4‑[¹⁸F]Fluoro‑m‑hydroxyphenethylguanidine: A Radiopharmaceutical for Quantifying Regional Cardiac Sympathetic Nerve Density with Positron Emission Tomography

4-[¹⁸F]­Fluoro-m-hydroxyphenethylguanidine ([¹⁸F]­4F-MHPG, [¹⁸F]1) is a new cardiac sympathetic nerve radiotracer with kinetic properties favorable for quantifying regional nerve density with PET and tracer kinetic analysis. An automated synthesis of [¹⁸F]1 was developed in which the intermediate 4-[¹⁸F]­fluoro-m-tyramine ([¹⁸F]16) was prepared using a diaryliodonium salt precursor for nucleophilic aromatic [¹⁸F]­fluorination. In PET imaging studies in rhesus macaque monkeys, [¹⁸F]1 demonstrated high quality cardiac images with low uptake in lungs and the liver. Compartmental modeling of [¹⁸F]1 kinetics provided net uptake rate constants K_i (mL/min/g wet), and Patlak graphical analysis of [¹⁸F]1 kinetics provided Patlak slopes K_p (mL/min/g). In pharmacological blocking studies with the norepinephrine transporter inhibitor desipramine (DMI), each of these quantitative measures declined in a dose-dependent manner with increasing DMI doses. These initial results strongly suggest that [¹⁸F]1 can provide quantitative measures of regional cardiac sympathetic nerve density in human hearts using PET.