Feasibility of Ultra-Low Dose PET/CT for Evaluation of ACL Grafts Using a Next Generation Digital Detector

1005 Objectives Combined PET/MR for the evaluation of ACL graft healing following surgery has proven to be feasible. Next generation digital PET/CT systems provide the advanced count statistics needed in order to consider FDG tracer dose reduction efforts for such non-oncologic applications of PET imaging. Using extensive simulations based on list mode acquired data, we want to establish an ultra-low FDG dose PET protocol to facilitate broader utilization including the potential of follow up examinations to assess graft healing. Methods 10 patients post-surgical ACL graft reconstruction had an MRI on a 3T Ingenia CX using the dedicated 16 channel knee coil, with both knees imaged sequentially. Dynamic PET/CT was performed on a pre-commercial release digital photon counting, high temporal time of flight resolution, next generation PET/CT system, Vereos. An in-house fabricated mold of the MR knee coil was used during PET acquisitions in order to ensure identical positioning between image sets. A single bed position (164 mm z-axis) centered on the knees was acquired following injection of 3 mCi (111MBq) 18F-FDG. Listmode data were acquired continuously for 75 minutes. The dynamic data were then reconstructed as 5 minute frames which is our standard methodology for quantitative assessment, and 2.5 minute and 1 minute frames, which serve as simulations of reduced count densities expected when 50% and 80% tracer dose reductions would be implemented. Patients were grouped by time since surgery and SUVmax was measured in the proximal, middle, and distal portions of the graft, femoral and tibial tunnels, the posterior cruciate ligament (PCL), and quadriceps muscle for reference. Matched ROIs were drawn in the contralateral knee. The percent difference from normal frames (5 min) was calculated for the measurements to estimate the impact of 50% and 80% tracer dose reduction. A blinded reader analysis on potential detrimental impacts on image quality was additionally performed. Results Among all patients and ROI assessments, the SUVmax in the graft and bone tunnels varied by less than 8% on average for the simulated 50% dose reduction (111 MBq vs. 56 MBq) and by 17% to the 80% dose reduction (111 MBq vs. 22 MBq). The SUVmax did trend predominately higher in the more count sparse images. The blinded visual assessment did not find any detrimental impact on relevant image quality for both simulation levels. Patients with more recent surgery were found to have less variation with shorter frames due to generally higher uptake levels. Measurements in background areas of the PCL and muscle had significantly (p Conclusions With the introduction of next generation digital PET/CT systems, molecular imaging of ACL grafts may be performed at extremely low radiation burden levels. While we are confident that imaging below 2 mSv total radiation exposure can be performed, a threshold leap to 1 mSv appears within reach which would make molecular PET/CT and PET/MRI a highly desirable precision and personalized medicine non-invasive methodology for patient critical sports medicine applications including the feasibility of follow up and therapy monitoring utilization.