title: MR-based attenuation correction using ultrashort-echo-time pulse sequences in dementia patients.
abstract: Attenuation correction (AC) is a critical requirement for quantitative PET reconstruction. Accounting for bone information in the attenuation map (μ map) is of paramount importance for accurate brain PET quantification. However, to measure the signal from bone structures represents a challenging task in MR. Recent (18)F-FDG PET/MR studies showed quantitative bias for the assessment of radiotracer concentration when bone was ignored. This work is focused on (18)F-FDG PET/MR neurodegenerative dementing disorders. These are known to lead to specific patterns of (18)F-FDG hypometabolism, mainly in superficial brain structures, which might suffer from attenuation artifacts and thus have immediate diagnostic consequences. A fully automatic method to estimate the μ map, including bone tissue using only MR information, is presented.
  
  
  METHODS
  The algorithm was based on a dual-echo ultrashort-echo-time MR imaging sequence to calculate the R2 map, from which the μ map was derived. The R2-based μ map was postprocessed to calculate an estimated distribution of the bone tissue. μ maps calculated from datasets of 9 patients were compared with their CT-based μ maps (μ mapCT) by determining the confusion matrix. Additionally, a region-of-interest comparison between reconstructed PET data, corrected using different μ maps, was performed. PET data were reconstructed using a Dixon-based μ map (μ mapDX) and a dual-echo ultrashort-echo-time-based μ map (μ mapUTE), which are both calculated by the scanner, and the R2-based μ map presented in this work was compared with reconstructed PET data using the μ mapCT as a reference.
  
  
  RESULTS
  Errors were approximately 20% higher using the μ mapDX and μ mapUTE for AC, compared with reconstructed PET data using the reference μ mapCT. However, PET AC using the R2-based μ map resulted, for all the patients and all the analyzed regions of interest, in a significant improvement, reducing the error to -5.8% to 2.5%.
  
  
  CONCLUSIONS
  The proposed method successfully showed significantly reduced errors in quantification, compared with the μ mapDX and μ mapUTE, and therefore delivered more accurate PET image quantification for an improved diagnostic workup in dementia patients.
authors: Nuklearmedizinische Klinik und Poliklinik, Klinikum Rechts der Isar, Technische Universität München, Munich, Germany; and jorge.cabello@tum.de.
authors: Jorge
authors: J
authors: Cabello
authors: Nuklearmedizinische Klinik und Poliklinik, Klinikum Rechts der Isar, Technische Universität München, Munich, Germany; and.
authors: Mathias
authors: M
authors: Lukas
authors: Nuklearmedizinische Klinik und Poliklinik, Klinikum Rechts der Isar, Technische Universität München, Munich, Germany; and TUM Neuroimaging Center (TUM-NIC), Technische Universität München, Munich, Germany.
authors: Stefan
authors: S
authors: Förster
authors: Nuklearmedizinische Klinik und Poliklinik, Klinikum Rechts der Isar, Technische Universität München, Munich, Germany; and.
authors: Thomas
authors: T
authors: Pyka
authors: Nuklearmedizinische Klinik und Poliklinik, Klinikum Rechts der Isar, Technische Universität München, Munich, Germany; and.
authors: Stephan G
authors: SG
authors: Nekolla
authors: Nuklearmedizinische Klinik und Poliklinik, Klinikum Rechts der Isar, Technische Universität München, Munich, Germany; and.
authors: Sibylle I
authors: SI
authors: Ziegler
mesh_terms: D000368:Aged; D000465:Algorithms; D016477:Artifacts; D001331:Automation; D001921:Brain / Q000000981:diagnostic imaging; D003704:Dementia / Q000000981:diagnostic imaging* / Q000473:pathology*; D005260:Female; D019788:Fluorodeoxyglucose F18 / Q000494:pharmacology*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D021621:Imaging, Three-Dimensional; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D049268:Positron-Emission Tomography; D011446:Prospective Studies; D019275:Radiopharmaceuticals / Q000494:pharmacology*; D015203:Reproducibility of Results; D012984:Software
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18
keywords: 18F-FDG PET; PET/MR; UTE sequence; attenuation correction; brain imaging