Neuromelanin-sensitive MRI of the substantia nigra distinguishes bipolar from unipolar depression

Motivation: Depression in bipolar disorder (BD-II) is frequently misdiagnosed as unipolar depression (UD), leading to inappropriate treatment and downstream complications. Goal(s): We aimed to evaluate neuromelanin (NM) MRI signal and volume changes in substantia nigra (SN) in HC, BD and UD patients. Approach: NM MRI was acquired and analyzed. Results: We found that compared with HC, patients with BD-II and UD had decreased CNR and increased volume on bilateral SN. The NM volume in BD-II group was increased compared to UD group. Furthermore, left and right NM volume exhibited the largest AUC for discriminating patient from HC, and BD from UD, respectively. Impact: Our findings revealed that abnormally decreased CNR and increased volume in SN region might underlie predisposition to BD-II and UD. NM MRI techniques can discriminate BD-II from UD and can be a useful clinical tool in evaluation of mental disorders.