title: On the accuracy and reproducibility of a novel probabilistic atlas-based generation for calculation of head attenuation maps on integrated PET/MR scanners.
abstract: OBJECTIVE
  To propose an MR-based method for generating continuous-valued head attenuation maps and to assess its accuracy and reproducibility. Demonstrating that novel MR-based photon attenuation correction methods are both accurate and reproducible is essential prior to using them routinely in research and clinical studies on integrated PET/MR scanners.
  
  
  METHODS
  Continuous-valued linear attenuation coefficient maps ("μ-maps") were generated by combining atlases that provided the prior probability of voxel positions belonging to a certain tissue class (air, soft tissue, or bone) and an MR intensity-based likelihood classifier to produce posterior probability maps of tissue classes. These probabilities were used as weights to generate the μ-maps. The accuracy of this probabilistic atlas-based continuous-valued μ-map ("PAC-map") generation method was assessed by calculating the voxel-wise absolute relative change (RC) between the MR-based and scaled CT-based attenuation-corrected PET images. To assess reproducibility, we performed pair-wise comparisons of the RC values obtained from the PET images reconstructed using the μ-maps generated from the data acquired at three time points.
  
  
  RESULTS
  The proposed method produced continuous-valued μ-maps that qualitatively reflected the variable anatomy in patients with brain tumor and agreed well with the scaled CT-based μ-maps. The absolute RC comparing the resulting PET volumes was 1.76 ± 2.33 %, quantitatively demonstrating that the method is accurate. Additionally, we also showed that the method is highly reproducible, the mean RC value for the PET images reconstructed using the μ-maps obtained at the three visits being 0.65 ± 0.95 %.
  
  
  CONCLUSIONS
  Accurate and highly reproducible continuous-valued head μ-maps can be generated from MR data using a probabilistic atlas-based approach.
authors: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, 02129, USA.|Division of Health Sciences and Technology, Massachusetts Institute of Technology, Cambridge, MA, USA.
authors: Kevin T
authors: KT
authors: Chen
authors: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, 02129, USA.
authors: David
authors: D
authors: Izquierdo-Garcia
authors: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, 02129, USA.|Department of Psychiatry, Massachusetts General Hospital, Boston, MA, USA.|Department of Radiology and Biomedical Imaging, University of California, San Francisco, San Francisco, CA, USA.
authors: Clare B
authors: CB
authors: Poynton
authors: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, 02129, USA.|Program in Biophysics, Harvard University, Cambridge, MA, USA.
authors: Daniel B
authors: DB
authors: Chonde
authors: Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, Charlestown, MA, 02129, USA. ccatana@nmr.mgh.harvard.edu.
authors: Ciprian
authors: http://orcid.org/0000-0002-3249-5971
authors: C
authors: Catana
mesh_terms: D000465:Algorithms; D000068598:Data Accuracy; D006257:Head / Q000033:anatomy & histology / Q000000981:diagnostic imaging*; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D064847:Multimodal Imaging / Q000295:instrumentation / Q000379:methods / Q000592:standards*; D017785:Photons; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods / Q000592:standards*
keywords: Attenuation correction; PET/MR; Probabilistic atlas; Reproducibility