title: Hybrid imaging for detection of carcinoma of unknown primary: A preliminary comparison trial of whole-body PET/MRI versus PET/CT.
abstract: OBJECTIVE
  The aim of this study is to evaluate and compare the diagnostic potential of integrated whole-body [18F]FDG-PET/MRI to [18F]FDG-PET/CT for detection of a potential primary cancer and metastases in patients suspected for cancer of unknown primary (CUP).
  
  
  METHODS
  A total of 20 patients (15 male, 5 female, age 53±13 years) suspect for CUP underwent a dedicated head and neck & whole-body [18F]FDG-PET/CT (Biograph mCT 128, Siemens Healthcare) and a subsequent simultaneous [18F]FDG-PET/MRI examination (Biograph mMR, Siemens Healthcare). Two readers rated the datasets (PET/CT; PET/MRI) regarding the detection of the primary cancer and metastases, lesion conspicuity (4-point ordinal scale) and diagnostic confidence (3-point ordinal scale). PET analysis comprised the assessment of maximum standardized uptake values (SUVmax) of all PET-positive lesions using volume of interest (VOI) analysis derived from the PET/CT and PET/MR datasets. All available data considering histology and imaging including prior and clinical follow-up examinations served as reference standard. Statistical analysis included comparison of mean values using Mann-Whitney U test and correlation of SUVmax using Pearson's correlation.
  
  
  RESULTS
  In 14 out of 20 patients 49 malignant lesions were present. The primary cancer could be correctly identified in 11/20 patients with both PET/CT and PET/MRI. PET/CT enabled the detection of a total 38 metastases, PET/MR respectively of 37 metastases (one lung metastasis <5mm was missed). PET/CT and PET/MRI showed comparably high lesion conspicuity (2.6±0.6 each), with superior assessment of cervical lesions in PET/MRI and an indicated superior assessment of pulmonary lesions in PET/CT. Diagnostic confidence was rated comparably high in PET/CT and PET/MRI (2.7±0.5 each). The mean values of SUVmax of all PET-positive lesions (PET/MRT 7.9±4.2 vs. PET/CT 7.2±3.5) showed a strong positive correlation between the SUVs derived from both hybrid imaging systems (Pearson's correlation r=0.927).
  
  
  CONCLUSIONS
  Both hybrid imaging techniques provide a comparable diagnostic ability for detection of primary cancer and metastases in patients with CUP, with comparably high lesion conspicuity and diagnostic confidence, offering superior assessment of cervical lesions in PET/MRI and potentially of pulmonary lesions in PET/CT. Furthermore, due to the significantly lower dose of ionizing radiation, PET/MRI may serve as a powerful alternative to PET/CT, particularly for therapy monitoring and/or surveillance considering the long-term cumulative dose.
authors: Department of Nuclear Medicine, University Hospital Essen, University Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany.
authors: Verena
authors: V
authors: Ruhlmann
authors: Department of Nuclear Medicine, University Hospital Essen, University Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany.
authors: Marcus
authors: M
authors: Ruhlmann
authors: Department of Nuclear Medicine, University Hospital Essen, University Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany.
authors: Alexander
authors: A
authors: Bellendorf
authors: Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, University Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany.
authors: Johannes
authors: J
authors: Grueneisen
authors: Department of Diagnostic and Interventional Radiology, University of Dusseldorf, Moorenstraße 5, 40225 Dusseldorf, Germany.
authors: Lino M
authors: LM
authors: Sawicki
authors: Department of Nuclear Medicine, University Hospital Essen, University Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany.
authors: Hong
authors: H
authors: Grafe
authors: Department of Diagnostic and Interventional Radiology and Neuroradiology, University Hospital Essen, University Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany.
authors: Michael
authors: M
authors: Forsting
authors: Department of Nuclear Medicine, University Hospital Essen, University Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany.
authors: Andreas
authors: A
authors: Bockisch
authors: Department of Nuclear Medicine, University Hospital Essen, University Duisburg-Essen, Hufelandstr. 55, 45122 Essen, Germany. Electronic address: verena.ruhlmann@uk-essen.de.
authors: Lale
authors: L
authors: Umutlu
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002277:Carcinoma / Q000000981:diagnostic imaging* / Q000556:secondary; D005260:Female; D019788:Fluorodeoxyglucose F18; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D064847:Multimodal Imaging / Q000379:methods*; D009382:Neoplasms, Unknown Primary / Q000000981:diagnostic imaging*; D000072078:Positron Emission Tomography Computed Tomography; D049268:Positron-Emission Tomography; D019275:Radiopharmaceuticals; D015203:Reproducibility of Results; D051598:Whole Body Imaging / Q000379:methods*
chemical_list: D019275:Radiopharmaceuticals; D019788:Fluorodeoxyglucose F18