Periodic Reporting for period 4 - COHERENCE (Exploiting light coherence in photoacoustic imaging) Período documentado: 2021-04-01 hasta 2021-09-30 Resumen del contexto y de los objetivos generales del proyecto Photoacoustic imaging is an emerging multi-wave imaging modality that couples light excitation to acoustic detection, via the photoacoustic effect (sound generation via light absorption). Photoacoustic imaging provides images of optical absorption (as opposed to optical scattering). As photoacoustic imaging relies on detecting ultrasound waves that are very weakly scattered in biological tissue, it can provide acoustic-resolution images of optical absorption non-invasively at large depths (up to several cm), where purely optical techniques have a poor resolution because of multiple scattering. As for conventional purely optical approaches, optical-resolution photoacoustic microscopy can also be performed non-invasively for shallow depth (< 1 mm), or invasively at depth by endoscopic approaches. However, photoacoustic imaging suffers several limitations. For imaging at greater depths, non-invasive photoacoustic imaging in the acoustic-resolution regime is limited by a depth-to-resolution ratio of about 100, because ultrasound attenuation increases with frequency. Optical-resolution photoacoustic endoscopy has very recently been introduced as a complementary approach, but is currently limited in terms of resolution (> 6 μm) and footprint (diameter > 2 mm).The overall objective of COHERENCE is to break the above limitations and reach diffraction-limited optical-resolution photoacoustic imaging at depth in tissue in vivo. To do so, the core concept of COHERENCE is to use and manipulate coherent light in photoacoustic imaging. Specifically, COHERENCE will develop novel methods based on speckle illumination, wavefront shaping and super-resolution imaging. COHERENCE will result in two prototypes for tissue imaging, an optical-resolution photoacoustic endoscope for minimally-invasive any-depth tissue imaging, and a non-invasive photoacoustic microscope with enhanced depth-to-resolution ratio, up to optical resolution in the multiply-scattered light regime.In terms of impact for the society, COHERENCE leads to the design of innovative biomedical instrumentations aiming at seeing deeper and better through organs, and therefore participates to the development of new diagnostic tools. Trabajo realizado desde el comienzo del proyecto hasta el final del período abarcado por el informe y los principales resultados hasta la fecha At the end of the project, two imaging prototypes were built: one non-invasive prototype of photoacoustic imaging device was designed, built and tested up to in vivo experiments (mouse brain imaging), and provided enhanced photoacoustic images of the vasculature, as compared to state-of-the-art devices (see illustration). A minimally-invasive laboratory endoscopic device was also designed and built, providing two types of optical contrasts (fluorescence and photoacoustic images), which has the potential to be further developped for in vivo brain imaging of small animals. The two prototypes will be further exploited to investigate and solve specific biomedical problems.The research to design the two instruments lead to one patent for each instrument, and several publications as research articles in peer-reviewed international journal and oral presentations. At the time of writing this report, 11 articles have been published, 3 are in preparation, and 2 patents have been filed. The corresponding results were presented at conferences through more than 25 oral presentations, given by all members of the team (PhD students, post-doctoral researches, permanent team members and principal investigator). Avances que van más allá del estado de la técnica e impacto potencial esperado (incluida la repercusión socioeconómica y las implicaciones sociales más amplias del proyecto hasta la fecha) For the non invasive imaging prototype, we introduced a new methods called photoacoustic fluctuation imaging, that should be easily implementable on commercial devices and could have a significant impact. A patent has been filed on the proposed approach.For the minimally invasive endoscopic device, we discovered a new optical memory effect in multi-mode fiber with square geometry, which paves the way towards calibration-free imaging methods through this kind of very small device. A patent has been filed on the proposed approach. publicsummary.png
