Tomosynthesis requires projection images from different viewing angles. Using a distributed x-ray source this can be
achieved without mechanical motion of the source with the potential for faster image acquisition speed. A distributed xray
tube has been designed and manufactured specifically for breast tomosynthesis. The x-ray tube consists of 31 field
emission x-ray sources with an angular range of 30°. The total dose is up to 100mAs with an energy range between 27
and 45 kVp. We discuss the source geometry and results from the characterization of the first prototype. The x-ray tube
uses field emission cathodes based on carbon nanotubes (CNT) as electron source. Prior to the manufacturing of the
sealed x-ray tube extensive testing on the field emission cathodes has been performed to verify the requirements for
commercial tomosynthesis systems in terms of emission current, focal spot size and tube lifetime.
Tomosynthesis imaging requires projection images from different viewing angles. Conventional systems use a moving xray
source to acquire the individual projections. Using a stationary distributed x-ray source with a number of sources that
equals the number of required projections, this can be achieved without any mechanical motion. Advantages are a
potentially faster image acquisition speed, higher spatial and temporal resolution and simple system design. We present
distributed x-ray sources based on carbon nanotube (CNT) field emission cathodes. The field emission cathodes deliver
the electrons required for x-ray production. CNT emitters feature a stable emission at high current density, a cold
emission, excellent temporal control of the emitted electrons and good configurability. We discuss the use of stationary
sources for two applications: (i) a linear tube for stationary digital breast tomosynthesis (sDBT), and (ii) a square tube for
on-board tomosynthesis image-guided radiation therapy (IGRT). Results from high energy distributed sources up to
160kVp are also presented.
As a widely adopted imaging modality for pre-clinical research, micro-CT is constantly facing the need of providing
better temporal as well as spatial resolution for a variety of imaging applications. Faster CT scanning speed is also
preferred for higher imaging throughput. We recently proposed a gantry-free multi-beam micro-CT (MBμCT) design
which has the potential to overcome some of the intrinsic limitations of current rotating-gantry CT technology. To
demonstrate its feasibility, we have constructed a testing system with a multi-beam field emission x-ray (MBFEX)
source array with a linear array of 20 individually controllable x-ray emitting pixels. Based on simulations of the electron
optics and preliminary experimental measurements the design of the MBFEX source has been further optimized. The
newly designed imaging system has been characterized and commissioned following our standard imaging protocol. It
has clearly shown improved system stability and enhanced imaging capability. As a result of reduced mechanical
rotation during imaging acquisition, we are expecting to achieve higher CT scanning speed without significantly
sacrificing imaging quality. This prototype MBμCT system, although still in its early development phase, has been
proved to be an ideal testing platform for the proposed gantry-free micro-CT scanner.
As a new three-dimensional breast imaging technique, breast tomosynthesis allows the reconstruction of an arbitrary set
of planes in the breast from a limited-angle series of x-ray projection images. The breast tomosynthesis technique has
been demonstrated as promising to improve early breast cancer detection. This paper represents a preliminary phantom
study and computer simulation results of different breast tomosynthesis reconstruction algorithms with a novel carbon
nanotube based multi-beam x-ray source. Five representative tomosynthesis reconstruction algorithms, including back
projection (BP), filtered back projection (FBP), matrix inversion tomosynthesis (MITS), maximum likelihood
expectation maximization (MLEM), and simultaneous algebraic reconstruction technique (SART) were investigated.
Tomosynthesis projection images of a phantom were acquired with the stationary multi-beam x-ray tomosynthesis
system. Reconstruction results from different algorithms were studied. A computer simulation study was further done to
investigate the sharpness of reconstructed in-plane structures and to see how effective each algorithm is at removing
out-of-plane blur with parallel-imaging geometries. Datasets with 9 and 25 projection images of a defined 3D spherical
object were simulated with a total view angle of 50 degrees. Results showed that the multi-beam x-ray system is capable
to generate 3D tomosynthesis images with faster speed compared with current commercial prototype systems. With
simulated parallel-imaging geometry, MITS and FBP showed edge enhancement in-plane performance. BP, FBP and
MLEM performed better at out-of-plane structure removal with larger number of projection images.
We have designed and built a stationary digital breast tomosynthesis (DBT) system containing a carbon nanotube
based field emission x-ray source array to examine the possibility of obtaining a reduced scan time and improved
image quality compared to conventional DBT systems. There are 25 individually addressable x-ray sources in our
linear source array that are evenly angularly spaced to cover an angle of 48°. The sources are turned on sequentially
during imaging and there is no motion of either the source or the detector. We present here an iterative reconstruction
method based on a modified Ordered-Subset Convex (MOSC) algorithm that was employed for the reconstruction of
images from the new DBT system. Using this algorithm based on a maximum-likelihood model, we reconstruct on
non-cubic voxels for increased computational efficiency resulting in high in-plane resolution in the images. We have
applied the reconstruction technique on simulated and phantom data from the system. Even without the use of the
subsets, the reconstruction of an experimental 9-beam system with 960×768 pixels took less than 6 minutes (10
iterations). The projection images of a simulated mammography accreditation phantom were reconstructed using
MOSC and a Simultaneous Algebraic Reconstruction technique (SART) and the results from the comparison between
the two algorithms allow us to conclude that the MOSC is capable of delivering excellent image quality when used in
tomosynthesis image reconstruction.
Currently all CT scanners collect the projection images sequentially, one at a time. The serial approach demands high x-ray
power which in turn limits the scanning speed of the CT scanners. To overcome the limitations of the current CT
scanners, the concept of stationary CT canners has been proposed to completely eliminate the need for gantry rotation. In
such multi-pixel x-ray system, multiple x-ray sources and detectors are distributed around the scanning tunnel. Based on
the multi-pixel x-ray system, we have recently demonstrated the feasibility of multiplexing radiography that enables
simultaneous collection of multiple projection images through multiplexing. A drastic increase of the speed and
reduction of the x-ray peak power can be potentially achieved without compromising the imaging quality. In this paper
we demonstrated novel Hadamard multiplexing radiography based on Hadamard transform technique using a carbon
nanotube based multi-pixel x-ray source. The combination of the multi-pixel x-ray and multiplexing technologies has the
potential to lead to a new generation of stationary CT scanners that have drastically increased throughput at reduced cost.
A stationary digital breast tomosynthesis (DBT) system using a carbon nanotube based multi-beam field emission x-ray
(MBFEX) source has been designed. The purpose is to investigate the feasibility of reducing the total imaging time,
simplifying the system design, and potentially improving the image quality comparing to the conventional DBT
scanners. The MBFEX source consists of 25 individually programmable x-ray pixels which are evenly angular spaced
covering a 48° field of view. The device acquires the projection images by electronically switching on and off the
individual x-ray pixels without mechanical motion of either the x-ray source or the detector. The designs of the x-ray
source and the imaging system are presented. Some preliminary results are discussed.
We have recently demonstrated the feasibility of frequency multiplexing radiography (FMR) technique based on the frequency division multiplexing (FDM) principle and the carbon nanotube field emission x-ray technology. The key component of the FMR technique is a multi-pixel carbon nanotube field emission x-ray source. The prototype multi-pixel x-ray source has a linear array of nine field emission x-ray pixels. By programming the control electronics, the multi-pixel x-ray source can generate spatially and temporally modulated x-ray radiation. During the multiplexing imaging process, all the x-ray pixels were turned on simultaneously with each beam modulated at different frequency. The superimposed x-ray signals generated by the multi-pixel x-ray source were captured using a high speed flat panel x-ray detector over a certain period of time. The collected composite images were then demultiplexed using a Fourier transform based algorithm to recover the original nine projection images from different view angles. The FMR technique can in principle increase the imaging speed and reduce the x-ray peak workload for applications such as computed tomography (CT). In this paper we evaluated the performance of this new radiographic imaging technique based on our simulation and experiment results. Imaging artifacts caused by the cross-talk among different frequency subchannels have been studied and the importance of orthogonal frequency division multiplexing (OFDM) has been demonstrated.
State-of-the-art tomographic imaging technique is based upon of simple serial imaging scheme. The tomographic scanners collect the projection images sequentially in the time domain, by a step-and-shoot process using a single-pixel x-ray source. The inefficient serial data collection scheme severely limits the data collection speed, which is critical for imaging of objects in rapid motion such as for diagnosis of cardiovascular diseases, CT fluoroscopy, and airport luggage inspection. Further improvement of the speed demands an increasingly high x-ray peak workload and gantry rotation speed, both of which have approached the engineering limits. Multiplexing technique, which has been widely adopted in communication devices and in certain analytical instruments, holds the promise to significantly increase the data throughput. It however, has not been applied to x-ray radiography, mainly due to limitations of the current x-ray source technology. Here we report a method for frequency multiplexing radiography (FMR) based on the frequency multiplexing principle and the carbon nanotube field emission x-ray technology. We show the feasibility of multiplexing radiography that enables simultaneous collection of multiple projection images. It has the potential to significantly increase the imaging speed for tomographic imaging without compromising the imaging quality.
In this study, we report a multi-beam x-ray imaging system that can generate a scanning x-ray beam to image an object from multiple projection angles without mechanical motion. The key part of this imaging system is a multi-beam field emission x-ray (MBFEX) source which comprises a linear array of gated electron emitting pixels. The pixels are individually addressable via a MOSFET (metal-oxide-semiconductor field effect transistor) based electronic circuit. The device can provide a tube current of 0.1-1 mA at 40 kVp with less than 300 μm focal spot size from each of the emitting pixels. Multilayer images of different phantoms were reconstructed to demonstrate its potential applications in tomographic imaging. Since no mechanical motion is needed and the electronic switching time is generally negligible the MBFEX system has the potential to simplify the system design and lead to a fast data acquisition for tomographic imaging.