Influence from high and ultra-high magnetic field on positron range measured with a 9.4TMR-BrainPET

MR-PET imaging in a combined simultaneously measuring hybrid scanner is expected to lead to an improved image resolution in a plane perpendicular to the MR-component´s main magnetic field. Here we report studies performed in a newly installed MR-PET scanner consisting of a 9.4T whole-body MR scanner and an APD-based BrainPET inserted in the MR bore. A brain phantom and a point source were filled with ¹⁸F or the non-standard positron emitter ¹²⁰I, which has a very high positron energy of up to 4 MeV. Emission scans of the phantom were recorded at different positions outside and inside the MR bore, so that the magnetic field at the BrainPET was 0 T, 3 T, 7 T or 9.4 T. The brain phantom filled with ¹⁸F showed no obvious resolution improvement with the magnetic field. This observation was in agreement with the practically unchanged FWHM of point spread profiles, which ranged from 2.77 mm to 2.89 mm for the different field strengths. A clear image improvement could be shown when the brain phantom was filled with ¹²⁰I. Our experimental study demonstrates that an integrated MR-PET with a magnetic field greater equal 3T provides an improved image resolution for high energy positron emitters.