Localization of raphe nuclei in the brainstem by PET-MRI fusion system: [F18]FDG and [C11]DASB study

Objectives The raphe nuclei, major serotonergic neurons, have not been easily identifiable by the conventional neuroimaging. This study reports the investigation of the imaging possibility of the raphe nuclei by FDG and the identification by the [C11]DASB using the new HRRT-PET and 7.0T-MRI fusion system.

Methods Six healthy volunteers were recruited for the study. In the first day, a bolus injection of [F18]FDG (185 MBq) was given to the subject. Then, [F18]FDG uptake was simultaneously performed with MR imaging for 30 minutes. After the transport of the subject to the PET by the shuttle bed system, PET scanning was conducted for 30 minutes. In the second day, PET scanning was carried out for 90 minutes with a bolus injection of [C11]DASB (555 MBq). MR imaging was conducted with the same scanning protocol as the previous day. After the completion of scanning, image fusion was then performed by the PET-MRI system.

Results The 7.0T MR image of the brainstem provided numerous landmark structures in the vicinity of the raphe nuclei, and [F18]FDG and [C11]DASB PET images have measured glucose metabolism and the serotonin transporter distribution, respectively. Interestingly, as shown, [F18]FDG and [C11]DASB showed great similarity in the distribution pattern and the locations of tracer uptake in the brainstem substructures. The uptake was then identified by help of the landmark structures observed by the 7.0T MR images. They were revealed as raphe nuclei such as dorsal raphe, central superior raphe, pontine raphe, raphe magnus, raphe obscurus, and raphe pallidus. These findings were same in all subjects.

Conclusions The [F18]FDG and [C11]DASB could image the raphe nuclei and guided us to find the exact locations by aid of several landmark structures identified by 7.0T MRI. It suggests many future studies related to serotonergic activities and disorders in the human brain.

Research Support The research was supported by the Converging Research Center Program through the Ministry of Education, Science and Technology (2010K001096)