Received: 17 December 2024 Revised: 22 April 2025 Accepted: 24 May 2025
DOI: 10.1002/mrm.30602
RESEARCH ARTICLE
B
1
-corrected breast T
1
mapping at ultralow field
Sheng Shen
1,2
Neha Koonjoo
1,2
Stephen E. Ogier
3,4
Thomas Boele
1,5
Mansi A. Saksena
2,6
Kathryn E. Keenan
3
Matthew S. Rosen
1,2,7
1
A.A. Martinos Center for Biomedical
Imaging, Department of Radiology,
Massachusetts General Hospital, Boston,
Massachusetts, USA
2
Harvard Medical School, Boston,
Massachusetts, USA
3
Physical Measurement Laboratory,
National Institute of Standards and
Technology, Boulder, Colorado, USA
4
Department of Physics, University of
Colorado, Boulder, Colorado, USA
5
Image X Institute, University of Sydney,
Sydney, New South Wales, Australia
6
Massachusetts General Hospital,
Division of Breast Imaging, Boston,
Massachusetts, USA
7
Department of Physics, Harvard
University, Cambridge, Massachusetts,
USA
Correspondence
Matthew S. Rosen, A.A. Martinos Center
for Biomedical Imaging, Department of
Radiology, Massachusetts General
Hospital, 149 13th Street, Suite 2301,
Charlestown MA 02129.
Email: msrosen@mgh.harvard.edu
Funding information
KiyomiandEdBairdMGHResearch
Scholar award; National Institutes of
Health, Grant/Award Number:
1R21CA267315
Abstract
Purpose: This study aims to develop an efficient T
1
mapping approach that is
free from systematic bias caused by B
1
inhomogeneity in ultralow-field (ULF)
MRI and to determine the T
1
values (without fat suppression) of breast tissues
at 6.5 mT.
Methods: We describe here a method for ULF T
1
mapping using a variable flip
angle approach for both mapping T
1
and B
1
.TheB
1
mapping is used to correct
the T
1
maps—and, unique to operation in the ULF regime, a B
1
map acquired in
a phantom can be applied to the in vivo T
1
mapping data, reducing in vivo scan
time. The T
1
mapping method was validated in vitro with copper sulphate phan-
toms at seven different concentrations. A breast phantom was scanned to test the
T
1
mapping protocol. Four healthy volunteers were recruited for T
1
mapping to
obtain in vivo T
1
values of breast tissues. No fat suppression was implemented
in this preliminary study.
Results: The copper sulphate phantom T
1
map measurements have less than
13% deviation from the reference T
1
values, and less than 6% deviation when the
reference T
1
was greater than 50 ms. Four healthy volunteers were scanned for
T
1
mapping. In these in vivo breast T
1
maps, the 25th to 75th percentiles ranged
from 79 to 243 ms at 6.5 mT.
Conclusion: Variable flip angle method can be used for both B
1
and T
1
mapping
at ULFs, which enables efficient in vivo T
1
mapping for ULF MRI.
KEYWORDS
breast MRI, T
1
mapping, ultralow field, variable flip angle method
Kathryn E. Keenan and Matthew S. Rosen contributed equally to this work.
Certain commercial equipment, instruments, software, or materials are identified in this paper in order to specify the experimental procedure ade-
quately. Such identification is not intended to imply recommendation or endorsement by NIST, nor is it intended to imply that the materials or
equipment identified are necessarily the best available for the purpose.
© 2025 International Society for Magnetic Resonance in Medicine. This article has been contributed to by U.S. Government employees and their work is in the public domain
in the USA.
Magn Reson Med. 2025;1–13. wileyonlinelibrary.com/journal/mrm 1
