Park Yang-Kyun, Sharp Gregory C
Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, USA
Department of Radiation Oncology, Massachusetts General Hospital, Boston, MA, USA.
Technol Cancer Res Treat. 2016 Apr;15(2):387-95. doi: 10.1177/1533034615576829. Epub 2015 Mar 20.
Gain calibration for X-ray imaging systems with a movable flat panel detector and an intrinsic crosshair is a challenge due to the geometry-dependent heel effect and crosshair artifact. This study aims to develop a gain correction method for such systems by implementing the Multi-Acquisition Gain Image Correction technique. Flood field images containing crosshair and heel effect were acquired in 4 different flat panel detector positions at fixed exposure parameters. The crosshair region was automatically detected using common image processing algorithms and removed by a simple interpolation procedure, resulting in a crosshair-removed image. A large kernel-based correction was then used to remove the heel effect. Mask filters corresponding to each crosshair region were applied to the resultant heel effect-removed images to invalidate the pixels of the original crosshair region. Finally, a seamless gain map was composed with corresponding valid pixels from the processed images either by the sequential replacement or by the selective averaging techniques developed in this study. Quantitative evaluation was performed based on normalized noise power spectrum and detective quantum efficiency improvement factor for the flood field images corrected by the Multi-Acquisition Gain Image Correction-based gain maps. For comparison purposes, a single crosshair-removed gain map was also tested. As a result, it was demonstrated that the Multi-Acquisition Gain Image Correction technique achieved better image quality than the crosshair-removed technique, showing lower normalized noise power spectrum values over most of spatial frequencies. The improvement was more obvious at the priori-crosshair region of the gain map. The mean detective quantum efficiency improvement factor was 1.09 ± 0.06, 2.46 ± 0.32, and 3.34 ± 0.36 in the priori-crosshair region and 2.35 ± 0.31, 2.33 ± 0.31, and 3.09 ± 0.34 in the normal region, for crosshair-removed, Multi-Acquisition Gain Image Correction-sequential replacement, and Multi-Acquisition Gain Image Correction-selective averaging techniques, respectively. Therefore, this study indicates that the introduced Multi-Acquisition Gain Image Correction technique is an appropriate method for gain calibration of an imaging system associated with a moving flat panel detector and an intrinsic crosshair.
对于配备可移动平板探测器和固有十字准线的X射线成像系统而言，由于几何形状相关的足跟效应和十字准线伪影，进行增益校准是一项挑战。本研究旨在通过实施多采集增益图像校正技术，为这类系统开发一种增益校正方法。在固定曝光参数下，于4个不同的平板探测器位置采集包含十字准线和足跟效应的泛射场图像。使用常见的图像处理算法自动检测十字准线区域，并通过简单的插值程序将其去除，从而得到一幅去除十字准线的图像。接着采用基于大内核的校正方法来消除足跟效应。将与每个十字准线区域对应的掩膜滤波器应用于所得的去除足跟效应的图像，以使原始十字准线区域的像素无效。最后，通过本研究开发的顺序替换或选择性平均技术，用处理后图像中的相应有效像素组成一个无缝增益图。基于多采集增益图像校正增益图校正后的泛射场图像的归一化噪声功率谱和探测量子效率改善因子进行定量评估。为作比较，还测试了单个去除十字准线的增益图。结果表明，多采集增益图像校正技术比去除十字准线技术实现了更好的图像质量，在大多数空间频率上显示出更低的归一化噪声功率谱值。在增益图的先验十字准线区域，这种改善更为明显。对于去除十字准线技术、多采集增益图像校正顺序替换技术和多采集增益图像校正选择性平均技术，在先验十字准线区域，平均探测量子效率改善因子分别为1.09±0.06、2.46±0.32和3.34±0.36，在正常区域分别为2.35±0.31、2.33±0.31和3.09±0.34。因此，本研究表明，所引入的多采集增益图像校正技术是用于与移动平板探测器和固有十字准线相关的成像系统增益校准的合适方法。
