Parallel transmit excitation at 1.5 T based on the minimization of a driving function for device heating

Area of Science:

• Medical Physics
• Biomedical Engineering
• Radiology

Background:

• Radiofrequency (RF) induced heating in long conductors is a significant safety concern in interventional Magnetic Resonance Imaging (iMRI).
• Minimizing electromagnetic field coupling and subsequent heating is crucial for safe iMRI procedures.

Purpose of the Study:

• To introduce a rapid method for reducing RF E-field coupling and heating in long conductors within an iMRI setting.
• To enhance the safety of iMRI by mitigating device heating.

Main Methods:

• Defined a device heating function (W) based on E-field integration and quasistatic approximation.
• Dynamically adjusted phases of four transmit channels in a 1.5 T MRI scanner.
• Measured RF induced heating using fiber-optic temperature sensing in phantom and in vivo experiments.
• Developed and tested a constrained minimization algorithm for phase and amplitude control.
• Validated the method using finite-difference time-domain (FDTD) simulations.

Main Results:

• Achieved a 92% reduction in device tip heating in phantom experiments by optimizing parallel transmit excitation.
• Demonstrated up to 90% heating reduction using a constrained minimization algorithm with independent amplitude control.
• The optimization computation required only 12 seconds on a standard CPU.
• FDTD simulations confirmed the quasistatic approach's validity and showed trends consistent with measured heating.
• Successfully reduced guidewire heating in vivo during iMRI procedures.

Conclusions:

• Additional degrees of freedom in parallel transmission systems effectively control RF induced heating in long conductors.
• A novel, rapid constrained optimization approach significantly improves RF safety in iMRI protocols.
• The presented method offers a practical solution for enhancing safety during interventional MRI procedures.