title: Numerical modeling of susceptibility-related MR signal dephasing with vessel size measurement: phantom validation at 3T.
abstract: OBJECTIVE
  MRI is used to obtain quantitative oxygenation and blood volume information from the susceptibility-related MR signal dephasing induced by blood vessels. However, analytical models that fit the MR signal are usually not accurate over the range of small blood vessels. Moreover, recent studies have demonstrated limitations in the simultaneous assessment of oxygenation and blood volume. In this study, a multiparametric MRI framework that aims to measure vessel radii in addition to magnetic susceptibility and volume fraction was introduced.
  
  
  METHODS
  The protocol consisted of gradient-echo sampling of the spin-echo, diffusion, T2, and B0 acquisitions. After correction steps, the data were postprocessed with a versatile numerical model of the MR signal. An important analytical model was implemented for comparison. The approach was validated in phantoms with coiling strings as proxy for blood vessels.
  
  
  RESULTS
  The feasibility of the vessel radius measurement is demonstrated. The numerical model shows an improved accuracy compared with the analytical approach. However, both methods overestimate the radius. The simultaneous measurement of the magnetic susceptibility and the volume fraction remains challenging.
  
  
  CONCLUSIONS
  The results suggest that this approach could be interesting in vivo to better characterize the microvasculature without contrast agent.
authors.affiliation: Department of Radiology and Biomedical Imaging, University of California, San Francisco, California, USA; Center for Imaging of Neurodegenerative Diseases, Department of Veterans Affairs Medical Center, San Francisco, California, USA.
authors.forename: Nicolas A
authors.initials: NA
authors.lastname: Pannetier
authors.forename: Maja
authors.initials: M
authors.lastname: Sohlin
authors.forename: Thomas
authors.initials: T
authors.lastname: Christen
authors.forename: Lothar
authors.initials: L
authors.lastname: Schad
authors.forename: Norbert
authors.initials: N
authors.lastname: Schuff
mesh_terms: D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted / Q000379:methods; D018810:Magnetic Resonance Angiography / Q000379:methods*; D008833:Microcirculation; D019047:Phantoms, Imaging
keywords: MR numerical model; diffusion; magnetic susceptibility; quantitative BOLD; vessel size measurement