# US 12,111,433 B2 · Counting response and beam hardening calibration method for a full size photon-counting CT system > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 12,111,433 B2 - Document ID: US12111433B2 - Status: Granted - Kind: B2 - Application number: 18/306,773 - Filed: 2023-04-25 - Published: 2023-08-24 - Granted: 2024-10-08 - Earliest claimed: 2021-01-22 - Assignees: Canon Medical Systems Corporation - Applicants: Canon Medical Systems Corporation - Inventors: Xiaohui Zhan; Xiaofeng Niu; Ilmar Hein - Web page: https://patentgrep.com/patent/US12111433B2 ## CPC - G01T 7/005: {calibration techniques (stabilization of spectrometer G01T1/40)} - A61B 6/032: {Transmission computed tomography [CT]} - A61B 6/4035: {the source being combined with a filter or grating} - A61B 6/4241: {using energy resolving detectors, e.g. photon counting} - A61B 6/4447: {Tiltable gantries} - A61B 6/5258: {involving detection or reduction of artifacts or noise} - A61B 6/583: {using calibration phantoms} - A61B 6/585: {Calibration of detector units} - G06T 7/10: Segmentation; Edge detection (motion-based segmentation G06T7/215) - G06T 12/10: Image preprocessing, e.g. calibration, positioning of sources or scatter correction - G06T 2207/10081: Computed x-ray tomography [CT] - G06T 2207/30004: Biomedical image processing - G06T 2211/448: involving metal artefacts, streaking artefacts, beam hardening or photon starvation - G01T: MEASUREMENT OF NUCLEAR OR X-RADIATION (radiation analysis of materials, mass spectrometry G01N23/00; tubes for determining the presence, intensity, density or energy of radiation or particles H01J47/00) - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) - G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL ## Abstract A method and a system for providing calibration for a polychromatic photon counting detector forward counting model. Measurements with multiple materials and known path lengths are used to calibrate the photon counting detector counting response of the forward model. The flux independent weighted bin response function is estimated using the expectation maximization method, and then used to estimate the pileup correction terms at plural tube voltage settings for each detector pixel. The beam hardening corrections are then applied to the measured projection data sinogram, and the corrected sinogram is reconstructed to the counting image at the selected single energy. ## Claims ### Claim 1 A method processing projection image data acquired by a photon counting computed tomography (CT) system, the method comprising: performing a plurality of calibration scans comprising an air scan and scans using a plurality of slabs of different materials, at an initial current intensity and at plural tube voltage settings of an X-ray tube, for each scan, to obtain counts for each energy bin; estimating calibration parameters based on the counts; obtaining a group of projection image data for each of a plurality of energy bands; generating, based on the group of projection image data, a first group of projection data corresponding to a first basis material and a second group of projection data corresponding to a second basis material; calculating a first beam hardening correction term relating to the first basis material based on the first group of projection data; calculating a second beam hardening correction term relating to the second basis material based on the second group of projection data; and generating an energy bin image corresponding to one energy band by using the first beam hardening correction term, the second beam hardening correction term and the one energy band among the plurality of energy bands, wherein estimating the calibration parameters comprises estimating first parameters, which are dependent on energy, based on counts; estimating second parameters which are dependent on total counts of all energy bins, based on the first parameters; and repeating, using each of a plurality of slabs, the steps of estimating first and second parameters for different current intensities other than an initial current intensity and at a same tube voltage to obtain the second parameters, respectively, for different current intensities, to generate tables of the estimated first parameters and second parameters. ### Claim 2 (depends on 1) The method according to claim 1, wherein calculating the first beam hardening correction term further comprises performing forward projection on the first group of projection data to estimate path lengths, and calculating first beam hardening correction terms for each view and each detector channel, and calculating the second beam hardening correction term further comprises performing forward projection on the second group of projection data to estimate path lengths, and calculating second beam hardening correction terms for each view and each detector channel. ### Claim 3 (depends on 1) The method according to claim 1, further comprising repeating calculating the beam hardening correction terms in object/patient scans based on the estimated calibration parameters using an iterative beam hardening correction of an initial uncorrected sinogram from the object/patient scans until an image quality of a corrected energy bin image exceeds a predetermined threshold. ### Claim 4 (depends on 3) The method according to claim 3, further comprising assessing image quality of the corrected counting image and if the quality of the corrected counting image does not satisfy predefined standards, estimating basis material path lengths from reconstructed image for the beam hardening correction. ### Claim 5 (depends on 1) The method according to claim 1, wherein an initial estimate of the first parameters is based on a lower energy window than a default hardware setting. ### Claim 6 (depends on 5) The method according to claim 5, wherein an initial estimate is based on a calculation of counts above E0-x, where E0 is a first energy threshold and 5 keV