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Scientific result | Europe | Simulation ＆ modelling | MRI
NeuroSpin researchers propose a new version of their compressed MRI acquisition algorithm, SPARKLING, extended to 3D imaging. Their method reduces acquisition time by a factor of 20 for T2*-weighted scans without compromising image quality.
The advent of very high field MRI allows us to obtain images of the human body, and in particular the brain, at previously unattained spatial resolutions. But these resolutions are achieved at the cost of a considerably long acquisition time. To overcome this constraint, researchers from the MIND team (ex-PARIETAL, NeuroSpin) and BAOBAB (NeuroSpin) have already developed a method based on a mathematical process, compressed sensing, to reconstruct complete high-resolution images from a minimal acquisition. The method has also benefited from the collaboration of this team with the Cosmostat laboratory (CEA-Irfu) during the COSMIC project.
SPARKLING, as it is called, has already shown its full potential on two-dimensional imaging (High-resolution MRI: how not to spend hours?). Researchers have extended the method to 3D imaging, used to achieve high resolution in the three directions of space. 3D imaging is still not widely used in clinical practice, yet it offers a gain in signal-to-noise ratio that is particularly useful for high-resolution imaging, or heteronuclear imaging (e.g. sodium imaging) at ultra-high magnetic field (7 Tesla, 7 T). But easier said than done: the data acquisition space of 3D imaging is itself more complex (a Fourier volume) than that of 2D imaging (a Fourier plane).
now, to do 3D MRI, SPARKLING proceeded with a sub-sampling in two dimensions,
plane by plane, and then stacked the planes, thus limiting the acceleration
according to the third dimension; the computation times to reconstitute the 3D
image were long. In a paper published in IEEE Transactions on Medical Imaging,
the same collaboration between MIND and BAOBAB has established a new algorithm
capable of performing true 3D subsampling of Fourier space. SPARKLING 3D uses
Fast Multipolar Methods (FMM), originally developed in astronomy to accelerate
the computation of long-range forces in "N-body problems". With these
techniques, the generation of the subsampling scheme trajectories now takes
only 6 to 10 hours depending on the target resolution of the images, instead of
several weeks in an initial attempt.
As a result, researchers have designed patterns with up to 10 million samples of Fourier space. Using retrospective and prospective studies on a phantom and in vivo acquisitions at 3 Tesla (3T), they show that this new optimization outperforms current 3D strategies (including those that proceed by stacking Fourier planes).
Overall, the method allows for 2.5-3.75x shorter scan times, without compromising image quality, compared to already accelerated 4x parallel imaging (compared to full Fourier space acquisition). The first steps demonstrated at 7T, notably in sodium imaging, suggest accelerations up to a factor of 64. To be continued...
 T2*-weighted MRI (T2 gradient echo sequence) is an MRI modality classically used in the clinic.
Chaithya GR, Pierre Weiss, Guillaume Daval-Frérot, Aurélien Massire, Alexandre Vignaud and Philippe Ciuciu. Optimizing full 3D SPARKLING trajectories for high-resolution Magnetic Reonance Imaging. | IEEE Transactions on Medical Imaging 2022, 07 March
CEA is a French government-funded technological research organisation in four main areas: low-carbon energies, defense and security, information technologies and health technologies. A prominent player in the European Research Area, it is involved in setting up collaborative projects with many partners around the world.