Determination of the appropriate b value and number of gradient directions for high-angular-resolution diffusion-weighted imaging

TY - JOUR

T1 - Determination of the appropriate b value and number of gradient directions for high-angular-resolution diffusion-weighted imaging

AU - Tournier, Jacques-Donald

AU - Calamante, Fernando

AU - Connelly, Alan

PY - 2013/12

Y1 - 2013/12

N2 - High-angular-resolution diffusion-weighted imaging (HARDI) is one of the most common MRI acquisition schemes for use with higher order models of diffusion. However, the optimal b value and number of diffusion-weighted (DW) directions for HARDI are still undetermined, primarily as a result of the large number of available reconstruction methods and corresponding parameters, making it impossible to identify a single criterion by which to assess performance. In this study, we estimate the minimum number of DW directions and optimal b values required for HARDI by focusing on the angular frequency content of the DW signal itself. The spherical harmonic (SH) series provides the spherical analogue of the Fourier series, and can hence be used to examine the angular frequency content of the DW signal. Using high-quality data acquired along 500 directions over a range of b values, we estimate that SH terms above l=8 are negligible in practice for b values up to 5000s/mm(2), implying that a minimum of 45 DW directions is sufficient to fully characterise the DW signal. l>0 SH terms were found to increase as a function of b value, levelling off at b=3000s/mm(2), suggesting that this value already provides the highest achievable angular resolution. In practice, it is recommended to acquire more than the minimum of 45 DW directions to avoid issues with imperfections in the uniformity of the DW gradient directions and to meet signal-to-noise requirements of the intended reconstruction method.

AB - High-angular-resolution diffusion-weighted imaging (HARDI) is one of the most common MRI acquisition schemes for use with higher order models of diffusion. However, the optimal b value and number of diffusion-weighted (DW) directions for HARDI are still undetermined, primarily as a result of the large number of available reconstruction methods and corresponding parameters, making it impossible to identify a single criterion by which to assess performance. In this study, we estimate the minimum number of DW directions and optimal b values required for HARDI by focusing on the angular frequency content of the DW signal itself. The spherical harmonic (SH) series provides the spherical analogue of the Fourier series, and can hence be used to examine the angular frequency content of the DW signal. Using high-quality data acquired along 500 directions over a range of b values, we estimate that SH terms above l=8 are negligible in practice for b values up to 5000s/mm(2), implying that a minimum of 45 DW directions is sufficient to fully characterise the DW signal. l>0 SH terms were found to increase as a function of b value, levelling off at b=3000s/mm(2), suggesting that this value already provides the highest achievable angular resolution. In practice, it is recommended to acquire more than the minimum of 45 DW directions to avoid issues with imperfections in the uniformity of the DW gradient directions and to meet signal-to-noise requirements of the intended reconstruction method.

KW - diffusion-weighted MRI

KW - high-angular-resolution diffusion-weighted MRI

KW - HARDI

KW - MULTIPLE FIBER ORIENTATIONS

KW - AXON DIAMETER DISTRIBUTION

KW - WHITE-MATTER

KW - WATER DIFFUSION

KW - HUMAN BRAIN

KW - SPHERICAL DECONVOLUTION

KW - SAMPLING SCHEMES

KW - TENSOR MRI

KW - MODEL

KW - TRACKING

U2 - 10.1002/nbm.3017

DO - 10.1002/nbm.3017

M3 - Article

SN - 0952-3480

VL - 26

SP - 1775

EP - 1786

JO - Nmr in Biomedicine

JF - Nmr in Biomedicine

IS - 12

M1 - N/A

ER -