Ultra-low Dose Na-18F Next-generation Digital PET/CT for Whole-body Osteoblastic Disease Assessment

Objectives Consistent qualitative and accurate quantitative assessment of Na-18F-avid osteoblastic lesions is essential for patients undergoing routine oncologic or non-oncologic bone imaging studies. At present, clinical Na-18F doses (average 400 MBq) contribute to whole-body radiation doses which are higher than desired especially when patients need extensive imaging throughout their healthcare. Our objective is to develop a methodology for substantial clinical Na-18F dose reduction leveraging the next-generation digital PET technology for bone imaging applications.

Methods As part of ongoing methodology development clinical trials, whole-body Na-18F digital PET/CT (Vereos) (dPET) imaging was performed and compared with conventional photomultiplier tube PET/CT (cPET) imaging. Digital PET imaging was acquired using list-mode which allows for subsequent subsampling to simulate lower dose levels or lower image count densities. Based on prior phantom validation studies, digital PET imaging data was used to generate subsampled PET reconstructions which utilizes only the desired subset of total events per bed volume. This enables the simulation of virtual dose reductions ranging as we have demonstrated previously by phantom and preclinical experiments. We down-sampled the datasets from its original in 10% increments covering 90% to 10%. In addition for further validation, we performed the whole-body digital PET scans also at 1/10 of the standard acquisition thus using a 9 sec/bed in addition to the standard 90 sec/bed. All images were visually and quantitatively assessed by blinded readers. All statistical assessments are performed at a 95% confidence level with appropriate correction for multiple comparisons.

Results Blinded reader quantitative and visual assessment of Na-18F-avid indicates that Na-18F dose reductions of 60% (~150 MBq) are achievable using dPET technology without impact on qualitative or quantitative assessment when compared with cPET technology. Visually, there is no significant loss of 18F-avidity in either normal bone (i.e., background uptake) or osteoblastic lesions with increasing simulated dose reduction. In addition, there is concordance between the simulated PET reconstructions and the corresponding reduced time/bed position digital PET acquisition. There appears to be the potential for modified reconstruction optimization of Na-18F, with the additional 9 sec/bed data sets providing the basis.

Conclusions This initial feasibility trial indicates that a Na-18F dose reduction by 60% (compared to current standard of care dosing without any negative impact) to about 150 MBq can be readily achieved with the next generation digital PET technology without any negative impact. While further optimization of reconstruction is still ongoing as data sets are generated, whole body Na-18F imaging at <100 MBq appears achievable using the next generation dPET.