Ultrasonic Endoscopes for DEEP Light Focusing

Informations projet

DEEP

N° de convention de subvention: 101002460

DOI

10.3030/101002460

Date de signature de la CE 8 Avril 2021

Date de début 1 Octobre 2021

Date de fin 30 Septembre 2026

Financé au titre de

• EXCELLENT SCIENCE - European Research Council (ERC)

Coût total

€ 1 862 462,00

Contribution de l’UE

€ 1 862 462,00

Coordonné par

UNIVERSITAT DE BARCELONA
Spain

Periodic Reporting for period 3 - DEEP (Ultrasonic Endoscopes for DEEP Light Focusing)

Période du rapport: 2024-10-01 au 2026-03-31

Résumé du contexte et des objectifs généraux du projet

Light scattering is a common phenomenon in nature but poses a significant challenge when trying to understand living systems. When we attempt to focus light within living tissue, scattering disperses the light, creating a diffuse glow instead of a well-defined spot. This diffusion occurs after only a few hundred microns and hinders our ability to explore biological complexity and disease mechanisms. Various technologies have been developed to tackle this issue, but they all achieve deeper light focusing by compromising either spatial or temporal precision or by increasing invasiveness. As of today, there is no tool capable of rapidly and precisely controlling light inside tissue or inside tissue-like constructs such as organoids.

The overall objective of this project is to fill this void by developing a new technology that can focus light at depths of 1 mm or more within tissue, in real-time, at sub-cellular resolution, and in a completely non-invasive manner. The proposed approach involves using ultrasound to create virtual endoscopes. Ultrasound waves, which are density waves, can penetrate deeply into tissue. By compressing and expanding the tissue, ultrasound can induce local changes in its optical properties. By designing ultrasonic waves with specific intensity distributions and shapes, we can generate refractive index gradients within the tissue. These gradients will function like embedded lenses or waveguides, enabling deep light focusing.

Ultrasonic endoscopes will provide an unprecedented control of light inside living tissue, opening the door to transformative advances in personalized medicine and molecular biology. But these advantages are not limited to tissue. Ultrasonic endoscopes will enable overcoming scattering and enable deep light focusing in any non-homogeneous scattering medium for its modification, characterization or even ablation.

Travail effectué depuis le début du projet jusqu’à la fin de la période considérée dans le rapport et principaux résultats atteints jusqu’à présent

So far, our primary efforts have focused on generating ultrasonic waves and evaluating their effectiveness for light-guiding. We experimented with various strategies and acoustic elements to produce ultrasound with tailored intensity profiles. We successfully demonstrated that using an ultrasound resonant cavity can enhance light focusing within tissue phantoms.

We have also advanced our understanding of the fundamental principles of ultrasonic endoscopes by simulating the effects of light propagation in media with modulated refractive indices. These simulations helped us identify the optimal conditions for light-guiding and predict the improvements in penetration depth.

Within the DEEP project, we developed a novel method for characterizing three-dimensional ultrasound fields in aqueous media. This is crucial for many ultrasound applications, such as bioimaging, acoustic tweezers, and optimizing ultrasonic endoscopes. Traditional methods using point-by-point scanning with a needle hydrophone are extremely time-consuming, often taking hours or days. We addressed this by creating an all-optical technology that can capture pressure fields in seconds.

Additionally, we have expanded the range of applications where ultrasound combined with light can be utilized. These include fast topographic microscopy and scan-less microscopy. In these cases, ultrasound plays a key role in modifying light properties, enabling light control at speeds and precisions previously unattainable.

Progrès au-delà de l’état des connaissances et impact potentiel prévu (y compris l’impact socio-économique et les conséquences sociétales plus larges du projet jusqu’à présent)

Most of the methods developed so far represent significant advancements beyond the state of the art in the fields of optics, acoustics, and imaging.

Our work demonstrates that ultrasonic endoscopes enable light guiding in scattering phantoms with an optical thickness of 15, a 7-fold improvement in light focusing compared to external lenses. The method is fast, only limited by the speed of sound within the medium, and the required pressure values render it de facto non-invasive. This is a first step toward extending light-focusing depth inside biological tissue.

We have also developed an all-optics system to characterize 3D pressure fields, retrieving information from a 100x100x100 point volume with micrometer resolution in just 10 seconds, compared to the 56 hours required by a needle-hydrophone. Such a drastic reduction in acquisition time represents a significant advancement toward the rapid characterization of pressure fields.

Additionally, we exploited the acousto-optic effect to enhance speed and flexibility in metrology and microscopy, offering real-time characterization of rapidly moving samples with previously unattainable precision and wavelength ranges.

So far, all our results have been demonstrated on test targets or phantom samples. We plan to start working on biological tissue, specifically colorectal organoids, in the near future. By combining simulation with experiments, we also plan to continuously improve the guiding effects of ultrasonic endoscopes. Additionally, we plan to combine ultrasonic endoscopes with state-of-the-art imaging, spectroscopy, and phototherapy techniques, including two-photon microscopy, photoacoustic microscopy, and fluorescence correlation spectroscopy, to further extend their operational depth.

At the end of the project, we expect to develop a novel non-invasive, and rapid approach for focusing light at a spatial resolution and depth not currently possible.