Dose Optimization in TOF-PET/MR Compared to TOF-PET/CT

Abstract

PurposeTo 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 MethodsA 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.ResultsThe 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.ConclusionThe 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.

Clinical evaluation of a block sequential regularized expectation maximization reconstruction algorithm in 18F-FDG PET/CT studies

“…The two readers subjectively evaluated GIQ of each PET data using a five-point scale and evaluated the criteria artifact, image sharpness (IS), noise, and lesion detectability (LD) using a four-point scale. The criteria used for these grades are summarized in Table 1 and are based on previously published studies assessing image quality [29][30][31] Multivariate linear regression analysis was carried out to assess independent predictors (i.e. reconstruction, lesion size, location) of quantitative parameters (i.e.…”

Reduction of 18F-FDG Dose in Clinical PET/MR Imaging by Using Silicon Photomultiplier Detectors

“…The newly available PET/magnetic resonance (MR) imaging systems can help reduce the absorbed radiation dose to patients (5)(6)(7). In these systems, the MR imaging component, which does not require the use of ionizing radiation, replaces the CT component for attenuation correction, anatomic correlation, and diagnostic lesion characterization.…”

“…Additionally, the PET component from the latest clinical timeof-flight (TOF)-PET/MR imaging systems has the potential to reduce radiation exposure even further. This system uses dedicated silicon photomultiplier (SiPM) detectors with increased sensitivity, which allows one to balance reduction of injected dose with acquisition time reduction (5,8,9). In a pilot study, PET image quality with this system was clinically acceptable at 50% of the injected fluorodeoxyglucose (FDG) dose used in conventional PET/CT (5).…”

PET/MRI: Reliability/Reproducibility of SUV Measurements

“…Overall the differences between both systems were mainly due to the TOF possibility on the mCT, which resulted in an overall better image quality, especially for the more challenging settings with higher background activity and small uptake volumes [62]. For the fully integrated PET/MR scanner with TOF, only a few studies were published comparing PET quantification on PET/CT and PET/ MR until today [44,55,57]. A prospective trial comparing TOF PET/CT (Discovery D 690 PET/CT, GE Healthcare) and TOF PET/MR (SIGNA PET/MR) in 75 patients based on phantom NECR curves investigated the potential dose reduction for PET/MR with equivalent image quality.…”

“…A prospective trial comparing TOF PET/CT (Discovery D 690 PET/CT, GE Healthcare) and TOF PET/MR (SIGNA PET/MR) in 75 patients based on phantom NECR curves investigated the potential dose reduction for PET/MR with equivalent image quality. They concluded that a reduction of FDG activity of slightly more the 50% can be achieved thanks to improvements in detector geometry and technologies [55].…”