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. 2025 Sep 24.
doi: 10.1002/mrm.70102. Online ahead of print.

Two-point B1 correction for CEST MRI by fusing voxel-wise interpolation and T1W voxel-clustering

Yifan Li  1 , Wenxuan Chen  1 , Yi Wang  2 , Xiaolei Song  1
Affiliations

Two-point B1 correction for CEST MRI by fusing voxel-wise interpolation and T1W voxel-clustering

Yifan Li et al. Magn Reson Med. .

Abstract

Purpose: As a sensitive metabolic MRI technique, CEST images are easily contaminated by B 1 $$ {\mathrm{B}}_1 $$ inhomogeneity due to strong dependence on saturation B 1 $$ {\mathrm{B}}_1 $$ . We aim to develop an efficient and robust two-point B 1 $$ {\mathrm{B}}_1 $$ -correction method.

Methods: The proposed method only acquires CEST images under two saturation B 1 $$ {\mathrm{B}}_1 $$ 's, { B 1 , high $$ {\mathrm{B}}_{1,\mathrm{high}} $$ , B 1 , low $$ {\mathrm{B}}_{1,\mathrm{low}} $$ }, with desired B 1 $$ {\mathrm{B}}_1 $$ in between. Besides, voxel-wise Z- B 1 $$ {\mathrm{B}}_1 $$ interpolation (branch A), we performed another Z- T 1 $$ {\mathrm{T}}_1 $$ - B 1 $$ {\mathrm{B}}_1 $$ calibration (branch B), which divided image voxels into bins according to the T 1 w $$ {\mathrm{T}}_1\mathrm{w} $$ image and fitted a Z- B 1 $$ {\mathrm{B}}_1 $$ curve for each bin. To ensure each voxel adopts a better-corrected value, we fused the images corrected from both branches, according to a mask predicted by a retrospectively trained model. For validation, glutamate CEST (GluCEST) experiments of phantom and healthy volunteers were acquired on a 5T scanner. A total of 14 B 1 $$ {\mathrm{B}}_1 $$ pairs from 2.4μT to 3.6μT were evaluated, with the 7- B 1 $$ {\mathrm{B}}_1 $$ -correction as gold standard.

Results: Across glutamate phantoms with three distinct layouts, branch B demonstrated reliable correction performance for 14 B 1 $$ {\mathrm{B}}_1 $$ pairs, achieving a mean absolute error (MAE) of Z(3 ppm) ≤ 5% in all 42 experiments. For six healthy volunteers, branch B yielded Z(3 ppm) images that closely matched the 7- B 1 $$ {\mathrm{B}}_1 $$ correction, and the MAE distributions proved robust to voxel-binning, fitting strategies, and the choice of B 1 $$ {\mathrm{B}}_1 $$ pair. After fusion, all volunteers displayed better structural similarity index measure (SSIM), than the lower ones corrected by either branch.

Conclusions: By only acquiring two B 1 ' s $$ {{\mathrm{B}}_1}^{\prime}\mathrm{s} $$ , our B 1 $$ {\mathrm{B}}_1 $$ -correction strategy proved comparable performance to multi- B 1 $$ {\mathrm{B}}_1 $$ methods, exhibiting robustness to B 1 $$ {\mathrm{B}}_1 $$ selection and slice positions.

Keywords: B1 inhomogeneity correction; GluCEST; chemical exchange saturation transfer; image fusion.

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References

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