Contribution of perfusion to the 11C‐acetate signal in brown adipose tissue assessed by DCE‐MRI and 68Ga‐DOTA PET in a rat model

Purpose Determine if dynamic contrast enhanced (DCE) ‐MRI and/or 68 gallium 1,4,7,10‐tetraazacyclododecane N, N′, N″, N‴‐tretraacetic acid (68Ga‐DOTA) positron emission tomography (PET) can assess perfusion in rat brown adipose tissue (BAT). Evaluate changes in perfusion between cold‐stimulated and heat‐inhibited BAT. Determine if the 11C‐acetate pharmacokinetic model can be constrained with perfusion information to improve assessment of BAT oxidative metabolism. Methods Rats were split into three groups. In group 1 (N = 6), DCE‐MRI with gadobutrol was compared directly to 68Ga‐DOTA PET following exposure to 10 °C for 48 h. 11C‐Acetate PET was also performed to assess oxidation. In group 2 (N = 4), only 68Ga‐DOTA PET was acquired following exposure to 10 °C for 48 h. Finally, in group 3 (N = 10), perfusion was assessed with DCE‐MRI in rats exposed to 10 °C or 30 °C for 48 h, and oxidation was measured with 11C‐acetate. Perfusion was quantified with a two‐compartment pharmacokinetic model, while oxidation was assessed by a four‐compartment model. Results DCE‐MRI and 68Ga‐DOTA PET provided similar perfusion measures, but a decrease in the perfusion signal was noted with longer imaging sessions. Exposure to 10 °C or 30 °C did not affect the perfusion measures, but the 11C‐acetate signal increased in BAT at 10 °C. Without prior information about blood volume, the 11C‐acetate compartment model overestimated blood volume and underestimated oxidation in 10 °C BAT. Conclusion Precise assessment of oxidation via 11C‐acetate PET requires prior information about blood volume which can be obtained by DCE‐MRI or 68Ga‐DOTA PET. Since perfusion can change rapidly, simultaneous PET‐MRI would be preferred.