Simultaneous MR-PET of human brain tumors – Initial experience

Objectives Demonstrate the feasibility of the prototype integrated MR-PET scanner developed by Siemens for performing simultaneous data acquisition in brain tumor patients.

Methods Subjects were injected with ~190 MBq of FDG and the distribution of the tracer was recorded at steady state. The images were reconstructed using the OP-OSEM 3D algorithm. MR data were acquired simultaneously using standard sequences (e.g. TSE, FLAIR, MPRAGE, MRA TOF and MRS). Advanced MR studies with DTI, and Gd-based DCE and DSC using EPI readout were also performed during the PET data acquisition. Ktrans, CBF, CBV, MTT maps were generated from these data.

Results No obvious artifacts caused by mutual interference were observed in the PET or the MR data. The maps obtained from the dynamic MR studies demonstrated regions with increased CBF, vascular permeability and microvascular proliferation that correlated with the region with increased glucose metabolism. However, these regions did not overlap perfectly, suggesting the distinct and complementary nature of the information provided by the two techniques in the assessment of the tumor environment.

Conclusions The simultaneous acquisition of MR and PET data is possible and, based on these preliminary studies, the two systems appear to not interfere with each other. Experiments with other PET tracers are underway. In addition to providing the anatomical context for analyzing the PET data, combining advanced functional imaging techniques could improve our understanding of the tumor microenvironment.