Ritschl Ludwig, Kuntz Jan, Fleischmann Christof, Kachelrieß Marc
Ziehm Imaging GmbH, Donaustraße 31, Nürnberg 90451, Germany.
Medical Physics in Radiology, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 280, Heidelberg 69120, Germany.
Med Phys. 2016 May;43(5):2295. doi: 10.1118/1.4944785.
In the last decade, C-arm-based cone-beam CT became a widely used modality for intraoperative imaging. Typically a C-arm CT scan is performed using a circular or elliptical trajectory around a region of interest. Therefore, an angular range of at least 180° plus fan angle must be covered to ensure a completely sampled data set. However, mobile C-arms designed with a focus on classical 2D applications like fluoroscopy may be limited to a mechanical rotation range of less than 180° to improve handling and usability. The method proposed in this paper allows for the acquisition of a fully sampled data set with a system limited to a mechanical rotation range of at least 180° minus fan angle using a new trajectory design. This enables CT like 3D imaging with a wide range of C-arm devices which are mainly designed for 2D imaging.
The proposed trajectory extends the mechanical rotation range of the C-arm system with two additional linear shifts. Due to the divergent character of the fan-beam geometry, these two shifts lead to an additional angular range of half of the fan angle. Combining one shift at the beginning of the scan followed by a rotation and a second shift, the resulting rotate-plus-shift trajectory enables the acquisition of a completely sampled data set using only 180° minus fan angle of rotation. The shifts can be performed using, e.g., the two orthogonal positioning axes of a fully motorized C-arm system. The trajectory was evaluated in phantom and cadaver examinations using two prototype C-arm systems.
The proposed trajectory leads to reconstructions without limited angle artifacts. Compared to the limited angle reconstructions of 180° minus fan angle, image quality increased dramatically. Details in the rotate-plus-shift reconstructions were clearly depicted, whereas they are dominated by artifacts in the limited angle scan.
The method proposed here employs 3D imaging using C-arms with less than 180° rotation range adding full 3D functionality to a C-arm device retaining both handling comfort and the usability of 2D imaging. This method has a clear potential for clinical use especially to meet the increasing demand for an intraoperative 3D imaging.
在过去十年中，基于C形臂的锥形束CT成为术中成像广泛使用的方式。典型的C形臂CT扫描是围绕感兴趣区域使用圆形或椭圆形轨迹进行的。因此，必须覆盖至少180°加扇角的角度范围，以确保获得完全采样的数据集。然而，专注于荧光透视等传统二维应用而设计的移动C形臂，可能限于小于180°的机械旋转范围，以提高操作性和易用性。本文提出的方法允许使用新的轨迹设计，在机械旋转范围至少为180°减扇角的系统中获取完全采样的数据集。这使得具有广泛二维成像设计的C形臂设备能够实现类似CT的三维成像。
所提出的轨迹通过两个额外的线性位移扩展了C形臂系统的机械旋转范围。由于扇形束几何形状的发散特性，这两个位移导致了额外的半个扇角的角度范围。在扫描开始时进行一次位移，接着进行旋转，然后进行第二次位移，由此产生的旋转加位移轨迹能够仅使用180°减扇角的旋转来获取完全采样的数据集。位移可以使用例如全电动C形臂系统的两个正交定位轴来执行。使用两个原型C形臂系统在体模和尸体检查中对该轨迹进行了评估。
所提出的轨迹能够实现无有限角度伪影的重建。与180°减扇角的有限角度重建相比，图像质量显著提高。旋转加位移重建中的细节清晰可辨，而在有限角度扫描中则主要被伪影所主导。
本文提出的方法采用旋转范围小于180°的C形臂进行三维成像，为C形臂设备增加了完整的三维功能，同时保持了操作舒适性和二维成像的易用性。这种方法在临床应用中具有明显的潜力，特别是为了满足对术中三维成像日益增长的需求。
