Department of Biomedical Engineering, Marquette University, PO Box 1881, Milwaukee, WI 53201, USA.
J Cardiovasc Comput Tomogr. 2011 May-Jun;5(3):145-8. doi: 10.1016/j.jcct.2011.04.003. Epub 2011 Apr 16.
Inverse-geometry computed tomography (IGCT) systems are being developed to provide improved volumetric imaging. In conventional multislice CT systems, x-rays are emitted from a small area and irradiate a large-area detector. In an IGCT system, x-ray sources are distributed over a large area, with each beam irradiating a small-area detector. Therefore, in the inverse geometry, a series of narrow x-ray beams are switched on and off while the gantry rotates. In conventional CT geometry, cone-beam and scatter artifacts increase with the imaged volume thickness. An inverse geometry may be less susceptible to scatter effects, because only a fraction of the field of view is irradiated at one time. The distributed source in the inverse geometry potentially improves sampling, leading to reduced cone-beam artifacts. In the inverse geometry, the tube current may be adjusted separately for each source location, which potentially reduces dose. Multiple IGCT prototypes have been constructed and tested on phantoms. A gantry-based IGCT system with one-second gantry rotation was developed, and images of phantoms and small animals were successfully acquired. Clinical feasibility with acceptable noise levels and scan times has not yet been shown. Overall, results from prototype systems suggest that the inverse geometry will enable imaging of a thick volume (∼16 cm) while potentially reducing cone-beam artifacts, scatter effects, and radiation dose. The magnitude of these benefits will depend on the specific IGCT implementation and need to be quantified relative to comparable multislice scanners.
反向几何计算断层摄影（IGCT）系统正在被开发以提供更好的容积成像。在传统的多层 CT 系统中，X 射线从一个小区域发射并照射大面积探测器。在 IGCT 系统中，X 射线源分布在一个大区域，每个光束照射小面积探测器。因此，在反向几何中，当机架旋转时，一系列窄 X 射线束被打开和关闭。在传统 CT 几何中，随着成像体积厚度的增加，锥形束和散射伪影增加。反向几何可能不太容易受到散射效应的影响，因为一次只有一部分视场被照射。反向几何中的分布式源有可能改善采样，从而减少锥形束伪影。在反向几何中，可以为每个源位置单独调整管电流，这可能会降低剂量。已经构建并在体模上测试了多个 IGCT 原型。已经开发出一种基于机架的 IGCT 系统，其机架旋转时间为 1 秒，成功获得了体模和小动物的图像。尚未证明具有可接受噪声水平和扫描时间的临床可行性。总体而言，原型系统的结果表明，反向几何将能够对厚体积（约 16 厘米）进行成像，同时潜在地减少锥形束伪影、散射效应和辐射剂量。这些益处的大小将取决于特定的 IGCT 实现，并且需要相对于可比的多层扫描仪进行量化。
