Skip to main content

Lund University Publications

LUND UNIVERSITY LIBRARIES

Correction of FLASH-based MT saturation in human brain for residual bias of B1-inhomogeneity at 3T

Helms, Gunther LU orcid ; Weiskopf, Nikolaus and Lutti, Antoine (2021)
Abstract
Background:
Magnetization transfer (MT) saturation reflects the additional saturation of the MRI signal imposed by an MT pulse and is largely driven by the saturation of the bound pool. This reduction of the bound polarization by the MT pulse is less efficient than predicted by the differential B1-square law of absorption. Thus, B1 inhomogeneities lead to a residual bias in the MT saturation maps. We derive a heuristic correction to reduce this bias for a widely used multi-parameter mapping protocol at 3T.
Methods:
The amplitude of the MT pulse was varied via the nominal flip angle to mimic variations in B1. The MT saturation's dependence on the actual flip angle features a linear correction term, which was determined... (More)
Background:
Magnetization transfer (MT) saturation reflects the additional saturation of the MRI signal imposed by an MT pulse and is largely driven by the saturation of the bound pool. This reduction of the bound polarization by the MT pulse is less efficient than predicted by the differential B1-square law of absorption. Thus, B1 inhomogeneities lead to a residual bias in the MT saturation maps. We derive a heuristic correction to reduce this bias for a widely used multi-parameter mapping protocol at 3T.
Methods:
The amplitude of the MT pulse was varied via the nominal flip angle to mimic variations in B1. The MT saturation's dependence on the actual flip angle features a linear correction term, which was determined separately for gray and white matter.
Results:
The deviation of MT saturation from differential B1-square law is well described by a linear decrease with the actual flip angle of the MT pulse. This decrease showed no significant differences between gray and white matter. Thus, the post hoc correction does not need to take different tissue types into account. Bias-corrected MT saturation maps appeared more symmetric and highlighted highly myelinated tracts.
Discussion:
Our correction involves a calibration that is specific for the MT pulse. While it can also be used to rescale nominal flip angles, different MT pulses and/or protocols will require individual calibration. Conclusion: The suggested B1 correction of the MT maps can be applied post hoc using an independently acquired flip angle map. (Less)
Please use this url to cite or link to this publication:
author
; and
organization
publishing date
type
Working paper/Preprint
publication status
published
subject
pages
15 pages
publisher
arXiv.org
project
hMRI Toolbox Team
language
English
LU publication?
yes
id
71013fde-4cf6-4e85-b4f6-7bbb10464d60
alternative location
https://arxiv.org/ftp/arxiv/papers/2104/2104.14878.pdf
https://arxiv.org/abs/2104.14878
date added to LUP
2021-05-03 09:02:05
date last changed
2022-03-16 14:01:31
@misc{71013fde-4cf6-4e85-b4f6-7bbb10464d60,
  abstract     = {{Background: <br/>Magnetization transfer (MT) saturation reflects the additional saturation of the MRI signal imposed by an MT pulse and is largely driven by the saturation of the bound pool. This reduction of the bound polarization by the MT pulse is less efficient than predicted by the differential B1-square law of absorption. Thus, B1 inhomogeneities lead to a residual bias in the MT saturation maps. We derive a heuristic correction to reduce this bias for a widely used multi-parameter mapping protocol at 3T. <br/>Methods: <br/>The amplitude of the MT pulse was varied via the nominal flip angle to mimic variations in B1. The MT saturation's dependence on the actual flip angle features a linear correction term, which was determined separately for gray and white matter. <br/>Results: <br/>The deviation of MT saturation from differential B1-square law is well described by a linear decrease with the actual flip angle of the MT pulse. This decrease showed no significant differences between gray and white matter. Thus, the post hoc correction does not need to take different tissue types into account. Bias-corrected MT saturation maps appeared more symmetric and highlighted highly myelinated tracts. <br/>Discussion:<br/>Our correction involves a calibration that is specific for the MT pulse. While it can also be used to rescale nominal flip angles, different MT pulses and/or protocols will require individual calibration. Conclusion: The suggested B1 correction of the MT maps can be applied post hoc using an independently acquired flip angle map.}},
  author       = {{Helms, Gunther and Weiskopf, Nikolaus and Lutti, Antoine}},
  language     = {{eng}},
  month        = {{05}},
  note         = {{Preprint}},
  publisher    = {{arXiv.org}},
  title        = {{Correction of FLASH-based MT saturation in human brain for residual bias of B1-inhomogeneity at 3T}},
  url          = {{https://arxiv.org/ftp/arxiv/papers/2104/2104.14878.pdf}},
  year         = {{2021}},
}