3.0 T Siemens Prisma human MRI scanner

 

Description of the new Prisma coming soon!

 

The CBS Neuroimaging Center operates a 3.0 T Siemens Tim Trio whole-body MRI system (Siemens Medical Solutions, Erlangen, Germany) which is fully equipped for advanced brain imaging. This scanner has a short-bore (2m) 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 with acceleration factors up to four-fold. The gradient rise time (200 mT/m/ms), peak gradient strength (40 mT/m per axis), and duty cycle are the best specifications in the industry for whole-body systems. Multi-dimensional parallel imaging capabilities enable echo-planar imaging (EPI) acquisitions at higher temporal resolution and with less geometric distortion. Two multi-channel RF head coils are available. The Siemens 32-channel head coil takes full advantage of the 32 receiver channel architecture, and provides the highest signal-to-noise ratio (SNR), especially on the periphery of the brain. A Siemens 12-channel (matrix) coil provides excellent SNR while also providing more space between the head and the coil for headphones and goggles for enhanced auditory and visual presentation. The matrix coil can be used in 4, 8 or 12-channel modes for added flexibility.

The state-of-the-art hardware of the Tim Trio system, fully supported by Siemens Medical Solutions, allows the latest advanced brain imaging protocols to be performed in a routine manner, and makes the imaging sessions less stressful for anxious subjects. For example, the EPI sequences used in fMRI suffer signal loss due to underlying magnetic field inhomogeneity - especially in regions like the orbital frontal cortex. This can be minimized 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 Tim Trio system create significantly less acoustic noise than those of earlier scanners. Reduction in acoustic noise is expected to substantially increase the percentage of adults and children that are able to complete their scanning sessions.

The performance of the Tim Trio system is monitored weekly for gradient linearity performance, and daily to ensure:
- minimal signal drift in EPI timeseries for fMRI,
- high temporal SNR in EPI timeseries for fMRI,
- consistent single image SNR for improved functional and structural MRI,
- minimal/consistent image ghost intensity on EPI and diffusion weighted images,
- lack of RF interference from other equipment that could cause image artifacts,
- lack of spiking due to gradient connections.
More details on the daily EPI timeseries stability/SNR, RF noise and spike checks and the weekly gradient linearity performance are available on additional pages.

In addition, we have begun using the fBIRN agar phantom on a 1-2 weekly basis to also document EPI time series stability, drift and temporal SNR in a manner consistent with other fBIRN sites. Results will appear soon.