title: Comparison of PET/CT and PET/MRI hybrid systems using a 68Ga-labelled PSMA ligand for the diagnosis of recurrent prostate cancer: initial experience.
abstract: OBJECTIVE
  (68)Ga-labelled HBED-CC-PSMA is a highly promising tracer for imaging recurrent prostate cancer (PCa). The intention of this study was to evaluate the feasibility of PET/MRI with this tracer.
  
  
  METHODS
  Twenty patients underwent PET/CT 1 h after injection of the (68)Ga-PSMA ligand followed by PET/MRI 3 h after injection. Data from the two investigations were first analysed separately and then compared with respect to tumour detection rate and radiotracer uptake in various tissues. To evaluate the quantification accuracy of the PET/MRI system, differences in SUVs between PET/CT and corresponding PET/MRI were compared with differences in SUVs between PET/CT 1 h and 3 h after injection in another patient cohort. This cohort was investigated using the same PET/CT system.
  
  
  RESULTS
  With PET/MRI, different diagnostic sequences, higher contrast of lesions and higher resolution of MRI enabled a subjectively easier evaluation of the images. In addition, four unclear findings on PET/CT could be clarified as characteristic of PCa metastases by PET/MRI. However, in PET images of the PET/MRI, a reduced signal was observed at the level of the kidneys (in 11 patients) and around the urinary bladder (in 15 patients). This led to reduced SUVs in six lesions. SUVmean values provided by the PET/MRI system were different in muscles, blood pool, liver and spleen.
  
  
  CONCLUSIONS
  PCa was detected more easily and more accurately with Ga-PSMA PET/MRI than with PET/CT and with lower radiation exposure. Consequently, this new technique could clarify unclear findings on PET/CT. However, scatter correction was challenging when the specific (68)Ga-PSMA ligand was used. Moreover, direct comparison of SUVs from PET/CT and PET/MR needs to be conducted carefully.
authors.affiliation: Department of Nuclear Medicine, University Hospital Heidelberg, INF 400, 69120, Heidelberg, Germany, a.afshar@gmx.de.
authors.forename: A
authors.initials: A
authors.lastname: Afshar-Oromieh
authors.forename: U
authors.initials: U
authors.lastname: Haberkorn
authors.forename: H P
authors.initials: HP
authors.lastname: Schlemmer
authors.forename: M
authors.initials: M
authors.lastname: Fenchel
authors.forename: M
authors.initials: M
authors.lastname: Eder
authors.forename: M
authors.initials: M
authors.lastname: Eisenhut
authors.forename: B A
authors.initials: BA
authors.lastname: Hadaschik
authors.forename: A
authors.initials: A
authors.lastname: Kopp-Schneider
authors.forename: M
authors.initials: M
authors.lastname: Röthke
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D004492:Edetic Acid / Q000031:analogs & derivatives*; D005709:Gallium Isotopes; D005710:Gallium Radioisotopes; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging; D009842:Oligopeptides; D049268:Positron-Emission Tomography; D011471:Prostatic Neoplasms / Q000175:diagnosis / Q000000981:diagnostic imaging*; D019275:Radiopharmaceuticals; D014057:Tomography, X-Ray Computed
chemical_list: D005709:Gallium Isotopes; D005710:Gallium Radioisotopes; D009842:Oligopeptides; D019275:Radiopharmaceuticals; C000718244:gallium 68 PSMA-11; D004492:Edetic Acid