title: PET/MRI in the Presence of Metal Implants: Completion of the Attenuation Map from PET Emission Data.
abstract: We present a novel technique for accurate whole-body attenuation correction in the presence of metallic endoprosthesis, on integrated non-time-of-flight (non-TOF) PET/MRI scanners. The proposed implant PET-based attenuation map completion (IPAC) method performs a joint reconstruction of radioactivity and attenuation from the emission data to determine the position, shape, and linear attenuation coefficient (LAC) of metallic implants.Methods:The initial estimate of the attenuation map was obtained using the MR Dixon method currently available on the Siemens Biograph mMR scanner. The attenuation coefficients in the area of the MR image subjected to metal susceptibility artifacts are then reconstructed from the PET emission data using the IPAC algorithm. The method was tested on 11 subjects presenting 13 different metallic implants, who underwent CT and PET/MR scans. Relative mean LACs and Dice similarity coefficients were calculated to determine the accuracy of the reconstructed attenuation values and the shape of the metal implant, respectively. The reconstructed PET images were compared with those obtained using the reference CT-based approach and the Dixon-based method. Absolute relative change (aRC) images were generated in each case, and voxel-based analyses were performed.Results:The error in implant LAC estimation, using the proposed IPAC algorithm, was 15.7% ± 7.8%, which was significantly smaller than the Dixon- (100%) and CT- (39%) derived values. A mean Dice similarity coefficient of 73% ± 9% was obtained when comparing the IPAC- with the CT-derived implant shape. The voxel-based analysis of the reconstructed PET images revealed quantification errors (aRC) of 13.2% ± 22.1% for the IPAC- with respect to CT-corrected images. The Dixon-based method performed substantially worse, with a mean aRC of 23.1% ± 38.4%.Conclusion:We have presented a non-TOF emission-based approach for estimating the attenuation map in the presence of metallic implants, to be used for whole-body attenuation correction in integrated PET/MR scanners. The Graphics Processing Unit implementation of the algorithm will be included in the open-source reconstruction toolbox Occiput.io.
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts nfuin@mgh.harvard.edu.
authors.forename: Niccolo
authors.initials: N
authors.lastname: Fuin
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts.
authors.forename: Stefano
authors.initials: S
authors.lastname: Pedemonte
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts.
authors.forename: Onofrio A
authors.initials: OA
authors.lastname: Catalano
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts.
authors.forename: David
authors.initials: D
authors.lastname: Izquierdo-Garcia
authors.affiliation: SDN-Istituto di Ricerca Diagnostica e Nucleare, IRCCS, Naples, Italy.|University of Naples Parthenope, Department of Motor Sciences and Healthiness, Naples, Italy.
authors.forename: Andrea
authors.initials: A
authors.lastname: Soricelli
authors.affiliation: SDN-Istituto di Ricerca Diagnostica e Nucleare, IRCCS, Naples, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Salvatore
authors.affiliation: Siemens Medical Solutions USA, MR RD Collaborations, Charlestown, Massachusetts; and.
authors.forename: Keith
authors.initials: K
authors.lastname: Heberlein
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts.
authors.forename: Jacob M
authors.initials: JM
authors.lastname: Hooker
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts.|Department of Applied Mathematics and Computer Science, Technical University of Denmark, Lyngby, Denmark.
authors.forename: Koen
authors.initials: K
authors.lastname: Van Leemput
authors.affiliation: Department of Radiology, Athinoula A. Martinos Center for Biomedical Imaging, Massachusetts General Hospital and Harvard Medical School, Charlestown, Massachusetts.
authors.forename: Ciprian
authors.initials: C
authors.lastname: Catana
mesh_terms: D000328:Adult; D000465:Algorithms; D016477:Artifacts; D005260:Female; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008670:Metals; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods; D019047:Phantoms, Imaging; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D019736:Prostheses and Implants; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D051598:Whole Body Imaging / Q000379:methods*
chemical_list: D008670:Metals
keywords: MLAA; attenuation correction; integrated PET/MR; metal implant