gd appears to be the filter material of choice when it is important to maintain a higher level of image contrast in the periphery, such as during angiography, since image contrast is not degraded with Gd while it is degraded substantially with Cu. Although contrast is degraded with Cu, Cu may be the preferred filter material for higher kVp procedures such as GI exams since the detected signal in the periphery would be substantially higher permitting either greater reduction in patient dose or a decrease in image noise for the same dose reduction.
感兴趣区域（ROI）荧光透视技术有改善图像质量并大幅降低辐射剂量的潜力。ROI成像的效用取决于用于滤波器的材料。使用计算机模拟评估用于X射线束整形ROI滤波器的各种材料，以确定它们的透射率以及作为千伏峰值（kVp）函数对射线照相图像质量的影响。还进行了选定的测量以验证模拟结果。钆（Gd）等稀土材料相较于铜（Cu）等传统滤波材料具有明显优势。针对40至100 kVp的射线束，研究了Gd和Cu滤波器对碘化铯（CsI）图像接收器在碘、钡、骨骼、脂肪的广泛厚度范围内以及一系列体模厚度下的透射率、对比度和对比度噪声比的影响。结果如下：（1）对于所有材料在所有kVp值下，Gd通常会增加图像对比度，而Cu会大幅降低对比度；（2）Gd的透射率随kVp的变化远小于Cu；（3）对于ROI中相同的信号以及提供相同入口体模比释动能的滤波器厚度，在较低kVp值时Gd提供比Cu更高的对比度噪声比，而在较高kVp值时Cu提供更高的对比度噪声比。作为碘浓度、滤波器厚度和kVp函数的透射率和对比度改善的分析结果与实验值相比良好。总之，当在外围保持较高水平的图像对比度很重要时，例如在血管造影期间，Gd似乎是首选的滤波材料，因为使用Gd时图像对比度不会降低，而使用Cu时会大幅降低。尽管使用Cu时对比度会降低，但Cu可能是更高kVp程序（如胃肠道检查）的首选滤波材料，因为在外围检测到的信号会大幅更高，这允许在相同剂量减少的情况下要么更大程度地降低患者剂量，要么降低图像噪声。
