Fast 3D Optoacoustic Mesoscopy of Neuromelanin Through Entire Human Midbrain Organoids at Single-Cell Resolution

Parkinson's disease is a devastating neurodegenerative disorder characterized by loss of neuromelanin-containing dopaminergic neurons. Novel 3D culture systems like human midbrain-like organoids (hMOs) enable new research avenues for patient-specific therapies, but cannot reach their full potential unless rapid optical imaging of entire organoids is enabled. Currently, hMOs have to undergo tissue clearing processes before imaging to overcome light scattering. Since tissue clearing is a lengthy chemical procedure, large ensemble studies and pharmacological longitudinal studies, which require live cultures, are impossible. To address this obstacle, raster scanning optoacoustic mesoscopy (RSOM) is considered for imaging intact hMOs. RSOM is an optical imaging technique that leverages the optoacoustic effect to overcome the need of tissue clearing. Moreover, by using tomographic principles, large specimens can be imaged within minutes. The results confirm that RSOM can image the neuromelanin distribution in complete hMOs at a single-cell resolution. Whole hMO volumes of standard size can be imaged in 4 min. Comparison with bright-field microscopy and histology confirms the ground truth of the RSOM images. This work opens several research opportunities regarding neuromelanin in hMOs with potential to boost research in Parkinson disease.