Determination of the appropriate b value and number of gradient directions for high-angular-resolution diffusion-weighted imaging.
TL;DR: This study estimates 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, and estimates that SH terms above l = 8 are negligible in practice for b values up to 5000 s/mm2, implying that a minimum of 45 DW directions is sufficient to fully characterise theDW signal.
Abstract: 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 5000 s/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 = 3000 s/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.
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TL;DR: A high-level overview of the features of the MRtrix3 framework and general-purpose image processing applications provided with the software is provided.
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...DWdata set 1was acquired on a Siemens TimTrio 3TMRI system equipped with a 32-channel receiver head coil and using a multi-shell acquisition scheme based on the recommendations in Tournier et al. (2013)....
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...Maximum likelihood estimation based on the Rice distribution was used to avoid a Rician bias in the true response functions (Tournier et al., 2013)....
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TL;DR: A high-level overview of the features of the MRtrix3 framework and general-purpose image processing applications provided with the software is provided.
Abstract: MRtrix3 is an open-source, cross-platform software package for medical image processing, analysis and visualization, with a particular emphasis on the investigation of the brain using diffusion MRI. It is implemented using a fast, modular and flexible general-purpose code framework for image data access and manipulation, enabling efficient development of new applications, whilst retaining high computational performance and a consistent command-line interface between applications. In this article, we provide a high-level overview of the features of the MRtrix3 framework and general-purpose image processing applications provided with the software.
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Cites methods from "Determination of the appropriate b ..."
...…(CSD) for single-shell fibre ODF estimation (Tournier et al., 2007, 2004) and multi-shell multi-tissue CSD for multi-shell data (Jeurissen et al., 2014), supported by several response function estimation algorithms (Dhollander et al., 2016; Tax et al., 2014; Tournier et al., 2013) (Figure 3)....
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TL;DR: An overview of the key concepts of tractography, the technical considerations at play, and the different types of tractographic algorithm, as well as the common misconceptions and mistakes that surround them are provided.
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Cites background from "Determination of the appropriate b ..."
...Experimental evidence suggests that the angular frequency content of the dMRI signal in the brain white matter levels off at a b‐value of approximately b = 3000 s/mm(2), suggesting that this b‐value achieves the highest practically available angular resolution.(122) Given this b‐value, the minimal number of unique diffusion encoding gradient orientations to fully characterize the angular frequency...
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TL;DR: This review focuses on studies of normative brain development from birth to early adulthood (˜25 years), and places particular emphasis on longitudinal studies and newer techniques that are being used to study microstructural white matter development.
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Cites background from "Determination of the appropriate b ..."
...Acquisition techniques such as high angular resolution diffusion imaging (HARDI)(Tuch et al., 2002) and diffusion spectrum imaging (DSI)(Wedeen et al., 2005) collect more directions than DTI and use higher b-values (Tournier et al., 2013)....
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..., 2005) collect more directions than DTI and use higher b-values (Tournier et al., 2013)....
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References
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