Hiroumi Kitajima, Presenter: Nothing to Disclose

Kelly Young, Abstract Co-Author: Nothing to Disclose

BOBBIE BURROW, Abstract Co-Author: Nothing to Disclose

John N. Oshinski PhD, Abstract Co-Author: Nothing to Disclose

Sherif Gamal Nour MD, Abstract Co-Author: Nothing to Disclose

Patients and support staff in the magnetic resonance (MR) scan room experience extended exposure to MR acoustic noise during interventional magnetic resonance imaging (MRI). Therefore, additional noise attenuation methods must be employed and levels must be monitored during procedures for proper safety.

 All subjects were scanned on a Siemens Espree 1.5 T MRI scanner (Siemens Medical Solutions, Erlangen, Germany) with a 6-channel body matrix coil and a 24-channel spine matrix coil. A combination of tri-plane 2D balanced gradient recalled echo (GRE), spoiled GRE, and fast spin echo (FSE), and 3D GRE were used for visualization and navigation. A Quest Noise Pro DLX Dosimeter was positioned outside the MR scan room and the probe was placed inside for noise monitoring. Samples were acquired each minute throughout the duration of the exam. Ear plugs with a noise reduction rating (NRR) of 28 or communication earmuffs with a signal-to-noise ratio (SNR) of 14 were used by patients and support staff.  

Occupational Safety and Health Administration (OSHA) mandates the 8-hour action level and exposure level at 85 and 90 dB, respectively. The peak exposure limit is 140 dB. During a venous sclerotherapy exam and a kidney biopsy procedure, the 8-hour exposure levels were 85.4 and 81.7 dB, the peak exposure levels were 116.4 and 117.3 dB, and scan durations were 205 and 85 minutes, respectively. Since a routine diagnostic exam typically last 30-45 min, interventional MRI subjects patients and support staff to significantly extended acoustic noise levels.

The acoustic noise caused by Lorenz forces between the gradient and static magnetic field contribute to levels that approach safety limits. The Food and Drug Administration (FDA) and International Electrotechnical Commission (IEC) require a noise warning at 99 dB and specify hearing damage at 140 dB, but the OSHA provides 8-hour exposure levels at lower levels. As interventional MRI becomes more widespread through various new applications, these extended exposure levels must be considered.

Previous studies investigating acoustics during MRI have focused on considerations during a diagnostic scan. Thus, the safety of longer studies in interventional MRI have not been thoroughly explored.

Kitajima, H, Young, K, BURROW, B, Oshinski, J, Nour, S, Acoustic Noise During Interventional MRI Approaches Mandated 8-Hour Exposure Limits.  Radiological Society of North America 2012 Scientific Assembly and Annual Meeting, November 25 - November 30, 2012 ,Chicago IL. http://archive.rsna.org/2012/12029013.html