Figure 1. Concept diagram for the effects of denervation and decreased vesicular sequestration on the uptake and fate of ¹⁸F-DA.

(A) Normally ¹⁸F-DA is taken up by sympathetic nerves via the cell membrane norepinephrine transporter (NET). Cytosolic ¹⁸F-DA mainly undergoes vesicular uptake via the VMAT, with subsequent loss of radioactivity via exocytotic release, and to a lesser extent undergoes oxidative deamination catalyzed by monoamine oxidase to form ¹⁸F-DOPAC. (B) Reduced sympathetic innervation decreases total neuronal uptake of ¹⁸F-DA, resulting in decreased initial myocardial radioactivity. The rate of loss of radioactivity is normal. (C) Reduced VMAT activity decreases radioactivity because augmented ¹⁸F-DOPAC production accelerates loss of cytosolic ¹⁸F-DA. (D) The combination of decreased sympathetic innervation and reduced VMAT activity decreases initial radioactivity, accelerates its loss, and increases ¹⁸F-DOPAC production. Dec., decreased; Inc., increased; Nml., normal; rad., myocardial ¹⁸F-DA–derived radioactivity.