MR imaging differentiation of Fe2+and Fe3+based on relaxation and magnetic susceptibility properties.
OBJECTIVE
The aim of this study is to evaluate the MR imaging behavior of ferrous (Fe2+) and ferric (Fe3+) iron ions in order to develop a noninvasive technique to quantitatively differentiate between both forms of iron.


METHODS
MRI was performed at 3 T in a phantom consisting of 21 samples with different concentrations of ferrous and ferric chloride solutions (between 0 and 10 mmol/L). A multi-echo spoiled gradient-echo pulse sequence with eight echoes was used for both T2* and quantitative susceptibility measurements. The transverse relaxation rate, R2* = 1/T2*, was determined by nonlinear exponential fitting based on the mean signals in each sample. The susceptibilities, χ, of the samples were calculated after phase unwrapping and background field removal by fitting the spatial convolution of a unit dipole response to the measured internal field map. Relaxation rate changes, ΔR2*(cFe), and susceptibility changes, Δχ(cFe), their linear slopes, as well as the ratios ΔR2*(cFe) / Δχ(cFe) were determined for all concentrations.


RESULTS
The linear slopes of the relaxation rate were (12.5 ± 0.4) s-1/(mmol/L) for Fe3+and (0.77 ± 0.09) s-1/(mmol/L) for Fe2+(significantly different, z test P < 0.0001). The linear slopes of the susceptibility were (0.088 ± 0.003) ppm/(mmol/L) for Fe3+and (0.079 ± 0.006) ppm/(mmol/L) for Fe2+. The individual ratios ΔR2*/Δχ were greater than 40 s-1/ppm for all samples with ferric solution and lower than 20 s-1/ppm for all but one of the samples with ferrous solution.


CONCLUSIONS
Ferrous and ferric iron ions show significantly different relaxation behaviors in MRI but similar susceptibility patterns. These properties can be used to differentiate ferrous and ferric samples.
Josef Lissner Laboratory for Biomedical Imaging, Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Marchioninistr. 15, 81377, Munich, Germany. od@dtrx.net.
Olaf
http://orcid.org/0000-0001-6182-5039
O
Dietrich
Department of Neurology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany.|German Center for Neurodegenerative Diseases (DZNE), Munich, Germany.
Johannes
J
Levin
Department of Neurology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany.
Seyed-Ahmad
SA
Ahmadi
Department of Neurology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany.
Annika
A
Plate
Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany.
Maximilian F
MF
Reiser
Department of Neurology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany.
Kai
K
Bötzel
Center for Neuropathology and Prion Research, Ludwig-Maximilians-University Munich, Munich, Germany.
Armin
A
Giese
Institute for Clinical Radiology, Ludwig-Maximilians-University Hospital Munich, Munich, Germany.
Birgit
B
Ertl-Wagner
D002712:Chlorides; D005290:Ferric Compounds; D007477:Ions / Q000737:chemistry*; D007501:Iron / Q000737:chemistry*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D019047:Phantoms, Imaging
D002712:Chlorides; D005290:Ferric Compounds; D007477:Ions; D007501:Iron; C024555:ferric chloride
Ferric and ferrous chloride; Iron; Magnetic resonance imaging; Magnetic susceptibility; Relaxation