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Simultaneous mapping of T1and B1+ in human brain at 7T

Olsson, Hampus LU ; Andersen, Mads LU ; Kadhim, Mustafa LU and Helms, Gunther LU orcid (2022) In Magnetic Resonance in Medicine 87(6). p.2637-2649
Abstract
Purpose
To map T1 and the local flip angle (B1+) in human brain using a single MP3RAGE sequence with 3 rapid acquisitions of gradient echoes (RAGEs).

Theory and methods
A third RAGE with a relatively high flip angle was appended to an MP2RAGE sequence. Through curve fitting and a rational approximation for small flip angles and short TR, closed form solutions for T1 and B1+ were derived. The influence of different k-space encoding schemes on precision and whether edge enhancement artifacts could be reduced with a saturation pulse applied prior to the third RAGE were explored. Validation of T1 estimates was performed using single-slice inversion... (More)
Purpose
To map T1 and the local flip angle (B1+) in human brain using a single MP3RAGE sequence with 3 rapid acquisitions of gradient echoes (RAGEs).

Theory and methods
A third RAGE with a relatively high flip angle was appended to an MP2RAGE sequence. Through curve fitting and a rational approximation for small flip angles and short TR, closed form solutions for T1 and B1+ were derived. The influence of different k-space encoding schemes on precision and whether edge enhancement artifacts could be reduced with a saturation pulse applied prior to the third RAGE were explored. Validation of T1 estimates was performed using single-slice inversion recovery (IR) and a subsequent region-of-interest–based comparison, whereas validation of B1+ was performed using a whole brain pixelwise comparison to a DREAM flip angle mapping protocol. Lastly, MP3RAGE was compared to T1-mapping by MP2RAGE with separate B1+ correction.

Results
Whole brain maps of T1 and B1+ at 1 mm isotropic resolution were obtained with MP3RAGE in 06:37 min. A linear–reverse centric–reverse centric phase-encoding order of the 3 RAGEs improved precision, and artifacts were successfully reduced with the saturation pulse. Estimations of T1 and B1+ deviated +2.5 ± 3.1% and −1.7 ± 8.6% from their respective references.

Conclusion
T1 and B1+ can be mapped simultaneously using MP3RAGE. The approach can be thought of as combining MP2RAGE with a dual flip angle T1-mapping protocol. Both maps can be solved for analytically and will be inherently co-registered at the high resolution associated with MPRAGE.
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author
; ; and
organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
7T, B1+ mapping, dual flip angle, MPRAGE, T1- mapping
in
Magnetic Resonance in Medicine
volume
87
issue
6
pages
2637 - 2649
publisher
John Wiley & Sons Inc.
external identifiers
  • scopus:85122733294
  • pmid:35037283
ISSN
1522-2594
DOI
10.1002/mrm.29151
project
Measuring T1 using MP2RAGE in Human Brain at 7T
Gradient echo-based quantitative MRI of human brain at 7T
language
English
LU publication?
yes
id
6b696448-0041-48ef-8695-74c71675414d
date added to LUP
2022-01-17 14:40:44
date last changed
2022-10-27 07:42:37
@article{6b696448-0041-48ef-8695-74c71675414d,
  abstract     = {{Purpose<br/>To map T<sub>1</sub> and the local flip angle (B<sub>1</sub><sup>+</sup>) in human brain using a single MP3RAGE sequence with 3 rapid acquisitions of gradient echoes (RAGEs).<br/><br/>Theory and methods<br/>A third RAGE with a relatively high flip angle was appended to an MP2RAGE sequence. Through curve fitting and a rational approximation for small flip angles and short TR, closed form solutions for T<sub>1</sub> and B<sub>1</sub><sup>+</sup> were derived. The influence of different k-space encoding schemes on precision and whether edge enhancement artifacts could be reduced with a saturation pulse applied prior to the third RAGE were explored. Validation of T<sub>1</sub> estimates was performed using single-slice inversion recovery (IR) and a subsequent region-of-interest–based comparison, whereas validation of B<sub>1</sub><sup>+</sup> was performed using a whole brain pixelwise comparison to a DREAM flip angle mapping protocol. Lastly, MP3RAGE was compared to T<sub>1</sub>-mapping by MP2RAGE with separate B<sub>1</sub><sup>+</sup> correction.<br/><br/>Results<br/>Whole brain maps of T<sub>1</sub> and B<sub>1</sub><sup>+</sup> at 1 mm isotropic resolution were obtained with MP3RAGE in 06:37 min. A linear–reverse centric–reverse centric phase-encoding order of the 3 RAGEs improved precision, and artifacts were successfully reduced with the saturation pulse. Estimations of T<sub>1</sub> and B<sub>1</sub><sup>+</sup> deviated +2.5 ± 3.1% and −1.7 ± 8.6% from their respective references.<br/><br/>Conclusion<br/>T<sub>1</sub> and B<sub>1</sub><sup>+</sup> can be mapped simultaneously using MP3RAGE. The approach can be thought of as combining MP2RAGE with a dual flip angle T<sub>1</sub>-mapping protocol. Both maps can be solved for analytically and will be inherently co-registered at the high resolution associated with MPRAGE.<br/>}},
  author       = {{Olsson, Hampus and Andersen, Mads and Kadhim, Mustafa and Helms, Gunther}},
  issn         = {{1522-2594}},
  keywords     = {{7T, B1+  mapping, dual flip angle, MPRAGE, T1- mapping}},
  language     = {{eng}},
  number       = {{6}},
  pages        = {{2637--2649}},
  publisher    = {{John Wiley & Sons Inc.}},
  series       = {{Magnetic Resonance in Medicine}},
  title        = {{Simultaneous mapping of T<sub>1</sub>and B<sub>1</sub><sup>+</sup> in human brain at 7T}},
  url          = {{http://dx.doi.org/10.1002/mrm.29151}},
  doi          = {{10.1002/mrm.29151}},
  volume       = {{87}},
  year         = {{2022}},
}