Computed tomography with resolution recovery
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Publication Number
US-7852980-B2
Publication Date
2010-12-14
Expiration Date
Abstract
A system and method for recovering resolution in an x-ray computed tomography system. The system includes an x-ray source, a two-dimensional sensing array, and a controller. The x-ray source projects an x-ray beam towards subject. The x-ray source includes an anode and a cathode, where the anode has a target for directing the x-ray beam. A two-dimensional sensing array receives an x-ray beam through the subject to generate an image. The target of the anode causes a shift variant blur of the x-ray beam received by the sensing array due to the angle between the target and the sensing array. The controller is in communication with the sensing array to control acquisition and processing of the image. The controller is configured to adjust for the shift variant blur of the x-ray beam.
Core Innovation
The invention is an x-ray computed tomography resolution-recovery approach that compensates for shift-variant blur caused by an extended line focal spot or target on an anode at an oblique angle to a pixelated 2D detector. The shift-variant blur arises in an image generated by the sensing array as a result of the target causing a shift variant blur of the x-ray beam received by the sensing array. A model-based iterative reconstruction is used to recover spatial resolution that is degraded by the shift-variant blur.
A controller or processing module pre-computes a system projection operator, represented as a matrix A, that incorporates shift-variant detector response via geometry. The geometry includes an angle between the target and pixels, and the line or spot size and shape and detector element shape, so the model corresponds to a pattern of contribution of each voxel to each detector pixel. The system projection operator is based on modeling finite integration of line integrals from source points to detector points.
The model is used in a likelihood-based objective to reconstruct attenuation and recover spatial resolution compared with traditional filtered backprojection. The likelihood-based objective includes a noise model and can account for terms such as scatter and blank scan. Test results using a line-pair phantom indicate improved spatial resolution recovery, with edges recovering better than the center, using the iterative model-based method.
Claims Coverage
The independent claims cover a computed tomography system and a computed tomography method that adjust for shift-variant blur by generating a model based on an angle between the target and each pixel, and by using that model for controller-based adjustment of acquisition or processing. Across the independent claims, the core inventive features include three to four features: an anode with a target, a sensing array with pixels receiving an x-ray beam through a subject to generate an image affected by shift-variant blur, and a controller that generates a shift-variant blur model corresponding to a voxel contribution pattern and adjusts for the blur.
Anode target inducing shift-variant blur imaged by a pixelated sensing array
An x-ray source includes an anode having a target, and a sensing array configured to receive the x-ray beam through the subject has a plurality of pixels to generate an image of the target area causing shift variant blur of the x-ray beam received by the sensing array.
Controller generates a shift-variant blur model from the angle between the target and each pixel
A controller in communication with the sensing array generates a model of the shift variant blur corresponding to a pattern of contribution of each voxel based on an angle between the target and each pixel of the sensing array.
Adjustment for shift-variant blur using the controller
The controller adjusts for the shift variant blur of the x-ray beam by using the controller in the system, or the method adjusts for the shift variant blur using the controller after generating the model.
Apparent-size-based shift-variant blur model from pixel location and orientation
The controller generates a model of the shift variant blur due to the apparent size of the target based on the location and orientation of each pixel of the plurality of pixels.
Across the independent claims, computed tomography is performed or implemented by projecting with an anode target and imaging with a pixelated sensing array, where the controller models shift-variant blur as a voxel contribution pattern based on an angle between the target and pixels, and in another independent claim based on apparent size from pixel location and orientation, and adjusts acquisition or processing to compensate for the blur.
Stated Advantages
Improved spatial resolution recovery compared to traditional filtered backprojection, as shown by a line-pair phantom with edges recovering better than the center.
Documented Applications
Computed tomography resolution recovery to compensate for shift-variant blur from an extended line or spot focal spot on an anode at an oblique angle to a pixelated detector, demonstrated using a line-pair phantom.
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