Fig. 1.

Cardiac sympathetic nerve transmission and tracer uptake. Schematics of sympathetic transmission and neuronal uptake of ¹¹C-HED and ¹²³I-MIBG for imaging of sympathetic neuronal innervation. Norepinephrine (NE) is synthesized and packaged in the nerve terminals and released into the synaptic cleft. Released NE binds to target receptors or is recycled to the sympathetic nerve terminal via norepinephrine transporter (NET) for repackaging or degradation. ¹¹C-HED and ¹²³I-MIBG radiotracers are also incorporated into the nerve terminals using NET-dependent mechanism. VMAT vesicular monoamine transporter, DOPA 3,4-dihydroxyphenylalanine