title: Segmentation-based MR attenuation correction including bones also affects quantitation in brain studies: an initial result of 18F-FP-CIT PET/MR for patients with parkinsonism.
abstract: Attenuation correction (AC) with an ultrashort echo time (UTE) sequence has recently been used in combination with segmentation for cortical bone identification for brain PET/MR studies. The purpose of this study was to evaluate the quantification of (18)F-fluoropropyl-carbomethoxyiodophenylnortropane ((18)F-FP-CIT) binding in brain PET/MR, particularly focusing on effects of UTE-based AC including bone segmentation.
  
  
  METHODS
  Sixteen patients with initially suspected parkinsonism were prospectively enrolled. An emission scan was acquired 110 min after (18)F-FP-CIT injection on a dedicated PET/MR scanner, immediately followed by another emission scan using a PET/CT scanner 120 min after the injection. A UTE-based attenuation map was used to classify the voxels into 3 tissues: bone, soft tissue, and air. All PET images were spatially normalized, and a specific-to-nonspecific dopamine transporter (DAT) binding ratio (BR) was calculated using statistical probabilistic anatomic mapping. The level of agreement was assessed with intraclass correlation coefficients (ICCs). Voxelwise comparison between PET images acquired from PET/MR and PET/CT was performed. We compared non-attenuation-corrected images to analyze UTE-based AC effects on DAT quantification.
  
  
  RESULTS
  BR in the putamen obtained from PET/MR and PET/CT showed low interequipment variability, whereas BR in the caudate nucleus showed significant variability (ICC = 0.967 and 0.682 for putamen and caudate nucleus, respectively). BR in the caudate nucleus was significantly underestimated by PET/MR, compared with PET/CT (mean difference of BR = 0.66, P < 0.0001). Voxelwise analysis revealed that PET/MR showed significantly low BR in the periventricular regions, which was caused by a misclassification of the ventricle as air on the attenuation map. We also compared non-AC images, revealing low interequipment variability even in the caudate nucleus (ICC = 0.937 and 0.832 for putamen and caudate nucleus, respectively).
  
  
  CONCLUSIONS
  Our data demonstrate spatial bias of the DAT BR on (18)F-FP-CIT PET/MR. Voxelwise analysis and comparison to non-AC images identified the misclassification of ventricle as air to be the cause of bias. To obtain reliable quantification for brain PET/MR studies including (18)F-FP-CIT PET, alternative and more reliable segmentation strategies are required.
authors.affiliation: Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea Department of Molecular Medicine and Biopharmaceutical Science, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Korea.
authors.forename: Hongyoon
authors.initials: H
authors.lastname: Choi
authors.affiliation: Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea Cancer Research Institute, Seoul National University, Seoul, Korea larrycheon@gmail.com movement@snu.ac.kr.
authors.forename: Gi Jeong
authors.initials: GJ
authors.lastname: Cheon
authors.affiliation: Department of Neurology, Seoul National University Hospital, Seoul, Korea larrycheon@gmail.com movement@snu.ac.kr.
authors.forename: Han-Joon
authors.initials: HJ
authors.lastname: Kim
authors.affiliation: Department of Radiology, Seoul National University College of Medicine, Seoul, Korea Center for Nanoparticle Research, Institute for Basic Science, and School of Chemical and Biological Engineering, Seoul National University, Seoul, Korea; and.
authors.forename: Seung Hong
authors.initials: SH
authors.lastname: Choi
authors.affiliation: Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea.
authors.forename: Jae Sung
authors.initials: JS
authors.lastname: Lee
authors.affiliation: Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea Department of Molecular Medicine and Biopharmaceutical Science, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Korea larrycheon@gmail.com movement@snu.ac.kr.
authors.forename: Yong-Il
authors.initials: YI
authors.lastname: Kim
authors.affiliation: Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea Cancer Research Institute, Seoul National University, Seoul, Korea.
authors.forename: Keon Wook
authors.initials: KW
authors.lastname: Kang
authors.affiliation: Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea Cancer Research Institute, Seoul National University, Seoul, Korea.
authors.forename: June-Key
authors.initials: JK
authors.lastname: Chung
authors.affiliation: Department of Molecular Medicine and Biopharmaceutical Science, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Korea Department of Radiological Sciences, University of California at Irvine, Irvine, California larrycheon@gmail.com movement@snu.ac.kr.
authors.forename: E Edmund
authors.initials: EE
authors.lastname: Kim
authors.affiliation: Department of Nuclear Medicine, Seoul National University Hospital, Seoul, Korea Department of Molecular Medicine and Biopharmaceutical Science, Graduate School of Convergence Science and Technology, Seoul National University, Seoul, Korea.
authors.forename: Dong Soo
authors.initials: DS
authors.lastname: Lee
mesh_terms: D000328:Adult; D000368:Aged; D000465:Algorithms; D001921:Brain / Q000000981:diagnostic imaging* / Q000473:pathology*; D002421:Caudate Nucleus / Q000000981:diagnostic imaging; D002555:Cerebrospinal Fluid; D050483:Dopamine Plasma Membrane Transport Proteins / Q000378:metabolism; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D020734:Parkinsonian Disorders / Q000503:physiopathology*; D049268:Positron-Emission Tomography / Q000379:methods*; D011336:Probability; D011699:Putamen / Q000000981:diagnostic imaging; D015203:Reproducibility of Results; D014326:Tropanes
chemical_list: D050483:Dopamine Plasma Membrane Transport Proteins; D014326:Tropanes; C087552:2-carbomethoxy-8-(3-fluoropropyl)-3-(4-iodophenyl)tropane
keywords: 18F-FP-CIT; PET/MR; UTE sequence; attenuation correction; brain PET