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NeuroSpin clinical platform

3T Clinical MRI


Leader: Alexis Amadon
(contact : alexis.amadon@cea.fr)

Published on 3 August 2017
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Figure 1: 3T Magnetom Prisma Fit MRI (Siemens Healthcare, Erlangen, Germany) with a table of its principles specifications.​

Main features

Operating frequency ​123 MHz​
Magnet inner diameter​​60 cm
B0 shielding​active
​Gradients strength28 mT/m​
Gradients​​ slewrate​200 (T/m)/s

​At NeuroSpin, we have a Magnetom Prisma Fit imager from Siemens Healthcare (Figure 1). This system is equipped with a whole-body gradient tunnel going up to 80 mT/m, a whole-body transmit RF coil, and head/neck phased-array coils going up to 64 receive elements distributed around the subject (Figure 2). By default, we suggest using the 64-channel coil for an optimal signal-to-noise ratio, but for difficult subjects (children, elderly, large heads), the use of a more spacious coil with 20 channels is recommended.

 
Figure 2: Head Neck 64 channel coil array manufactured.​

The current user interface of our Prisma Fit is Syngo MR, in its VE-11 version. Besides the vendor’s traditional acquisition sequences, other sequences are available for spectroscopy, perfusion MRI (ASL sequence), static and RF field mapping (particularly for quantitative MRI and relaxometry), or simultaneous-multi-slice Echo-Planar imaging. The image reconstruction from the latter sequence is performed on a dedicated GPU-based server to avoid dead time between exams. The details of available sequences is given on NeuroSpin’s wiki.

The exams on our 3T almost all have recourse to functional MRI (fMRI) and come under three types of research protocols:

​Methodology protocols (on healthy volunteers): they aim at improving imaging techniques and data processing to obtain richer information on the human brain. For instance, one project compares the sensitivity to detect cerebral activations with ASL (perfusion measurement) and BOLD (blood oxygen level) sequences during motor tasks. Other projects analyze the potential of diffusion MRI for fMRI or for iron quantification in the brain.

  1. ​​Cognitive protocols (on healthy volunteers): they tend to decipher how the human brain works. In particular, they seek to localize with the finest resolution zones activated during language (syntax and semantics), reading, number processing, mathematical analysis, or neuron networks activated at rest or related to conscience. These neurocognitive exams are also performed on children of all ages in the framework of cerebral development studies.

  2. Clinical protocols (healthy volunteers and patients) may relate to children learning disorders (dyslexia, dyspraxia, dyscalculia…), neuropsychiatric pathologies (epilepsy, schizophrenia, autism…), or cerebral aging (longitudinal follow-up of elderly). These protocols encompass studies with pharmaceutical partners willing to test the impact of new medication, in particular on memory.

  3. For fMRI, there is a set of tools available for subject stimulation, be it visual (via video-projector) or auditory (headphones). As a feedback, the subject’s attention can be recorded with an eye-tracker or via press-buttons made available to him/her inside the scanner.

In most exams, diffusion MRI, one of NeuroSpin specialty, is generally acquired to allow tractography of white matter fibers, among other things. It constitutes a good complement to traditional anatomical imaging weighted by transverse or longitudinal relaxation time. Diffusion MRI can also be used as a source of functional or metabolic information.