title: Simultaneous evaluation of brain tumour metabolism, structure and blood volume using [(18)F]-fluoroethyltyrosine (FET) PET/MRI: feasibility, agreement and initial experience.
abstract: OBJECTIVE
  Both [(18)F]-fluoroethyltyrosine (FET) PET and blood volume (BV) MRI supplement routine T1-weighted contrast-enhanced MRI in gliomas, but whether the two modalities provide identical or complementary information is unresolved. The aims of the study were to investigate the feasibility of simultaneous structural MRI, BV MRI and FET PET of gliomas using an integrated PET/MRI scanner and to assess the spatial and quantitative agreement in tumour imaging between BV MRI and FET PET.
  
  
  METHODS
  A total of 32 glioma patients underwent a 20-min static simultaneous PET/MRI acquisition on a Siemens mMR system 20 min after injection of 200 MBq FET. The MRI protocol included standard structural MRI and dynamic susceptibility contrast (DSC) imaging for BV measurements. Maximal relative tumour FET uptake (TBRmax) and BV (rBVmax), and Dice coefficients were calculated to assess the quantitative and spatial congruence in the tumour volumes determined by FET PET, BV MRI and contrast-enhanced MRI.
  
  
  RESULTS
  FET volume and TBRmax were higher in BV-positive than in BV-negative scans, and both VOLBV and rBVmax were higher in FET-positive than in FET-negative scans. TBRmax and rBVmax were positively correlated (R (2) = 0.59, p < 0.001). FET and BV positivity were in agreement in only 26 of the 32 patients and in 42 of 63 lesions, and spatial congruence in the tumour volumes as assessed by the Dice coefficients was generally poor with median Dice coefficients exceeding 0.1 in less than half the patients positive on at least one modality for any pair of modalities. In 56 % of the patients susceptibility artefacts in DSC BV maps overlapped the tumour on MRI.
  
  
  CONCLUSIONS
  The study demonstrated that although tumour volumes determined by BV MRI and FET PET were quantitatively correlated, their spatial congruence in a mixed population of treated glioma patients was generally poor, and the modalities did not provide the same information in this population of patients. Combined imaging of brain tumour metabolism and perfusion using hybrid PET/MR systems may provide complementary information on tumour biology, but the potential clinical value remains to be determined in future trials.
authors.affiliation: Department of Clinical Physiology Nuclear Medicine and PET, Copenhagen University Hospital Rigshospitalet Blegdamsvej, Blegdamsvej 9, 2100, Copenhagen, Denmark. ohen0009@regionh.dk.
authors.forename: Otto M
authors.initials: OM
authors.lastname: Henriksen
authors.affiliation: Department of Radiology, Copenhagen University Hospital Rigshospitalet Blegdamsvej, Blegdamsvej 9, 2100, Copenhagen, Denmark.
authors.forename: Vibeke A
authors.initials: VA
authors.lastname: Larsen
authors.affiliation: Department of Oncology, Copenhagen University Hospital Rigshospitalet Blegdamsvej, Blegdamsvej 9, 2100, Copenhagen, Denmark.
authors.forename: Aida
authors.initials: A
authors.lastname: Muhic
authors.affiliation: Department of Clinical Physiology Nuclear Medicine and PET, Copenhagen University Hospital Rigshospitalet Blegdamsvej, Blegdamsvej 9, 2100, Copenhagen, Denmark.
authors.forename: Adam E
authors.initials: AE
authors.lastname: Hansen
authors.affiliation: Functional Imaging Unit, Department of Clinical Physiology Nuclear Medicine and PET, Copenhagen University Hospital Rigshospitalet Glostrup, Ndr. Ringvej 57, 2600, Glostrup, Denmark.
authors.forename: Henrik B W
authors.initials: HBW
authors.lastname: Larsson
authors.affiliation: Department of Oncology, Copenhagen University Hospital Rigshospitalet Blegdamsvej, Blegdamsvej 9, 2100, Copenhagen, Denmark.
authors.forename: Hans S
authors.initials: HS
authors.lastname: Poulsen
authors.affiliation: Department of Clinical Physiology Nuclear Medicine and PET, Copenhagen University Hospital Rigshospitalet Blegdamsvej, Blegdamsvej 9, 2100, Copenhagen, Denmark.
authors.forename: Ian
authors.initials: I
authors.lastname: Law
mesh_terms: D001810:Blood Volume; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology*; D005240:Feasibility Studies; D005910:Glioma / Q000175:diagnosis / Q000378:metabolism / Q000473:pathology / Q000503:physiopathology; D006801:Humans; D008279:Magnetic Resonance Imaging; D064847:Multimodal Imaging; D049268:Positron-Emission Tomography; D012189:Retrospective Studies; D013997:Time Factors; D047368:Tumor Burden; D014443:Tyrosine / Q000031:analogs & derivatives*
chemical_list: C545932:(18F)fluoroethyltyrosine; D014443:Tyrosine
keywords: Blood volume; Glioma; PET/MRI; [18F]-fluoro-ethyl-tyrosine