Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, 69120 Heidelberg, Germany and Institute of Medical Physics, Friedrich-Alexander-University (FAU) of Erlangen-Nürnberg, Henkestraße 91, 91052 Erlangen, Germany.
Med Phys. 2013 Oct;40(10):101909. doi: 10.1118/1.4819826.
Today's standard imaging technique in interventional radiology is the single- or biplane x-ray fluoroscopy which delivers 2D projection images as a function of time (2D+T). This state-of-the-art technology, however, suffers from its projective nature and is limited by the superposition of the patient's anatomy. Temporally resolved tomographic volumes (3D+T) would significantly improve the visualization of complex structures. A continuous tomographic data acquisition, if carried out with today's technology, would yield an excessive patient dose. Recently the authors proposed a method that enables tomographic fluoroscopy at the same dose level as projective fluoroscopy which means that if scanning time of an intervention guided by projective fluoroscopy is the same as that of an intervention guided by tomographic fluoroscopy, almost the same dose is administered to the patient. The purpose of this work is to extend authors' previous work and allow for patient motion during the intervention.
The authors propose the running prior technique for adaptation of a prior image. This adaptation is realized by a combination of registration and projection replacement. In a first step the prior is deformed to the current position via affine and deformable registration. Then the information from outdated projections is replaced by newly acquired projections using forward and backprojection steps. The thus adapted volume is the running prior. The proposed method is validated by simulated as well as measured data. To investigate motion during intervention a moving head phantom was simulated. Real in vivo data of a pig are acquired by a prototype CT system consisting of a flat detector and a continuously rotating clinical gantry.
With the running prior technique it is possible to correct for motion without additional dose. For an application in intervention guidance both steps of the running prior technique, registration and replacement, are necessary. Reconstructed volumes based on the running prior show high image quality without introducing new artifacts and the interventional materials are displayed at the correct position.
The running prior improves the robustness of low dose 3D+T intervention guidance toward intended or unintended patient motion.
介入放射学目前的标准成像技术是单平面或双平面 X 射线透视，它可以提供时间（2D+T）的二维投影图像。然而，这项最先进的技术由于其投影性质而受到限制，并受到患者解剖结构的叠加的限制。时间分辨的断层体积（3D+T）将显著改善复杂结构的可视化。如果使用当今的技术进行连续断层数据采集，将会对患者产生过高的剂量。最近，作者提出了一种方法，该方法可以在与透视透视相同的剂量水平下进行断层透视，这意味着如果在透视透视引导下进行的干预的扫描时间与在断层透视引导下进行的干预的扫描时间相同，则向患者给予几乎相同的剂量。这项工作的目的是扩展作者以前的工作，并允许患者在干预期间移动。
作者提出了用于适应先验图像的运行先验技术。这种自适应是通过配准和投影替换的组合来实现的。在第一步中，通过仿射和变形配准将先验变形到当前位置。然后，通过正向和反向投影步骤，用新采集的投影替换过时的投影信息。由此得到的体积即为运行先验。该方法通过模拟数据和测量数据进行了验证。为了研究干预期间的运动，模拟了一个移动头部的体模。使用由平板探测器和平滑旋转的临床龙门架组成的原型 CT 系统，对猪的真实体内数据进行了采集。
使用运行先验技术，可以在不增加剂量的情况下纠正运动。对于干预引导的应用，运行先验技术的两个步骤，即配准和替换，都是必要的。基于运行先验重建的体积具有较高的图像质量，不会引入新的伪影，并且可以将介入材料显示在正确的位置。
运行先验技术提高了低剂量 3D+T 干预引导对预期或非预期患者运动的鲁棒性。
