New Technologies Allow for Faster Brain fMRIs

Researchers from University of California, Berkeley, University of Minnesota, and Oxford University have developed new technology to speed up how fast neuro fMRI functions. In a study published in PLoS ONE, the researchers were able to achieve large reductions in echo planar imaging (EPI) of whole brain scan time at 3 and 7 Tesla even though the sampling rate was increased 6-fold and the peak functional sensitivity was improved by 60%:

Using echo planar imaging (EPI), fMRI vividly distinguishes oxygenated blood funneling into working areas of the brain from deoxygenated blood in less active areas.With EPI, a single pulse of radio waves is used to excite the hydrogen atoms, but the magnetic fields are rapidly reversed several times to elicit about 50 to 100 echoes before the atoms settle down. The multiple echoes provide a high-resolution picture of the brain.

In 2002, Feinberg [David Feinberg, physicist and adjunct professor at UC Berkeley and president of the company Advanced MRI Technologies] proposed using a sequence of two radio pulses to obtain two times the information in the same amount of time. Dubbed simultaneous image refocusing (SIR) EPI, it has proved useful in fMRI and for 3-D imaging of neuronal axonal fiber tracks, though the improvement in scanning speed is limited because with a train of more than four times as many echoes, the signal decays and the image resolution drops.

Another acceleration improvement, multiband excitation of several slices using multiple coil detection, was proposed in the U.K. at about the same time by David Larkman for spinal imaging. The technique was recently used for fMRI by Steen Moeller and colleagues at the University of Minnesota. This technique, too, had limitations, primarily because the multiple coils are relatively widely spaced and cannot differentiate very closely spaced images.

In collaboration with Essa Yacoub, senior author on the paper, and Kamil Ugurbil, director of the University of Minnesota’s Center for Magnetic Resonance Research and co-leader of the Human Connectome Project, Feinberg combined these techniques to get significantly greater acceleration than either technique alone while maintaining the same image resolution.

“With the two methods multiplexed, 10, 12 or 16 images the product of their two acceleration factors were read out in one echo train instead of one image,” Feinberg said.

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