Nuklearmedizin 2020; 59(02): 127-128
DOI: 10.1055/s-0040-1708242
Wissenschaftliche Vorträge
Medizinische Physik
© Georg Thieme Verlag KG Stuttgart · New York

Parameterisation of Positron Range Effects in PET/MRI

A Berger
1   Medical University of Vienna, QIMP Team, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
,
I Rausch
1   Medical University of Vienna, QIMP Team, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
,
H Kertesz
1   Medical University of Vienna, QIMP Team, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
,
JL Herraiz
2   Universidad Complutense de Madrid, Grupo de Física Nuclear and UPARCOS, Madrid, Spain
,
A López-Montes
2   Universidad Complutense de Madrid, Grupo de Física Nuclear and UPARCOS, Madrid, Spain
,
M Conti
3   Siemens Medical Solutions, Knoxville TN, United States
,
T Beyer
1   Medical University of Vienna, QIMP Team, Center for Medical Physics and Biomedical Engineering, Vienna, Austria
› Author Affiliations
Further Information

Publication History

Publication Date:
08 April 2020 (online)

 

Ziel/Aim Positron range (PR) limits the spatial resolution of PET images. Further it is affected by magnetic fields such as in PET/MR systems, thereby causing an axial elongation of the PR that degrades image quality and introduces artefacts. We present a mathematical modelling approach of PR in the presence of external magnetic fields as a prior to post-reconstruction PR correction.

Methodik/Methods GATE (GEANT4 Application for Tomographic Emission) simulations of point sources of various radionuclides with significant mean PR (Rmean) (1mm-5.5mm in water) (F-18, Ga-68, Rb-82 and I-124) were performed in three different tissues (water, lung and bone). Simulations were performed for static magnetic fields (B0) of 0T (no magnetic field), 1.5T, 3T, 5T, 7T and 9.4T along the main PET system axis (z-axis). The 3D distribution of all positron annihilation points was modelled as a direct product of the radial distribution of annihilation events, and a 1D height-distribution that intrinsically models the impact of B0 according to the performed GATE simulations. Mean 3D- (Rmean) as well as 1DPR in x/z plane was calculated from emission and annihilation coordinates of the simulation output.

Ergebnisse/Results Elongated annihilation point distributions were observed for high B0 for all simulated isotopes. The line profiles of positron annihilation points of I-124/Ga-68 show a relative reduction of positron range of up to 53 %/62 % perpendicular to the B0 axis for 9.4T respectively. Absolute reduction of Rmean for F-18/Ga-68 in water (0.32/1.94 mm), bone (0.09/0.34 mm) and lung (1.58/6.89 mm) was observed for increasing B0 from 0.0T to 9.4T. Theoretical PR calculations and known PR values were in good agreement (18F in water 3.0 % difference).

Schlussfolgerungen/Conclusions A parameterized mathematical model of PR effects in magnetic field was established and can be used as a prior to post-reconstruction PR correction, so as to help improve quantification in dosimetry or radiation therapy.

Acknowledgment: This project is supported by Siemens Healthineers.