Patients with Parkinson’s disease (PD) have elevated levels of brain iron, especially in the nigrostriatal dopaminergic system. The purpose of this study was to evaluate the iron deposition in the substantia nigra (SN) and other deep gray matter nuclei of PD patients using quantitative susceptibility mapping (QSM) and its clinical relationship, and to explore whether there is a gradient of iron deposition pattern in globus pallidus (GP)–fascicula nigrale (FN)–SN pathway. Thirty-three PD patients and 26 age- and sex-matched healthy volunteers (HVs) were included in this study. Subjects underwent brain MRI and constructed QSM data. The differences in iron accumulation in the deep gray matter nuclei of the subjects were compared, including the PD group and the control group, the early-stage PD (EPD) group and the late-stage PD (LPD) group. The iron deposition pattern of the GP–FN–SN pathway was analyzed. The PD group showed increased susceptibility values in the FN, substantia nigra pars compacta (SNc), internal globus pallidus (GPi), red nucleus (RN), putamen and caudate nucleus compared with the HV group (P < 0.05). In both PD and HV group, iron deposition along the GP–FN–SN pathway did not show an increasing gradient pattern. The SNc, substantia nigra pars reticulata (SNr) and RN showed significantly increased susceptibility values in the LPD patients compared with the EPD patients. PD is closely related to iron deposition in the SNc. The condition of PD patients is related to the SNc and the SNr. There is not an increasing iron deposition gradient along the GP–FN–SN pathway. The source and mechanism of iron deposition in the SN need to be further explored, as does the relationship between the iron deposition in the RN and PD.

Background: Diffusion tensor image analysis along the perivascular space (DTI-ALPS) has been used for diagnosing Alzheimer’s disease (AD); however, few studies have examined the relationship between the DTI-ALPS index and cortical metrics, and the differentiation between AD severity levels remains unclear. This study aimed to explore the differences in DTI-ALPS index and cortex among AD patients with varying severities and to analyze the interactions between DTI-ALPS index, cortical metrics, and cognitive function. Methods: A total of 19 individuals with mild cognitive impairment (MCI), 17 individuals exhibiting mild AD, 25 individuals with moderate AD, and 28 healthy controls (HC) who were matched for age, sex, and education level were recruited. All the participants underwent diffusion tensor imaging (DTI) magnetic resonance imaging (MRI), followed by the calculation of the DTI-ALPS index to assess lymphatic system function. FreeSurfer (v7.4.1) was used to calculate thickness, volume, local gyre index, and area. One-way analysis of variance (ANOVA) was performed to compare the differences among HC, MCI, mild AD, and moderate AD groups. Pearson correlation analysis was employed to investigate the connection between the DTI-ALPS index and cognitive function, along with cortical metrics. Results: The HC, MCI, mild AD, and moderate AD groups exhibited significant differences in the DTI-ALPS index of the left hemisphere (P=0.008), whereas 13 cortical metrics revealed a statistical significance between groups (P<0.05). In the left hemisphere, the DTI-ALPS index showed a positive trend with the Montreal Cognitive Assessment (MoCA) score (r=0.397, P<0.001). Higher DTI-ALPS was also associated with an increase in 10 cortical metrics after controlling for age, sex, and education. Conclusions: There is a significant relationship between the DTI-ALPS index, cortical metrics, and cognitive function. This result may suggest that lymphatic dysfunction indicated by the DTI-ALPS index could mirror cortical structural degeneration and cognitive decline within the pathological process of AD. DTI-ALPS can be used as an indicator of structural degeneration and decline in cognitive function in AD.