Development of a new generation of imaging technique

July 07 2011

A discovery presented by Mickael Tanter, a director of research for Inserm, and his collaborators in the "Wave Physics for Medicine" team at the Institut Langevin, CNRS/ESPCI, have published an article in the journal Nature Methods, describing a very promising new imaging technique: fUltrasound (functional Ultrasound imaging of the brain). This is an ultrasensitive imaging technique based on studying blood flow. It allows very subtle changes in brain activity to be visualized. The resolution and sensitivity of this new technique makes it possible, for example, to monitor the development of an epileptic seizure over the whole of the brain of a small animal, a task that is currently not possible using functional MRI.

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Next Generation Imaging

The technique of functional MRI (fMRI) has revolutionized neurosciences over the past 10 years and more. It visualizes the parts of a patient's brain that are activated in response to a stimulus (visual, audio, etc.) by locating the influx of blood which is produced in the activated region. Functional MRI, like positron emission tomography (PET), is now indispensable in neurosciences and cognitive sciences. However, both those techniques have a weak point: although they penetrate deeply into the tissue, their resolution and sensitivity are limited. In particular, it is difficult to obtain images of transient events and/or events affecting the whole of the brain (epileptic seizures, for example).

Although ultrasound Doppler echo imaging is commonly used to view real-time blood flows in many organs, until now it has not been capable of observing the many tiny vessels in the brain and hence visualizing cerebral activity.

To go beyond the limits of conventional Doppler echo imaging, researchers from Inserm and CNRS have developed a novel technique that is effective on two fronts: fUltrasound (functional cerebral ultrasound) is both sensitive (capable of filming the fine vascularisation of the brain) and able to achieve excellent temporal and spatial resolution. To considerably increase the sensitivity of conventional echo imaging, the researchers developed an ultra-rapid imaging technique, which measures the movement of blood over the entire brain several thousand times per second (as opposed to several tens of times per second as was previously possible). This increase in the number of measurements allows blood flow to be detected in very small vessels, where subtle variations are linked to cerebral activity.

To test the effectiveness of this new technique, two researchers from the team, Gabrielle Montaldo and Emilie Macé, collaborated with two researchers from the Institut du Cerveau et de la Moëlle épinière (France's Brain and Spine Institute) to film, in real time:

  • The response of the cerebral cortex during stimulation of the whiskers of a rat:

 

When the researchers stimulate the whiskers of a rat, an influx of blood appears very clearly in the somatosensory cortex of the animal, a sign of activity in this area.

  • The development of an epileptic seizure over the entire brain of a rat:

 

At the peak moment in the seizure, the volume of blood increases strongly in the two hemispheres of the brain and waves propagate slowly in the various regions of the brain.

For Mickaël Tanter and Mathias Fink, Director of the Institut Langevin, the potential applications of this new technique, which possesses the advantage of being both portable and relatively inexpensive, are considerable. From a technical point of view, it could be used to study newborn babies were fMRI is very difficult to carry out, or even to study foetuses during pregnancy and hence to obtain a better understanding of how the brain develops. In adults, it could be used to locate the focus points of epileptic incidents by intraoperative imaging. On the research side, functional ultrasound should allow biologists to answer many fundamental questions in neuroscience because of its spatiotemporal resolution and the unequalled sensitivity offered by this new imaging approach.


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Sources

Functional ultrasound imaging of the brain, Nature Methods July 2011

Research contact

Mickael Tanter
Inserm Research Director
Institut Langevin (CNRS UMR 7587)
Ecole Supérieure de Physique et Chimie Industrielles Tel: 01 40 79 45 43

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