https://phys.org/news/2018-10-high-resolution-mri.html

"When frequencies become higher, wavelengths become shorter, and your magnetic field loses uniformity," says Elena Semouchkina, an associate professor of electrical and computer engineering at Michigan Technological University. "Uniformity is important for high-resolution images, so we proposed a new approach to developing these probes."

A Common Design, Tuned with Optics