# US 2023/0056540 A1 · List mode image reconstruction method and nuclear medicine diagnostic apparatus > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2023/0056540 A1 - Document ID: US20230056540A1 - Status: Published application - Kind: A1 - Application number: 17/910,468 - Filed: 2020-03-16 - Published: 2023-02-23 - Earliest claimed: 2020-03-16 - Assignees: Shimadzu Corporation - Applicants: Shimadzu Corporation - Inventors: Tetsuya KOBAYASHI; Yoshihiro YAMADA - Web page: https://patentgrep.com/patent/US20230056540A1 ## CPC - G01T 1/2985: {In depth localisation, e.g. using positron emitters; Tomographic imaging (longitudinal and transverse section imaging; apparatus for radiation diagnosis sequentially in different planes, steroscopic radiation diagnosis); (using external radiation sources A61B6/02)} - G06T 12/20: Inverse problem, i.e. transformations from projection space into object space - A61B 6/037: {Emission tomography} - A61B 6/5258: {involving detection or reduction of artifacts or noise} - G01T 1/161: Applications in the field of nuclear medicine, e.g. in vivo counting {(apparatus for radiation diagnosis A61B6/00)} - G06T 12/00: Tomographic reconstruction from projections - G06T 2211/424: Iterative - 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) - G06T: IMAGE DATA PROCESSING OR GENERATION, IN GENERAL - A61B: DIAGNOSIS; SURGERY; IDENTIFICATION (usefulness limited to only animals A61D) ## Abstract A list mode image reconstruction method includes a step of dividing list mode data into a plurality of subsets and a step of acquiring a subset balance coefficient based on the number of events in the plurality of subsets. ## Claims ### Claim 1 A list mode image reconstruction method for reconstructing a radioactivity distribution image of a subject from list mode data collected by a nuclear medicine diagnostic apparatus by iterative calculation, the list mode image reconstruction method comprising the steps of: dividing the list mode data into a plurality of subsets; acquiring subset balance coefficients based on the number of events in the plurality of subsets; acquiring back projection values based on the list mode data; acquiring corrected back projection values by multiplying the back projection values by the subset balance coefficients; acquiring a back projection image based on the corrected back projection values, and updating the radioactivity distribution image based on the back projection image. ### Claim 2 (depends on 1) The list mode image reconstruction method as recited in claim 1, wherein the step of acquiring the subset balance coefficients includes a step of acquiring the subset balance coefficient based on a ratio of the number of ideal events in a reconstruction time range to the number of ideal events in each subset. ### Claim 3 (depends on 2) The list mode image reconstruction method as recited in claim 2, wherein the step of acquiring the subset balance coefficients includes a step of acquiring the subset balance coefficient based on a ratio of an average number of ideal events in the reconstruction time range to the number of ideal events in each subset. ### Claim 4 (depends on 2) The list mode image reconstruction method as recited in claim 2, wherein the step of acquiring the subset balance coefficients includes a step of acquiring the subset balance coefficients based on a ratio of the number of ideal events in the reconstruction time range to a value acquired by multiplying the number of ideal events in each subset by the number of subsets. ### Claim 5 (depends on 2) The list mode image reconstruction method as recited in claim 2, wherein the number of ideal events is a number acquired by correcting the number of measured events by at least one factor selected from four physical factors consisting of radioactive decay, counting loss of a detector, variation of detection efficiency of a detector, and photon attenuation by the subject. ### Claim 6 (depends on 1) The list mode image reconstruction method as recited in claim 1, wherein the step of acquiring the subset balance coefficients includes a step of acquiring the subset balance coefficient for each subset. ### Claim 7 (depends on 1) The list mode image reconstruction method as recited in claim 1, wherein the step of dividing the list mode data into the plurality of subsets includes a step of dividing the list mode data into the plurality of subsets by any one of an equal number of events division method, an equal number of ideal events division method, an equal event interval division method, and an equal time interval division method. ### Claim 8 A nuclear medicine diagnostic apparatus comprising: a detection unit configured to detect radiation generated from a radiopharmaceutical agent in a subject; and an operation unit configured to reconstruct a radioactivity distribution image of the subject from list data as a detection result of radiation by the detection unit by iterative calculation, wherein the operation unit divides the list mode data into a plurality of subsets, acquires subset balance coefficients based on the number of events in the plurality of subsets, acquires back projection values based on the list mode data, acquires a corrected back projection value by multiplying the back projection values by the subset balance coefficients, and acquires a back projection image based on the corrected back projection values, and updates the radioactivity distribution image based on the back projection image. ### Claim 9 (depends on 8) The nuclear medicine diagnostic apparatus as recited in claim 8, wherein the operation unit is configured to acquire the subset balance coefficients based on a ratio of the number of ideal events in a reconstruction time range to the number of ideal events in each subset. ### Claim 10 (depends on 9) The nuclear medicine diagnostic apparatus as recited in claim 9, wherein the operation unit is configured to acquire the subset balance coefficients based on a ratio of the average number of ideal events in the reconstruction time range to an average number of ideal events in each subset. ### Claim 11 (depends on 9) The nuclear medicine diagnostic apparatus as recited in claim 9, wherein the operation unit is configured to acquire the subset balance coefficients based on a ratio of the number of ideal events in the reconstruction time range to a value obtained by multiplying the number of ideal events in each subset by the number of subsets.