Kvale Lovmo, M. | bioRxiv Science

bioRxiv2024

Optical tomography reconstructing 3D motion and structure of multiple-scattering samples under rotational actuation

Optical Diffraction Tomography (ODT) has emerged as a powerful tool for imaging biological cells in a non-invasive and label-free manner. However, conventional approaches using ODT by varying the illumination are plagued by the missing cone problem, which introduces ambiguity and deteriorates the axial resolution in the reconstruction. Although utilizing object rotation has the potential to yield isotropic resolution, experimental control or prior retrieval of the rotational parameters is challenging. In this work, we demonstrate ODT of multiple-scattering samples undergoing variable rotational motion, unlocking the potential for isotropic resolution in non-contact systems. We introduce a comprehensive reconstruction method to jointly retrieve both sample and rotational motion in 3D. An interferometric setup enables the recording of amplitude and phase data while the object is rotated in a non-contact manner around one or more chosen axes in an acoustofluidic device. We evaluate the tomographic reconstruction performance of the method for clusters of micro-beads and highlight its suitability for biomedical application beyond single cells, demonstrating high-resolution reconstruction of dense cancer spheroids containing more than 100 cells.

bioengineering↗

bioRxiv2023

Ultrasound-Induced Reorientation for Multi-Angle Optical Coherence Tomography

Organoid and spheroid technology have recently provided great insights into oncology, developmental biology as well as personalized medicine. Among the methods to optically monitor the structural and functional organization of such samples, optical coherence tomography (OCT) has emerged as an excellent, label-free approach. Mature organoids, however, are often too opaque for OCT due to regions of strong attenuation. This leads to severe artifacts and reduced morphological tissue information in the reconstruction, since the far-side of the specimen is not reachable. Access to multi-angle views of OCT is therefore highly desirable. This aligns with another problem affecting certain goals of organoid research: The sample needs to be embedded in a growth scaffold such as Matrigel, whereas freely floating objects would not suffer from confinement and be more easily accessible for mechanical or chemical probing. Here we present ULTrasound-Induced reorientation for Multi-Angle-OCT (ULTIMA-OCT), a solution overcoming these limitations. By inserting a small 3D-printed acoustic trap to a spectral-domain OCT system, acoustic actuation enables contact-free levitation and finely tunable stepwise reorientation of samples such as zebrafish larvae and tumor spheroids, in a controlled and reproducible manner. This enables tomographic reconstruction of (sub-)mm samples with enhanced penetration depth and reduced attenuation artifacts, by means of a model-based algorithm we developed. We show that this approach is able to fuse the diverse multi-angle OCT volumes for a joint recovery of 3D-reconstruction of reflectivity, attenuation, refractive index and position registration for zebrafish larvae. We believe that our approach represents a powerful enabling tool for developmental biology and organoid research.

bioengineering↗