Lateral Asymmetry and Spatial Difference of Iron Deposition in the Substantia Nigra of Patients with Parkinson Disease Measured with Quantitative Susceptibility Mapping

Abstract

Background and purpose: Quantitative susceptibility mapping is useful for assessing iron deposition in the substantia nigra of patients with Parkinson disease. We aimed to determine whether quantitative susceptibility mapping is useful for assessing the lateral asymmetry and spatial difference in iron deposits in the substantia nigra of patients with Parkinson disease.

Materials and methods: Our study population comprised 24 patients with Parkinson disease and 24 age- and sex-matched healthy controls. They underwent 3T MR imaging by using a 3D multiecho gradient-echo sequence. On reconstructed quantitative susceptibility mapping, we measured the susceptibility values in the anterior, middle, and posterior parts of the substantia nigra, the whole substantia nigra, and other deep gray matter structures in both hemibrains. To identify the more and less affected hemibrains in patients with Parkinson disease, we assessed the severity of movement symptoms for each hemibrain by using the Unified Parkinson's Disease Rating Scale.

Results: In the posterior substantia nigra of patients with Parkinson disease, the mean susceptibility value was significantly higher in the more than the less affected hemibrain substantia nigra (P < .05). This value was significantly higher in both the more and less affected hemibrains of patients with Parkinson disease than in controls (P < .05). Asymmetry of the mean susceptibility values was significantly greater for patients than controls (P < .05). Receiver operating characteristic analysis showed that quantitative susceptibility mapping of the posterior substantia nigra in the more affected hemibrain provided the highest power for discriminating patients with Parkinson disease from the controls.

Conclusions: Quantitative susceptibility mapping is useful for assessing the lateral asymmetry and spatial difference of iron deposition in the substantia nigra of patients with Parkinson disease.

Fig 1.

A 59-year-old woman with Parkinson disease. A, QSM, axial section at the level of the basal ganglia. ROIs as large as possible were placed. Areas encircled in red, green, and blue are the caudate nucleus, putamen, and globus pallidus. B, QSM, axial section at the level of the midbrain. The encircled area identifies the red nucleus medial to the substantial nigra.

Fig 2.

ROIs on the substantia nigra on QSM images. Multiplanar reconstruction coronal images were selected at the 3 planes, that is, the anterior (red line), middle (light orange line), and posterior (blue line) edges of the red nucleus on axial QSM images (A), to measure spatial susceptibility differences in the anterior, middle, and posterior parts of the SN. To avoid contamination by the subthalamic nuclei, we placed an ROI on the aSN (B), mSN (C), and pSN (D) below the caudal edge of the RN on coronal QSM images. The averaged value of the aSN, mSN, and pSN was defined as the value of the whole SN. Solid arrow indicates the SN; dotted arrow, the RN.

Fig 3.

Boxplots of the mean susceptibility value (in parts per billion) of the more and the less affected hemibrains in patients with PD and healthy controls. Mean susceptibility values of the whole (A), anterior (B), middle (C), and posterior (D) parts of the substantia nigra. Lines in boxes indicate the median; lower and upper limits of boxes, the 25th and 75th percentiles, respectively; and whiskers, the 10th and 90th percentiles. Outliers are shown as individual points. One asterisk indicates P < .05; double asterisks, P < .001. ppb indicates parts per billion; MAB, more affected hemibrain; LAB, less affected hemibrain; HC, healthy controls.

Fig 4.

Diagnostic performance of QSM of the substantia nigra for discriminating patients with PD from healthy subjects. A, More affected hemibrain versus healthy controls. B, Less affected hemibrain versus healthy controls for the whole SN, and the anterior, middle, and posterior parts of the SN, respectively.