Apparatus and method for dynamic calibration of spectral CT with rotating X-ray source and stationary energy discriminating detectors
View Patent ↗An apparatus and method for dynamically calibrating a computed-tomography (CT) scanner that includes a rotating X-ray source and a plurality of stationary energy-discriminating detectors configured to capture incident X-ray photons emitted from the X-ray source. A bowtie filter with a unique geometry and material composition is used to generate reference beams of a desired intensity. The apparatus includes a processor that is configured to remove a scattering background based on data obtained from the reference beams and compute a change in a predetermined calibration function.
1. A computed-tomography (CT) apparatus, comprising:
a rotating X-ray source;
a plurality of stationary energy-discriminating detectors configured to capture incident X-ray photons emitted from the X-ray source;
a bowtie filter configured to generate reference beams of respective desired intensities outside a scan field of view; and
a processor configured to
obtain reference count rates corresponding to the reference beams incident on a detector outside the scan field of view, and
update a calibration function based on the obtained reference count rates at the detector, wherein the updated calibration function is used to determine X-ray intensities from scan count rates obtained at the detector when the detector is within the scan field of view.
2. The CT apparatus of claim 1 , wherein the X-ray source and the bowtie filter generate
the reference beams including a leading reference beam and a trailing reference beam.
3. The CT apparatus of claim 2 , wherein both the leading reference beam and the trailing
reference beam are used to update the calibration function.
4. The CT apparatus of claim 1 , wherein the processor is configured to update a respective calibration function for each detector of the plurality of energy-discriminating detectors.
5. The CT apparatus of claim 1 , wherein a change in the calibration function is time-dependent.
6. The CT apparatus of claim 1 , wherein the bowtie filter includes an air channel to create
an X-ray of desired intensity.
7. The CT apparatus of claim 1 , wherein the processor is further configured to perform scattering correction based on data collected when the reference beams are incident on the detector.
8. The CT apparatus of claim 1 , wherein the processor is configured to update the calibration function by calculating a change in the calibration function using a first-order approximation.
9. A method for calibrating a computed-tomography (CT) scanner, comprising:
generating reference beams of respective desired intensities outside a scan field of view;
capturing incident X-ray photons at an energy-discriminating detector;
obtaining reference count rates corresponding to the reference beams incident on the detector when the detector is outside the scan field of view;
updating a calibration function based on the obtained reference count rates at the detector, wherein the updated calibration function is used to determine X-ray intensities from scan count rates obtained at the detector when the detector is within the scan field of view.
10. A non-transitory computer readable medium having stored thereon a program that when executed by a computer, causes a computed-tomography apparatus to perform the steps of:
generating reference beams of respective desired intensities outside a scan field of view;
capturing incident X-ray photons at an energy-discriminating detector;
obtaining reference count rates corresponding to the reference beams incident on the detector when the detector is outside the scan field of view;
updating a calibration function based on the obtained reference count rates at the detector, wherein the updated calibration function is used to determine X-ray intensities from scan count rates obtained at the detector when the detector is within the scan field of view.