title: Probabilistic Air Segmentation and Sparse Regression Estimated Pseudo CT for PET/MR Attenuation Correction.
abstract: OBJECTIVE
  To develop a positron emission tomography (PET) attenuation correction method for brain PET/magnetic resonance (MR) imaging by estimating pseudo computed tomographic (CT) images from T1-weighted MR and atlas CT images.
  
  
  METHODS
  In this institutional review board-approved and HIPAA-compliant study, PET/MR/CT images were acquired in 20 subjects after obtaining written consent. A probabilistic air segmentation and sparse regression (PASSR) method was developed for pseudo CT estimation. Air segmentation was performed with assistance from a probabilistic air map. For nonair regions, the pseudo CT numbers were estimated via sparse regression by using atlas MR patches. The mean absolute percentage error (MAPE) on PET images was computed as the normalized mean absolute difference in PET signal intensity between a method and the reference standard continuous CT attenuation correction method. Friedman analysis of variance and Wilcoxon matched-pairs tests were performed for statistical comparison of MAPE between the PASSR method and Dixon segmentation, CT segmentation, and population averaged CT atlas (mean atlas) methods.
  
  
  RESULTS
  The PASSR method yielded a mean MAPE ± standard deviation of 2.42% ± 1.0, 3.28% ± 0.93, and 2.16% ± 1.75, respectively, in the whole brain, gray matter, and white matter, which were significantly lower than the Dixon, CT segmentation, and mean atlas values (P < .01). Moreover, 68.0% ± 16.5, 85.8% ± 12.9, and 96.0% ± 2.5 of whole-brain volume had within ±2%, ±5%, and ±10% percentage error by using PASSR, respectively, which was significantly higher than other methods (P < .01).
  
  
  CONCLUSIONS
  PASSR outperformed the Dixon, CT segmentation, and mean atlas methods by reducing PET error owing to attenuation correction.
authors.affiliation: From the Biomedical Research Imaging Center (Y.C., Y.Z.L., W.L., D.S., D.L., H.A.), Department of Radiology (Y.C., Y.Z.L., W.L., D.S., H.A.), and Department of Biomedical Engineering (M.J., Y.Z.L., W.L., D.L., H.A.), University of North Carolina at Chapel Hill, 106 Mason Farm Rd, CB 7513, Chapel Hill, NC 27599; and Mallinckrodt Institute of Radiology, Washington University School of Medicine, St Louis, Mo (Y.S., T.B., B.G.R.).
authors.forename: Yasheng
authors.initials: Y
authors.lastname: Chen
authors.forename: Meher
authors.initials: M
authors.lastname: Juttukonda
authors.forename: Yi
authors.initials: Y
authors.lastname: Su
authors.forename: Tammie
authors.initials: T
authors.lastname: Benzinger
authors.forename: Brian G
authors.initials: BG
authors.lastname: Rubin
authors.forename: Yueh Z
authors.initials: YZ
authors.lastname: Lee
authors.forename: Weili
authors.initials: W
authors.lastname: Lin
authors.forename: Dinggang
authors.initials: D
authors.lastname: Shen
authors.forename: David
authors.initials: D
authors.lastname: Lalush
authors.forename: Hongyu
authors.initials: H
authors.lastname: An
mesh_terms: D000368:Aged; D000388:Air; D001927:Brain Diseases / Q000175:diagnosis*; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015233:Models, Statistical; D059906:Neuroimaging / Q000379:methods*; D049268:Positron-Emission Tomography / Q000379:methods*; D014057:Tomography, X-Ray Computed / Q000379:methods*