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Distributed X-ray Source Technology

Background

X-ray radiation is widely used today for applications including medical imaging and therapy, homeland security ,and industrial inspection. The basic design of the x-ray tubes however has not changed significantly since the discovery of Roentgen over a hundred years ago. A conventional x-ray tube is comprised of a metal filament (cathode) which emits electrons when resistively heated to over 1000oC, and a metal target (anode) that emits x-ray when bombarded by the accelerated electrons. The thermionic x-ray technology has several intrinsic shortcomings that limit the performance of the current commercial x-ray imaging systems. These include the high cathode operating temperature, low temporal resolution, limited programmability, and, especially, lack of a distributed x-ray source. The difficulty to manufacture x-ray sources with spatially distributed x-ray focal spots limits the performance of the computed tomography (CT) scanners.

Figure 1: Schematics of a rotating anode x-ray tube (Left) and the Siemens Straton rotating envelop tube (Right).

CT technique enables reconstruction of a 3D image of an object by collection of hundreds of 2D projection images from different projection angles. Over 40,000 CT scanners have now been installed worldwide for applications such medical imaging and airport baggage screening. In most of the current CT scanners, a single source x-ray tube is mechanically rotated around an object to collect the multiple projection images required for reconstruction.  This process limits the data acquisition rate and puts a high demand on the output power of the x-ray tube. In the current state-of-art clinical CT scanner, the gantry rotates at ~3Hz and the x-ray tube operates at ~100kW, both of which have approached their physical limits.

           Schematic of third generation CT        

Figure 2: A schematic showing the working principle of the current CT scanners (Left) and a picture of a commercial clinical CT scanner (Right).

Electron Field Emission  

Electron field emission is a quantum tunneling process where an electrical field is used to extract electrons. No heating is required, and the emission current can be controlled and modulated instantaneously by the external field. The “cold” cathode technology also enables the fabrication of matrix addressable distributed electron sources which can be used in a variety of vacuum electronic devices to not only replace the hot filaments but also add new capabilities and functionality. The lack of reliable high performance electron field emitters have in the past prevented the development of this technology Nanomaterials including carbon nanotubes have shown promising electron field emission properties. The potential of utilizing these novel field emitters for devices such as field emission flat panel display, electron microscope, microwave amplifier, and x-ray tube is being actively investigated in industry and academic labs worldwide. Xintek is a leader in the field of nanotechnology. Its proprietary nanomaterial based field emission electron sources have superior emission properties including high emission current and long term stability. Field emission x-ray tubes have been manufactured using Xintek’s cold cathodes which are capable of generating sufficient flux for diagnostic x-ray imaging.

XinRay´s Field Emission Multi-Pixel X-ray Technology

Our new distributed x-ray source generates digitized x-ray radiation with fine control of the spatial distribution and temporal modulation of the x-ray radiation. The flexibility in the distibuted configuration and unparalleled programming capability allow system vendors to design new systems with enhanced performance and new capabilities. In particular, the spatially distributed x-ray source makes it possible to design gantry-free CT systems with faster scanning speed and potentially better imaging quality compared to the current systems. Our x-ray tubes are typically customer designed to meet the specific requirements from the system vendors. We also provide the control electronics and the power supplies. We work closely with the system vendors to interface the x-ray source with the system.

                

 

 

 

 

 

 

 

 

 

 

 

 

Figure 3: A schematic illustrating the concept of stationary CT scanner with multiple x-ray source (Left) and a prototype source fabricated by XinRay (Right).

 

 
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