title: Flow-compensated intravoxel incoherent motion diffusion imaging.
abstract: OBJECTIVE
  The pseudo-diffusion coefficient D* in intravoxel incoherent motion (IVIM) imaging was found difficult to seize. Flow-compensated diffusion gradients were used to test the validity of the commonly assumed biexponential limit and to determine not only D*, but also characteristic timescale τ and velocity v of the incoherent motion.
  
  
  METHODS
  Bipolar and flow-compensated diffusion gradients were inserted into a flow-compensated single-shot EPI sequence. Images were obtained from a pipe-shaped flow phantom and from healthy volunteers. To calculate the IVIM signal outside the biexponential limit, a formalism based on normalized phase distributions was developed.
  
  
  RESULTS
  The flow-compensated diffusion gradients caused less signal attenuation than the bipolar ones. A signal dependence on the duration of the flow-compensated gradients was found at low b-values in the volunteer datasets. The characteristic IVIM parameters were estimated to be v = 4.60 ± 0.34 mm/s and τ = 144 ± 10 ms for liver and v = 3.91 ± 0.54 mm/s and τ = 224 ± 47 ms for pancreas.
  
  
  CONCLUSIONS
  Our results strongly indicate that the biexponential limit does not adequately model the diffusion signal in liver and pancreas. By using both bipolar and flow-compensated diffusion gradients of different duration, the characteristic timescale and velocity of the incoherent motion can be determined.
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Andreas
authors.initials: A
authors.lastname: Wetscherek
authors.affiliation: Quantitative Imaging-Based Disease Characterization, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Bram
authors.initials: B
authors.lastname: Stieltjes
authors.affiliation: Medical Physics in Radiology, German Cancer Research Center (DKFZ), Heidelberg, Germany.|Quantitative Imaging-Based Disease Characterization, German Cancer Research Center (DKFZ), Heidelberg, Germany.
authors.forename: Frederik Bernd
authors.initials: FB
authors.lastname: Laun
mesh_terms: D000465:Algorithms; D001783:Blood Flow Velocity / Q000502:physiology*; D006801:Humans; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D021621:Imaging, Three-Dimensional / Q000379:methods*; D008102:Liver Circulation / Q000502:physiology*; D018810:Magnetic Resonance Angiography / Q000295:instrumentation / Q000379:methods*; D009038:Motion; D019047:Phantoms, Imaging; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity
keywords: IVIM; MRI; correlation time; diffusion; flow compensation; perfusion