3T noise levels may require solution from out of the blue

March 21, 2005

Headphones developed for use on jet aircraft flight lines may be just the ticket for the imaging industry’s fledgling benchmark of high-performance MR scanning.

Headphones developed for use on jet aircraft flight lines may be just the ticket for the imaging industry's fledgling benchmark of high-performance MR scanning.

Noise levels in 3T scanners can reach up to 130 dB, exceeding the safety limit of 80 dB for chronic noise exposure. The din threatens interventional radiologists, technologists, and other workers in the scanner's range with permanent hearing loss.

Standard foam headsets or earplugs have a limited effect. Aviation headphones can cut the decibel level in half, using active noise-cancellation technology. But there's a problem. The technology used on the tarmac is not MR-compatible.

Enter Phone-Or. The Israeli company has reengineered the noise-cancellation technology to work in the MR suite. The modified headgear includes an earpiece and a microphone that beams identical but polarized audio signals, neutralizing incoming acoustic waves from the scanner. The technology is called opto-acoustical active noise control, because both the microphone and the earpiece work on the principle of light.

The device has been tested using an MR simulator with its maximal acoustic output set near 590 Hz. The device was able to attenuate the fundamental resonance - acoustic noise inside the scanner - by 40 to 50 dB, with an overall resonance reduction of 20 to 30 dB. Noise reduction did not include the contribution made from the passive ear protection component of the device.

The company's move into ear protection is a bit of a diversion for Phone-Or, which has focused more on recording rather than damping sound waves. Its microphones use optical technology to sense changes in light caused by sounds reverberating from a membrane. Phone-Or makes several such microphones for use in MR scanners.