Overview of the BIAC 4T Scanner The 4 Tesla scanner is a passively shielded GE LX NVi system. Like the 3 T scanner, it is equipped with a high power 41-mT/m gradient system and four-channel parallel receivers at 1MHz sampling frequency that enable single-shot echo-planar and spiral imaging. It uses broadband transmission to enable multiple frequency excitation schemes, which are important for multi-nuclei imaging and spectroscopy experiments. To ensure high homogeneity critical for fMRI experiments at high field, the 4 T scanner is equipped with high-order room-temperature resistive shimming coils in addition to the super-conducting shimming coils.
The 4T scanner uses several main types of structural imaging techniques: T1 Imaging, T2-weighted coplanar and 2D Proton Density.
Functional sequences are designed to map out patterns of activity at different regions of the brain. BIAC built functional sequences upon the spiral waveform originated from Stanford (Dr. Gary Glover) and echo-planar waveform originated from MCW (Dr. Eric Wong currently at UCSD). Spiral imaging is a technique for fast image acquisition that uses sinusoidally changing gradients to trace a corkscrew trajectory through k-space. K-space is a notation scheme used to describe MRI data. Echo-planar imaging (EPI), is a technique that allows for the collection of an entire two-dimensional image by changing spatial gradients rapidly following a single electromagnetic pulse from a transmitter coil.
Each of these techniques has its advantages and its disadvantages: