Improved encoding strategy for CPMG-based Bloch-Siegert B(1)(+) mapping.

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Quantitative MRI Techniques
• Pulse Sequence Development

Background:

• Bloch-Siegert (BS) based B(1+) mapping encodes quantitative B(1+) information using off-resonant pulses.
• Existing BS methods (BS-SE, BS-FLASH) have been extended to Carr, Purcell, Meiboom, Gill (CPMG)-based sequences (BS-CPMG-TSE, BS-CPMG-MSE).
• Current BS-CPMG methods require two separate MRI experiments for B(1+) map calculation.

Purpose of the Study:

• To develop a modified encoding strategy for CPMG BS-based methods to enable simultaneous B(1+) mapping in a single experiment.
• To overcome the limitation of requiring two separate MRI experiments for B(1+) map calculation.
• To investigate a technique for simultaneous B(1+) and T(2) mapping and single-shot B(1+) mapping.

Main Methods:

• A modified encoding strategy using a "bipolar" off-resonant BS pulse before the refocusing pulse train was investigated.
• This strategy encodes phase information into different echo images within a single echo train.
• The method was applied to BS-CPMG-MSE for simultaneous B(1+), M(0), and T(2) mapping and to turbo-spin echo imaging for single-shot B(1+) mapping.

Main Results:

• Simultaneous B(1+) and T(2) mapping was achieved in a single BS-CPMG-MSE experiment.
• Single-shot B(1+) mapping was enabled using the modified method applied to turbo-spin echo imaging.
• The presented modification intrinsically minimizes phase-based image artifacts in BS-CPMG-TSE experiments.

Conclusions:

• The developed modified encoding strategy significantly streamlines the process of quantitative B(1+) mapping.
• This technique allows for simultaneous B(1+) and T(2) mapping, as well as single-shot B(1+) mapping, in a single MRI experiment.
• The method offers potential for reduced scan times and improved image quality by minimizing artifacts in BS-CPMG-TSE.