title: Insights on the relaxation of liposomes encapsulating paramagnetic Ln-based complexes.
abstract: OBJECTIVE
  To describe and quantify the different relaxation mechanisms operating in suspensions of liposomes that encapsulate paramagnetic lanthanide(III) complexes.
  
  
  METHODS
  The transverse relaxation rate of lanthanide-loaded liposomes receives contribution from the exchange between intraliposomal and bulk water protons, and from magnetic susceptibility effects. Phospholipids vesicles encapsulating different Ln(III)-HPDO3A complexes (Ln = Eu, Gd, or Dy) were prepared using the conventional thin film rehydration method. Relaxation times (T1 , T2 , and T2*) were measured at 14 Tesla (T) and 25 °C. The effect of compartmentalization of the paramagnetic agent inside the liposomal cavity was evaluated by means of an IRON-modified MRI sequence.
  
  
  RESULTS
  NMR measurements demonstrated that Curie spin relaxation is the dominant contribution (> 90%) to the observed transverse relaxation rate of paramagnetic liposomes. This was further confirmed by MRI that showed the ability of the liposome entrapped lanthanide complexes to generate IRON-MRI positive contrast in a size dependent manner.
  
  
  CONCLUSIONS
  The Curie spin relaxation mechanism is by far the principal mechanism involved in the T2 shortening of the water protons in suspension of paramagnetic liposomes at 14T. The access to IRON contrast extends the potential of such nanosystems as MRI contrast agents.
authors.affiliation: Department of Molecular Biotechnology and Health Sciences, University of Torino, Torino, Italy.|Porto Conte Ricerche Srl, Tramariglio, Alghero (SS), Italy.
authors.forename: Gilberto
authors.initials: G
authors.lastname: Mulas
authors.affiliation: Department of Molecular Biotechnology and Health Sciences, University of Torino, Torino, Italy.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: Ferrauto
authors.affiliation: Department of Molecular Biotechnology and Health Sciences, University of Torino, Torino, Italy.
authors.forename: Walter
authors.initials: W
authors.lastname: Dastrù
authors.affiliation: Porto Conte Ricerche Srl, Tramariglio, Alghero (SS), Italy.
authors.forename: Roberto
authors.initials: R
authors.lastname: Anedda
authors.affiliation: Department of Molecular Biotechnology and Health Sciences, University of Torino, Torino, Italy.|Center for Molecular & Preclinical Imaging, Department of Molecular Biotechnology and Health Sciences, University of Torino, Torino, Italy.
authors.forename: Silvio
authors.initials: S
authors.lastname: Aime
authors.affiliation: Department of Molecular Biotechnology and Health Sciences, University of Torino, Torino, Italy.|Center for Molecular & Preclinical Imaging, Department of Molecular Biotechnology and Health Sciences, University of Torino, Torino, Italy.
authors.forename: Enzo
authors.initials: E
authors.lastname: Terreno
mesh_terms: D003287:Contrast Media / Q000737:chemistry* / Q000528:radiation effects; D004058:Diffusion; D017097:Electric Impedance; D005682:Gadolinium / Q000737:chemistry / Q000528:radiation effects; D006571:Heterocyclic Compounds / Q000737:chemistry* / Q000528:radiation effects; D007811:Lanthanum / Q000737:chemistry / Q000528:radiation effects; D008081:Liposomes / Q000737:chemistry*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008422:Materials Testing; D053769:Nanocapsules / Q000737:chemistry* / Q000648:ultrastructure; D009942:Organometallic Compounds / Q000737:chemistry* / Q000528:radiation effects; D019047:Phantoms, Imaging; D010743:Phospholipids / Q000737:chemistry*
chemical_list: D003287:Contrast Media; D006571:Heterocyclic Compounds; D008081:Liposomes; D053769:Nanocapsules; D009942:Organometallic Compounds; D010743:Phospholipids; C062402:gadoteridol; D007811:Lanthanum; D005682:Gadolinium
keywords: MRI; lanthanides; liposomes; magnetic susceptibility