3T MR System

The IRC operates a 3T Siemens Trio Total imaging matrix (Tim) whole-body MRI system (Siemens Medical Solutions, Erlangen, Germany) which is fully equipped for advanced brain imaging. This system has a short-bore (2 m) magnet, a fast gradient system that provides high-speed structural and functional imaging, and a 32-channel data acquisition system with 32 1-MHz receiver channels for parallel imaging. The gradient rise time (200 mT/m/ms), peak gradient strength (40 mT/m per axis), and duty cycle (100% using full gradient strength on all three axes) are the best specifications in the industry for whole-body systems. Multi-dimensional parallel imaging capabilities enable EPI acquisitions at higher temporal resolution and with less geometric distortion. Three multi-channel RF head coils are available: a new Siemens 32-channel brain coil that takes full advantage of the 32 receiver channels and provides the highest signal-to-noise ratio, a new 12-channel coil that provides excellent SNR while also providing more space between the head and the coil for headphones and goggles for enhanced auditory and visual presentation, and the original In-vivo, Inc. 8-channel head coil upgraded for the Trio Tim system to allow investigators to use the same coil for ongoing research studies.

The UC Davis IRC recently upgraded their 8-channel 3T Trio System with the Trio Tim system discussed above. This upgrade enables improvements in the brain imaging protocols originally developed on the Trio system. For EPI sequences used in fMRI, signal loss due to underlying B0 inhomogeneity, for example in the orbital frontal cortex (OFC), is greatly reduced by reducing the effective echo time (TE), echo spacing (ESP) and by increasing the k-space acquisition matrix size, using parallel imaging. Another benefit resulting from increased spatial and temporal SNR is reduced total exam time. Studies with children and patients with anxiety generally are higher quality when the time in the scanner is less. The gradients of the Trio Tim system create significantly less noise pressure than the gradients of the Trio system. Siemens reports that acoustic noise pressure from the gradient pulses in the Trio Tim system is just 10% of the noise pressure produced by the same gradient pulses in the Trio system. Many participants, particularly children and patients with anxiety disorders, complain about the acoustic noise of the scanner. Reduction in acoustic noise is expected to substantially increase the percentage of adults and children that are able to complete their scanning sessions.

Early experience with the Trio Tim system confirms that this upgraded system has significantly better performance compared to the original Trio system. Test images show the following improvements:

  1. Reduction in signal drift in EPI timeseries for fMRI,
  2. Increases in temporal SNR in EPI timeseries for fMRI,
  3. Increases in single image SNR for improved contrast in structural MRI,
  4. Decreases in image ghost intensity on EPI and diffusion weighted images,
  5. Reduction in image distortion caused by non-linear gradients.

These results are consistent with the experiences of University of Minnesota (Bryon Mueller, Kelvin Lim), University of Southern California (Jiancheng Zhuang), Northwestern University (Todd Parrish), and UC San Francisco (Vibhas Deshpande, PhD of Siemens Healthcare).

The MNS option provides spectroscopic imaging and spectral analysis of Na-23, P-31, C-13, O-17, Xe-129, Li-7, He-3 and others. The Siemens multinuclear spectroscopy analysis package performs water suppression, phase correction, apodization, zero filling, spectral transformation, base line correction, automatic and manual phase correction, curve fitting and peak labeling, and computation of relative metabolite concentration, with customizable settings.