Feasibility of 18 F-FDG Dose Reductions in Breast Cancer PET/MRI.

Rationale: The goal of this study was to determine the level of clinically acceptable 18 F-fluoro-2-deoxy-D-glucose (18 F-FDG) dose reduction in time of flight (TOF) - positron emission tomography/magnetic resonance imaging (PET/MRI) in patients with breast cancer. Methods: Twenty-six consecutive female patients with histologically proven breast cancer were analyzed (median age, 51 years; range, 34 - 83 years). Simulated dose-reduced PET images were generated by un-listing the list mode data on PET/MRI. The acquired 20 minutes PET frame was reconstructed in 5 ways: a reconstruction of the first 2 minutes with 3 iterations and 28 subsets for reference, and reconstructions simulating 100%, 20%, 10%, 5% of the original dose. General image quality and artifacts (GIQ+A), image sharpness (IS), noise (N), and lesion detectability (LD) were analyzed using a four-point scale. Qualitative parameters were compared by using the non-parametric Friedman test for multiple samples and the Wilcoxon signed-rank test for paired samples. Comparison of different groups of independent samples was performed using the Mann-Whitney-U-Test. Results: Overall, 355 lesions (71 lesions with five different reconstructions each) were evaluted. The 20 minutes reconstruction with 100% injected dose showed the best results in all categories. In GIQ+A, IS and N the reconstructions with a simulated dose of 20% and 10% were significantly better than the 2 minutes reconstructions (p<=0.001). Furthermore, 20%, 10%, and 5% reconstructions did not yield different results compared to the 2 minutes reconstruction in LD of the primary lesion. Using 10% of the injected dose a calculated mean dose of 22.6 +/- 5.5 MBq (range 17.9 - 36.9 MBq) would have been applied, resulting in an estimated whole-body radiation burden of 0.5 +/- 0.1 mSv (range 0.4 - 0.7 mSv). Conclusion: 10% of the standard dose of 18 F-FDG (reduction of up to 90%) results in clinically acceptable PET-image quality in TOF PET/MRI. The calculated radiation exposure would be comparable to the effective dose of a single digital mammography. A reduction of radiation burden to this level might justify partial-body examinations with PET/MRI for dedicated indications.