title: Evaluation of an attenuation correction method for PET/MR imaging of the head based on substitute CT images.
abstract: OBJECTIVE
  The aim of this study was to evaluate MR-based attenuation correction of PET emission data of the head, based on a previously described technique that calculates substitute CT (sCT) images from a set of MR images.
  
  
  METHODS
  Images from eight patients, examined with (18)F-FLT PET/CT and MRI, were included. sCT images were calculated and co-registered to the corresponding CT images, and transferred to the PET/CT scanner for reconstruction. The new reconstructions were then compared with the originals. The effect of replacing bone with soft tissue in the sCT-images was also evaluated.
  
  
  RESULTS
  The average relative difference between the sCT-corrected PET images and the CT-corrected PET images was 1.6% for the head and 1.9% for the brain. The average standard deviations of the relative differences within the head were relatively high, at 13.2%, primarily because of large differences in the nasal septa region. For the brain, the average standard deviation was lower, 4.1%. The global average difference in the head when replacing bone with soft tissue was 11%.
  
  
  CONCLUSIONS
  The method presented here has a high rate of accuracy, but high-precision quantitative imaging of the nasal septa region is not possible at the moment.
authors.affiliation: Department of Radiation Sciences, Umeå University, 90187, Umeå, Sweden, anne.larsson.stromvall@vll.se.
authors.forename: Anne
authors.initials: A
authors.lastname: Larsson
authors.forename: Adam
authors.initials: A
authors.lastname: Johansson
authors.forename: Jan
authors.initials: J
authors.lastname: Axelsson
authors.forename: Tufve
authors.initials: T
authors.lastname: Nyholm
authors.forename: Thomas
authors.initials: T
authors.lastname: Asklund
authors.forename: Katrine
authors.initials: K
authors.lastname: Riklund
authors.forename: Mikael
authors.initials: M
authors.lastname: Karlsson
mesh_terms: D001932:Brain Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000532:radiotherapy; D019788:Fluorodeoxyglucose F18; D005910:Glioma / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000532:radiotherapy; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007091:Image Processing, Computer-Assisted / Q000379:methods*; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D015233:Models, Statistical; D064847:Multimodal Imaging / Q000295:instrumentation / Q000379:methods*; D049268:Positron-Emission Tomography / Q000295:instrumentation / Q000379:methods*; D019275:Radiopharmaceuticals; D011879:Radiotherapy Dosage; D012044:Regression Analysis; D014057:Tomography, X-Ray Computed
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18