Is ¹⁸F-DOPA a valid cardiac sympathetic neuroimaging agent?

¹⁸F-Dopamine positron emission tomography is a validated method for identifying cardiac noradrenergic deficiency, a characteristic feature of Lewy body forms of neurogenic orthostatic hypotension; however, ¹⁸F-dopamine is a research drug. Brain ¹⁸F-DOPA positron emission tomography is FDA-approved. Since ¹⁸F-DOPA is converted to ¹⁸F-dopamine in the heart, ¹⁸F-DOPA might be useful for cardiac sympathetic neuroimaging. We compared ¹⁸F-DOPA with ¹⁸F-dopamine in patients who either had or did not have low ¹⁸F-dopamine-derived radioactivity.

Brain and cardiac ¹⁸F-DOPA scanning and cardiac ¹⁸F-dopamine scanning were done on separate days in patient groups with neurogenic orthostatic hypotension or Parkinsonism or control subjects across a range of values for ¹⁸F-dopamine-derived radioactivity. The lower limit of normal for myocardial ¹⁸F-dopamine-derived radioactivity was 6000 Bq-kg/cc-MBq. We also examined inter-relationships among cardiac ¹⁸F-DOPA-derived radioactivity, cardiac ¹⁸F-dopamine-derived radioactivity, putamen/occipital cortex ratios of ¹⁸F-DOPA-derived radioactivity, and Unified Parkinson Disease Rating Scale scores in patients with or without Parkinsonism. For putamen/occipital cortex ratios, the cutoff value was 2.70.

Twelve subjects had severely decreased and eight normal cardiac ¹⁸F-dopamine-derived radioactivity. Cardiac ¹⁸F-DOPA-derived radioactivity did not distinguish the two groups and was unrelated to ¹⁸F-dopamine-derived radioactivity. Left ventricular myocardial ¹⁸F-DOPA-derived radioactivity was poorly resolved from that in the chamber. Putamen/occipital cortex ratios of ¹⁸F-DOPA-derived radioactivity were negatively correlated with Unified Parkinson Disease Rating Scale scores (− 0.67, p = 0.0015).

¹⁸F-DOPA does not seem to be a valid cardiac sympathetic neuroimaging agent, although brain ¹⁸F-DOPA scanning provides a biomarker of Parkinsonism.