Echolocating electricity through the skull, in HD

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Science Translational Medicine  26 Feb 2020:
Vol. 12, Issue 532, eabb0791
DOI: 10.1126/scitranslmed.abb0791


Ultrasound can make high-resolution images of electrical fields across intact human skulls.

The ideal functional neuroimaging technique would be able to noninvasively visualize the neural activity of any brain region with high sensitivity, as well as high spatial and temporal resolution. Recent work from Preston et al. at the University of Arizona brings us one step closer to that ideal. The Arizona group showed that using a conventional ultrasound transducer, they could visualize with high spatial and temporal resolution the electrical fields produced by individual leads of a deep brain stimulating (DBS) electrode placed deep within intact human skulls.

To accomplish this feat, Preston and colleagues made use of acoustoelectric imaging (AEI), wherein time-varying electrical fields could be recorded using pulsed transmit-receive ultrasound. Prior studies had shown that AEI could be used to record the electrical current densities of beating hearts and could image the anatomic location of DBS electrodes but usually necessitated the use of specialized hardware to do so. In this study, the authors now build on that foundation to show that AEI could not only transcranially localize DBS electrodes but also could visualize the electrical fields they produced, while maintaining a spatial resolution on the order of 1 mm and a temporal resolution on the order of 0.1 ms. Importantly, they were able to do so using an off-the-shelf clinical ultrasound transducer that was imaging a conventional clinical DBS electrode transmitting usual current amplitudes, without the use of specialized hardware that would necessitate additional regulatory approvals. This paves the way for high-resolution functional mapping of how a DBS stimulus may propagate through neural circuits in humans.

It should be noted that this study was completed using fixed human skulls filled with saline. Next steps would be to assess how well this approach may see DBS currents within living brains with intact skulls and to see if AEI could even visualize physiologic neural electrical activity through the background of living brain tissue. Although we are not there quite yet, these results bring us one step closer to the ideal technique for functional neuroimaging.

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