Rudin S, Bednarek D R, Yang C Y
Department of Radiology, Toshiba Stroke Research Center, School of Medicine and Biomedical Sciences, The State University of New York at Buffalo, 14215, USA.
Med Phys. 1999 Jul;26(7):1359-64. doi: 10.1118/1.598631.
In region-of-interest (ROI) radiologic imaging, the x-ray beam is attenuated peripherally to the region of interest to reduce patient exposure. This attenuation reduces the peripheral image brightness which may cause contrast in the periphery to also be reduced due to video chain nonlinearity. For optimal viewing, it is necessary that the image brightness and contrast in the periphery be brought back to the levels in the ROI. Previously, digital subtraction angiography roadmapping equipment has been used for this equalization; however, the procedure is not independent of patient and gantry motion. A new motion independent method to achieve this equalization involves dividing the real-time video signal into two digital streams one of which is brightness and contrast enhanced. A pre-acquired binary mask image is created by thresholding the image of a uniform object obtained with the ROI filter in place. This binary mask is used to control the recombination of the two image streams in a digital pipeline processor in order to select the ROI from the unprocessed stream and the periphery from the enhanced stream. This system provides image equalization at 30 frame/s for real-time ROI imaging display. Images from this method demonstrate excellent image quality even for peripheral exposure reduction factors exceeding 10.
在感兴趣区域（ROI）放射成像中，X射线束在感兴趣区域的周边被衰减，以减少患者的辐射剂量。这种衰减会降低周边图像的亮度，由于视频链的非线性，这可能会导致周边的对比度也降低。为了实现最佳观察效果，有必要将周边的图像亮度和对比度恢复到感兴趣区域的水平。以前，数字减影血管造影路图设备已被用于这种均衡处理；然而，该过程并不独立于患者和机架运动。一种新的独立于运动的实现这种均衡的方法，涉及将实时视频信号分成两个数字流，其中一个数字流的亮度和对比度得到增强。通过对在安装了ROI滤波器的情况下获得的均匀物体的图像进行阈值处理，创建一个预先获取的二值掩模图像。这个二值掩模用于控制数字流水线处理器中两个图像流的重组，以便从未处理的流中选择感兴趣区域，从增强的流中选择周边区域。该系统以30帧/秒的速度提供图像均衡，用于实时ROI成像显示。即使周边辐射剂量减少因子超过10，该方法生成的图像也显示出优异的图像质量。
