Nucl Med Mol Imaging.  2014 Mar;48(1):26-32.

Evaluation of Dixon Sequence on Hybrid PET/MR Compared with Contrast-Enhanced PET/CT for PET-Positive Lesions

  • 1Department of Nuclear medicine, Yeungnam University Hospital, #317-1 Daemyung 5-dongNam-gu Daegu 705-717, Republic of Korea.


Hybrid positron emission tomography and magnetic resonance (PET/MR) imaging performs a two-point Dixon MR sequence for attenuation correction. However, MR data in hybrid PET/MR should provide anatomic and morphologic information as well as an attenuation map. We evaluated the Dixon sequence of hybrid PET/MR for anatomic correlation of PET-positive lesions compared with contrast-enhanced PET/computed tomography (CT) in patients with oncologic diseases.
Twelve patients underwent a single injection, dual imaging protocol. PET/CTwas performed with an intravenous contrast agent (85+/-13 min after 18F-FDG injection of 403+/-45 MBq) and then (125+/-19 min after injection) PET/MR was performed. Attenuation correction and anatomic allocation of PETwere performed using contrast-enhanced CT for PET/CT and Dixon MR sequence for hybrid PET/MR. The Dixon MR sequence and contrast-enhanced CT were compared for anatomic correlation of PET-positive lesions (scoring scale ranging from 0 to 3 for visual ratings). Additionally, standardized uptake values (SUVs) for the detected lesions were assessed for quantitative comparison.
Both hybrid PET/MRand contrast-enhanced PET/CT identified 55 lesions with increased FDG uptake in ten patients. In total, 28 lymph nodes, 11 bone lesions, 3 dermal nodules, 3 pleural thickening lesions, 2 thyroid nodules, 1 pancreas, 1 liver, 1 ovary, 1 uterus, 1 breast, 1 soft tissue and 2 lung lesions were present. The best performance was observed for anatomic correlation of PET findings by the contrast-enhanced CT scans (contrast-enhanced CT, 2.64+/-0.70; in-phase, 1.29+/-1.01; opposed-phase, 1.29+/-1.15; water-weighted, 1.71+/-1.07; fat weighted, 0.56+/-1.03). A significant difference was observed between the scores obtained from the contrast-enhanced CT and all four coregistered Dixon MR images. Quantitative evaluation revealed a high correlation between the SUVsmeasured with hybrid PET/MR (SUVmean, 2.63+/-1.62; SUVmax, 4.30+/-2.88) and contrast-enhanced PET/CT (SUVmean, 3.88+/-2.30; SUVmax, 6.53+/-4.04) in PET-positive lesions (SUVmean, rho=0.93; SUVmax, rho=0.95), although hybrid PET/MR presented a decrease of SUVs compared with contrast-enhanced PET/CT (mean reduction; SUVmean, 32.44+/-15.64 %; SUVmax, 35.16+/-12.59 %).
Despite different attenuation correction approaches, the SUV of PET-positive lesions correlated well between hybrid PET/MR and contrast-enhanced PET/CT. However Dixon MR images acquired for attenuation correction were insufficient to provide anatomic information of PET images because of low spatial resolution. Thus, additionalMR sequence with fast and higher resolution may be necessary for anatomic information.


Positronemission tomography; Positronemission tomography and computed tomography; Magnetic resonance imaging; Fluorodeoxyglucose F-18; Neoplasms

MeSH Terms

Evaluation Studies as Topic
Fluorodeoxyglucose F18
Lymph Nodes
Magnetic Resonance Imaging
Positron-Emission Tomography
Positron-Emission Tomography and Computed Tomography*
Thyroid Nodule
Tomography, X-Ray Computed
Fluorodeoxyglucose F18
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