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. 2023 Apr;89(4):1385-1400.
doi: 10.1002/mrm.29524. Epub 2022 Nov 13.

B 1 + $$ {B}_1^{+} $$ -correction of magnetization transfer saturation maps optimized for 7T postmortem MRI of the brain

Ilona Lipp  1 , Evgeniya Kirilina  1 , Luke J Edwards  1 , Kerrin J Pine  1 , Carsten Jäger  1   2 , Tobias Gräßle  3 ; EBC Consortium  1 ; Nikolaus Weiskopf  1   4 , Gunther Helms  1   5
Affiliations

B 1 + $$ {B}_1^{+} $$ -correction of magnetization transfer saturation maps optimized for 7T postmortem MRI of the brain

Ilona Lipp et al. Magn Reson Med. 2023 Apr.

Abstract

Purpose: Magnetization transfer saturation ( MTsat $$ \mathrm{MTsat} $$ ) is a useful marker to probe tissue macromolecular content and myelination in the brain. The increased B 1 + $$ {B}_1^{+} $$ -inhomogeneity at ≥ 7 $$ \ge 7 $$ T and significantly larger saturation pulse flip angles which are often used for postmortem studies exceed the limits where previous MTsat $$ \mathrm{MTsat} $$ B 1 + $$ {B}_1^{+} $$ correction methods are applicable. Here, we develop a calibration-based correction model and procedure, and validate and evaluate it in postmortem 7T data of whole chimpanzee brains.

Theory: The B 1 + $$ {B}_1^{+} $$ dependence of MTsat $$ \mathrm{MTsat} $$ was investigated by varying the off-resonance saturation pulse flip angle. For the range of saturation pulse flip angles applied in typical experiments on postmortem tissue, the dependence was close to linear. A linear model with a single calibration constant C $$ C $$ is proposed to correct bias in MTsat $$ \mathrm{MTsat} $$ by mapping it to the reference value of the saturation pulse flip angle.

Methods: C $$ C $$ was estimated voxel-wise in five postmortem chimpanzee brains. "Individual-based global parameters" were obtained by calculating the mean C $$ C $$ within individual specimen brains and "group-based global parameters" by calculating the means of the individual-based global parameters across the five brains.

Results: The linear calibration model described the data well, though C $$ C $$ was not entirely independent of the underlying tissue and B 1 + $$ {B}_1^{+} $$ . Individual-based correction parameters and a group-based global correction parameter ( C = 1 . 2 $$ C=1.2 $$ ) led to visible, quantifiable reductions of B 1 + $$ {B}_1^{+} $$ -biases in high-resolution MTsat $$ \mathrm{MTsat} $$ maps.

Conclusion: The presented model and calibration approach effectively corrects for B 1 + $$ {B}_1^{+} $$ inhomogeneities in postmortem 7T data.

Keywords: MRI; calibration; chimpanzee; magnetization transfer; postmortem; transmit field; ultra high-field.

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References

REFERENCES

    1. Weiskopf N, Edwards L, Helms G, Mohammadi S, Kirilina E. Quantitative magnetic resonance imaging of brain anatomy: towards in-vivo histology. Nature Rev Phys. 2021;3:570-588.
    1. Natu VS, Gomez J, Barnett M, et al. Apparent thinning of human visual cortex during childhood is associated with myelination. Proc Nat Acad Sci. 2019;116:20750-20759.
    1. Edwards LJ, Kirilina E, Mohammadai S, Weiskopf N, Microstructural imaging of human neocortex in vivo. NeuroImage. 2018;182:184-206.
    1. Paquola C, Bethlehem RA, Seidlitz J, et al. Shifts in myeloarchitecture characterise adolescent development of cortical gradients. eLife. 2019;8:e50482.
    1. Whitaker KJ, Vértes PE, Romero-Garcia R, et al. Adolescence is associated with genomically patterned consolidation of the hubs of the human brain connectome. PNAS. 2016;113:9105-9110.

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