title: Quantitative Evaluation of Segmentation- and Atlas-Based Attenuation Correction for PET/MR on Pediatric Patients.
abstract: Pediatric imaging is regarded as a key application for combined PET/MR imaging systems. Because existing MR-based attenuation-correction methods were not designed specifically for pediatric patients, we assessed the impact of 2 potentially influential factors: inter- and intrapatient variability of attenuation coefficients and anatomic variability. Furthermore, we evaluated the quantification accuracy of 3 methods for MR-based attenuation correction without (SEGbase) and with bone prediction using an adult and a pediatric atlas (SEGwBONEad and SEGwBONEpe, respectively) on PET data of pediatric patients.
  
  
  METHODS
  The variability of attenuation coefficients between and within pediatric (5-17 y, n = 17) and adult (27-66 y, n = 16) patient collectives was assessed on volumes of interest (VOIs) in CT datasets for different tissue types. Anatomic variability was assessed on SEGwBONEad/pe attenuation maps by computing mean differences to CT-based attenuation maps for regions of bone tissue, lungs, and soft tissue. PET quantification was evaluated on VOIs with physiologic uptake and on 80% isocontour VOIs with elevated uptake in the thorax and abdomen/pelvis. Inter- and intrapatient variability of the bias was assessed for each VOI group and method.
  
  
  RESULTS
  Statistically significant differences in mean VOI Hounsfield unit values and linear attenuation coefficients between adult and pediatric collectives were found in the lungs and femur. The prediction of attenuation maps using the pediatric atlas showed a reduced error in bone tissue and better delineation of bone structure. Evaluation of PET quantification accuracy showed statistically significant mean errors in mean standardized uptake values of -14% ± 5% and -23% ± 6% in bone marrow and femur-adjacent VOIs with physiologic uptake for SEGbase, which could be reduced to 0% ± 4% and -1% ± 5% using SEGwBONEpe attenuation maps. Bias in soft-tissue VOIs was less than 5% for all methods. Lung VOIs showed high SDs in the range of 15% for all methods. For VOIs with elevated uptake, mean and SD were less than 5% except in the thorax.
  
  
  CONCLUSIONS
  The use of a dedicated atlas for the pediatric patient collective resulted in improved attenuation map prediction in osseous regions and reduced interpatient bias variation in femur-adjacent VOIs. For the lungs, in which intrapatient variation was higher for the pediatric collective, a patient- or group-specific attenuation coefficient might improve attenuation map accuracy. Mean errors of -14% and -23% in bone marrow and femur-adjacent VOIs can affect PET quantification in these regions when bone tissue is ignored.
authors.affiliation: Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard-Karls University Tübingen, Tübingen, Germany Department of Empirical Inference, Max Planck Institute for Intelligent Systems, Tübingen, Germany; and ilja.bezrukov@med.uni-tuebingen.de.
authors.forename: Ilja
authors.initials: I
authors.lastname: Bezrukov
authors.affiliation: Diagnostic and Interventional Radiology, Department of Radiology, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Holger
authors.initials: H
authors.lastname: Schmidt
authors.affiliation: Diagnostic and Interventional Radiology, Department of Radiology, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Sergios
authors.initials: S
authors.lastname: Gatidis
authors.affiliation: Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard-Karls University Tübingen, Tübingen, Germany Department of Empirical Inference, Max Planck Institute for Intelligent Systems, Tübingen, Germany; and.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Mantlik
authors.affiliation: Diagnostic and Interventional Radiology, Department of Radiology, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Jürgen F
authors.initials: JF
authors.lastname: Schäfer
authors.affiliation: Diagnostic and Interventional Radiology, Department of Radiology, University Hospital Tübingen, Tübingen, Germany.
authors.forename: Nina
authors.initials: N
authors.lastname: Schwenzer
authors.affiliation: Werner Siemens Imaging Center, Department of Preclinical Imaging and Radiopharmacy, Eberhard-Karls University Tübingen, Tübingen, Germany.
authors.forename: Bernd J
authors.initials: BJ
authors.lastname: Pichler
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000465:Algorithms; D001842:Bone and Bones / Q000000981:diagnostic imaging; D002648:Child; D002675:Child, Preschool; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D009369:Neoplasms / Q000000981:diagnostic imaging; D049268:Positron-Emission Tomography; D015203:Reproducibility of Results; D014057:Tomography, X-Ray Computed; D051598:Whole Body Imaging
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: PET/MR; atlas; attenuation correction; segmentation