title: Scatter and crosstalk corrections for (99m)Tc/(123)I dual-radionuclide imaging using a CZT SPECT system with pinhole collimators.
abstract: OBJECTIVE
  The energy spectrum for a cadmium zinc telluride (CZT) detector has a low energy tail due to incomplete charge collection and intercrystal scattering. Due to these solid-state detector effects, scatter would be overestimated if the conventional triple-energy window (TEW) method is used for scatter and crosstalk corrections in CZT-based imaging systems. The objective of this work is to develop a scatter and crosstalk correction method for (99m)Tc/(123)I dual-radionuclide imaging for a CZT-based dedicated cardiac SPECT system with pinhole collimators (GE Discovery NM 530c/570c).
  
  
  METHODS
  A tailing model was developed to account for the low energy tail effects of the CZT detector. The parameters of the model were obtained using (99m)Tc and (123)I point source measurements. A scatter model was defined to characterize the relationship between down-scatter and self-scatter projections. The parameters for this model were obtained from Monte Carlo simulation using SIMIND. The tailing and scatter models were further incorporated into a projection count model, and the primary and self-scatter projections of each radionuclide were determined with a maximum likelihood expectation maximization (MLEM) iterative estimation approach. The extracted scatter and crosstalk projections were then incorporated into MLEM image reconstruction as an additive term in forward projection to obtain scatter- and crosstalk-corrected images. The proposed method was validated using Monte Carlo simulation, line source experiment, anthropomorphic torso phantom studies, and patient studies. The performance of the proposed method was also compared to that obtained with the conventional TEW method.
  
  
  RESULTS
  Monte Carlo simulations and line source experiment demonstrated that the TEW method overestimated scatter while their proposed method provided more accurate scatter estimation by considering the low energy tail effect. In the phantom study, improved defect contrasts were observed with both correction methods compared to no correction, especially for the images of (99m)Tc in dual-radionuclide imaging where there is heavy contamination from (123)I. In this case, the nontransmural defect contrast was improved from 0.39 to 0.47 with the TEW method and to 0.51 with their proposed method and the transmural defect contrast was improved from 0.62 to 0.74 with the TEW method and to 0.73 with their proposed method. In the patient study, the proposed method provided higher myocardium-to-blood pool contrast than that of the TEW method. Similar to the phantom experiment, the improvement was the most substantial for the images of (99m)Tc in dual-radionuclide imaging. In this case, the myocardium-to-blood pool ratio was improved from 7.0 to 38.3 with the TEW method and to 63.6 with their proposed method. Compared to the TEW method, the proposed method also provided higher count levels in the reconstructed images in both phantom and patient studies, indicating reduced overestimation of scatter. Using the proposed method, consistent reconstruction results were obtained for both single-radionuclide data with scatter correction and dual-radionuclide data with scatter and crosstalk corrections, in both phantom and human studies.
  
  
  CONCLUSIONS
  The authors demonstrate that the TEW method leads to overestimation in scatter and crosstalk for the CZT-based imaging system while the proposed scatter and crosstalk correction method can provide more accurate self-scatter and down-scatter estimations for quantitative single-radionuclide and dual-radionuclide imaging.
authors.affiliation: Department of Diagnostic Radiology, Yale University, New Haven, Connecticut 06520 and Department of Engineering Physics, Tsinghua University, Beijing 100084, China.
authors.forename: Peng
authors.initials: P
authors.lastname: Fan
authors.affiliation: Institute of Nuclear Medicine, University College London, London WC1E 6BT, United Kingdom and Centre for Medical Radiation Physics, University of Wollongong, New South Wales 2522, Australia.
authors.forename: Brian F
authors.initials: BF
authors.lastname: Hutton
authors.affiliation: Department of Nuclear Medicine, Karolinska University Hospital, Stockholm 14186, Sweden.
authors.forename: Maria
authors.initials: M
authors.lastname: Holstensson
authors.affiliation: Department of Medical Radiation Physics, Lund University, Lund 222 41, Sweden.
authors.forename: Michael
authors.initials: M
authors.lastname: Ljungberg
authors.affiliation: Department of Radiology, University of Massachusetts Medical School, Worcester, Massachusetts 01655.
authors.forename: P Hendrik
authors.initials: PH
authors.lastname: Pretorius
authors.affiliation: Department of Diagnostic Radiology, Yale University, New Haven, Connecticut 06520.
authors.forename: Rameshwar
authors.initials: R
authors.lastname: Prasad
authors.affiliation: Department of Engineering Physics, Tsinghua University, Beijing 100084, China.
authors.forename: Tianyu
authors.initials: T
authors.lastname: Ma
authors.affiliation: Department of Engineering Physics, Tsinghua University, Beijing 100084, China.
authors.forename: Yaqiang
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Department of Engineering Physics, Tsinghua University, Beijing 100084, China.
authors.forename: Shi
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Internal Medicine, Yale Translational Research Imaging Center, Yale University, New Haven, Connecticut 06520.
authors.forename: Stephanie L
authors.initials: SL
authors.lastname: Thorn
authors.affiliation: Department of Internal Medicine, Yale Translational Research Imaging Center, Yale University, New Haven, Connecticut 06520.
authors.forename: Mitchel R
authors.initials: MR
authors.lastname: Stacy
authors.affiliation: Department of Internal Medicine, Yale Translational Research Imaging Center, Yale University, New Haven, Connecticut 06520.
authors.forename: Albert J
authors.initials: AJ
authors.lastname: Sinusas
authors.affiliation: Department of Diagnostic Radiology, Yale University, New Haven, Connecticut 06520.
authors.forename: Chi
authors.initials: C
authors.lastname: Liu
mesh_terms: D002104:Cadmium; D003198:Computer Simulation; D006321:Heart / Q000000981:diagnostic imaging; D006801:Humans; D007457:Iodine Radioisotopes; D016013:Likelihood Functions; D008954:Models, Biological; D009010:Monte Carlo Method; D019047:Phantoms, Imaging; D017785:Photons; D019275:Radiopharmaceuticals; D012542:Scattering, Radiation; D013667:Technetium; D013691:Tellurium; D015899:Tomography, Emission-Computed, Single-Photon / Q000295:instrumentation* / Q000379:methods*; D014057:Tomography, X-Ray Computed; D015032:Zinc
chemical_list: C474490:CdZnTe; D007457:Iodine Radioisotopes; D019275:Radiopharmaceuticals; D002104:Cadmium; D013667:Technetium; D015032:Zinc; D013691:Tellurium