MRI shielded mocap
A Qualisys MRI system is installed at New York University (NYU) in the Brain Imaging Center, which adds a third dimension to the functional magnetic resonance imaging (fMRI) research at NYU.
The system is primarily used by researchers from the Curtis Lab, headed by Clayton Curtis, Ph.D. The Curtis Lab, part of NYU’s department of psychology, uses functional magnetic resonance imaging (fMRI) and eye-tracking to study how incoming sensory information is used, along with internal goals, to select the best choice of action. fMRI is similar to clinical MRI, but instead of making pictures of the anatomy of the brain, fMRI researchers measure and characterize brain function. The new, real-time motion capture system will add a third dimension to NYU’s research by making biomechanical data, collected from tiny, retro-reflective markers attached to the subject’s hands, available synchronously to MRI and eye tracking.
Equipment used in conjunction with an MRI scanner may not cause any electromagnetic interference (EMI) as that can result in artifacts and loss in the MRI image quality. Qualisys MRI is modified to be completely shielded – in effect creating a Faraday cage. Cables are shielded too and the camera power supply is placed outside of the scanner room and fed through a filter panel. This means that any emitted noise from the supply will not interfere with the scanner.
Although most modern MRI scanners have a very rapid drop off in magnetic field strength close to the scanner itself, materials used inside an MRI room should be non-metallic to the extent possible. Qualisys MRI is purpose-built and differs from a regular motion capture camera by having had most of its metallic parts replaced. The housing is made out of die-cast aluminum. Steel fasteners are replaced by brass screws and the calibration L-frame and wand are completely non-metallic.
Recent noise tests performed by a user at the Behavioral Brain Sciences Center at the University of Birmingham, confirm that the system really has little or no effect on scanner performance. Qualisys MRI camera running at 250 Hz showed a SNR (signal-to-noise-ratio) figure of 106. Average SNR is around 105 with about +/- 10 variations. Images were also visually inspected for artifacts and they all appeared clean.
The Qualisys motion capture system allows us to examine the neuroscience of the human motor system under naturalistic conditions in a more quantitative way than ever beforeTrenton Jerde