A modified semi-empirical formula to calculate the maximum positron range affected by different magnetic field strengths for PET/MRI scanner

Abstract

A modified semi-empirical formula that relates the maximum range of the positron to the strength of different magnetic field strengths is developed via Monte Carlo simulation. The formula is derived as an extension to the existing formula of no magnetic field. COMSOL Multiphysics is used to simulate the different physics, including electromagnetic physics and charged particle tracking physics. The Monte Carlo simulation technique by COMSOL is employed to study the effect of magnetic field strength on the positron range PET/MRI scan of the head's tumor. The magnetic field varies in the range 1-10 Tesla. The simulation code using positron emission is conducted by the Monte Carlo method. Simulation results show that changing the magnetic field affects the particle trajectory and hence the maximum positron range. The elliptic trajectory causes a reduction in displacement between the original location of emission and the location of annihilation, which permits an increased photon emission per unit volume of the tumor and hence a better image resolution. The main contribution of the paper is the formulation of a new semi-empirical relation taking into account the presence of a magnetic field by simulating different particle trajectories for the different magnetic field strengths.

The effect of magnetic field strength on the positron range and projected annihilation artifact in integrated PET/MR systems: A GATE Monte Carlo study

“…The site of the source differs from the site of annihilation and resulting in the degradation of spatial resolution and blurring in PET images. It is expected that the spatial resolution of PET improves in simultaneous PET/MR imaging 18–27 …”

“…It is expected that the spatial resolution of PET improves in simultaneous PET/MR imaging. [18][19][20][21][22][23][24][25][26][27] The first experimental studies to measure the annihilation point-spread function (aPSF) had low accuracy because detector size was comparable to the positron range. 28 Later studies using analytical models, assumed positron to be monoenergetic and with symmetric range.…”