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.