Scanners

3.0 Tesla MR Imaging Suite

BIAC's 3.0 Tesla scanner is a research-dedicated GE Signa EXCITE HD system that uses an actively shielded magnet design to restrict fringe magnetic fields. This scanner is equipped with high-power 40-mT/m gradients at 150 T/m/s slew rate that enables single-shot echo-planar and spiral imaging at 64 x 64 and 128 x 128 matrices. The 3.0 T has an eight channel head coil for parallel imaging at high bandwidth up to 1MHz, in addition to the volume birdcage head coil. The high sensitivity of surface coil arrays can thus be applied to functional MRI without sacrificing whole-volume coverage. In addition, it uses broadband transmission to enable multiple frequency excitation schemes important for multi-nuclei imaging and spectroscopy experiments. To ensure high homogeneity critical for fMRI experiments at high field, the 3.0 T scanner is equipped with high order room-temperature resistive shimming coils in addition to the super-conducting shimming coils.

The scanner is controlled by a Linux workstation, which is connected via an exclusive high-speed BIT 3 network interface. This second system hosts GE's Advanced Development Workstation environment and is used for real-time acquisition and display of reconstructed images. A MRI-compatible physiological monitoring system (In-Vivo Research) provides continuous measurement of ECG, end-tidal CO2, respiration, and non-invasive blood pressure. Visual stimuli are displayed via computer projector (NEC) and a custom throw lens (Buhl Optical) on a screen within the scanner bore. Audio stimuli are presented using MR-compatible headphones (Resonance Technologies). Somatosensory stimuli are delivered using a constant-current stimulator (Grass Electronics). Subject responses are obtained from a Resonance Technology fiber optic response box and/or joystick. Custom software is used for physiological and artifact monitoring and for real-time data analysis.

Several experimental control packages are used, including E-Prime, Presentation, the Psychophysics Toolbox for MATLAB, and the CIGAL and fScan programming environments developed by Dr. Jim Voyvodic at BIAC.

4.0 Tesla MR Imaging Suite

The 4.0 Tesla scanner is a passively shielded GE LX NVi system. Like the 3.0 T scanner, it is equipped with a high power 41-mT/m gradient system and a fast, 1MHz sampling frequency receiver that enable single-shot echo-planar and spiral imaging at 64 x 64 and 128 x 128 matrices. Similarly, it uses broadband transmission to enable multiple frequency excitation schemes important for multi-nuclei imaging and spectroscopy experiments.

To ensure high homogeneity critical for fMRI experiments at high field, the 4.0 T scanner is equipped with high order room-temperature resistive shimming coils in addition to the super-conducting shimming coils. An automatic shimming routine with flexible manual control is used to control the shimming coils. A high-pass birdcage coil is used to achieve uniform excitation and reception at 4.0 T. A thin copper mesh is used along with the coil to achieve electromagnetic shielding without causing severe eddy current-induced artifacts.

The scanner is controlled by a Silicon Graphics Octane workstation. Visual stimuli are displayed via LCD goggles, while audio stimuli are presented using MR-compatible headphones (Resonance Technologies). Subject responses are obtained from a fiber optic response box and/or joystick. Custom software is used for physiological and artifact monitoring and for real-time data analysis. All experimental control software available on the 3.0 T scanner is also available for the 4.0 T scanner.

7.0 Tesla MR Imaging Suite

BIAC's 7.0 Tesla scanner is a Bruker BioSpec system with a 31 cm bore size and active shield to restrict fringe magnetic fields. This scanner is equipped with two separate gradient systems, one at 20 cm diameter with 200 mT/m strength, the other at 12 cm diameter and 400 mT/m strength for high resolution microscopic MR imaging. It comes with broadband and dual-channel transmission, four-channel parallel receivers, as well as assorted RF coils for different nuclei, including 1H, 13C, 19F, 31P, to allow versatile imaging and spectroscopy experiments to be carried out. To facilitate animal handling, specialized animal cradles are in place to rats and mice, with mounting points for surface coils, fixation points for the animal, water bed for temperature conditioning, provision for inhalation anesthesia, and physiological monitoring equipment. The scanner is controlled by a Linux workstation, installed with PARAVISION software to coordinate synchronized communication among various hardware components.

MRI Simulation Facilities

To acclimate patients to the MRI scanner experience, the BIAC has constructed an MRI simulator system using a decommissioned GE scanner. The system includes a mock MRI scanner, a goggle-based auditory and visual stimulus presentation and data recording system, a head-movement monitoring system, and two control computers. The MRI simulator looks, sounds, and feels just like a real MRI scanner. This system is used to introduce participants to the identical experimental procedures that they will experience in the actual scanner, and to train children to participate in functional neuroimaging studies. This is done to ensure participant comfort and data quality.

BIAC faculty have also installed a WhisperRoom™ sound-attenuating chamber within the MRI simulator suite. This chamber is used for testing experimental paradigms and for behavioral studies, and it contains an eye-tracking system (Applied Science Laboratories).