title: Potential in reducing scan times of HARDI by accurate correction of the cross-term in a hemispherical encoding scheme.
abstract: OBJECTIVE
  To reduce the scan time of high angular resolution diffusion imaging (HARDI) by using the hemispherical encoding scheme with the cross-term correction.
  
  
  METHODS
  Unidirectional and 45 degrees crossing phantoms were built to evaluate the accuracy of the fiber orientation estimation when using a hemispherical encoding scheme with and without the cross-term correction. The q-ball imaging using the spherical harmonic basis was adopted for estimation of fiber orientation. By recalculating the diffusion gradient strengths, we make the actual b value in all directions equal to the expected b value for the correction of the cross-term.
  
  
  RESULTS
  The separation angles measured on the crossing phantom are 42.67 degrees +/- 1.50 degrees , 42.75 degrees +/- 2.10 degrees , and 42.93 degrees +/- 2.78 degrees for cross-term-free results, for the results from the hemispherical encoding scheme with and without the cross-term correction. The angular errors in mapping the unidirectional phantom are 1.87 degrees -2.29 degrees and 4.01 degrees -4.92 degrees for the results using the hemispherical encoding scheme with and without correcting for the cross-term at different b values.
  
  
  CONCLUSIONS
  Using the hemispherical encoding scheme with the cross-term correction can potentially halve the scan time of HARDI and obtain accurate fiber orientation estimation simultaneously. This will be helpful in the clinical application of HARDI.
authors.affiliation: Department of Electrical Engineering, National Taiwan University, Taipei, Taiwan.
authors.forename: Kuan-Hung
authors.initials: KH
authors.lastname: Cho
authors.forename: Chun-Hung
authors.initials: CH
authors.lastname: Yeh
authors.forename: Yi-Ping
authors.initials: YP
authors.lastname: Chao
authors.forename: Jiun-Jie
authors.initials: JJ
authors.lastname: Wang
authors.forename: Jyh-Horng
authors.initials: JH
authors.lastname: Chen
authors.forename: Ching-Po
authors.initials: CP
authors.lastname: Lin
mesh_terms: D001931:Brain Mapping / Q000379:methods; D038524:Diffusion Magnetic Resonance Imaging / Q000379:methods*; D007089:Image Enhancement / Q000379:methods; D007091:Image Processing, Computer-Assisted / Q000379:methods; D009412:Nerve Fibers / Q000648:ultrastructure; D019047:Phantoms, Imaging; D013997:Time Factors