We developed an advanced clearing method with superior fluorescence-preserving capability for 3D imaging of whole organs.

Tissue optical clearing techniques have provided important tools for large‐volume imaging. Aqueous‐based clearing methods are known for good fluorescence preservation and scalable size maintenance, but are limited by long incubation time, insufficient clearing performance, or requirements for specialized devices. Additionally, few clearing methods are compatible with widely used lipophilic dyes while maintaining high clearing performance. Here, to address these issues, m‐xylylenediamine (MXDA) is firstly introduced into tissue clearing and used to develop a rapid, highly efficient aqueous clearing method with robust lipophilic dyes compatibility, termed MXDA‐based Aqueous Clearing System (MACS). MACS can render whole adult brains highly transparent within 2.5 days and is also applicable for other intact organs. Meanwhile, MACS possesses ideal compatibility with multiple probes, especially for lipophilic dyes. MACS achieves 3D imaging of the intact neural structures labeled by various techniques. Combining MACS with DiI labeling, MACS allows reconstruction of the detailed vascular structures of various organs and generates 3D pathology of glomeruli tufts in healthy and diabetic kidneys. Therefore, MACS provides a useful method for 3D mapping of intact tissues and is expected to facilitate morphological, physiological, and pathological studies of various organs.

Three-dimensional (3-D) imaging of intact brain is indispensable for high-resolution mapping of neuronal networks, which is valuable for understanding brain structural–functional relationships.¹ 2. ^{– 3} Except for the widespread histological sectioning methods and emerging automated serial-sectioning and imaging approaches, optical imaging techniques make the 3-D imaging of thick brain tissues possible via optical sectioning with no need of thin slicing,⁴ 5. ^{– 6} such as confocal microscopy, two-photon microscopy, light-sheet microscopy, and so on. However, the imaging depth of these microscopies suffers from strong light scattering of brain tissues.^1,7,8

Intraventricular hemorrhage is one of the most fatal forms of brain injury that is a common complication of premature infants. However, the therapy of this type of hemorrhage is limited, and new strategies are needed to reduce hematoma expansion. Here we show that the meningeal lymphatics is a pathway to remove red blood cells from the brain’s ventricular system of male human, adult and newborn rodents and is a target for non-invasive transcranial near infrared photobiomodulation. Our results uncover the clinical significance of phototherapy of intraventricular hemorrhage in 4-day old male rat pups that have the brain similar to a preterm human brain. The course of phototherapy in newborn rats provides fast recovery after intraventricular hemorrhage due to photo-improvements of lymphatic drainage and clearing functions. These findings shed light on the mechanisms of phototherapy of intraventricular hemorrhage that can be a clinically relevant technology for treatment of neonatal intracerebral bleedings.