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.