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

Purpose: To reduce the scan time of high angular resolution diffusion imaging (HARDI) by using the hemispherical encoding scheme with the cross-term correction. Materials and Methods: Unidirectional and 45° 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° ± 1.50°, 42.75° ± 2.10°, and 42.93° ± 2.78° 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°-2.29° and 4.01°-4.92° for the results using the hemispherical encoding scheme with and without correcting for the cross-term at different b values. Conclusion: 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.