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Technical Note: Transconvolution based equalization of positron energy effects for the use of 68 Ge/ 68 Ga phantoms in determining 18 F PET recovery
Author(s) -
Prenosil George A.,
Hentschel Michael,
Fürstner Markus,
Krause Thomas,
Weitzel Thilo,
Klaeser Bernd
Publication year - 2017
Publication title -
medical physics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.473
H-Index - 180
eISSN - 2473-4209
pISSN - 0094-2405
DOI - 10.1002/mp.12330
Subject(s) - imaging phantom , positron , positron emission tomography , nuclear medicine , isotope , physics , positron emission , materials science , optics , nuclear physics , medicine , electron
Purpose Avoiding measurement variability from 18 F phantom preparation by using 68 Ge/ 68 Ga phantoms for the determination of 18 F recovery curves ( RC ) in clinical quality assurance measurements and for PET / CT site qualification in multicentre clinical trials. Methods RC s were obtained from PET / CT measurements of seven differently sized phantom spheres filled either with 18 F or with 68 Ga. RC s for the respective other isotope were then determined by two different methods: In the first method, images were convolved with positron range transconvolution functions derived from positron annihilation distributions found in literature. This method generated recasted images matching images using the respective other isotope. In the second method, the PET / CT system's isotope independent (intrinsic) point spread function was determined from said phantom measurements and convolved with numerical representations simulating hot spheres filled with the respective other isotope. These simulations included the isotope specific positron annihilation distributions. Recovered activity concentrations were compared between recasted images, simulated images, and the originally acquired images. Results 18 F and 68 Ga recovery was successfully determined from image acquisitions of the respective opposite isotope as well as from the simulations. 68 Ga RC s derived from 18 F data had a normalized root‐mean‐square deviation ( NRMSD ) from real 68 Ga measurements of 0.019% when using the first method and of 0.008% when using the second method. 18 F RC s derived from 68 Ga data had a NRMSD from real 18 F measurements of 0.036% when using the first method and of 0.038% when using the second method. Conclusions Applying the principles of transconvolution, 18 F RC s can be recalculated from 68 Ga phantom measurements with excellent accuracy. The maximal additionally introduced error was below 0.4% of the error currently accepted for RC s in the site qualification of multicentre clinical trials by the EARL program of the European Association of Nuclear Medicine ( EANM ). Therefore, our methods legitimately allow for the use of long‐lived solid state 68 Ge/ 68 Ga phantoms instead of manually prepared 18 F phantoms to characterize comparability of 18 F measurements across different imaging sites or of longitudinal 18 F measurements at a single PET / CT system.