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Dose Optimization in TOF-PET/MR Compared to TOF-PET/CT
Marcelo A Queiroz1, Gaspar Delso2, Scott Wollenweber2
1Department of Medical Imaging, Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland.
Purpose:
To evaluate the possible activity reduction in FDG-imaging in a Time-of-Flight (TOF) PET/MR, based on cross-evaluation of patient-based NECR (noise equivalent count rate) measurements in PET/CT, cross referencing with phantom-based NECR curves as well as initial evaluation of TOF-PET/MR with reduced activity.
Materials And Methods:
A total of 75 consecutive patients were evaluated in this study. PET/CT imaging was performed on a PET/CT (time-of-flight (TOF) Discovery D 690 PET/CT). Initial PET/MR imaging was performed on a newly available simultaneous TOF-PET/MR (Signa PET/MR). An optimal NECR for diagnostic purposes was defined in clinical patients (NECRP) in PET/CT. Subsequent optimal activity concentration at the acquisition time ([A]0) and target NECR (NECRT) were obtained. These data were used to predict the theoretical FDG activity requirement of the new TOF-PET/MR system. Twenty-five initial patients were acquired with (retrospectively reconstructed) different imaging times equivalent for different activities on the simultaneous PET/MR for the evaluation of clinically realistic FDG-activities.
Results:
The obtained values for NECRP, [A]0 and NECRT were 114.6 (± 14.2) kcps (Kilocounts per second), 4.0 (± 0.7) kBq/mL and 45 kcps, respectively. Evaluating the NECRT together with the phantom curve of the TOF-PET/MR device, the theoretical optimal activity concentration was found to be approximately 1.3 kBq/mL, which represents 35% of the activity concentration required by the TOF-PET/CT. Initial evaluation on patients in the simultaneous TOF-PET/MR shows clinically realistic activities of 1.8 kBq/mL, which represent 44% of the required activity.
Conclusion:
The new TOF-PET/MR device requires significantly less activity to generate PET-images with good-to-excellent image quality, due to improvements in detector geometry and detector technologies. The theoretically achievable dose reduction accounts for up to 65% but cannot be fully translated into clinical routine based on the coils within the FOV and MR-sequences applied at the same time. The clinically realistic reduction in activity is slightly more than 50%. Further studies in a larger number of patients are needed to confirm our findings.
Insights
New Time-of-Flight PET/MR scanners significantly reduce required FDG activity for high-quality imaging. This advancement offers over 50% dose reduction in clinical settings, enhancing patient safety.
Area of Science:
- Nuclear Medicine
- Medical Imaging Technology
- Radiochemistry
Background:
- Positron Emission Tomography (PET) combined with Magnetic Resonance Imaging (PET/MR) offers advanced diagnostic capabilities.
- Optimizing radiotracer activity is crucial for balancing image quality and radiation dose.
- Time-of-Flight (TOF) technology in PET systems improves signal-to-noise ratio and lesion detectability.
Purpose of the Study:
- To assess the potential reduction in Fluorodeoxyglucose (FDG) activity for Time-of-Flight (TOF) PET/MR imaging.
- To compare noise equivalent count rate (NECR) measurements between PET/CT and TOF PET/MR.
- To evaluate initial clinical performance of TOF PET/MR with reduced FDG activity.
Main Methods:
- Seventy-five patients underwent PET/CT and simultaneous TOF PET/MR imaging.
- Optimal NECR (NECRP) was determined in clinical PET/CT scans.
- Theoretical FDG activity requirements for TOF PET/MR were predicted using NECR data and phantom studies; initial patient scans used reduced activity levels.
Main Results:
- The TOF PET/MR system theoretically requires approximately 1.3 kBq/mL, which is 35% of the activity needed for TOF PET/CT.
- Initial patient evaluations on the TOF PET/MR demonstrated clinically feasible activity levels of 1.8 kBq/mL (44% of TOF PET/CT requirement).
- A clinically realistic activity reduction of over 50% was observed.
Conclusions:
- The new TOF PET/MR system enables high-quality PET imaging with significantly reduced FDG activity due to improved detector technology.
- Theoretical dose reduction can reach up to 65%, though clinical routine may be slightly lower due to hardware constraints (coils, MR sequences).
- Further large-scale studies are warranted to confirm these findings and optimize clinical protocols.
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