Managing geometric misalignment in x-ray imaging systems

Patent metadata

Field	Value
Publication number	US-10610191-B2
Application number	US-201715642754-A
Country	US
Kind code	B2
Filing date	Jul 6, 2017
Priority date	Jul 6, 2017
Publication date	Apr 7, 2020
Grant date	Apr 7, 2020

Abstract

Disclosed is a method for management of geometric misalignment in an x-ray imaging system having an x-ray source, a photon-counting x-ray detector and an intermediate collimator structure in the x-ray path between the x-ray source and the x-ray detector. The x-ray detector includes a plurality of pixels, and the collimator structure includes a plurality of collimator cells, wherein each of at least a subset of the collimator cells corresponds to a N×M matrix of pixels, where at least one of N and M is greater than one. The method includes monitoring, for a designated subset of pixels including at least two pixels that are affected differently by shadowing from the collimator structure due to geometric misalignment, output signals from the pixels of the designated subset, and determining the occurrence of geometric misalignment based on the monitored output signals from the pixels of the designated subset of pixels.

First claim

The invention claimed is:

1. A method for management of geometric misalignment in an x-ray imaging system having an x-ray source, a photon-counting x-ray detector and an intermediate collimator structure in an x-ray path between the x-ray source and the x-ray detector,
wherein the x-ray detector comprises a plurality of pixels, and the collimator structure comprises a plurality of collimator cells, wherein each of at least a subset of the collimator cells corresponds to an N×M matrix of pixels, where at least one of N and M is greater than one, wherein the method comprises:
monitoring, for a designated subset of pixels including at least two pixels that are affected differently by shadowing from the collimator structure due to geometric misalignment, output signals from the pixels of the designated subset of pixels; and
determining the occurrence of geometric misalignment based on the monitored output signals from the pixels of the designated subset of pixels.

2. The method of claim 1 , wherein said at least two pixels have different responses to the shadowing, and the different responses are monitored by measuring the output signals.

3. The method of claim 1 , wherein the method further comprises i) estimating at least one parameter representing the geometric misalignment and/or ii) correcting for the geometric misalignment based on the monitored output signals from the pixels of the designated subset of pixels and/or iii) performing post-processing of the output signals and/or iv) image reconstruction based on the parameter(s) representing the geometric misalignment and/or based on the monitored output signals from the pixels of the designated subset of pixels.

4. The method of claim 1 , wherein the effect of the geometric misalignment on the output signal(s), or on value(s) based on the output signal(s), of at least one pixel is corrected for based on the monitored output signals from the pixels of the designated subset of pixels.

5. The method of claim 4 , wherein said at least one pixel is located behind the object/subject to be imaged during image acquisition.

6. The method of claim 1 , wherein the output signals from the pixels represent photon counts of the pixels.

7. The method of claim 1 , wherein the output signals from the pixels of the designated subset of pixels are measured during image acquisition of an object/subject and located outside of the object/subject to be imaged during measurement.

8. The method of claim 1 , wherein said at least two pixels that are affected differently by shadowing are located with respect to the collimator structure such that they experience different shadowing from the collimator structure due to geometric misalignment.

9. The method of claim 1 , wherein said at least two pixels that are affected differently by shadowing include a first subset of one or more pixels having an increase in the number of photon counts as a consequence of the shadowing and a second subset of one or more pixels having a decrease in the number of photon counts as a consequence of the shadowing.

10. The method of claim 1 , wherein each of the collimator cells has a first side and a second opposite side, and at least one of the pixels of the designated subset is located on the first side of a collimator cell and at least one of the pixels of the designated subset is located on the second opposite side of the same or another collimator cell.

11. The method of claim 10 , wherein the x-ray detector comprises a number of detector modules, and the pixels located on opposite sides of a collimator cell belong to different detector modules of the x-ray detector.

12. The method of claim 1 , wherein the geometric misalignment includes a relative geometric misalignment between the x-ray source and the x-ray detector.

13. The method of claim 1 , wherein the direction and/or degree of pixel shadowing caused by the geometric misalignment is/are determined based on the monitored output signals from the pixels of the designated subset of pixels.

14. The method of claim 1 , wherein the x-ray detector is a photon-counting and energy-discriminating x-ray detector, and the effect of the geometric misalignment on the photon count(s) of said at least one pixel is corrected for based on the monitored output signals, or on value(s) based on the output signal(s), of the pixels of the designated subset of pixels and the associated photon energy information obtained from the photon-counting and energy-discriminating x-ray detector.

15. The method of claim 14 , wherein the photon-counting and energy-discriminating x-ray detector is configured to classify the detected photons into energy bins, and the step of correcting for the effect of the geometric misalignment on the photon count(s) comprises applying correction to the photon count(s) in the energy bins of the said at least one pixel based on the monitored photon counts of the pixels of the designated subset of pixels and the associated photon energy information.

16. The method of claim 15 , wherein correction factors are determined based on at least one parameter representing the geometric misalignment and basis material thickness.

17. The method of claim 16 , wherein the correction factors are determined and applied for the photon counts in lower energy bins.

18. The method of claim 1 , wherein a geometric misalignment is distinguished from a drop in current-to-peak-kilovoltage ratio (mA/kVp) of the x-ray source based on the monitored output signals of the pixels of the designated subset of pixels.

19. The method of claim 1 , wherein the management of geometric misalignment includes supervision and/or handling of the geometric misalignment such as monitoring and/or correcting/calibrating for the geometric misalignment.

20. A system configured for management of geometric misalignment in an x-ray imaging system having an x-ray source, a photon-counting x-ray detector and an intermediate collimator structure an x-ray path between the x-ray source and the x-ray detector,
wherein the x-ray detector comprises a plurality of pixels, and the collimator structure comprises a plurality of collimator cells, wherein each of at least a subset of the collimator cells corresponds to an N×M matrix of pixels, where at least one of N and M is greater than one,
wherein the system is configured to monitor, for a designated subset of pixels including at least two pixels that are affected differently by shadowing from the collimator structure due to geometric misalignment, output signals from the pixels of the designated subset of pixels; and
wherein the system is configured to determine the occurrence of geometric misalignment based on the monitored output signals from the pixels of the designated subset of pixels.

21. The system of claim 20 , wherein said at least two pixels have different responses to the shadowing, and the system is configured to monitor the different responses by measuring the output signals.

22. The system of claim 20 , wherein the system is further configured to estimate at least one parameter representing the geometric misalignment and/or correct for the geometric misalignment based on the monitored output signals from the pixels of the designated subset of pixels and/or iii) perform post-processing of the output signals and/or iv) image reconstruction based on the parameter(s) representing the geometric misalignment and/or based on the monitored output signals from the pixels of the designated subset of pixels.

23. An

Assignees

• Prismatic Sensors Ab

Inventors

• Sjolin Martin
• Liu Xuejin
• Danielsson Mats

Classifications

• A61B6/5252

  removing objects from field of view, e.g. removing patient table from a CT image · CPC title

• A61B6/586

  Detection of faults or malfunction of the device · CPC title

• A61B6/4291

  the detector being combined with a grid or grating · CPC title

• A61B6/5258

  involving detection or reduction of artifacts or noise · CPC title

• A61B6/585

  Calibration of detector units · CPC title