Empirical transmit field bias correction of T1w/T2w myelin maps
Matthew F. Glasser,
Timothy S. Coalson,
Michael P. Harms,
Junqian Xu,
Graham L. Baum,
Joonas A. Autio,
Edward J. Auerbach,
Douglas N. Greve,
Essa Yacoub,
David C. Van Essen,
Nicholas A. Bock,
Takuya Hayashi
Affiliations
Matthew F. Glasser
Departments of Radiology,; Neuroscience, and; Corresponding author.
Timothy S. Coalson
Neuroscience, and
Michael P. Harms
Psychiatry, Washington University Medical School, St. Louis, MO, United States
Junqian Xu
Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States; Departments of Radiology and Psychiatry, Baylor College of Medicine, Houston, TX, United States
Graham L. Baum
Department of Psychology, Harvard University, Cambridge, MA, United States
Joonas A. Autio
RIKEN Center for Biosystems Dynamics Research, Kobe, Japan
Edward J. Auerbach
Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States
Douglas N. Greve
Athinoula A. Martinos Center for Biomedical Imaging, Department of Radiology, Massachusetts General Hospital, Harvard Medical School, Boston, MA, United States
Essa Yacoub
Center for Magnetic Resonance Research, University of Minnesota, Minneapolis, MN, United States
David C. Van Essen
Neuroscience, and
Nicholas A. Bock
Department of Psychology, Neuroscience and Behaviour, McMaster University, Hamilton, ON, Canada
Takuya Hayashi
RIKEN Center for Biosystems Dynamics Research, Kobe, Japan
T1-weighted divided by T2-weighted (T1w/T2w) myelin maps were initially developed for neuroanatomical analyses such as identifying cortical areas, but they are increasingly used in statistical comparisons across individuals and groups with other variables of interest. Existing T1w/T2w myelin maps contain radiofrequency transmit field (B1+) biases, which may be correlated with these variables of interest, leading to potentially spurious results. Here we propose two empirical methods for correcting these transmit field biases using either explicit measures of the transmit field or alternatively a ‘pseudo-transmit’ approach that is highly correlated with the transmit field at 3T. We find that the resulting corrected T1w/T2w myelin maps are both better neuroanatomical measures (e.g., for use in cross-species comparisons), and more appropriate for statistical comparisons of relative T1w/T2w differences across individuals and groups (e.g., sex, age, or body-mass-index) within a consistently acquired study at 3T. We recommend that investigators who use the T1w/T2w approach for mapping cortical myelin use these B1+ transmit field corrected myelin maps going forward.
