Multi-source inverse geometry CT: a new system concept for x-ray computed tomography

Abstract

Third-generation CT architectures are approaching fundamental limits. Spatial resolution is limited by the focal spot size and the detector cell size. Temporal resolution is limited by mechanical constraints on gantry rotation speed, and alternative geometries such as electron-beam CT and two-tube-two-detector CT come with severe tradeoffs in terms of image quality, dose-efficiency and complexity. Image noise is fundamentally linked to patient dose, and dose-efficiency is limited by finite detector efficiency and by limited spatio-temporal control over the X-ray flux. Finally, volumetric coverage is limited by detector size, scattered radiation, conebeam artifacts, Heel effect, and helical over-scan. We propose a new concept, multi-source inverse geometry CT, which allows CT to break through several of the above limitations. The proposed architecture has several advantages compared to third-generation CT: the detector is small and can have a high detection efficiency, the optical spot size is more consistent throughout the field-of-view, scatter is minimized even when eliminating the anti-scatter grid, the X-ray flux from each source can be modulated independently to achieve an optimal noise-dose tradeoff, and the geometry offers unlimited coverage without cone-beam artifacts. In this work we demonstrate the advantages of multi-source inverse geometry CT using computer simulations.

What is inverse-geometry CT?

“…Phantom and small animal images were successfully acquired on the prototype system. 7,8 IGCT systems illustrated in Figure 2 represent specific examples from a continuum of inverted geometries, as explained and illustrated by De Man et al 2 Starting with the fully inverted geometry (Fig. 2a), the source size can be reduced while adding detector arrays to maintain the FOV Figure 1 Conventional CT geometry with a cone-beam of x-rays emitted from a small source spot and irradiating a largearea detector.…”

“…A variety of inverted geometries were proposed in the literature, differing in the size of the distributed source, the number of source locations, and the detector size, as illustrated in Figure 2. [1][2][3][4][5] In a conventional CT geometry, x-rays emit continuously within a wide cone beam throughout an acquisition. In an inverse-geometry system, x-ray beams emit sequentially from a series of 2-dimensional locations, with one narrow x-ray beam irradiating a fraction of the field of view (FOV) at one time.…”

A new method to combine 3D reconstruction volumes for multiple parallel circular cone beam orbits

“…2͒. 32 The use of multiple source rows in the axial direction can result in the ability to image a thick volume in a single gantry rotation without cone beam artifacts. The MS-IGCT system has distributed sources in the transverse direction, each collecting data from a portion of the field-of-view ͑FOV͒, but the projection data of sources located at the same z-position can be rebinned into a full FOV cone beam data set, so the reconstruction problem reduces to the same one as for multiple parallel circular orbits.…”

CT Systems

“…Currently, newer experimental CT designs are being evaluated, such as inverse geometry CT systems [46,47]. They use an X-ray tube with multiple distributed focal spots which sequentially illuminate a small detector to cover the examination object with several ''sub-projections'', see Fig. 14.…”