title: Contrast mechanisms associated with neuromelanin-MRI.
abstract: To investigate the physical mechanisms associated with the contrast observed in neuromelanin MRI.
  
  
  
  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).
  
  
  
  Concentration-dependent T1and T2shortening 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.
  
  
  
  The primary mechanism underlying contrast in neuromelanin-MRI appears to be the T1reduction 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 T1plays a role in determining the MT-weighted signal, the magnetization transfer ratio is reduced in the presence of melanin-iron complexes. Magn Reson Med 78:1790-1800, 2017. © 2016 International Society for Magnetic Resonance in Medicine.
authors.affiliation: Department of Neuroradiology, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Milan, Italy.|Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milan, Italy.
authors.forename: Paula
authors.initials: P
authors.lastname: Trujillo
authors.affiliation: Department of Neuroradiology, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Summers
authors.affiliation: Institute of Biomedical Technologies, National Research Council of Italy, Segrate, Italy.
authors.forename: Emanuele
authors.initials: E
authors.lastname: Ferrari
authors.affiliation: Institute of Biomedical Technologies, National Research Council of Italy, Segrate, Italy.
authors.forename: Fabio A
authors.initials: FA
authors.lastname: Zucca
authors.affiliation: Department of Chemistry, University of Pavia, Pavia, Italy.
authors.forename: Michela
authors.initials: M
authors.lastname: Sturini
authors.affiliation: Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milan, Italy.
authors.forename: Luca T
authors.initials: LT
authors.lastname: Mainardi
authors.affiliation: Department of Electronics, Information and Bioengineering, Politecnico di Milano, Milan, Italy.
authors.forename: Sergio
authors.initials: S
authors.lastname: Cerutti
authors.affiliation: Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: Alex K
authors.initials: AK
authors.lastname: Smith
authors.affiliation: Vanderbilt University Institute of Imaging Science, Vanderbilt University, Nashville, Tennessee, USA.|Department of Biomedical Engineering, Vanderbilt University, Nashville, Tennessee, USA.|Department of Radiology and Radiological Sciences, Vanderbilt University, Nashville, Tennessee, USA.
authors.forename: Seth A
authors.initials: SA
authors.lastname: Smith
authors.affiliation: Institute of Biomedical Technologies, National Research Council of Italy, Segrate, Italy.
authors.forename: Luigi
authors.initials: L
authors.lastname: Zecca
authors.affiliation: Department of Neuroradiology, Fondazione IRCCS Ca' Granda - Ospedale Maggiore Policlinico, Milan, Italy.
authors.forename: Antonella
authors.initials: A
authors.lastname: Costa
mesh_terms: D006801:Humans; D007501:Iron / Q000737:chemistry; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008543:Melanins / Q000032:analysis* / Q000737:chemistry*; D008954:Models, Biological; D019047:Phantoms, Imaging; D013378:Substantia Nigra / Q000737:chemistry
chemical_list: D008543:Melanins; C014121:neuromelanin; D007501:Iron
keywords: MRI; magnetization transfer; neuromelanin; relaxation