A small, low-cost Magnetically Shielded Room

Magnetoencephalography (MEG) and other biomagnetic recordings are generally made inside a magnetically shielded room (MSR) to suppress environmental magnetic noise. Traditional MSRs built for superconducting MEG systems are very large (for example 3.9 x 2.9 x 2.3 m) and cost around $1M.

Optical MEG systems, such as QZFM based MEG, can be very compact and do not require such a large MSR. Magnetic Shields Limited (MSL), UK, has now commercialized a smaller yet comfortable room suitable for most MEG paradigms with optical sensors. The smaller room costs roughly $150k and has internal dimensions of 1.3×1.3×2 m.

The small ‘phone-booth’ style room comes with all essential features such as LED lights, airflow, and access holes for MEG system cabling. The room can also be outfitted with a projection system for visual and other stimuli. We are working with MSL to further customize the room with QZFM specific MEG requirements such as a residual field cancellation system and sensor position and localization system.

Photos of MSL’s small MSR (from outside) installed at UT Southwestern Medical Center. Courtesy: Elizabeth Davenport

Inside the small MSR at UT

Type: 2 layer Mumetal + 1 layer copper
Dimensions: 1.3 x 1.3 x 2 m (internal); 1.6 x 1.6 x 2.4 m (external)
2,200 kg
Shielding factor: For the above room: 0.01 Hz – 903; 0.1 Hz – 989; 1 Hz – 3914;10 Hz – 7500; 100 Hz – 3661 (Measured by MSL)
Residual field: < 3nT (typical 1-2 nT or lower) in the center of the room; after degaussing  {measured with QZFM}
Gradient field:  dBx/dx = 1.7; dBy/dx = 1; dBz/dx = 1; dBx/dy =1.3; dBy/dy = 3; dBz /dy = 1.7; dBx/dz = 0.4; dBy/dz = 1.7;  dBz/dz = 0.6 (units: nT/fT; z-axis is along the height of the room; measured over one foot in the center of the room; number can vary over time and after degaussing)
Noise floor:
<15 fT/sqrt[Hz]  (more precise measurements and noise floor to be included soon)   

Overall conclusion: This room is an excellent, low-cost choice for a QZFM based MEG system.

MSL brochure for OPM-MSR