Nigrostriatal imaging in patients with clinically uncertain Parkinsonian syndromes: a head-to-head comparison between SPECT, PET, and MRI.

PURPOSE: Neurodegenerative parkinsonism is characterized by degeneration of the dopaminergic nigrostriatal pathways and a reduction in nigral neuromelanin. Dopamine transporter (DAT) imaging assesses presynaptic striatal dopaminergic function and is typically performed with [123I]FP-CIT SPECT-CT, but has recently also become available with [18F]FE-PE2I PET-CT. Magnetic resonance imaging (MRI) can explore disease-related changes by quantifying neuromelanin and iron deposition associated with the loss of nigral neurons. METHODS: In this study, we conducted a head-to-head comparison of [¹²³I]FP-CIT SPECT, [¹⁸F]FE-PE2I PET, and nigral MRI in 35 patients referred for diagnostic DAT imaging. Nigral MRI was performed with neuromelanin-sensitive gradient echo magnetization-transfer contrast MRI and iron-sensitive STrategically Acquired Gradient Echo (STAGE) MRI. Patient satisfaction with SPECT and PET was recorded via questionnaires. RESULTS: Eighteen patients were diagnosed with neurodegenerative parkinsonism with a median symptom duration of 29 months. DAT availability as measured with SPECT and PET showed complete concordance across cases, correlated strongly, and demonstrated equally excellent diagnostic performance. Patient questionnaire items were either not different between modalities or in favor of SPECT. Nigral neuromelanin content was reduced in patients with neurodegenerative parkinsonism and provided intermediate diagnostic accuracy, with indications of lower neuromelanin with disease duration. Midbrain iron content did not differ between groups and provided no diagnostic information. CONCLUSION: Our findings indicate that in early-stage parkinsonism, DAT neuroimaging with SPECT and PET provides comparable and superior diagnostic value relative to nigral MRI.