2022-11-13Zeitschriftenartikel
B1+ -correction of magnetization transfer saturation maps optimized for 7T postmortem MRI of the brain
Purpose:
Magnetization transfer saturation (
) is a useful marker to probe tissue macromolecular content and myelination in the brain. The increased
-inhomogeneity at T and significantly larger saturation pulse flip angles which are often used for postmortem studies exceed the limits where previous
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
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 is proposed to correct bias in
by mapping it to the reference value of the saturation pulse flip angle.
Methods:
was estimated voxel-wise in five postmortem chimpanzee brains. “Individual-based global parameters” were obtained by calculating the mean
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
was not entirely independent of the underlying tissue and
. Individual-based correction parameters and a group-based global correction parameter () led to visible, quantifiable reductions of
-biases in high-resolution
maps.
Conclusion:
The presented model and calibration approach effectively corrects for
inhomogeneities in postmortem 7T data.
