title: Imaging with (124)I in differentiated thyroid carcinoma: is PET/MRI superior to PET/CT?
abstract: OBJECTIVE
  The aim of this study was to compare integrated PET/CT and PET/MRI for their usefulness in detecting and categorizing cervical iodine-positive lesions in patients with differentiated thyroid cancer using (124)I as tracer.
  
  
  METHODS
  The study group comprised 65 patients at high risk of iodine-positive metastasis who underwent PET/CT (low-dose CT scan, PET acquisition time 2 min; PET/CT2) followed by PET/MRI of the neck 24 h after (124)I administration. PET images from both modalities were analysed for the numbers of tracer-positive lesions. Two different acquisition times were used for the comparisons, one matching the PET/CT2 acquisition time (2 min, PET/MRI2) and the other covering the whole MRI scan time (30 min, PET/MRI30). Iodine-positive lesions were categorized as metastasis, thyroid remnant or inconclusive according to their location on the PET/CT images. Morphological information provided by MRI was considered for evaluation of lesions on PET/MRI and for volume information.
  
  
  RESULTS
  PET/MRI2 detected significantly more iodine-positive metastases and thyroid remnants than PET/CT2 (72 vs. 60, p = 0.002, and 100 vs. 80, p = 0.001, respectively), but the numbers of patients with at least one tumour lesion identified were not significantly different (21/65 vs. 17/65 patients). PET/MRI30 tended to detect more PET-positive metastases than PET/MRI2 (88 vs. 72), but the difference was not significant (p = 0.07). Of 21 lesions classified as inconclusive on PET/CT, 5 were assigned to metastasis or thyroid remnant when evaluated by PET/MRI. Volume information was available in 34 % of iodine-positive metastases and 2 % of thyroid remnants on PET/MRI.
  
  
  CONCLUSIONS
  PET/MRI of the neck was found to be superior to PET/CT in detecting iodine-positive lesions. This was attributed to the higher sensitivity of the PET component, Although helpful in some cases, we found no substantial advantage of PET/MRI over PET/CT in categorizing iodine-positive lesions as either metastasis or thyroid remnant. Volume information provided by MRI for some iodine-positive lesions might be useful in dosimetry.
authors.affiliation: Medical Faculty, Department of Nuclear Medicine, University of Duisburg-Essen, Hufelandstr. 55, 45122, Essen, Germany. ina.binse@uk-essen.de.
authors.forename: I
authors.initials: I
authors.lastname: Binse
authors.affiliation: Medical Faculty, Department of Nuclear Medicine, University of Duisburg-Essen, Hufelandstr. 55, 45122, Essen, Germany.
authors.forename: T D
authors.initials: TD
authors.lastname: Poeppel
authors.affiliation: Medical Faculty, Department of Nuclear Medicine, University of Duisburg-Essen, Hufelandstr. 55, 45122, Essen, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Ruhlmann
authors.affiliation: Medical Faculty, Department of Nuclear Medicine, University of Duisburg-Essen, Hufelandstr. 55, 45122, Essen, Germany.
authors.forename: B
authors.initials: B
authors.lastname: Gomez
authors.affiliation: Medical Faculty, Department of Radiology, University of Duisburg-Essen, Essen, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Umutlu
authors.affiliation: Medical Faculty, Department of Nuclear Medicine, University of Duisburg-Essen, Hufelandstr. 55, 45122, Essen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Bockisch
authors.affiliation: Medical Faculty, Department of Nuclear Medicine, University of Duisburg-Essen, Hufelandstr. 55, 45122, Essen, Germany.
authors.forename: S J
authors.initials: SJ
authors.lastname: Rosenbaum-Krumme
mesh_terms: D000328:Adult; D000368:Aged; D005260:Female; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007457:Iodine Radioisotopes / Q000627:therapeutic use; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D000072078:Positron Emission Tomography Computed Tomography; D012008:Recurrence; D013964:Thyroid Neoplasms / Q000000981:diagnostic imaging* / Q000473:pathology / Q000532:radiotherapy; D055815:Young Adult
chemical_list: D007457:Iodine Radioisotopes
keywords: Differentiated thyroid carcinoma; Iodine-124; PET/CT; PET/MRI