High-resolution MRI machines can achieve greater resolution when radio probes are changed from coils to antennas, reported researchers in a recent study published in Transactions on Microwave Theory and Techniques.
Led by Elena Semouchkina, with Michigan Technological University in Houghton, Michigan, the team found radio frequency probes with structures based off microstrip patch antennas (MPA) increased MRI resolution compared to traditional surface coils.
"When frequencies become higher, wavelengths become shorter, and your magnetic field loses uniformity," said Semouchkina in a Michigan Tech story. "Uniformity is important for high resolution images, so we proposed a new approach to developing these probes."
Conventional coils have frequency limits—if too high, they cannot create the uniformity at the volume needed. MPAs allow waves to oscillate in the area formed between the patch and ground plane electrodes. Current in the patch electrode and oscillating magnetic fields surrounding the patch provide an even and strong magnetic field, the authors added. Semouchkina et al. also found their discovery to be somewhat simple and cheap.
"While the complexity of birdcage coils increases with the increase in operation frequency, patch-based probes can provide quality performance in the higher microwave range while still having a relatively simple structure," Semouchkina said.
Due to the damage high-frequency radio waves inflict on humans, the study was only performed in high frequency machines—unlike those used in hospitals. However, frequencies up to 21.1 Teslas can be used to test animal models and tissue samples, the team noted.