Accelerated 3D multi-channel B 1 + mapping at 7 T for the brain and heart

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Biophysics
• Medical Imaging Technology

Background:

• Accurate transmit field (B1) mapping is crucial for parallel transmit (pTx) applications at 7 Tesla (7T) MRI.
• Current B1 mapping techniques can be time-consuming, limiting their clinical applicability, especially for dynamic applications like cardiac imaging.

Purpose of the Study:

• To develop and validate a rapid method for acquiring volumetric multi-channel B1 maps.
• To achieve acquisition times of under 14 seconds for whole-brain and 23 heartbeats for whole-heart imaging at 7T.

Main Methods:

• Combined three techniques: transmit low rank (TxLR), absolute B1 mapping (Sandwich), and B1 time-interleaved acquisition of modes (B1TIAMO).
• Evaluated using in silico simulations, retrospective undersampling of a B1 map library, and prospective Cartesian undersampled acquisitions in phantoms and human subjects (brain and heart) at 7T.

Main Results:

• Demonstrated acquisition of volumetric multi-channel B1 maps with acceleration factors of 4.
• Achieved whole-heart imaging within 23 heartbeats, a previously unattainable speed.
• Reported root-mean-square (RMS) errors of 4.2° for cardiac and 1.9° for brain B1 maps compared to fully sampled data.

Conclusions:

• The proposed method offers a fast and accurate solution for parallel transmit calibration in the brain at 7T.
• It shows significant promise as a viable technique for parallel transmit calibration in cardiac imaging.