This IEEE UFFC Latin American Webinar, moderated by Stefan Catheline, featured two presentations on advanced ultrasound techniques for characterizing soft biological tissues. The first talk, by David from the Center of Bio Informatics and Photonics, detailed the use of pulsed photoacoustics (laser-induced ultrasound) to non-invasively assess the elastic properties and potentially water content of coffee plant leaves. The method involves generating guided plate waves with a pulsed laser and detecting them with a laser Doppler vibrometer, subsequently analyzing dispersion curves to estimate effective elastic moduli using an isotropic plate model, finding sensitivity to water content primarily in wave amplitude and higher-order mode cutoffs at the frequencies studied.
The second presentation, by Professor Nicola Benich from Universidad de la Republica, Uruguay, surveyed recent advances in skeletal muscle elastography. This included shear wave elastography for measuring anisotropic elastic moduli and viscosity in beef samples (requiring diffraction correction), and extensive work on surface wave elastography. The physics of near-field surface waves (including leaky/supershear waves) versus far-field Lamb waves was discussed, alongside applications using contact piezoelectric sensors for monitoring beef maturation in agri-food settings and tracking in vivo muscle contraction dynamics in humans. Finally, ongoing work on 3D passive elastography using row-column arrays for volumetric shear speed imaging was briefly presented. The session concluded with a Q&A addressing model assumptions, experimental challenges, and specific application details.
IEEE UFFC Latin America Webinar: Elasticity Characterization
0:00:02 Webinar Kick-off: Javier Broome welcomes attendees to the first IEEE UFFC Latin American Webinar, outlining logistics (Q&A via chat in English/Spanish/Portuguese, session recording).
0:01:14 Moderator Introduction: Stefan Catheline is introduced as the moderator, an expert in wave physics, elastography, and time reversal.
0:02:11 Session Overview: Stefan Catheline introduces the theme: exploring elasticity from two different perspectives with an early career and a senior speaker.
0:02:47 First Speaker Introduction: David, a PhD candidate from the Center of Bio Informatics and Photonics, is introduced to present on pulsed photoacoustics.
0:03:50 Presentation 1: Pulsed Photoacoustics (David): Focuses on non-invasive, non-contact evaluation of coffee leaf elastic properties and water content using laser ultrasound.
0:04:52 Technique: Uses a pulsed laser (500nm) to generate thermoelastic waves and a Laser Doppler Vibrometer (LDV) to detect resulting surface vibrations (guided plate waves).
0:05:50 Wave Physics: Explains the generation of shear and longitudinal waves, reflections, and formation of symmetric and anti-symmetric guided plate waves (Lamb waves). Mentions the Rayleigh-Lamb model for analysis.
0:07:07 Measurement & Analysis: Uses scanning mirrors to map wave propagation along the midrib and lamina of the leaf. Extracts dispersion curves (phase velocity vs. frequency).
0:09:08 Key Observation (Water Content): Wave amplitude shows sensitivity to leaf water content (higher amplitude for drier leaves).
0:10:16 Anisotropy: Demonstrates anisotropy by comparing dispersion and phase velocity plots along the midrib versus in the lamina.
0:11:36 Elastic Property Estimation: Uses an inverse problem approach, fitting the Rayleigh-Lamb model to experimental dispersion curves to find effective longitudinal and transverse wave speeds, yielding elastic moduli comparable to other methods.
0:13:31 Potential Applications: Useful for plant histology, developing new vegetation indices, and integrating into IoT architectures for precision agriculture.
0:14:49 Second Speaker Introduction: Professor Nicola Benich from Universidad de la Republica, Uruguay, is introduced to discuss skeletal muscle elastography.
0:16:59 Muscle Model: Treats muscle as a transversely isotropic (TI), incompressible soft solid requiring 3 independent elastic constants.
0:17:49 Shear Wave Elastography (SWE): Discusses generating shear waves with focused ultrasound pushes. Shear Horizontal (SH) waves are simpler to analyze for anisotropy.
0:18:51 Viscosity Measurement: Describes work on measuring shear wave attenuation in beef, highlighting the need to correct for geometric diffraction effects to isolate viscosity. Shows viscosity results are comparable to literature.
0:22:18 Surface Wave Elastography Physics: Explains that near the source, surface waves include leaky/supershear waves besides the Rayleigh wave, leading to frequency dispersion even in purely elastic media due to interference. Distinguishes this from plate (Lamb) modes which dominate further from the source or in bounded media.
0:29:43 Surface Wave Applications (Agri-food): Uses contact piezoelectric sensors to measure surface wave dispersion on cheese, liver, and beef samples to estimate shear velocity. Developed a prototype for monitoring beef maturation over time, showing decreasing elasticity. Ongoing project for slaughterhouse classification.
0:33:49 Surface Wave Applications (In Vivo): Developed a bracelet with sensors to measure shear elasticity changes in human biceps and triceps during controlled isometric contractions, correlating results with muscle activation. Ongoing PhD work on miniaturization.
0:35:37 3D Passive Elastography: Briefly presents ongoing collaboration using a Row-Column Array (RCA) probe and passive (finger tapping) excitation to reconstruct 3D shear wave speed maps in phantoms.
0:37:50 Conclusion: Summarizes the different elastography approaches being researched, emphasizing ongoing work and the need for further theoretical development for TI solids.
1:00:51 Announcements: Details provided for the next Latin America webinar (Sept 1st) and an upcoming UFFC Virtual Lecture (July 12th). A request to complete a survey is made.