Journal
MAGNETIC RESONANCE IN MEDICINE
Volume 78, Issue 5, Pages 1790-1800Publisher
WILEY
DOI: 10.1002/mrm.26584
Keywords
neuromelanin; MRI; magnetization transfer; relaxation
Funding
- Fondazione IRCCS Ca' Granda Ospedale Maggiore Policlinico di Milano
- Italian Ministry of Education, University, and Research
- National Research Programme (PNR)
- CNR Flagship InterOmics Project [PB.P05]
- PNR-CNR
- Grigioni Foundation for Parkinson's disease, Milan, Italy
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Purpose: To investigate the physical mechanisms associated with the contrast observed in neuromelanin MRI. Methods: Phantoms having different concentrations of synthetic melanins with different degrees of iron loading were examined on a 3 Tesla scanner using relaxometry and quantitative magnetization transfer (MT). Results: Concentration-dependent T-1 and T-2 shortening was most pronounced for the melanin pigment when combined with iron. Metal-free melanin had a negligible effect on the magnetization transfer spectra. On the contrary, the presence of iron-laden melanins resulted in a decreased magnetization transfer ratio. The presence of melanin or iron (or both) did not have a significant effect on the macromolecular content, represented by the pool size ratio. Conclusion: The primary mechanism underlying contrast in neuromelanin-MRI appears to be the T-1 reduction associated with melanin-iron complexes. The macromolecular content is not significantly influenced by the presence of melanin with or without iron, and thus the MT is not directly affected. However, as T-1 plays a role in determining the MT-weighted signal, the magnetization transfer ratio is reduced in the presence of melanin-iron complexes. (C) 2016 International Society for Magnetic Resonance in Medicine.
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