Dataset Information

The effect of and correction for through-slice dephasing on 2D gradient-echo double angle B1+ mapping.

ABSTRACT:

Purpose

To show that B0$$ {\mathrm{B}}_0 $$ variations through slice and slice profile effects are two major confounders affecting 2D dual angle B1+$$ {\mathrm{B}}_1^{+} $$ maps using gradient-echo signals and thus need to be corrected to obtain accurate B1+$$ {\mathrm{B}}_1^{+} $$ maps.

Methods

The 2D gradient-echo transverse complex signal was Bloch-simulated and integrated across the slice dimension including nonlinear variations in B0$$ {\mathrm{B}}_0 $$ inhomogeneities through slice. A nonlinear least squares fit was used to find the B1+$$ {\mathrm{B}}_1^{+} $$ factor corresponding to the best match between the two gradient-echo signals experimental ratio and the Bloch-simulated ratio. The correction was validated in phantom and in vivo at 3T.

Results

For our RF excitation pulse, the error in the B1+$$ {\mathrm{B}}_1^{+} $$ factor scales by approximately 3.8% for every 10 Hz/cm variation in B0$$ {\mathrm{B}}_0 $$ along the slice direction. Higher accuracy phantom B1+$$ {\mathrm{B}}_1^{+} $$ maps were obtained after applying the proposed correction; the root mean square B1+$$ {\mathrm{B}}_1^{+} $$ error relative to the gold standard B1+$$ {\mathrm{B}}_1^{+} $$ decreased from 6.4% to 2.6%. In vivo whole-liver T1$$ {\mathrm{T}}_1 $$ maps using the corrected B1+$$ {\mathrm{B}}_1^{+} $$ map registered a significant decrease in T1$$ {\mathrm{T}}_1 $$ gradient through slice.

Conclusion

B0$$ {\mathrm{B}}_0 $$ inhomogeneities varying through slice were seen to have an impact on the accuracy of 2D double angle B1+$$ {\mathrm{B}}_1^{+} $$ maps using gradient-echo sequences. Consideration of this confounder is crucial for research relying on accurate knowledge of the true excitation flip angles, as is the case of T1$$ {\mathrm{T}}_1 $$ mapping using a spoiled gradient recalled echo sequence.

SUBMITTER: Belsley G

PROVIDER: S-EPMC10952755 | biostudies-literature | 2024 Apr

REPOSITORIES: biostudies-literature

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Publications

The effect of and correction for through-slice dephasing on 2D gradient-echo double angle B 1 + mapping.

Belsley Gabriela G Tyler Damian J DJ Robson Matthew D MD Tunnicliffe Elizabeth M EM

Magnetic resonance in medicine 20231229 4

<h4>Purpose</h4>To show that B 0 $$ {\mathrm{B}}_0 $$ variations through slice and slice profile effects are two major confounders affecting 2D dual angle B 1 + $$ {\mathrm{B}}_1^{+} $$ maps using gradient-echo signals and thus need to be corrected to obtain accurate B 1 + $$ {\mathrm{B}}_1^{+} $$ maps.<h4>Methods</h4>The 2D gradient-echo transverse complex signal was Bloch-simulated and integrated across the slice dimension including nonlinear variations in B 0 $$ {\mathrm{B}}_0 ...[more]

PMID: 38156827

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