title: Iron mapping using the temperature dependency of the magnetic susceptibility.
abstract: OBJECTIVE
  The assessment of iron content in brain white matter (WM) is of high importance for studying neurodegenerative diseases. While R2 * mapping and quantitative susceptibility mapping is suitable for iron mapping in gray matter, iron mapping in WM still remains an unsolved problem. We propose a new approach for iron mapping, independent of diamagnetic contributions of myelin by assessing the temperature dependency of the paramagnetic susceptibility.
  
  
  METHODS
  We used unfixed human brain slices for relaxometry and calculated R2 ' as a measure for microscopic susceptibility variations at several temperatures (4°C-37°C) at 3 Tesla. The temperature coefficient of R2 ' (TcR2p) was calculated by linear regression and related to the iron concentration found by subsequent superconducting quantum interference device (SQUID) magnetometry and by inductively coupled plasma mass spectrometry.
  
  
  RESULTS
  In line with SQUID measurements, R2 ' mapping showed a linear temperature dependency of the bulk susceptibility with the highest slope in gray matter. Even in WM, TcR2p yielded a high linear correlation with the absolute iron concentration.
  
  
  CONCLUSIONS
  According to Curie's law, only paramagnetic matter exhibits a temperature dependency while the diamagnetism shows no effect. We have demonstrated that the temperature coefficient (TcR2p) can be used as a measure of the paramagnetic susceptibility despite of an unknown diamagnetic background.
authors.affiliation: Department of Neurology, Medical University of Graz, Austria.
authors.forename: Christoph
authors.initials: C
authors.lastname: Birkl
authors.forename: Christian
authors.initials: C
authors.lastname: Langkammer
authors.forename: Heinz
authors.initials: H
authors.lastname: Krenn
authors.forename: Walter
authors.initials: W
authors.lastname: Goessler
authors.forename: Christina
authors.initials: C
authors.lastname: Ernst
authors.forename: Johannes
authors.initials: J
authors.lastname: Haybaeck
authors.forename: Rudolf
authors.initials: R
authors.lastname: Stollberger
authors.forename: Franz
authors.initials: F
authors.lastname: Fazekas
authors.forename: Stefan
authors.initials: S
authors.lastname: Ropele
mesh_terms: D000368:Aged; D000465:Algorithms; D001923:Brain Chemistry; D002102:Cadaver; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007501:Iron / Q000032:analysis* / Q000737:chemistry*; D060526:Magnetic Fields; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013817:Thermography / Q000379:methods*; D014018:Tissue Distribution; D066127:White Matter / Q000737:chemistry* / Q000648:ultrastructure
chemical_list: D007501:Iron
keywords: Curie constant; Curie's law; MRI and temperature; SQUID; iron in white matter; iron quantification; magnetic susceptibility