Non-metallic earbuds for auditory stimuli in MRI scanners - Project Summary/Abstract
Magnetic resonance imaging (MRI) has led to significant advances in the study of brain structure and
function. In studies of auditory perception and speech-related functions, the earphones used to deliver
stimuli in an MR scanner must not contain ferrous or magnetic metals due to the scanner's immense
magnetic field strength. In addition, the strong magnetic gradients and radio frequency energy used during a
scan can induce electric currents even in non-ferrous metal components, which must be carefully designed
to prevent excessive heating. Finally, any metallic structures can interfere with the imaging process, leading
to artifacts in the image. New imaging protocols to improve spatial resolution and temporal sensitivity can
increase energy deposition and heating in materials with magnetic susceptibility that were unaffected under
older imaging protocols. While most of the world's MR scanners use magnetic field strengths of 3 Tesla (T)
or less, the demand for higher imaging resolution drives demand for scanners with greater field strength,
making them a fast-growing sector of the scanner market. Increasingly, research centers are installing
human MR systems capable of static field strengths of 7T or higher, with about 100 such scanners installed
worldwide; a handful of 9T scanners are already in operation, and a massive 11.7T human system is online
at the Neurospin facility in France. For animal research, small-bore scanners with ultra-high fields are in
use. The growing presence of ultra-high field systems will require earphones that can provide research-
grade auditory stimuli without compromising safety or introducing image distortions. There is no
commercially available audio driver that is free of metallic components. Even our company's current
earbuds—mostly used in 1.5T and 3T scanners—include some (non-ferrous) metallic components as
mechanical sound amplifiers and electrical conductors. Successive generations of earbud models have
progressively reduced metallic components to minimize imaging artifacts and heating, but this iterative
material reduction is no longer sufficient. Instead, a fundamentally new approach is required—we propose
to build earbuds entirely free of metallic components. For this, we will develop a novel audio driver that
does not require metal parts to deliver research-quality audio stimuli. The design will then be tested in 7T
and 11.7T scanners.
