Nagesh S V Setlur, Rana R, Russ M, Ionita Ciprian N, Bednarek D R, Rudin S
Toshiba Stroke and Vascular Research Center, University at Buffalo.
Proc SPIE Int Soc Opt Eng. 2016 Feb 27;9783. doi: 10.1117/12.2216916. Epub 2016 Mar 31.
Small pixel high resolution direct x-ray detectors have the advantage of higher spatial sampling and decreased blurring characteristic. The limiting factors for such systems becomes the degradation due to the focal spot size. One solution is a smaller focal spot; however, this can limit the output of the x-ray tube. Here a software solution of deconvolving with an estimated focal spot blur is presented. To simulate images from a direct detector affected with focal-spot blur, first a set of high-resolution stent images (FRED from Microvention, Inc., Tustin, CA) were acquired using a 75μm pixel size Dexela-Perkin-Elmer detector and frame averaged to reduce quantum noise. Then the averaged image was blurred with a known Gaussian blur. To add noise to the blurred image a flat-field image was multiplied with the blurred image. Both the ideal and the noisy-blurred images were then deconvolved with the known Gaussian function using either threshold-based inverse filtering or Weiner deconvolution. The blur in the ideal image was removed and the details were recovered successfully. However, the inverse filtering deconvolution process is extremely susceptible to noise. The Weiner deconvolution process was able to recover more of the details of the stent from the noisy-blurred image, but for noisier images, stent details are still lost in the recovery process.
小像素高分辨率直接X射线探测器具有更高空间采样和降低模糊特性的优势。此类系统的限制因素是由于焦点尺寸导致的图像退化。一种解决方案是使用更小的焦点；然而，这会限制X射线管的输出。本文提出了一种通过估计焦点模糊进行去卷积的软件解决方案。为了模拟受焦点模糊影响的直接探测器的图像，首先使用75μm像素尺寸的Dexela - Perkin - Elmer探测器采集一组高分辨率支架图像（来自Microvention公司，加利福尼亚州图斯廷市的FRED），并进行帧平均以降低量子噪声。然后用已知的高斯模糊对平均后的图像进行模糊处理。为了给模糊图像添加噪声，将平场图像与模糊图像相乘。接着，使用基于阈值的逆滤波或维纳去卷积，将理想图像和有噪声的模糊图像都与已知的高斯函数进行去卷积。理想图像中的模糊被去除，细节得以成功恢复。然而，逆滤波去卷积过程对噪声极其敏感。维纳去卷积过程能够从有噪声的模糊图像中恢复更多支架细节，但对于噪声更大的图像，支架细节在恢复过程中仍然会丢失。
