Simultaneous whole-body time-of-flight ¹⁸F-FDG PET/MRI: A pilot study comparing SUV_max with PET/CT and assessment of MR image quality

Purpose: The recent introduction of hybrid PET/MRI scanners in clinical practice has shown promising initial results for several clinical scenarios. However, the first generation of combined PET/MRI lacks time-of-flight (TOF) technology. Herewe report the results of the first patients to be scanned on a completely novel fully integrated PET/MRI scanner with TOF.

Materials and Methods: We analyzed data from patients who underwent a clinically indicated ¹⁸F FDG PET/CT, followed by PET/MRI. Maximum standardized uptake values (SUV_max) were measured from ¹⁸F FDG PET/MRI and ¹⁸F FDG PET/CT for lesions, cerebellum, salivary glands, lungs, aortic arch, liver, spleen, skeletal muscle, and fat. Two experienced radiologists independently reviewed the MR data for image quality.

Results: Thirty-six patients (19 men, 17 women, mean [±standard deviation] age of 61 ± 14 years [range: 27-86 years]) with a total of 69 discrete lesions met the inclusion criteria. PET/CT images were acquired at a mean (±standard deviation) of 74 ± 14 minutes (range: 49-100 minutes) after injection of 10 ± 1 mCi (range: 8-12 mCi) of ¹⁸F FDG. PET/MRI scans started at 161 ± 29 minutes (range: 117 - 286 minutes) after the ¹⁸F FDG injection. All lesions identified on PET from PET/CTwere also seen on PET from PET/MRI. The mean SUV_max values were higher from PET/MRI than PET/CT for all lesions. No degradation of MR image quality was observed.

Conclusion: The data obtained so far using this investigational PET/MR system have shown that the TOF PET system is capable of excellent performance during simultaneous PET/MR with routine pulse sequences. MR imaging was not compromised. Comparison of the PET images from PET/CT and PET/MRI show no loss of image quality for the latter. These results support further investigation of this novel fully integrated TOF PET/MRI instrument.