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Maxwell-compensated design of asymmetric gradient waveforms for tensor-valued diffusion encoding.

Szczepankiewicz, Filip LU ; Westin, Carl-Fredrik and Nilsson, Markus LU (2019) In Magnetic Resonance in Medicine 82(4). p.1424-1437
Abstract
PURPOSE:
Diffusion encoding with asymmetric gradient waveforms is appealing because the asymmetry provides superior efficiency. However, concomitant gradients may cause a residual gradient moment at the end of the waveform, which can cause significant signal error and image artifacts. The purpose of this study was to develop an asymmetric waveform designs for tensor-valued diffusion encoding that is not sensitive to concomitant gradients.

METHODS:
The "Maxwell index" was proposed as a scalar invariant to capture the effect of concomitant gradients. Optimization of "Maxwell-compensated" waveforms was performed in which this index was constrained. Resulting waveforms were compared to waveforms from literature, in terms of... (More)
PURPOSE:
Diffusion encoding with asymmetric gradient waveforms is appealing because the asymmetry provides superior efficiency. However, concomitant gradients may cause a residual gradient moment at the end of the waveform, which can cause significant signal error and image artifacts. The purpose of this study was to develop an asymmetric waveform designs for tensor-valued diffusion encoding that is not sensitive to concomitant gradients.

METHODS:
The "Maxwell index" was proposed as a scalar invariant to capture the effect of concomitant gradients. Optimization of "Maxwell-compensated" waveforms was performed in which this index was constrained. Resulting waveforms were compared to waveforms from literature, in terms of the measured and predicted impact of concomitant gradients, by numerical analysis as well as experiments in a phantom and in a healthy human brain.

RESULTS:
Maxwell-compensated waveforms with Maxwell indices below 100 (mT/m)2 ms showed negligible signal bias in both numerical analysis and experiments. By contrast, several waveforms from literature showed gross signal bias under the same conditions, leading to a signal bias that was large enough to markedly affect parameter maps. Experimental results were accurately predicted by theory.

CONCLUSION:
Constraining the Maxwell index in the optimization of asymmetric gradient waveforms yields efficient diffusion encoding that negates the effects of concomitant fields while enabling arbitrary shapes of the b-tensor. This waveform design is especially useful in combination with strong gradients, long encoding times, thick slices, simultaneous multi-slice acquisition, and large FOVs. (Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
Maxwell terms, asymmetric gradient waveforms, concomitant gradients, tensor-valued diffusion encoding
in
Magnetic Resonance in Medicine
volume
82
issue
4
pages
1424 - 1437
publisher
Wiley Online Library
external identifiers
  • scopus:85066505297
  • pmid:31148245
ISSN
1522-2594
DOI
10.1002/mrm.27828
language
English
LU publication?
yes
id
587a72b4-133a-4c42-8130-4018502ab9f2
date added to LUP
2019-06-20 12:41:54
date last changed
2020-02-19 05:33:40
@article{587a72b4-133a-4c42-8130-4018502ab9f2,
  abstract     = {PURPOSE:<br/>Diffusion encoding with asymmetric gradient waveforms is appealing because the asymmetry provides superior efficiency. However, concomitant gradients may cause a residual gradient moment at the end of the waveform, which can cause significant signal error and image artifacts. The purpose of this study was to develop an asymmetric waveform designs for tensor-valued diffusion encoding that is not sensitive to concomitant gradients.<br/><br/>METHODS:<br/>The "Maxwell index" was proposed as a scalar invariant to capture the effect of concomitant gradients. Optimization of "Maxwell-compensated" waveforms was performed in which this index was constrained. Resulting waveforms were compared to waveforms from literature, in terms of the measured and predicted impact of concomitant gradients, by numerical analysis as well as experiments in a phantom and in a healthy human brain.<br/><br/>RESULTS:<br/>Maxwell-compensated waveforms with Maxwell indices below 100 (mT/m)2 ms showed negligible signal bias in both numerical analysis and experiments. By contrast, several waveforms from literature showed gross signal bias under the same conditions, leading to a signal bias that was large enough to markedly affect parameter maps. Experimental results were accurately predicted by theory.<br/><br/>CONCLUSION:<br/>Constraining the Maxwell index in the optimization of asymmetric gradient waveforms yields efficient diffusion encoding that negates the effects of concomitant fields while enabling arbitrary shapes of the b-tensor. This waveform design is especially useful in combination with strong gradients, long encoding times, thick slices, simultaneous multi-slice acquisition, and large FOVs.},
  author       = {Szczepankiewicz, Filip and Westin, Carl-Fredrik and Nilsson, Markus},
  issn         = {1522-2594},
  language     = {eng},
  month        = {05},
  number       = {4},
  pages        = {1424--1437},
  publisher    = {Wiley Online Library},
  series       = {Magnetic Resonance in Medicine},
  title        = {Maxwell-compensated design of asymmetric gradient waveforms for tensor-valued diffusion encoding.},
  url          = {http://dx.doi.org/10.1002/mrm.27828},
  doi          = {10.1002/mrm.27828},
  volume       = {82},
  year         = {2019},
}