title: An evaluation of the contributions of diffusion and exchange in relaxation enhancement by MRI contrast agents.
abstract: Magnetic compounds are known to enhance water proton relaxation, either by diffusion or by proton exchange. An experimental procedure to distinguish both mechanisms is proposed and validated by relaxation measurements made in water-methanol solutions of Dy(3+), Ni(2+), Gd(3+), Tempo, and AMI-25. The test discriminates according to the character of the transverse relaxation in water-methanol solutions: a mono-exponential decay corresponds to diffusion, while a bi-exponential decay indicates the contribution of a proton exchange. The study of ferritin and akaganeite particle solutions confirms the occurrence of a proton exchange between protons belonging to hydroxyl groups of the particle surface and free water protons.
authors.affiliation: Biological Physics Department, University of Mons-Hainaut, Mons B-7000, Belgium. yves.gossuin@umh.ac.be
authors.forename: Yves
authors.initials: Y
authors.lastname: Gossuin
authors.forename: Alain
authors.initials: A
authors.lastname: Roch
authors.forename: Robert N
authors.initials: RN
authors.lastname: Muller
authors.forename: Pierre
authors.initials: P
authors.lastname: Gillis
mesh_terms: D003287:Contrast Media / Q000737:chemistry; D003497:Cyclic N-Oxides / Q000737:chemistry; D003911:Dextrans; D004058:Diffusion; D004419:Dysprosium / Q000737:chemistry; D005290:Ferric Compounds; D005293:Ferritins / Q000737:chemistry; D052203:Ferrosoferric Oxide; D005682:Gadolinium / Q000737:chemistry; D007501:Iron / Q000737:chemistry; D008279:Magnetic Resonance Imaging; D008280:Magnetics; D058185:Magnetite Nanoparticles; D000432:Methanol; D009532:Nickel / Q000737:chemistry; D010087:Oxides / Q000737:chemistry; D012996:Solutions; D014867:Water
chemical_list: D003287:Contrast Media; D003497:Cyclic N-Oxides; D003911:Dextrans; D005290:Ferric Compounds; D058185:Magnetite Nanoparticles; D010087:Oxides; D012996:Solutions; D014867:Water; D004419:Dysprosium; D009532:Nickel; C092844:ferric oxyhydroxide; D005293:Ferritins; D005682:Gadolinium; D007501:Iron; C065507:ferumoxides; C003959:TEMPO; D052203:Ferrosoferric Oxide; D000432:Methanol