title: The potential of relaxation-weighted sodium magnetic resonance imaging as demonstrated on brain tumors.
abstract: OBJECTIVE
  : Total tissue sodium (Na) content is associated with the viability of cells and can be assessed by Na magnetic resonance imaging. However, the resulting total sodium signal (NaT) represents a volume-weighted average of different sodium compartments assigned to the intra- and extracellular space. In addition to the spin-density weighted contrast of NaT imaging, relaxation-weighted (NaR) sequences were applied. The aim of this study was to evaluate the potential of NaR imaging for tissue characterization and putative additional benefits to NaT imaging.
  
  
  METHODS
  : For NaT and NaR imaging, novel magnetic resonance imaging sequences were established and applied in 16 patients suffering from brain tumors (14 WHO grade I-IV and 2 metastases). All Na sequences were based on density-adapted three-dimensional radial projection reconstruction to obtain short echo times and high signal-to-noise ratio efficiency.
  
  
  RESULTS
  : NaT imaging revealed increased signal intensities in 15 of 16 brain tumors before therapy. In addition, NaR imaging enabled further differentiation of these lesions; all glioblastomas demonstrated higher NaR signal intensities as compared with WHO grade I-III tumors. Thus, NaR imaging allowed for correct separation between WHO grade I-III and WHO grade IV gliomas. In contrast to the NaT signal, the NaR signal correlated with the MIB-1 proliferation rate of tumor cells.
  
  
  CONCLUSIONS
  : These results serve as a proof of concept that NaR imaging reveals important physiological tissue characteristics different from NaT imaging. Furthermore, they indicate that the combined use of NaT and NaR imaging might add valuable information for the functional in vivo characterization of brain tissue.
authors.affiliation: Department of Medical Physics in Radiology, German Cancer Research Center, Im Neuenheimer Feld, Heidelberg, Germany.
authors.forename: Armin Michael
authors.initials: AM
authors.lastname: Nagel
authors.forename: Michael
authors.initials: M
authors.lastname: Bock
authors.forename: Christian
authors.initials: C
authors.lastname: Hartmann
authors.forename: Lars
authors.initials: L
authors.lastname: Gerigk
authors.forename: Jan-Oliver
authors.initials: JO
authors.lastname: Neumann
authors.forename: Marc-André
authors.initials: MA
authors.lastname: Weber
authors.forename: Martin
authors.initials: M
authors.lastname: Bendszus
authors.forename: Alexander
authors.initials: A
authors.lastname: Radbruch
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Wick
authors.forename: Heinz-Peter
authors.initials: HP
authors.lastname: Schlemmer
authors.forename: Wolfhard
authors.initials: W
authors.lastname: Semmler
authors.forename: Armin
authors.initials: A
authors.lastname: Biller
mesh_terms: D000328:Adult; D001932:Brain Neoplasms / Q000175:diagnosis* / Q000473:pathology; D002555:Cerebrospinal Fluid; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000295:instrumentation / Q000379:methods*; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D013223:Statistics as Topic