Simultaneous PET/MR body imaging in rats. Initial experiences with an integrated PET/MRI scanner

We recently developed an integrated positron emission tomography (PET)/magnetic resonance imaging (MRI) (iPET/MRI) scanner for small animals, which had relatively large field-of-view (FOV) covering up to the size of a rat body. The purpose of this study was to report results of simultaneous PET/MRI of a rat body using this scanner with some radiotracers. C-11-methionine (MET), F-18-fluorodeoxyglucose (FDG), or F-18-sodium fluoride (NaF) was injected as a radiotracer for PET portion in addition to gadolinium-ethoxybenzyl-diethylenetriamine penta-acetic acid, a hepatobiliary contrast agent, for MRI portion. Simultaneous PET/MRI was performed in normal rats. PET, MRI, and co-registered fusion images were evaluated regarding image quality and feasibility for rat imaging studies. MET uptake was clearly shown in the liver and pancreas, which was confirmed with magnetic resonance (MR) and fused PET/MR images. PET/MR images depicted intense FDG uptake in the brain, Harderian glands, and myocardium. NaF uptake was observed in all bones and joints within FOV, except in ribs, which was well recognized with the help of MR and fused PET/MR images. This study demonstrated that simultaneous PET/MRI with an integrated dual-modality molecular imaging scanner was a feasible technique for imaging studies targeting on a rat body. However, further developments including attenuation correction methods are required to use this technique routinely in rat imaging studies. (author)