title: Diffusion weighted imaging with circularly polarized oscillating gradients.
abstract: OBJECTIVE
  The short diffusion time regime provides an interesting probe for tissue microstructure and can be investigated with oscillating gradient spin echo (OGSE) experiments. Several studies report new contrasts in preclinical settings and the first in vivo human experiments have recently been presented. One major hurdle in practical implementation is the low effective diffusion weighting provided at high frequency with limited gradient strength.
  
  
  BACKGROUND
  As a solution to the low diffusion weighting of OGSE, circularly polarized OGSE (CP-OGSE) is introduced. CP-OGSE gives a twofold increase in diffusion weighting with encoding in a plane rather than in one direction. CP-OGSE can be used for rotationally invariant acquisitions on anisotropic tissues.
  
  
  METHODS
  Experiments with a 4.7 T preclinical scanner on a postmortem monkey brain as well as simulations were performed using conventional OGSE and CP-OGSE.
  
  
  RESULTS
  Simulations and experiments show that CP-OGSE provides the same microstructural information as OGSE but provides more robust parameter estimates with limited gradient strength.
  
  
  CONCLUSIONS
  CP-OGSE can be an important contribution for making OGSE imaging more effective in clinical imaging settings with limited gradient strength. Furthermore, the improved diffusion weighting can also be used to expand the investigated frequency range.
authors.affiliation: Danish Research Centre for Magnetic Resonance, Centre for Functional and Diagnostic Imaging and Research, Copenhagen University Hospital Hvidovre, Denmark.
authors.forename: Henrik
authors.initials: H
authors.lastname: Lundell
authors.forename: Casper Kaae
authors.initials: CK
authors.lastname: Sønderby
authors.forename: Tim B
authors.initials: TB
authors.lastname: Dyrby
mesh_terms: D000465:Algorithms; D000818:Animals; D002531:Cerebellum / Q000033:anatomy & histology*; D002522:Chlorocebus aethiops; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D007089:Image Enhancement / Q000379:methods*; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D009991:Oscillometry / Q000379:methods*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D012815:Signal Processing, Computer-Assisted; D012984:Software
keywords: circularly polarized; diffusion tensor imaging; oscillating gradient spin echo; short diffusion time