title: Quantifying magnetic nanoparticles in non-steady flow by MRI.
abstract: OBJECTIVE
  This work compares the measured R*2 of magnetic nanoparticles to their corresponding theoretical values in both gel phantoms and dynamic water flows on the basis of the static dephasing theory.
  
  
  METHODS
  The magnetic moment of a nanoparticle solution was measured by a magnetometer. The R*2 of the nanoparticle solution doped in a gel phantom was measured at both 1.5 and 4.7 T. A total of 12 non-steady state flow experiments with different nanoparticle concentrations were conducted. The R*2 at each time point was measured.
  
  
  RESULTS
  The theoretical R*2 on the basis of the magnetization of nanoparticles measured by the magnetometer agree within 11% of MRI measurements in the gel phantom study, a significant improvement from previous work. In dynamic flow experiments, the total R*2 calculated from each experiment agrees within 15% of the theoretical R*2 for 10 of the 12 cases. The MRI phase values are also reasonably predicted by the theory. The diffusion effect does not seem to contribute significantly.
  
  
  CONCLUSIONS
  Under certain situations with known R*2, the static dephasing theory can be used to quantify the susceptibility or concentration of nanoparticles in either a static or dynamic flow environment at a given time point. This approach may be applied to in vivo studies.
authors.affiliation: Department of Radiology, Wayne State University, Detroit, MI 48201, USA.
authors.forename: Yimin
authors.initials: Y
authors.lastname: Shen
authors.forename: Yu-Chung N
authors.initials: YC
authors.lastname: Cheng
authors.forename: Gavin
authors.initials: G
authors.lastname: Lawes
authors.forename: Jaladhar
authors.initials: J
authors.lastname: Neelavalli
authors.forename: Chandran
authors.initials: C
authors.lastname: Sudakar
authors.forename: Ronald
authors.initials: R
authors.lastname: Tackett
authors.forename: Hari P
authors.initials: HP
authors.lastname: Ramnath
authors.forename: E Mark
authors.initials: EM
authors.lastname: Haacke