Keyword:

Focal Length: distance from a lens or a mirror to the focal point (point in which parallel light rays meet)

Full-width at Half Maximum (FWHM): difference between the two values of independent variables at which the dependent variables are equal to half of the maximum value

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Neuromodulation: the alteration of nerve activity by delivering electrical or pharmaceutical agents directly to a target area of the brain

Habenula: portion of brain responsible for regulating diverse types of emotion-related behaviors

Deep Brain Stimulation (DBS): electrical stimulation using implantable electrodes

Transcranial Magnetic Stimulation (TMS): non-invasive stimulation of brain using magnetic fields

Transcranial Direct Current Stimulation (tDCS): neuromodulation that uses constant, low direct current delivered via electrodes non-invasively

Beam Profile: 2D intensity plot of a beam at a given location along the beam path

Goal: Make neuromodulating device that is non-invasive, cheap, does not involve too much circuitry, and that has a high axial and lateral focal resolution.

Why dual transducer instead of others:

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Axial resolution is determined by the center frequency, focal length (F), and aperture size (a1) while frequency and focal length are kept constant

⇒ with a linear array with aperture in meter-scale VS dual array with aperture of centimeter-scale

⇒ two orders of magnitude greater aperture needed for phased array in order to get same focal area

Other modes of neuromodulation:

  1. tFUS (transcranial focused ultrasound stimulation)
    1. highly specific targeting using ultrasound neuromodulation is difficult
    2. non-invasive & theoretically capable of targeting deep brain structures with high spatial resolution
    3. curved single-element piezoelectric ultrasound transducers with elliptical focal spots caused the focal volume to span across a large axial distance
  2. Modified tFUS (with higher-frequency ultrasound, modulated ultrasound waves, beamforming)
    1. all had poor axial resolution (high mediolateral and anteroposterior specificity but low dorsoventral specificity)
  3. Use array of transducers and apply phase delay to cause beamforming (check Figure above)

Results