title: Clinical Evaluation of Zero-Echo-Time Attenuation Correction for Brain 18F-FDG PET/MRI: Comparison with Atlas Attenuation Correction.
abstract: Accurate attenuation correction (AC) on PET/MR is still challenging. The purpose of this study was to evaluate the clinical feasibility of AC based on fast zero-echo-time (ZTE) MRI by comparing it with the default atlas-based AC on a clinical PET/MR scanner.
  
  
  METHODS
  We recruited 10 patients with malignant diseases not located on the brain. In all patients, a clinically indicated whole-body18F-FDG PET/CT scan was acquired. In addition, a head PET/MR scan was obtained voluntarily. For each patient, 2 AC maps were generated from the MR images. One was atlas-AC, derived from T1-weighted liver acquisition with volume acceleration flex images (clinical standard). The other was ZTE-AC, derived from proton-density-weighted ZTE images by applying tissue segmentation and assigning continuous attenuation values to the bone. The AC map generated by PET/CT was used as a silver standard. On the basis of each AC map, PET images were reconstructed from identical raw data on the PET/MR scanner. All PET images were normalized to the SPM5 PET template. After that, these images were qualified visually and quantified in 67 volumes of interest (VOIs; automated anatomic labeling, atlas). Relative differences and absolute relative differences between PET images based on each AC were calculated.18F-FDG uptake in all 670 VOIs and generalized merged VOIs were compared using a paired t test.
  
  
  RESULTS
  Qualitative analysis shows that ZTE-AC was robust to patient variability. Nevertheless, misclassification of air and bone in mastoid and nasal areas led to the overestimation of PET in the temporal lobe and cerebellum (%diff of ZTE-AC, 2.46% ± 1.19% and 3.31% ± 1.70%, respectively). The |%diff| of all 670 VOIs on ZTE was improved by approximately 25% compared with atlas-AC (ZTE-AC vs. atlas-AC, 1.77% ± 1.41% vs. 2.44% ± 1.63%, P < 0.01). In 2 of 7 generalized VOIs, |%diff| on ZTE-AC was significantly smaller than atlas-AC (ZTE-AC vs. atlas-AC: insula and cingulate, 1.06% ± 0.67% vs. 2.22% ± 1.10%, P < 0.01; central structure, 1.03% ± 0.99% vs. 2.54% ± 1.20%, P < 0.05).
  
  
  CONCLUSIONS
  The ZTE-AC could provide more accurate AC than clinical atlas-AC by improving the estimation of head-skull attenuation. The misclassification in mastoid and nasal areas must be addressed to prevent the overestimation of PET in regions near the skull base.
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland tetsuro.sekine@gmail.com.|Department of Radiology, Nippon Medical School, Tokyo, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Sekine
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Edwin E G W
authors.initials: EE
authors.lastname: Ter Voert
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland.|Institute of Pharmacology & Toxicology, University of Zurich, Zurich, Switzerland.|PMOD Technologies Ltd., Zurich, Switzerland.
authors.forename: Geoffrey
authors.initials: G
authors.lastname: Warnock
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Alfred
authors.initials: A
authors.lastname: Buck
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland.|Department of Neuroradiology, University Hospital Zurich, Zurich, Switzerland.
authors.forename: Martin
authors.initials: M
authors.lastname: Huellner
authors.affiliation: Department of Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland.|Division of Diagnostic and Interventional Radiology, Department of Medical Radiology, University Hospital Zurich, Zurich, Switzerland; and.
authors.forename: Patrick
authors.initials: P
authors.lastname: Veit-Haibach
authors.affiliation: GE Healthcare Waukesha, Wisconsin.
authors.forename: Gaspar
authors.initials: G
authors.lastname: Delso
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000000981:diagnostic imaging*; D005240:Feasibility Studies; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D007700:Kinetics; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D000072078:Positron Emission Tomography Computed Tomography
chemical_list: D019788:Fluorodeoxyglucose F18
keywords: 18F-FDG; PET/MR; ZTE; atlas-based; attenuation correction; brain