Correction of magnetization transfer saturation maps optimized for 7T postmortem MRI of the brain

Ilona Lipp, Evgeniya Kirilina, Luke J. Edwards, Kerrin J. Pine, Carsten Jäger, Tobias Grässle, EBC Consortium (medarbetare), Nikolaus Weiskopf, Gunther Helms

Forskningsoutput: TidskriftsbidragArtikel i vetenskaplig tidskriftPeer review

Sammanfattning

Purpose
Magnetization transfer saturation (MTsat) is a useful marker to probe tissue macromolecular content and myelination in the brain. The increased B1+ inhomogeneity at  7T and significantly larger saturation pulse flip angles which are often used for postmortem studies exceed the limits where previous B1+
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 B1+ dependence of 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 is proposed to correct bias in MTsat by mapping it to the reference value of the saturation pulse flip angle.

Methods
MTsat was estimated voxel-wise in five postmortem chimpanzee brains. “Individual-based global parameters” were obtained by calculating the mean
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 was not entirely independent of the underlying tissue and B1+. Individual-based correction parameters and a group-based global correction parameter (C=1.2) led to visible, quantifiable reductions of B1+-biases in high-resolution MTsat maps.

Conclusion
The presented model and calibration approach effectively corrects for B1+
inhomogeneities in postmortem 7T data.
Originalspråkengelska
Sidor (från-till)1385-1400
Antal sidor16
TidskriftMagnetic Resonance in Medicine
Volym89
Nummer4
Tidigt onlinedatum2022 nov. 14
DOI
StatusPublished - 2023 apr.

Ämnesklassifikation (UKÄ)

  • Medicinsk bildbehandling

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