Potential in reducing scan times of HARDI by accurate correction of the cross-term in a hemispherical encoding scheme

To reduce the scan time of high angular resolution diffusion imaging (HARDI) by using the hemispherical encoding scheme with the cross-term correction.

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.

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.

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.