title: IVIM analysis of brain tumors: an investigation of the relaxation effects of CSF, blood, and tumor tissue on the estimated perfusion fraction.
abstract: OBJECTIVE
  We sought to investigate the dependence of intravoxel incoherent motion (IVIM)-related perfusion fraction (f) estimates on the transverse relaxation of brain tissue, blood, and cerebrospinal fluid (CSF), attempting to overcome the influence of CSF on conventional f maps.
  
  
  METHODS
  Eighteen patients with gliomas underwent DWI with 14 b-values (0-1,300 s/mm(2)) and two distinct echo times (TEs). Regions of interest representing tumour and normal brain tissue were analysed by calculating the f values for both TEs. A mask for pixels with relevant CSF partial volume was subsequently created. The f values were tested for significant differences.
  
  
  RESULTS
  We found statistically significant differences between the two TEs in the f values for cortical and juxtacortical structures and non-enhancing areas of the tumour /oedema. Normal white matter and gadolinium-enhancing tumour tissue appeared insensitive to TE variation. In all tissue types examined, the masking of voxels with considerable CSF content was able to overcome issues of erroneous f estimation and calculation of f values insensitive to TE changes was feasible.
  
  
  CONCLUSIONS
  Due to the complex interaction in the relaxation rates of CSF, blood, and tumour tissue, the estimation of f values is affected by the choice of TE. Only f values in normal white matter and tumour tissue--which largely comprise blood voxels with minor CSF partial volume--may be clinically applicable in the present form of IVIM-based DWI analysis. Going a step further, and after removing voxels with heavily TE-susceptible f values, we were able to obtain accurate and TE-independent f values in contrast-enhancing tumour tissue, white matter, and grey matter, which were essentially consistent with those reported in the literature.
authors.affiliation: Department of Neuroradiology, Eberhard Karls University, Hoppe-Seyler-Str. 3, 72076, Tübingen, Germany, sotirios.bisdas@uni-tuebingen.de.
authors.forename: Sotirios
authors.initials: S
authors.lastname: Bisdas
authors.forename: Uwe
authors.initials: U
authors.lastname: Klose
mesh_terms: D000328:Adult; D000368:Aged; D001932:Brain Neoplasms / Q000097:blood / Q000134:cerebrospinal fluid / Q000473:pathology*; D003287:Contrast Media; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D005260:Female; D005910:Glioma / Q000097:blood / Q000134:cerebrospinal fluid / Q000473:pathology*; D006801:Humans; D007090:Image Interpretation, Computer-Assisted; D008297:Male; D008875:Middle Aged; D009038:Motion; D009942:Organometallic Compounds; D059629:Signal-To-Noise Ratio
chemical_list: D003287:Contrast Media; D009942:Organometallic Compounds; C090600:gadobutrol