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Application of the static dephasing regime theory to superparamagnetic iron‐oxide loaded cells
Author(s) -
Bowen Chris V.,
Zhang Xiaowei,
Saab George,
Gareau Paula J.,
Rutt Brian K.
Publication year - 2002
Publication title -
magnetic resonance in medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.696
H-Index - 225
eISSN - 1522-2594
pISSN - 0740-3194
DOI - 10.1002/mrm.10192
Subject(s) - dephasing , iron oxide , superparamagnetism , oxide , iron oxide nanoparticles , nanoparticle , chemistry , magnetic moment , relaxation (psychology) , nuclear magnetic resonance , magnetic susceptibility , magnetic nanoparticles , analytical chemistry (journal) , magnetization , materials science , nanotechnology , condensed matter physics , crystallography , physics , chromatography , magnetic field , medicine , organic chemistry , quantum mechanics
Abstract The relaxation rates of iron‐oxide nanoparticles compartmentalized within cells were studied and found to satisfy predictions of the static dephasing (SD) regime theory. THP‐1 cells in cell culture were loaded using two different iron‐oxide nanoparticles (superparamagnetic iron‐oxide (SPIO) and ultrasmall SPIO (USPIO)) with four different iron concentrations (0.05, 0.1, 0.2, and 0.3 mg/ml) and for five different incubation times (6, 12, 24, 36, and 48 hr). Cellular iron‐oxide uptake was assessed using a newly developed imaging version of MR susceptometry, and was found to be linear with both dose and incubation time. R 2 *sensitivity to iron‐oxide loaded cells was found to be 70 times greater than for R 2 , and 3100 times greater than for R 1 . This differs greatly from uniformly distributed nanoparticles and is consistent with a cellular bulk magnetic susceptibility (BMS) relaxation mechanism. The cellular magnetic moment was large enough that R 2 ′ relaxivity agreed closely with SD regime theory predictions for all cell samples testedwhere the local magnetic dose (LMD) is the sample magnetization due to the presence of iron‐oxide particles). Uniform suspensions of SPIO and USPIO produced R 2 ′ relaxivities that were a factor of 3 and 8 less, respectively, than SD regime theory predictions. These results are consistent with theoretical estimates of the required mass of iron per compartment needed to guarantee SD‐regime‐dominant relaxivity. For cellular samples, R 2 was shown to be dependent on both the concentration and distribution of iron‐oxide particles, while R 2 ′ was sensitive to iron‐oxide concentration alone. This work is an important first step in quantifying cellular iron content and ultimately mapping the density of a targeted cell population. Magn Reson Med 48:52–61, 2002. © 2002 Wiley‐Liss, Inc.