Current computed tomography (CT) scanners rotate fast to reduce motion artifact. X-ray tube must work in a high power to make the image clear under short exposure time. However, the life span of such a tube may be shortened. In this paper, we propose a novel double sources CT imaging system, which puts two of the same X-ray sources closely with each other. The system is different from current dual source CT with orthogonal X-ray sources. In our system, each projection is taken twice by these two sources to enhance the exposure value and then recovered to a single source projection for image reconstruction. The proposed system can work like normal single source CT system, while halving down the working power for each tube.
Current computed tomography (CT) scanners acquire multiple projection images (~1000 frames) [
In this paper, a novel CT imaging system is developed by placing two of the same X-ray tubes close to each other, along with a common detector. The system is different from current dual source CT system, where two sets of tube detectors are placed orthogonally [
In the following sections, first we describe the structure of adjacent double X-ray sources and then propose a method to separate the overlapped projections for image reconstruction. For demonstration, fan-beam data acquisition and image reconstruction are presented, but the method can be easily extended to cone beam image reconstruction. Lastly, we discuss the potential benefits and limitations of the proposed method.
The structure of traditional CT scanner system is illustrated in Figure
(a) Current CT scanner system using a single-beam X-ray source and arc detector, whose focus is located in the source. (b) The proposed adjacent double X-ray sources system, in which the focus of the arc detector is located in the rotating center.
In this illustration about proposed double X-ray sources scanning system, sources are labeled as S1 and S2. As shown in Figure
Just like the Hadamard multiplexing radiography (HMR) method [
As an example for the
Rotation of the adjacent double X-ray sources system.
For simplicity and clarity, in Figure
Overlapped projections with the drifted detector. In two adjacent overlapped projections, there exist two original projected signals that come from the same angle source and that are accepted by the drifted detector.
The flow chart of the general imaging and data processing procedure for this adjacent double X-ray sources system is shown in Figure
Flow chart of the imaging procedure of the adjacent double X-ray sources system. The incident X-ray comes from two sources transmitted through the object and formed an overlapped X-ray projection recorded by the arc X-ray detector. After a complete set of overlapped projections were acquired, the proposed algorithm was applied to the projection data to recover the original projection images.
By means of variable substitution, we get the FBP method for the fan-beam reconstruction [
Illustration of the two kinds of arc detectors.
To demonstrate the feasibility of the proposed system, the Shepp-Logan phantom was applied to simulate double sources exposure. The opening angle of the two sources to the rotation center was
Sinogram of projections: from left to right it is under single X-ray source, overlapped and separated under double X-ray sources.
The Shepp-Logan phantom is shown in Figure
(a) Shepp-Logan phantom. (b) Reconstructed image from the projections under single X-ray source. (c) Reconstructed image from the signals separated from the overlapped projections under two X-ray sources. Display window: [0.1 0.3].
Profile comparison between reconstructed (solid red line) and true image (dashed blue line) on the horizontal and vertical central line.
In the simulation above, we present preliminary studies that demonstrate image reconstruction noise-free with the overlapped projections under adjacent double X-ray sources. In this imaging system, two X-ray sources must be the same, that is, the machine model, radiation field of photons. In practice, radiation field could be adjusted by the working voltage and current. Our results are provided about the fan-beam reconstruction, but the method is suitable for cone beam CT; just make sure that the two adjacent X-ray sources are placed parallel to the rotating direction and that the opening angle of the two sources to rotation center agree with the acquisition angle. In normal CT scanning, we take hundreds of projections during one circle. The angle rotated between two sampling is so small that two X-ray sources must be placed close to each other. We could place two identical cathode filament in one X-ray tube. However, sparse projections reconstruction acquires fewer projections than conventional methods; the sampling angle is relatively big, which facilitates placing two X-ray tubes together.
As compared to traditional CT system, the proposed adjacent double X-ray sources system can squeeze double X-ray photons during one unit exposure time; thus, it can easily enhance the illumination for some situations that need a high exposure rate such as fat patients. Also, high exposure rate during one unit exposure time gives the ability to halve down the projections acquisition time to reduce the motion artifact. On the other hand, if fast exposure is not required, two sources that work in a half power can give enough X-ray photons, which can prolong the lifetime of the tubes.
The main advantage of such a configuration is the power, since the two tubes can operate simultaneously. However, several issues should be tackled before it can be used in clinic. First, scatter is a big issue that can influence the quality of the reconstructed images. Figure
Antiscatter collimators.
In this paper, we developed a novel structure of CT system with adjacent double X-ray sources. In the proposed system, two X-ray sources work simultaneously. Therefore, the tube can work longer under the same exposure dose as traditional single source or it can give a high exposure rate for some situations such as fat patients. Because the sources are not necessary to be modulated and the reconstruction method is based on the FBP algorithm, the system can be realized by current X-ray tube technology and CT structure.
This work was supported in part by Grants from the National Natural Science Foundation of China (NSFC: 81171402), the NSFC Joint Research Fund for Overseas Research Chinese, the Hong Kong and Macao Young Scholars (30928030), the National Basic Research Program 973 (2010CB732606) from the Ministry of Science and Technology of China, and the Guangdong Innovative Research Team Program (no. 2011S013) of China.