Visual and Auditory Presentation Systems
Visual System: The visual projection system for the Siemens Trio 3T scanner has been designed to present high resolution in-bore images with tightly controlled timing necessary for recording event-related potentials (ERP) simultaneously with fMRI data acquisition. The heart of the system is the digital, Epson PowerLite Pro G6470WU, 3-LCD projector. The lens assembly for projection within the bore of the magnet consists of an Epson Long Throw Zoom Lens (ELPLL06). The lens can project a 1920x1200 pixel image on the rear projection screen. The projector and lens assembly is vibration-stabilized by a bench top vibration isolation platform from Minus K Technology. The whole assembly is located on a sturdy height-adjustable table from Baker Industries. The projector is located outside of the MRI scan room and projects into the magnet room though a dedicated wave-guide.
Auditory System: Auditory stimuli are presented during scanning via two high-fidelity systems designed for the MR environment: MR confon GmbH Headphones and Sensimetric model S14 Insert Earphones. The Confon headphones contain electrodynamic transducers for a broad, flat, frequency response and use construction-grade Peltor earmuffs for passive damping of gradient noise. By using electrodynamic rather than pneumatic transduction, this system produces sound quality comparable to a home stereo, with 88dB signal-to-noise ratio (SNR) and high channel separation. During a functional MRI scanning session, sounds can be presented at detection-threshold levels between "sparse" acquisitions or at conversational levels (approx. 75-80 dB) during continuous scanning. The S14 Insert Earphones are used in head coils with insufficient space for earmuffs. They use piezo-electric transducers and Comply foam canal tips to achieve both good frequency response and high attenuation of scanner noise.
Eye-Movement Monitoring Equipment
For the 3T MRI system, the eye-tracking system is the Applied Science Laboratories (ASL, Inc. Bedford, MA) Model 504 with long-range optics. It includes the series 5000 control unit with long-range remote optics and multi-speed camera with telephoto lens needed for the MRI environment, two 9-inch black and white monitors, one 5-inch LCD monitor for the MRI scan room, and the EYEPOS package for real-time conversion of the eye movements into numerical pupil position and diameter data streams. The system includes a custom PC with two frame grabbers, one capable of supporting 240 Hz eye imaging, and the other capable of recording to disk the entire image of the eye during the MRI scan.
Stimulus Presentation and Button Response Recording Equipment
On both the 3T and 1.5T MRI systems, investigators use Windows workstations to deliver visual paradigms. Stimulus presentation and button-press response acquisition is controlled by the e-Prime (Psychology Software Tools, Inc.) or Presentation software system (Neurobehavioral Systems, Inc.). Subjects respond with button presses obtained with specially constructed 5-finger MR-compatible fiber-optic devices held in both left and right hands (Photon Control Inc.). The metal-free keypads are connected via fiber optic cable to an optoelectronic controller unit.
Physiological Monitoring and System Diagnostics Equipment
Two computers, one dedicated to each MRI system, provide for acquisition of MRI system events, as well as acquisition of physiological waveforms from the subject being scanned. Each computer has three data acquisition boards and the National Instruments Labview Professional Development software for creating virtual instruments to automate the acquisition of diagnostic or physiological data. These computers have been programmed using Labview to collect and analyze waveforms of the MRI system events during a pulse sequence simultaneously with cardiac, respiratory, galvanic skin response, and other physiological signals from the subject. For the 3T system, the Siemens Measurement Acquisition and Test Environment (MATE) software tool, which is built into the MRI system, also provides detection of heart rate, breathing, and peripheral pulse with 10 to 20 ms resolution.
Mock MRI System
The simulated environment of an MRI system, consisting of a wood mock-up of an MRI system, non-functioning RF coils, and including a built-in speaker system for playing back recordings of the pulse sequence sounds (purchased in 2001 from Psychology Software Tools, Inc.) is located in Room 1121 of the IRC. This environment also includes the visual and auditory stimulus presentation systems that are used in the actual MRI environment. Using the mock MRI system, potential subjects for the MRI scanning sessions can be acclimated to and trained for fMRI studies. A headphone-mounted motion detector trains subjects to become aware of their own head motion, which must be minimized during an actual scan.