A new portal imager consisting of four vertically stacked conventional electronic portal imaging device (EPID) layers has been constructed in pursuit of improved detective quantum efficiency (DQE). We hypothesize that super-resolution (SR) imaging can also be achieved in such a system by shifting each layer laterally by half a pixel relative to the layer above. Super-resolution imaging will improve resolution and contrast-to-noise ratio (CNR) in megavoltage (MV) planar and cone beam computed tomography (MV-CBCT) applications. Simulations are carried out to test this hypothesis with digital phantoms. To assess planar resolution, 2 mm long iron rods with 0.3 × 0.3 mm2 square cross-section are arranged in a grid pattern at the center of a 1 cm thick solid water. For measuring CNR in MV-CBCT, a 20 cm diameter digital phantom with 8 inserts of different electron densities is used. For measuring resolution in MV-CBCT, a digital phantom featuring a bar pattern similar to the Gammex™ phantom is used. A 6 MV beam is attenuated through each phantom and detected by each of the four detector layers. Fill factor of the detector is explicitly considered. Projections are blurred with an estimated point spread function (PSF) before super-resolution reconstruction. When projections from multiple shifted layers are used in SR reconstruction, even a simple shift-add fusion can significantly improve the resolution in reconstructed images. In the reconstructed planar image, the grid pattern becomes visually clearer. In MV-CBCT, combining projections from multiple layers results in increased CNR and resolution. The inclusion of two, three and four layers increases CNR by 40%, 70% and 99%, respectively. Shifting adjacent layers by half a pixel almost doubles resolution. In comparison, using four perfectly aligned layers does not improve resolution relative to a single layer.

中文翻译：

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多层 EPID 中的超分辨率成像

为了提高探测量子效率 (DQE)，已经构建了一种由四个垂直堆叠的传统电子门户成像设备 (EPID) 层组成的新型门户成像器。我们假设在这样的系统中也可以通过将每一层相对于上面的层横向移动半个像素来实现超分辨率 (SR) 成像。超分辨率成像将提高兆电压 (MV) 平面和锥形束计算机断层扫描 (MV-CBCT) 应用中的分辨率和对比度噪声比 (CNR)。进行模拟以用数字体模检验这一假设。为了评估平面分辨率，将横截面为 0.3 × 0.3 mm2 正方形的 2 mm 长铁棒以网格图案排列在 1 cm 厚的固体水的中心。对于测量 MV-CBCT 中的 CNR，使用具有 8 个不同电子密度的插入物的 20 cm 直径数字体模。为了测量 MV-CBCT 中的分辨率，使用了具有类似于 Gammex™ 体模的条形图案的数字体模。6 MV 光束通过每个体模衰减，并由四个检测器层中的每一个检测到。明确考虑了检测器的填充因子。在超分辨率重建之前，使用估计的点扩散函数 (PSF) 模糊投影。当在 SR 重建中使用来自多个移位层的投影时，即使是简单的移位相加融合也可以显着提高重建图像的分辨率。在重建的平面图像中，网格图案在视觉上变得更加清晰。在 MV-CBCT 中，组合来自多个层的投影可提高 CNR 和分辨率。包含两个，三层和四层分别将 CNR 提高了 40%、70% 和 99%。将相邻层移动半个像素几乎会使分辨率翻倍。相比之下，使用四个完美对齐的层并不会提高相对于单层的分辨率。