which results in a trilaminar pattern (Fig 1). The use of 3-T SWI has yielded similar nigrosome 1 findings (Fig 2, A-D) (22)(23)(24)(25)(26)(27)(28). Across the literature, different terms, such as swallow tail sign, SN dorsolateral hyperintensity, or simply nigrosome 1, refer to nigrosome 1 appearance.
Nigrosome Imaging in PDOn both 3-and 7-T MRI scans, patients with PD show nigral hyperintensity loss (15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). This loss of nigral hyperintensity reflects signal hypointensity due to iron deposition associated with dopaminergic neuronal loss. When using 7-T MRI, the diagnosis of PD based on nigral hyperintensity loss compared with the healthy population has shown high diagnostic performance, with sensitivity and specificity of up to 100% (21). The diagnostic performance for PD using nigral hyperintensity loss at 3-T SWI compared with healthy control subjects varies but is generally satisfactory (22-28). Moreover, the asymmetric nigrosome involvement correlates with asymmetry in clinical motor symptoms (24,28). This variability in diagnostic performance may be due to diversity in the imaging protocols and study populations (Table ). However, a meta-analysis of 3-T SWI studies on the diagnosis of PD reported sensitivity of 94.6% and specificity of 94.4%, which provide sufficient evidence for the high diagnostic performance of 3-T SWI (29). When comparing 3-and 7-T MRI of the SN, the sensitivity, specificity, and diagnostic accuracy for PD diagnosis were higher with 7-T MRI (93%, 100%, 96%, respectively) than with 3-T MRI (79%, 94%, 86%, respectively) (19).Rapid eye movement sleep behavior disorder (RBD) is a common sleep-related symptom in patients with PD. Especially idiopathic RBD is known as the premotor disease prior to the development of synucleinopathy, such as PD or dementia with Lewy bodies (DLB) (30,31). A high rate of loss of nigral hyperintensity was observed in patients with idiopathic RBD (30,31). Bae et al (31) showed that patients with idiopathic RBD with loss of nigral hyperintensity had lower dopamine transporter uptake at SPECT than those with intact nigral signal, progressing into overt PD or DLB, suggesting that nigrosome imaging could be a marker for synucleinopathy conversion risk in premotor disease. Further studies with larger and more diverse prodromal cohorts with longitudinal followup will provide greater insights.