Studying the effects of metallic components of PET-insert on PET and MRI performance due to gradient switching

Abstract

Inserting positron emission tomography (PET) detection modules inside an MRI bore imposes extra challenges owing to the behavior of metallic materials in a strong magnetic field. The metallic parts even when placed outside an MRI field of view may not only disturb MRI performance, but could also increase temperature and vibrations, leading to premature failure of PET electronics. To investigate the compatibility of detection modules inside 3 T, 7 T and 9.4 T MRI bore, a theoretical study of the metal induced artifacts originating from component materials of electronic circuit is presented. The LabPET II detection module and a modified version of it in which the connector was replaced by ball grid array (BGA) were studied. In addition, the effect of eddy current and the associated heat loss on the PET detection module have been examined using COMSOL Multiphysics® simulations for 10 kHz and 100 kHz gradient switching. Results show that displacement artifacts resulting from the presence of small amounts of ferromagnetic metal and the heating effects of metal due to gradient switching can be compensated by using the slightly modified LabPET II detection module. Thus, the LabPET II system would be MR-compatible with some minor adjustments to operate effectively inside an MRI bore without interfering with its performance.

Performance investigation of LabPET II detector technology in an MRI-like environment

“…In addition to the aforementioned noise attenuation measures, removing all ferromagnetic materials, such as the adaptor board connector, from the scanner FOV or using components in very small packaging sizes were also considered as the future work to minimize the inhomogeneity of the magnetic field. Considering that the LabPET II ASICs are made of silicon and aluminum, which are paramagnetic materials, and taking into account that the other components in modified LabPET II DM will be selected with a small footprint to accommodate the limited PCB size, from the material point of view, the modified LabPET II DM will be an MR-compatible unit that preserves the magnetic field homogeneity (Moghadam et al 2019). Further information on the LabPET II technology can be found in Bérard et al (2009), Arpin et al (2011), Njejimana et al (2012, Bergeron et al (2015) and Gaudin et al (2019).…”

“…An inevitable source of interferences between PET and MRI is the magnetic field inhomogeneity resulting from the presence of components inserted in the MRI having different material susceptibility in comparison with air. In fact, ferromagnetic materials exert severe effects on the homogeneity (Schenck 1996) and the principal strategy to minimize such an impact consists of removing any ferromagnetic materials from the MRI field-ofview (FOV) or replacing them with low-susceptibility and low-conductivity metallic materials, as already investigated for the LabPET II detection module (DM) in Moghadam et al (2019). Furthermore, differential signaling eliminates the stray magnetic field effects and better preserves the homogeneity of the main magnetic field.…”