Burion Steve, Funk Tobias
Triple Ring Technologies.
J Vis Exp. 2011 Sep 11(55):3236. doi: 10.3791/3236.
X-ray fluoroscopy is widely used for image guidance during cardiac intervention. However, radiation dose in these procedures can be high, and this is a significant concern, particularly in pediatric applications. Pediatrics procedures are in general much more complex than those performed on adults and thus are on average four to eight times longer. Furthermore, children can undergo up to 10 fluoroscopic procedures by the age of 10, and have been shown to have a three-fold higher risk of developing fatal cancer throughout their life than the general population. We have shown that radiation dose can be significantly reduced in adult cardiac procedures by using our scanning beam digital x-ray (SBDX) system-- a fluoroscopic imaging system that employs an inverse imaging geometry (Figure 1, Movie 1 and Figure 2). Instead of a single focal spot and an extended detector as used in conventional systems, our approach utilizes an extended X-ray source with multiple focal spots focused on a small detector. Our X-ray source consists of a scanning electron beam sequentially illuminating up to 9,000 focal spot positions. Each focal spot projects a small portion of the imaging volume onto the detector. In contrast to a conventional system where the final image is directly projected onto the detector, the SBDX uses a dedicated algorithm to reconstruct the final image from the 9,000 detector images. For pediatric applications, dose savings with the SBDX system are expected to be smaller than in adult procedures. However, the SBDX system allows for additional dose savings by implementing an electronic adaptive exposure technique. Key to this method is the multi-beam scanning technique of the SBDX system: rather than exposing every part of the image with the same radiation dose, we can dynamically vary the exposure depending on the opacity of the region exposed. Therefore, we can significantly reduce exposure in radiolucent areas and maintain exposure in more opaque regions. In our current implementation, the adaptive exposure requires user interaction (Figure 3). However, in the future, the adaptive exposure will be real time and fully automatic. We have performed experiments with an anthropomorphic phantom and compared measured radiation dose with and without adaptive exposure using a dose area product (DAP) meter. In the experiment presented here, we find a dose reduction of 30%.
X射线荧光透视检查在心脏介入手术的图像引导中被广泛应用。然而，这些手术中的辐射剂量可能很高，这是一个重大问题，尤其是在儿科应用中。儿科手术总体上比成人手术复杂得多，因此平均时长是成人手术的四到八倍。此外，儿童在10岁前可能要接受多达10次荧光透视检查，并且已证明他们一生中患致命癌症的风险比普通人群高三倍。我们已经表明，通过使用我们的扫描束数字X射线（SBDX）系统——一种采用反向成像几何结构的荧光透视成像系统（图1、视频1和图2），可以在成人心脏手术中显著降低辐射剂量。与传统系统中使用的单个焦点和扩展探测器不同，我们的方法利用具有多个焦点的扩展X射线源聚焦在一个小探测器上。我们的X射线源由一个扫描电子束依次照亮多达9000个焦点位置组成。每个焦点将成像体积的一小部分投射到探测器上。与传统系统中最终图像直接投射到探测器上不同，SBDX使用一种专用算法从9000张探测器图像重建最终图像。对于儿科应用，预计SBDX系统的剂量节省比成人手术要小。然而，SBDX系统通过实施电子自适应曝光技术可以进一步节省剂量。这种方法的关键是SBDX系统的多束扫描技术：我们不是用相同的辐射剂量照射图像的每个部分，而是可以根据所照射区域的不透明度动态改变曝光量。因此，我们可以显著降低在射线可透过区域的曝光，并在更不透明的区域保持曝光。在我们目前的实现中，自适应曝光需要用户交互（图3）。然而，在未来，自适应曝光将是实时且完全自动的。我们使用一个人体模型进行了实验，并使用剂量面积积（DAP）仪比较了有无自适应曝光时测量的辐射剂量。在此呈现的实验中，我们发现剂量降低了30%。
