Simultaneous C-11 methionine (MET) PET and contrast-enhanced (CE) MR rat imaging with an integrated PET/MRI system: Initial experience

Objectives We developed a fully integrated(i) PET/MRI system for small animal imaging. The purpose of this study was to demonstrate simultaneous MET PET and CE MR in vivo rat imaging using this system.

Methods The iPET/MRI system consists of DOI block detectors made of LGSO, optical fibers(~80cm), PSPMTs for PET, RF coil(ϕ7.6cm) and 0.3T Nd-Fe-B permanent magnet for MRI. Approx. 74MBq of MET for PET and 0.009mmol of Gadoxetate(Gd-EOB-DTPA: hepatobiliary contrast agent) for MRI was injected i.v. to each rat under isoflurane anesthesia. Simultaneous PET(list mode) and MR(fast low angle shot<FLASH> T1-weighted sequence, TR/TE=50/5msec) imaging was performed at appropriate time points from head to abdomen. During MRI acquisition, PET data were acquired in 3 axial position by moving the PET detector ring to cover ~5cm axial FOV. PET, MR, and co-registered fusion images were evaluated regarding image quality and feasibility for rat imaging.

Results Simultaneous PET/MR imaging was successfully performed with good image quality, in spite of short half-life of C-11. CE T1-w FLASH MRI with EOB represented relatively high signal intensity in the liver and kidneys, providing excellent mapping images. Intense MET uptake was observed in the liver and pancreas on PET, both of which were well recognized on MR and fusion images. MET uptake was also observed in the salivary glands.

Conclusions Simultaneous C-11 MET PET and CE MR imaging with an iPET/MRI system was demonstrated to be a feasible and promising technique for rat imaging studies.

Research Support Program for Promotion of Fundamental Studies in Health Sciences of the National Institute of Biomedical Innovations (No. 06-35)