PET [11C]acetate is also a perfusion tracer for kidney evaluation purposes

Abstract

Rationale: Renal positron emission tomography (PET) functional imaging allows non-invasive and dynamic measurements of functional and metabolic parameters. [¹⁵O]H₂O is used as a perfusion tracer, and [¹¹C]acetate as an oxidative metabolism in this purpose, requiring two injections to assess those fundamental parameters. Yet, in cardiac physiology study, the high first-pass myocardial extraction fraction of [¹¹C]acetate allowed to use its influx rate as a blood flow marker too. Since [¹¹C]acetate has been characterized by a 20-25% single pass renal extraction in dogs, it could be used as a potential tracer for renal perfusion. The aim of this study was to determine whether [¹¹C]acetate influx rate can be used as quantitative in vivo marker of kidney perfusion in human.

Methods: In 10 healthy subjects, dynamic PET acquisitions were performed after [¹⁵O]H₂O and [¹¹C]acetate injections spaced by a 15-minute interval. As previously validated, with compartmental modeling of kinetics, renal perfusion and oxidative metabolism were estimated respectively with influx rate of [¹⁵O]H₂O and efflux rate of [¹¹C]acetate. Additionally, influx rate of [¹¹C]acetate was regressed to influx rate of [¹⁵O]H₂O.

Results: Renal time activity curves of [¹¹C]-acetate was best fitted with a mono compartmental model compared to a bi-compartmental model (p < 0.0001). [¹¹C]acetate influx rate was significantly correlated with perfusion quantified with [¹⁵O]H₂O (r² = 0.37, p < 0.001) at baseline. This regression allowed the computation of a renal [¹¹C]acetate extraction fraction (EF), and further the computation of renal blood flow from its influx rate.

Conclusion: In healthy subjects, over a wide range of renal perfusion, direct estimates of renal oxygen consumption as well as tissue perfusion can be obtained by PET with a single tracer [¹¹C]acetate. This approach needs to be validated in CKD patients, and would be of great interest to design clinical protocol aiming at evaluating ischemic nephropathies candidate to revascularization.

Keywords: Acetate; PET-MRI; Renal functional parameters; Renal oxidative metabolism; Renal perfusion.