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

Marcelo A Queiroz; Gaspar Delso; Scott Wollenweber; Timothy Deller; Konstantinos Zeimpekis; Martin Huellner; Felipe de Galiza Barbosa; Gustav von Schulthess; Patrick Veit-Haibach

doi:10.1371/journal.pone.0128842

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

PLoS One. 2015 Jul 6;10(7):e0128842. doi: 10.1371/journal.pone.0128842. eCollection 2015.

Authors

Marcelo A Queiroz¹, Gaspar Delso², Scott Wollenweber², Timothy Deller², Konstantinos Zeimpekis¹, Martin Huellner³, Felipe de Galiza Barbosa¹, Gustav von Schulthess¹, Patrick Veit-Haibach³

Affiliations

¹ Department of Medical Imaging, Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland.
² GE Healthcare, Waukesha, Wisconsin, United States of America.
³ Department of Medical Imaging, Nuclear Medicine, University Hospital Zurich, Zurich, Switzerland; Department of Medical Imaging, Diagnostic and Interventional Radiology, University Hospital Zurich, Zurich, Switzerland.

Abstract

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.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Humans
Magnetic Resonance Imaging*
Multimodal Imaging*
Positron-Emission Tomography*
Radiation Dosage*
Tomography, X-Ray Computed*

Grants and funding

This research project was supported by an institutional research grant from GE Healthcare. Co-authors Gaspar Delso, Scott D. Wollenweber and Timothy Deller are employed by GE Healthcare. GE Healthcare provided support in the form of salaries for authors GD, SDW and TD, but did not have any additional role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript. The specific roles of these authors are articulated in the ‘author contributions’ section.