Abstract
This second article of the 2-part review builds on the theoretic background provided by the first article to cover the major technical factors that affect image quality in diffusion imaging, including the acquisition sequence, magnet field strength, gradient amplitude, and slew rate as well as multichannel radio-frequency coils and parallel imaging. The sources of many common diffusion image artifacts are also explored in detail. The emphasis is on optimizing these technical factors for state-of-the-art diffusion-weighted imaging and diffusion tensor imaging (DTI) based on the best available evidence in the literature. An overview of current methods for quantitative analysis of DTI data and fiber tractography in clinical research is also provided.
Highlights
One increasingly popular technique for diffusion-weighted imaging (DWI) is a multishot fast spin-echo (FSE) sequence called periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER), which continually oversamples the center of k-space to mitigate motion artifacts without the need for gating.[24]
Using 30 directions is recommended for routine clinical diffusion tensor imaging (DTI) studies as long as time permits, and even more directions would be useful primarily when more sophisticated diffusion modeling such as high angular resolution diffusion imaging (HARDI) is contemplated to better delineate connectivity in regions of complex white matter architecture such as crossing fiber tracts.[39,40,41]
Continued improvements in the technology of diffusion MR imaging will ensure that the current state-ofthe-art will be rapidly superseded
Summary
SUMMARY: This second article of the 2-part review builds on the theoretic background provided by the first article to cover the major technical factors that affect image quality in diffusion imaging, including the acquisition sequence, magnet field strength, gradient amplitude, and slew rate as well as multichannel radio-frequency coils and parallel imaging. One increasingly popular technique for DWI is a multishot FSE sequence called periodically rotated overlapping parallel lines with enhanced reconstruction (PROPELLER), which continually oversamples the center of k-space (ie, self-navigation) to mitigate motion artifacts without the need for gating.[24] This has been shown to improve detection of small acute infarcts, especially at the skull base and in the posterior fossa, where SS-EPI has the greatest susceptibility-induced distortions.[25,26] PROPELLER has not overtaken SS-EPI for routine brain DWI, likely because of its much longer scanning times. Unlike routine clinical DTI, acquisitions for fiber tractography must be Typical optimized whole-brain DTI acquisition parameters in a 1.5T or 3T MR imaging system*
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