Spatial variations and precise location of substantia nigra hyperechogenicity in Parkinson’s disease using TCS-MR fusion imaging

Substantia nigra hyperechogenicity (SNH) assessed by transcranial sonography (TCS) is a neuroimaging biomarker of Parkinson's disease (PD), but its actual location and spatial changes are poorly understood. We aimed to evaluate the location and spatial progression of SNH in PD utilizing TCS-MR fusion imaging. This prospective study enrolled eighty-four PD patients and sixty-two controls. The plane with the largest area of red nucleus, the plane with the largest area of SNH, and the plane where the red nucleus is just out of view were selected and segmented, respectively, and echogenicity indices were calculated. SNH could present in SN, dorsal band of SN, red nucleus, and ventral tegmental area, and had two orientations. In the left midbrain, the anterior-posterior orientation had longer disease duration, larger SNH area, and higher Hoehn-Yahr stage than medial-lateral orientation. The anterior-posterior orientation and accumulation in various nuclei of SNH may serve as promising neuroimaging markers for PD progression.