title: Diffusional mechanisms augment the fluorine MR relaxation in paramagnetic perfluorocarbon nanoparticles that provides a "relaxation switch" for detecting cellular endosomal activation.
abstract: OBJECTIVE
  To develop a physical model for the (19)F relaxation enhancement in paramagnetic perfluorocarbon nanoparticles (PFC NP) and demonstrate its application in monitoring cellular endosomal functionality through a "(19)F relaxation switch" phenomenon.
  
  
  METHODS
  An explicit expression for (19)F longitudinal relaxation enhancement was derived analytically. Monte-Carlo simulation was performed to confirm the gadolinium-induced magnetic field inhomogeneity inside the PFC NP. Field-dependent T(1) measurements for three types of paramagnetic PFC NPs were carried out to validate the theoretical prediction. Based on the physical model, (19)F and (1)H relaxation properties of macrophage internalized paramagnetic PFC NPs were measured to evaluate the intracellular process of NPs by macrophages in vitro.
  
  
  RESULTS
  The theoretical description was confirmed experimentally by field-dependent T(1) measurements. The shortening of (19)F T(1) was found to be attributed to the Brownian motion of PFC molecules inside the NP in conjunction with their ability to permeate into the lipid surfactant coating. A dramatic change of (19)F T(1) was observed upon endocytosis, revealing the transition from intact bound PFC NP to processed constituents.
  
  
  CONCLUSIONS
  The proposed first-principle analysis of (19)F spins in paramagnetic PFC NP relates their structural parameters to the special MR relaxation features. The demonstrated "(19)F relaxation switch" phenomenon is potentially useful for monitoring cellular endosomal functionality.
authors.affiliation: Department of Physics, Washington University in St. Louis, Missouri, USA.
authors.forename: Lingzhi
authors.initials: L
authors.lastname: Hu
authors.forename: Lei
authors.initials: L
authors.lastname: Zhang
authors.forename: Junjie
authors.initials: J
authors.lastname: Chen
authors.forename: Gregory M
authors.initials: GM
authors.lastname: Lanza
authors.forename: Samuel A
authors.initials: SA
authors.lastname: Wickline
mesh_terms: D000818:Animals; D002460:Cell Line; D004058:Diffusion; D011992:Endosomes / Q000502:physiology*; D005461:Fluorine / Q000032:analysis; D005466:Fluorocarbons / Q000032:analysis*; D008262:Macrophage Activation / Q000502:physiology*; D008264:Macrophages / Q000502:physiology*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods*; D058185:Magnetite Nanoparticles / Q000032:analysis* / Q000737:chemistry; D051379:Mice
chemical_list: D005466:Fluorocarbons; D058185:Magnetite Nanoparticles; D005461:Fluorine