Methods, apparatus, and computer-program products for increasing accuracy in cone-beam computed tomography
AssigneeVarian Medical Systems, Inc.
InventorLarry Partain
Life of this patent
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Abstract
Disclosed are methods, systems, and computer-product programs for increasing accuracy in cone-beam computed tomography (CBCT) by obscuring portions of the radiation source so that the radiation only passes through the specific areas of the patient related to the regions-of-interest to the doctor. The obscuring action causes less radiation scattering to occur in the patient's body, thereby reducing a major source of error in the image accuracy caused by scattered radiation. Scattered radiation received by detector pixels that are obscured by direct-line of sight radiation may be used to estimate the scattered radiation in the un-obscured portion, which can be used to further increase the accuracy of the image.
Claims25
A method of operating a cone-beam CT scanning system, the system having a two-dimensional pixel array having a first dimension, a second dimension, a number Xpix of pixels in the first dimension, and number of Ypix pixels in the second dimension, Xpix being greater than one hundred and Ypix being greater than ten, the system further having a source of radiation that emits a cone-beam of radiation that normally covers all of the pixels of the pixel array, the method comprising:
- determining an extent of the pixel array that the cone-beam radiation will receive direct-path radiation passing through a target volume of an object during a rotational scan of the object, the rotation scan including a plurality of projections of the object taken at a corresponding plurality of relative angles between the object and the source of radiation, the extent of the angles being equal to or greater than 180 degrees, the target volume being smaller than the volume of the object;
- and
- obscuring a portion of the cone beam of radiation such that direct rays of the radiation cover at least the determined extent, but less than 85 percent of the pixel array.
A method of reconstructing projection data comprising:
- acquiring a first set of radiographic projections of an object that has been taken by a system having a pixel array with a plurality of pixels and a radiation source, the radiation source capable of covering all of the pixels of the pixel array with direct rays of radiation, wherein each radiographic projection has been taken with a portion of the pixels of the pixel array obscured from direct rays of radiation from the radiation source, wherein each radiographic projection of the first set comprises image values for all of pixels of the pixel array;
- acquiring an indication of which pixels of the pixel array have been obscured from direct rays of radiation from the radiation source;
- generating estimates of scattered radiation from the image values that are from the first set of radiographic projections and that are for pixels of the pixel array that have been obscured from direct rays of radiation from the radiation source;
- generating corrected radiographic projections from the first set of radiographic projections and the estimates of the scattered radiation;
- and
- performing a truncated reconstruction of the object using the first set of the radiographic projections and the indication of which pixels have been obscured from direct rays of radiation from the radiation source;
- wherein performing the truncated reconstruction generates a reconstruction from the corrected radiographic projections.
A computer-program product that directs a data processor to reconstruct projection data, the product comprising:
- a tangible non-transitory computer-readable medium;
- a first set of instructions embodied on the computer-readable medium that directs a data processor to acquire a first set of radiographic projections of an object that has been taken by a system having a pixel array with a plurality of pixels and a radiation source, the radiation source normally covering all of the pixels of the pixel array with direct rays of radiation, wherein each radiographic projection has been taken with a portion of the pixels of the pixel array obscured from direct rays of radiation from the radiation source, wherein each radiographic projection of the first set comprises image values for all of pixels of the pixel array;
- a second set of instructions embodied on the computer-readable medium that directs the data processor to acquire an indication of which pixels of the pixel array have been obscured from direct rays of radiation from the radiation source;
- a third set of instructions embodied on the computer-readable medium that directs the data processor to perform a truncated reconstruction of the object using the first set of the radiographic projections and the indication of which pixels have been obscured from direct rays of radiation from the radiation source;
- and
- a fourth set of instructions embodied on the computer-readable medium that directs the data processor to store the results of the truncated reconstruction on a tangible computer-readable memory;
- and
- a fifth set of instructions embodied on the computer-readable medium that directs the data processor to generate estimates of scattered radiation from the image values that are from the first set of radiographic projections and that are for pixels of the pixel array that have been obscured from direct rays of radiation from the radiation source, and to generate corrected radiographic projections from the first set of radiographic projections and the estimates of the scattered radiation;
- and
- wherein the third set of instructions directs the data processor to perform the truncated reconstruction using the corrected radiographic projections.
Dependencies are inferred from the claim text.