Rapid and simplified post-processing for simultaneous B 0 $$ {\mathrm{B}}_0 $$ and B 1 $$ {\mathrm{B}}_1 $$ mapping...

Area of Science:

• Medical Imaging
• Magnetic Resonance Imaging
• Quantitative Imaging

Background:

• Accurate $B$₀ and $B$₁ inhomogeneity correction is vital for reliable Chemical Exchange Saturation Transfer (CEST) imaging, especially at ultra-high fields (UHF).
• The WASABI technique offers high-fidelity $\delta \omega$ and $B$₁ mapping but is hindered by slow post-processing and susceptibility to local minima.

Purpose of the Study:

• To develop an alternative to the WASABI Levenberg-Marquardt approach for $B$₀ and $B$₁ mapping.
• To enhance both the speed and accuracy of post-processing for quantitative CEST imaging at UHF.

Main Methods:

• Derived a direct relationship between $\delta \omega$, $B$₁ values, and WASABI Z-spectrum information.
• Developed a novel optimization approach named RAbi DIstance SearcH (RADISH).
• Validated the method using seven in vivo 7T brain datasets.

Main Results:

• RADISH accelerated post-processing by two orders of magnitude compared to WASABI.
• Achieved improved estimation accuracy across all brain slices, with $\delta \omega$ and $B$₁ map agreement within 1 Hz and 0.5%, respectively.
• Reduced whole-head artifacts from 3.90% to 1.05%.

Conclusions:

• RADISH offers significant improvements in speed and robustness for generating $\delta \omega$ and $B$₁ maps.
• The enhanced reliability of RADISH contributes to making quantitative CEST imaging at UHF more feasible for clinical applications.