A Comparison of Substantia Nigra T1 Hyperintensity in Parkinson's Disease Dementia, Alzheimer's Disease and Age-Matched Controls: Volumetric Analysis of Neuromelanin Imaging

Abstract

Objective: Neuromelanin loss of substantia nigra (SN) can be visualized as a T1 signal reduction on T1-weighted high-resolution imaging. We investigated whether volumetric analysis of T1 hyperintensity for SN could be used to differentiate between Parkinson's disease dementia (PDD), Alzheimer's disease (AD) and age-matched controls.

Materials and methods: This retrospective study enrolled 10 patients with PDD, 18 patients with AD, and 13 age-matched healthy elderly controls. MR imaging was performed at 3 tesla. To measure the T1 hyperintense area of SN, we obtained an axial thin section high-resolution T1-weighted fast spin echo sequence. The volumes of interest for the T1 hyperintense SN were drawn onto heavily T1-weighted FSE sequences through midbrain level, using the MIPAV software. The measurement differences were tested using the Kruskal-Wallis test followed by a post hoc comparison.

Results: A comparison of the three groups showed significant differences in terms of volume of T1 hyperintensity (p < 0.001, Bonferroni corrected). The volume of T1 hyperintensity was significantly lower in PDD than in AD and normal controls (p < 0.005, Bonferroni corrected). However, the volume of T1 hyperintensity was not different between AD and normal controls (p = 0.136, Bonferroni corrected).

Conclusion: The volumetric measurement of the T1 hyperintensity of SN can be an imaging marker for evaluating neuromelanin loss in neurodegenerative diseases and a differential in PDD and AD cases.

Keywords: Alzheimer disease; Dementia; High-resolution T1-weighted imaging; Magnetic resonance; Neuromelanin; Parkinsonian disorders; Substantia nigra.

Fig. 1. VOI placement of neuromelanin-sensitive T1 hyperintensity volume of SN by level-set VOI tool.

Dotted lined area is T1 hyperintense area of right SN in control subject. SN = substantia nigra, VOI = volume of interest

Fig. 2. Differences for SN between PDD, AD and control subjects in neuromelanin-sensitive T1-weighted imaging.

Axial T1-weighted fast spin-echo (TR/TE, 600/14 ms; section thickness, 2.5 mm) MR images reveal neuromelanin containing SN in red color. Compared with control subject (A), mean T1 hyperintensity of SN seems to be reduced with preserved volume in patient with AD (B). Mean signal intensity and volume of T1 hyperintensity of SN is decreased in patient with PDD (C). AD = Alzheimer's disease, MR = magnetic resonance, PDD = Parkinson's disease dementia, SN = substantia nigra, TE = echo time, TR = repetition time

Fig. 3. Boxplot of T1 hyperintensity volume of PDD, AD and control subjects.

Line across box represents median value. Box ends represent first and third quartiles. End points of each graph represent smallest and largest values. Median volume of T1 hyperintensity of SN is lowest in PDD group of patients compared with patients with AD and control subjects. On other hand, volume of T1 hyperintensity is partly overlapped between patients with AD and control subjects. AD = Alzheimer's disease, PDD = Parkinson's disease dementia

Fig. 4. Boxplot of mean normalized T1 hyperintensity of PDD, AD and control subjects.

Line across box represents median value. Box ends represent first and third quartiles. End points of each graph represent smallest and largest values. Median value of T1 hyperintensity of SN is lowest in PDD group of patients compared with patients with AD and control subjects. On other hand, wide range of T1 hyperintensity is noted for patients with AD. AD = Alzheimer's disease, PDD = Parkinson's disease dementia, SI = signal intensity