Okay, here is the abstract and summary for the LAWS Webinar 2 transcript.
Abstract:
This webinar, the second in the UFFC-S Latin America Webinar Series, featured talks by Dr. Héctor Estrada and Dr. Marco A. B. Andrade, moderated by Dr. Karen Volke-Sepúlveda. Dr. Estrada presented his work on optically-guided transcranial ultrasound stimulation (TUS) in mice. He detailed the FLUS system, which combines a spherical ultrasound transducer array with wide-field optical calcium imaging to study neuromodulation in vivo. Key findings include the identification of a "fluoro-thermal tag" – a decrease in fluorescence corresponding to ultrasound-induced temperature changes – allowing real-time visualization of the ultrasound focus and potential thermal confounds. The system was also used to assess functional connectivity changes and safety thresholds, observing minor vascular damage and cortical spreading depression at specific pressure levels. Dr. Andrade discussed various acoustic levitation methods for manipulating objects in mid-air. He explained the underlying theory of acoustic radiation force and reviewed techniques including standing wave levitation (demonstrating multi-droplet manipulation with phased arrays), inverted near-field acoustic levitation (for contactless handling), far-field levitation (suspending large objects), and single-beam levitation using phased arrays. The talks were followed by a Q&A session addressing technical details and potential applications of both technologies.
0:14 Introduction & Announcements: The webinar begins with introductions and announcements regarding the IEEE IUS conference (including a Latin American panel) and a job opportunity at Verasonics in Colombia.
3:45 Early Career Talk (Héctor Estrada): Optically-guided Transcranial Ultrasound Stimulation (TUS) in Mice: Introduction to Dr. Estrada and his research aiming to understand how ultrasound affects neurons using optical methods.
5:23 Need for Precise TUS: TUS shows promise for treating brain disorders (Alzheimer's, epilepsy), but the mechanism is unclear, and precise targeting is needed, especially in small animal models like mice.
8:56 FLUS System: Development of a Focused Light-Ultrasound System (FLUS) using a spherical transducer array (3 MHz) with an optical aperture, allowing simultaneous wide-field calcium fluorescence imaging in transgenic mice in vivo through the skull. Provides focus below 400 microns.
9:37 Fluoro-Thermal Tag: Observation of a decrease (dip) in fluorescence intensity at the ultrasound focus (~3 MPa). This is identified as a thermal effect (fluorescence decreases with temperature).
11:19 Application of Thermal Tag: This effect serves as a real-time, in vivo indicator ("fluoro-thermal tag") of the ultrasound focus position, relative intensity, and potential thermal confounds during experiments.
12:29 Functional Connectivity & Safety: Functional connectivity analysis (correlating brain region activity) shows changes only at higher pressures (3.9 MPa), which corresponds to histological findings of minor vascular damage (small lesion). No damage was seen at 3 MPa.
14:03 Cortical Spreading Depression (CSD): Even higher pressures (4.5 MPa) consistently triggered CSD, a wave of biochemical imbalance.
14:49 TUS Conclusion: The FLUS system and fluoro-thermal tag are valuable tools for guiding TUS, assessing safety thresholds, detecting thermal effects, and studying neuromodulation mechanisms.
16:16 Main Talk (Marco A. B. Andrade): Acoustic Levitation Methods: Introduction to Dr. Andrade and his work on suspending and manipulating objects using sound waves.
18:07 Acoustic Levitation Theory: Explanation of acoustic radiation force counteracting gravity, using the Gorkov potential equation for particles smaller than the wavelength.
22:58 Standing Wave Levitation: Using a transducer and reflector to create pressure nodes where small particles (< lambda) can be trapped. Applications shown include sample analysis combined with synchrotron X-rays and multi-droplet manipulation (merging, moving) using a 16x16 phased array (40 kHz).
32:34 Inverted Near-Field Levitation: Technique where the transducer levitates an object below it, applicable when the transducer radius (R) to wavelength (lambda) ratio is below approx. 0.38. Demonstrated manipulating Surface Mount Device (SMD) components contactlessly.
37:21 Far-Field Levitation: Levitating larger objects where the object itself acts as a reflector, creating a standing wave between it and the transducer(s). Demonstrated levitating a 50 mm diameter sphere.
39:34 Single Beam Levitation: Using a phased array of transducers to shape a complex acoustic field that traps an object without needing a reflector. Demonstrated levitating a hemisphere (~90 mm dia); simulated vs. measured pressure fields shown.
(Hector): Scaling FLUS for humans (needs different design), frequency effects in TUS (significant for large changes, e.g., >1 octave), coupling medium (degassed water & membrane), functional connectivity changes linked to damage threshold.