Quantitative MR imaging of brain iron: a postmortem validation study.
OBJECTIVE
To investigate the relationship between transverse relaxation rates R2 and R2*, the most frequently used surrogate markers for iron in brain tissue, and chemically determined iron concentrations.


METHODS
This study was approved by the local ethics committee, and informed consent was obtained from each individual's next of kin. Quantitative magnetic resonance (MR) imaging was performed at 3.0 T in seven human postmortem brains in situ (age range at death, 38-81 years). Following brain extraction, iron concentrations were determined with inductively coupled plasma mass spectrometry in prespecified gray and white matter regions and correlated with R2 and R2* by using linear regression analysis. Hemispheric differences were tested with paired t tests.


RESULTS
The highest iron concentrations were found in the globus pallidus (mean ± standard deviation, 205 mg/kg wet mass ± 32), followed by the putamen (mean, 153 mg/kg wet mass ± 29), caudate nucleus (mean, 92 mg/kg wet mass ± 15), thalamus (mean, 49 mg/kg wet mass ± 11), and white matter regions. When all tissue samples were considered, transverse relaxation rates showed a strong linear correlation with iron concentration throughout the brain (r² = 0.67 for R2, r² = 0.90 for R2*; P < .001). In white matter structures, only R2* showed a linear correlation with iron concentration. Chemical analysis revealed significantly higher iron concentrations in the left hemisphere than in the right hemisphere, a finding that was not reflected in the relaxation rates.


CONCLUSIONS
Because of their strong linear correlation with iron concentration, both R2 and R2* can be used to measure iron deposition in the brain. Because R2* is more sensitive than R2 to variations in brain iron concentration and can detect differences in white matter, it is the preferred parameter for the assessment of iron concentration in vivo.
Langkammer
Christian
C
Department of Neurology and Division of Neuroradiology, Medical University of Graz, Auenbruggerplatz 22, 8036 Graz, Austria.
Krebs
Nikolaus
N
Goessler
Walter
W
Scheurer
Eva
E
Ebner
Franz
F
Yen
Kathrin
K
Fazekas
Franz
F
Ropele
Stefan
S
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001923:Brain Chemistry; D002102:Cadaver; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007501:Iron / Q000032:analysis*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D013058:Mass Spectrometry / Q000295:instrumentation; D008875:Middle Aged; D012044:Regression Analysis; D012680:Sensitivity and Specificity; D018709:Statistics, Nonparametric
D007501:Iron