An Adjustable-Length Dipole Using Forced-Current Excitation for 7T MR

Area of Science:

• Magnetic Resonance Imaging (MRI)
• Radiofrequency (RF) Engineering
• Medical Imaging Technology

Background:

• Ultrahigh field (UHF) MRI, particularly for body and spine imaging, faces challenges with large field-of-view (FOV) requirements.
• RF transmission in UHF MRI is difficult due to demands on the length and depth of the B1+ field.
• Traditional long dipole antennas for continuous current distribution suffer from poor B1+ field falloff at the ends, impacting B1+/sqrt(SARmax) efficiency.

Purpose of the Study:

• To develop an improved RF transmission solution for UHF body and spine MRI.
• To enhance B1+ field uniformity and efficiency across different field-of-view (FOV) requirements.
• To present a novel segmented element design with forced-current excitation and a switching circuit.

Main Methods:

• Exploration of different element types and arrangements for RF transmission antennas.
• Design and implementation of a segmented dipole antenna utilizing forced-current excitation and a switching circuit.
• Benchtop and phantom testing of the switchable segmented dipole on a 7T whole-body MRI scanner.

Main Results:

• The segmented dipole design allows for flexible FOV switching and power distribution without additional amplifiers.
• The switchable mode dipole demonstrated a large FOV capability in its 'long mode'.
• Improved B1+/sqrt(SARmax) efficiency was achieved in a smaller FOV using the 'short mode'.

Conclusions:

• The proposed segmented dipole design offers a viable solution for overcoming RF transmission challenges in UHF body MRI.
• The switchable nature of the antenna provides adaptability for different imaging scenarios, enhancing both FOV and efficiency.
• This technology has the potential to improve the quality and applicability of UHF MRI for clinical diagnostics.