Contribution of perfusion to the ¹¹ C-acetate signal in brown adipose tissue assessed by DCE-MRI and ⁶⁸ Ga-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 (⁶⁸ Ga-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 ¹¹ C-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 ⁶⁸ Ga-DOTA PET following exposure to 10 °C for 48 h. ¹¹ C-Acetate PET was also performed to assess oxidation. In group 2 (N = 4), only ⁶⁸ Ga-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 ¹¹ C-acetate. Perfusion was quantified with a two-compartment pharmacokinetic model, while oxidation was assessed by a four-compartment model.

Results: DCE-MRI and ⁶⁸ Ga-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 ¹¹ C-acetate signal increased in BAT at 10 °C. Without prior information about blood volume, the ¹¹ C-acetate compartment model overestimated blood volume and underestimated oxidation in 10 °C BAT.

Conclusion: Precise assessment of oxidation via ¹¹ C-acetate PET requires prior information about blood volume which can be obtained by DCE-MRI or ⁶⁸ Ga-DOTA PET. Since perfusion can change rapidly, simultaneous PET-MRI would be preferred.