Assessment of MR compatibility of a PET insert developed for simultaneous multiparametric PET/MR imaging on an animal system operating at 7 T.

The combination of positron emission tomography and MR in one system is currently emerging and opens up new domains in the functional examinations of living systems. This article reports on relevant influences of a positron emission tomography insert on MR imaging. The basic conditions of main magnetic field and RF field homogeneity were measured as well as image quality and signal-to-noise ratio when applying the usual MR sequence types including echo-planar techniques. Moreover, the influence of the positron emission tomography insert on the RF noise level and on RF interferences was measured by comparing results achieved with and without the positron emission tomography insert. The temporal stability of EPI imaging with and without the positron emission tomography insert was assessed. Small but significant decreases in the signal-to-noise ratio were revealed when the positron emission tomography insert was present, whereas B(0) and B(1) homogeneity as well as RF noise level were not adversely affected. A higher signal intensity drift was found for EPI imaging studies; however, this can be compensated by post processing. In summary, this study shows that positron emission tomography inserts can be designed for and used within an MR system practically, without substantially affecting the MR image quality.