Improved accuracy of the biodistribution and internal radiation dosimetry of ¹³N‐ammonia using a total‐body PET/CT scanner

Abstract

BackgroundConventional short‐axis PET typically utilizes multi‐bed multi‐pass acquisition to produce quantitative whole‐body dynamic images and cannot record all the uptake information simultaneously, resulting in errors when fitting the time‐activity curves (TACs) and calculating radiation doses.PurposeThe aim of this study is to evaluate the 13N‐ammonia biodistribution and the internal radiation doses using a 194 cm long total‐body PET/CT scanner (uEXPLORER), and make a comparison with the previous short‐axis PET results.MethodsTen subjects (age 40–74 years) received 13N‐NH3 injection (418.1‐670.81 MBq) and were under a dynamic scan for about 60 min with using a 3‐dimensional whole‐body protocol. ROIs were drawn visually on 11 major organs (brain, thyroid, gallbladder, heart wall, kidneys, liver, pancreas, spleen, lungs, bone marrow, and urinary bladder content) for each subject. TACs were generated using Pmod and the absorbed radiation doses were calculated using Olinda 2.2. To compare with the conventional PET/CT, five points were sampled on uEXPLORER's TACs to mimic the result of a short‐axis PET/CT (15 cm axial FOV, consisted of 9 or 10 bed positions). Then the TACs were obtained using the multi‐exponential fitting method, and the residence time and radiation dose were also calculated and compared with uEXPLORER.ResultsThe highest absorbed organ doses were the pancreas, thyroid, spleen, heart wall, and kidneys for the male. For the female, the first five highest absorbed organ dose coefficients were the pancreas, heart wall, spleen, lungs, and kidneys. The lowest absorbed dose was found in red marrow both for male and female. The simulated short‐axis PET can fit TACs well for the gradually‐changed uptake organs but typically underestimated for the rapid‐uptake organs during the first‐10 min, resulting in errors in the calculated radiation dose.ConclusionuEXPLORER PET/CT can measure 13N‐ammonia's TACs simultaneously in all organs of the whole body, which can provide more accurate biodistribution and radiation dose estimation compared with the conventional short‐axis scanners.

Current progress and future perspectives in total‐body PET imaging, part I: Data processing and analysis

“…Currently, most research in TB-PET data processing is focused on 18 F-FDG imaging, and the potential for non-FDG tracers must be leveraged. Some pioneering works have attempted imaging with 68 Ga-DOTATATE [116], 68 Ga-PSMA [117], 68 Ga-FAPI [118][119][120], 13 N-ammonia [121], 89 Zr [122,123], 18 F-Fluciclovine [124], 11 Cmethionine [125], Y-90 [126], and 82 Rb [127]. However, the optimal data processing methods differ considerably between non-FDG tracers, and need to be adapted accordingly.…”

Current progress and future perspectives in total‐body positron emission tomography/computed tomography. Part II: Clinical applications

“…Owing to its ultra-high sensitivity, TB-PET has emerged as a prominent research tool for enhancing the accuracy of internal radiation dose calculations in clinical applications [24,25]. Yu et al [24] demonstrated that TB-PET is capable of simultaneously measuring the time-course activity of 13 N-ammonia in all organs of the body. This capability offers more precise biodistribution data and radiation dose estimations compared with SAFOV PET.…”

“…Yu et al. [24] demonstrated that TB‐PET is capable of simultaneously measuring the time‐course activity of 13 N‐ammonia in all organs of the body. This capability offers more precise biodistribution data and radiation dose estimations compared with SAFOV PET.…”

“…Owing to its ultra‐high sensitivity, TB‐PET has emerged as a prominent research tool for enhancing the accuracy of internal radiation dose calculations in clinical applications [24, 25]. Yu et al.…”