METRIC

The METRIC (MEthodology and insTrumentation for human and non-human pRimate ultra-hIgh field magnetiC resonance imaging – Méthodologie Pour la Recherche en Imagerie Clinique) laboratory is part of the BAOBAB (CEA, CNRS, Paris-Saclay University) Unit in the NeuroSpin department.

General view on METRIC: The METRIC laboratory dedicates itself to leveraging the potential of ultra-high field MRI scanners by tackling fundamental physics problems: RF field inhomogeneity, static field (B0) inhomogeneity, SAR and temperature control, motion, field fluctuations, gradient-magnet interactions and fast and efficient MR acquisitions (anatomical, functional). We thrive on the challenge of making MRI at ultra-high field powerful and accessible to the neuroscience and medical communities to address important questions related to neurodegenerative diseases, psychiatry and cognitive sciences.

Teams

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ACQUISITION:

Leader:

The acquisition team works on MR methodology aimed at leveraging the potential of Ultra-High Field MR scanners. This includes many challenges such as parallel transmission, sequence programming (fMRI, anatomical, quality control), non-cartesian acquisitions, field monitoring, SAR/temperature control and motion correction. Since the birth of NeuroSpin, many of these problems have been explored at 7T to prepare for the investigations at the unprecedented field strength of 11.7T, where emphasis is now put. The acquisition team works together with the instrumentation team to make the Iseult 11.7T project a success by providing the tools needed to extract unique data on the functions and anatomy of the pathological and healthy human brain.

INSTRUMENTATION:

Leader:

Our team conducts hardware developments for MRI instrumentation at Ultra-High-Field (UHF). Primarily we design and build RF head coils suited for NeuroSpin needs, mainly for humans but also for animals for fMRI studies. We put a strong emphasis on parallel transmit coils and receive arrays for our clinical 7T and 11.7T scanners. We also develop original multi-coil arrays dedicated to human and NHP brain shimming.

Gallery

SCOTCH shim array

EPI imaging is improved thanks to the SCOTCH prototype - in this example, signal is recovered in the ventro-medial prefrontal cortex. Distortions along the phase-encode dimension are also reduced (EPI acceleration - CAIPIRINHA 2x2 in both images). Bottom left - first two layers of our 48-coil prototype. Bottom right - the three layers surround our home-made 8-Tx/32-Rx RF coil.

MRI at 11.7T

Top - The first in-vivo brain images at 11.7T were acquired with this 8-Tx/32-Rx Iseult coil composed of 15 dipoles, 16 loops and a patch. Bottom - An original honeycomb-shaped High Impedance Coil array was built on a neoprene cap to target Temporal Lobes fMRI at 11.7 T. Bottom right - SNR improvement over the temporal lobes thanks to this array.

Sparkling

Iterative optimization of the Sparkling sampling for a 2D GRE. The final sampling fulfills Compressed Sensing criteria and is compatible with hardware limits (gradient amplitude and slew rate). Such an acquisition is highly accelerated compared to the fully sampled Cartesian acquisition (courtesy C. Lazarus, CEA BAOBAB & INRIA MIND)

SAR

Measuring non-invasively the temperature rise occurring in cerebral MR exams.

Parallel transmission technology

With 7 Tesla MRI (300 MHz), the image contrast (here we present 3D T2 weighted images with and without suppression of the fluid’s signal) is often impacted by the non-uniformity of the transmitted RF field. With a single transmit architecture (sTX, left image), this problem is difficult to mitigate, even with the use of high power adiabatic RF pulses for spin inversion. The parallel transmission technology (pTX), coupled with a pulse design strategy involving constrained non-convex (numerical) optimizations, can solve this problem while maintaining the RF energy deposition in the body low. The presented pTX pulses make use of parameterization-free RF and magnetic field gradient waveforms obtained by application of a GRAPE (Gradient Ascent Pulse Engineering) algorithm.

In vivo imaging at high resolution at 11.7T

Boulant, N., Mauconduit, F., Gras, V. et al. In vivo imaging of the human brain with the Iseult 11.7-T MRI scanner. Nat Methods 21, 2013–2016 (2024).