Normative Values of Neuromelanin-Sensitive MRI Signal in Older Adults Obtained Using a Turbo Spin Echo Sequence.

BACKGROUND: The integrity and function of catecholamine neurotransmitter systems can be assessed using neuromelanin-sensitive MRI (NM-MRI). The relevance of this method to neurodegenerative and psychiatric disorders is becoming increasingly evident, and it has potential as a clinical biomarker. PURPOSE: To support future application of NM-MRI as a clinical biomarker by defining the normative range of NM-MRI signal and volume metrics in cognitively normal older adults. STUDY TYPE: Prospective. POPULATION: A total of 152 cognitively normal older adults aged 53-86 years old, including 41 participants who had follow-up NM-MRI data collected 9-16 months later. FIELD STRENGTH/SEQUENCE: A 3.0 T; NM-MRI turbo spin echo and T1-weighted magnetization-prepared rapid acquisition with gradient echo sequences. ASSESSMENT: NM-MRI images were processed to yield summary measures of volume and signal (contrast-to-noise ratio, CNR) for the substantia nigra (SN) and locus coeruleus (LC) using a recently developed software employing a fully automated algorithm. Change in these metrics over time was also assessed. STATISTICAL TESTS: Mean and standard deviation of NM-MRI metrics were calculated; change over time was tested for significance using 1-sample t-tests. P values < 0.05 were considered statistically significant. RESULTS: At baseline SN signal (CNR) was 10.02% (left) and 10.28% (right) and LC signal was 24.71% (left) and 20.42% (right). Baseline SN volume was 576 mm3 (left) and 540 mm3 (right) and LC volume was 6.31 mm3 (left) and 6.30 mm3 (right). The only NM-MRI metric showing significant change was a decrease in left SN volume (t40  = -2.57, P = 0.014). DATA CONCLUSION: We report normative values for NM-MRI signal and volume in the SN and LC of cognitively normal older adults and explore their change over time. These values may help future efforts to use NM-MRI as a clinical biomarker by facilitating identification of patients with extreme NM-MRI values. TECHNICAL EFFICACY STAGE: 1.