Ultrahigh-field MRI whole-slice and localized RF field excitations using the same RF transmit array.

Area of Science:

• Medical Physics
• Magnetic Resonance Imaging
• Electromagnetism

Background:

• Ultra-high-field (UHF) magnetic resonance imaging (MRI) offers enhanced signal-to-noise ratio but faces challenges in achieving uniform and localized radio frequency (RF) field excitation.
• Existing RF coil technologies often require separate setups for whole-slice and localized excitation, limiting flexibility in UHF MRI protocols.

Purpose of the Study:

• To numerically implement and validate a multiport driving mechanism for a transverse electromagnetic (TEM) resonator/coil in UHF MRI.
• To demonstrate the capability of achieving both homogenous whole-slice and highly localized RF field excitation within the same slices using a single RF transmit array.

Main Methods:

• Numerical implementation of a multiport driving mechanism based on electromagnetic and phased array antenna theories.
• Full-wave modeling of a standard TEM resonator/coil loaded with a high-resolution, 18-tissue human head mesh at 7 Tesla (7 T).
• Simulation of RF field excitation patterns for both homogenous whole-slice and localized targeting.

Main Results:

• The proposed multiport driving mechanism successfully achieved homogenous whole-slice RF excitation across axial, sagittal, and coronal planes within the human head model.
• The same RF transmit array was also capable of producing highly localized RF field excitation within specific regions of interest in the same slices.
• Numerical simulations confirmed the feasibility of dual-mode RF excitation (homogenous and localized) at 7 T (298 MHz for proton imaging).

Conclusions:

• A novel multiport driving mechanism enables flexible RF field control in UHF MRI, allowing for both uniform and localized excitation with a single RF coil.
• This approach, grounded in electromagnetic principles, enhances the versatility of standard TEM resonators for advanced imaging applications at 7 T.
• The findings pave the way for improved imaging sequences and diagnostic capabilities in UHF MRI of the human head.