title: Hybrid PET/MRI of intracranial masses: initial experiences and comparison to PET/CT.
abstract: Simultaneous PET and MRI using new hybrid PET/MRI systems promises optimal spatial and temporal coregistration of structural, functional, and molecular image data. In a pilot study of 10 patients with intracranial masses, the feasibility of tumor assessment using a PET/MRI system comprising lutetium oxyorthosilicate scintillators coupled to avalanche photodiodes was evaluated, and quantification accuracy was compared with conventional PET/CT datasets.
  
  
  METHODS
  All measurements were performed with a hybrid PET/MRI scanner consisting of a conventional 3-T MRI scanner in combination with an inserted MRI-compatible PET system. Attenuation correction of PET/MR images was computed from MRI datasets. Diagnoses at the time of referral were low-grade astrocytoma (n = 2), suspicion of low-grade astrocytoma (n = 1), anaplastic astrocytoma (World Health Organization grade III; n = 1), glioblastoma (n = 2), atypical neurocytoma (n = 1), and meningioma (n = 3). In the glial tumors, (11)C-methionine was used for PET; in the meningiomas, (68)Ga-DOTATOC was administered. Tumor-to-gray matter and tumor-to-white matter ratios were calculated for gliomas, and tracer uptake of meningiomas was referenced to nasal mucosa. PET/MRI was performed directly after clinically indicated PET/CT examination.
  
  
  RESULTS
  In all patients, the PET datasets showed similar diagnostic image quality on the hybrid PET/MRI and the PET/CT studies; however, slight streak artifacts were visible in coronal and sagittal sections when using the higher intrinsic resolution of the PET/MRI insert. Prefiltering of images with a 4-mm gaussian filter at a resolution comparable to that of the PET/CT system virtually eliminated these artifacts. Although acquisition of the PET/MR images started at 30-60 min after PET/CT (20.4-min half-life of (11)C) acquisition, the signal-to-noise ratio was good enough, thus underlining the high sensitivity of the PET insert, compared with whole-body PET systems. The computed tumor-to-reference tissue ratios exhibited an excellent accordance between the PET/MRI and PET/CT systems, with a Pearson correlation coefficient of 0.98. Mean paired relative error was 7.9% +/- 12.2%. No significant artifacts or distortions were detected in the simultaneously acquired MR images using the PET/MRI scanner.
  
  
  CONCLUSIONS
  Structural, functional, and molecular imaging in patients with brain tumors is feasible with diagnostic imaging quality using simultaneous hybrid PET/MR image acquisition.
authors.affiliation: Department of Diagnostic and Interventional Radiology, Eberhard-Karls University Tübingen, Tübingen, Germany. andreas.boss@med.uni-tuebingen.de
authors.forename: Andreas
authors.initials: A
authors.lastname: Boss
authors.forename: Sotirios
authors.initials: S
authors.lastname: Bisdas
authors.forename: Armin
authors.initials: A
authors.lastname: Kolb
authors.forename: Matthias
authors.initials: M
authors.lastname: Hofmann
authors.forename: Ulrike
authors.initials: U
authors.lastname: Ernemann
authors.forename: Claus D
authors.initials: CD
authors.lastname: Claussen
authors.forename: Christina
authors.initials: C
authors.lastname: Pfannenberg
authors.forename: Bernd J
authors.initials: BJ
authors.lastname: Pichler
authors.forename: Matthias
authors.initials: M
authors.lastname: Reimold
authors.forename: Lars
authors.initials: L
authors.lastname: Stegger
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology*; D003627:Data Interpretation, Statistical; D005260:Female; D005710:Gallium Radioisotopes; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008715:Methionine; D008875:Middle Aged; D015282:Octreotide / Q000031:analogs & derivatives; D010865:Pilot Projects; D049268:Positron-Emission Tomography / Q000379:methods*; D019275:Radiopharmaceuticals; D014055:Tomography, Emission-Computed
chemical_list: D005710:Gallium Radioisotopes; D019275:Radiopharmaceuticals; D008715:Methionine; D015282:Octreotide; C106246:Edotreotide