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

Abstract

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 6000Bq-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.