William Waters

Multi-source inverse-geometry CT: From system concept to research prototype

Third-generation CT architectures are approaching fundamental limits. Dose-efficiency is limited by finite detector efficiency and by limited control over the X-ray flux spatial profile. Increasing the volumetric coverage comes with increased scattered radiation, cone-beam artifacts, Heel effect, wasted dose and cost. Spatial resolution is limited by focal spot size and detector cell size. Temporal resolution is limited by mechanical constraints, and alternative geometries such as electron-beam CT and dual-source CT come with severe tradeoffs in terms of image quality, dose-efficiency and complexity. The concept of multi-source inverse-geometry CT (IGCT) breaks through several of the above limitations [1-3], promising a low-dose high image quality volumetric CT architecture. In this paper, we present recent progress with the design and integration efforts of the first gantry-based multi-source CT scanner.

Multisource inverse-geometry CT — Prototype system integration

Todays 3rd generation CT scanners have one or two X-ray tubes, with one focal spot or “source” per vacuum chamber or “tube”. Our first multi-source inverse geometry CT prototype has eight X-ray sources. We have demonstrated multisource imaging with an 8-spot X-ray tube on a stationary gantry and a rotating phantom. We present an update on the development of the gantry-based multi-source CT scanner: we combine the multi-source X-ray tube and gantry rotation producing the first multi-source gantry-based CT scanner prototype. Currently the system is in the process of being upgraded to 32 X-ray sources to provide a larger field-of-view and to demonstrate the concept of virtual bowtie.

Design and characterization of electron beam focusing for X-ray generation in novel medical imaging architecture.

A novel electron beam focusing scheme for medical X-ray sources is described in this paper. Most vacuum based medical X-ray sources today employ a tungsten filament operated in temperature limited regime, with electrostatic focusing tabs for limited range beam optics. This paper presents the electron beam optics designed for the first distributed X-ray source in the world for Computed Tomography (CT) applications. This distributed source includes 32 electron beamlets in a common vacuum chamber, with 32 circular dispenser cathodes operated in space charge limited regime, where the initial circular beam is transformed into an elliptical beam before being collected at the anode. The electron beam optics designed and validated here are at the heart of the first Inverse Geometry CT system, with potential benefits in terms of improved image quality and dramatic X-ray dose reduction for the patient.