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Article Abstract
Purpose: Determination of the minimum number of gradient directions (N) for robust measurement of spherical mean diffusion weighted signal (S¯).
Methods: Computer simulations were employed to characterize the relative standard deviation (RSD) of the measured spherical mean signal as a function of the number of gradient directions (N). The effects of diffusion weighting b-value and signal-to-noise ratio (SNR) were investigated. Multi-shell high angular resolution Human Connectome Project diffusion data were analyzed to support the simulation results.
Results: RSD decreases with increasing N, and the minimum number of N needed for RSD ≤ 5% is referred to as N. At high SNRs, N increases with increasing b-value to achieve sufficient sampling. Simulations showed that N is linearly dependent on the b-value. At low SNRs, N increases with increasing b-value to reduce the noise. RSD can be estimated as σS¯N, where σ = 1/SNR is the noise level. The experimental results were in good agreement with the simulation results. The spherical mean signal can be measured accurately with a subset of gradient directions.
Conclusion: As N is affected by b-value and SNR, we recommend using 10 × b / b (b = 1 ms/μm) uniformly distributed gradient directions for typical human diffusion studies with SNR ~ 20 for robust spherical mean signal measurement.
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| http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6186434 | PMC |
| http://dx.doi.org/10.1016/j.mri.2018.08.020 | DOI Listing |
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