Department of Mechanical Engineering, SUNY at Buffalo, 3435 Main Street, Buffalo, New York 14214, USA.
Med Phys. 2010 Feb;37(2):694-703. doi: 10.1118/1.3284540.
Cone-beam rotational angiography (CBRA) is widely used in the modern clinical settings. In a number of procedures, the area of interest is often considerably smaller than the field of view (FOV) of the detector, subjecting the patient to potentially unnecessary x-ray dose. The authors therefore propose a filter-based method to reduce the dose in the regions of low interest, while supplying high image quality in the region of interest (ROI).
For such procedures, the authors propose a method of filtered region of interest (FROI)-CBRA. In the authors' approach, a gadolinium filter with a circular central opening is placed into the x-ray beam during image acquisition. The central region is imaged with high contrast, while peripheral regions are subjected to a substantial lower intensity and dose through beam filtering. The resulting images contain a high contrast/intensity ROI, as well as a low contrast/intensity peripheral region, and a transition region in between. To equalize the two regions' intensities, the first projection of the acquisition is performed with and without the filter in place. The equalization relationship, based on Beer's law, is established through linear regression using corresponding filtered and nonfiltered data. The transition region is equalized based on radial profiles.
Evaluations in 2D and 3D show no visible difference between conventional FROI-CBRA projection images and reconstructions in the ROI. CNR evaluations show similar image quality in the ROI, with a reduced CNR in the reconstructed peripheral region. In all filtered projection images, the scatter fraction inside the ROI was reduced. Theoretical and experimental dose evaluations show a considerable dose reduction; using a ROI half the original FOV reduces the dose by 60% for the filter thickness of 1.29 mm.
These results indicate the potential of FROI-CBRA to reduce the dose to the patient while supplying the physician with the desired image detail inside the ROI.
锥形束旋转血管造影（CBRA）在现代临床环境中得到了广泛应用。在许多程序中，感兴趣区域通常比探测器的视场（FOV）小得多，这会使患者受到潜在的不必要的 X 射线剂量。因此，作者提出了一种基于滤波器的方法，用于降低低兴趣区域的剂量，同时在感兴趣区域（ROI）提供高质量的图像。
对于此类程序，作者提出了一种过滤感兴趣区域（FROI）-CBRA 的方法。在作者的方法中，在图像采集期间，将具有圆形中央开口的钆滤波器放置在 X 射线束中。中央区域以高对比度成像，而外围区域通过光束滤波受到显著较低的强度和剂量。所得图像包含高对比度/强度 ROI 以及低对比度/强度外围区域和两者之间的过渡区域。为了使两个区域的强度相等，在有和没有滤波器的情况下进行采集的第一次投影。基于 Beer 定律的均衡关系通过使用相应的滤波和非滤波数据进行线性回归来建立。基于径向轮廓对过渡区域进行均衡。
在 2D 和 3D 中的评估表明，传统的 FROI-CBRA 投影图像与 ROI 中的重建之间没有明显差异。CNR 评估显示 ROI 中的图像质量相似，重建的外围区域中的 CNR 降低。在所有滤波投影图像中，ROI 内的散射分数都降低了。理论和实验剂量评估表明剂量有相当大的降低；使用 ROI 为原始 FOV 的一半，对于 1.29mm 的滤波器厚度，剂量降低 60%。
这些结果表明，FROI-CBRA 有可能降低患者的剂量，同时为医生提供 ROI 内所需的图像细节。
