Jang, M. et al. Nat. Commun. 11, 710 (2020).

Imaging at depth within biological specimens is a long-standing goal of optical microscopy. However, such deep-tissue imaging is limited by light interacting with the specimen, which leads to light scattering. ‘Gating’ strategies, which are effective at filtering out multiply scattered waves, have been developed to bypass these limitations. Jang et al. present a complementary gating approach called space gating, which is based on interferometric detection schemes developed for photoacoustic imaging. Space gating is applied at the object plane and uses selective measurement of the ballistic wave that is modulated by a high-frequency ultrasound focus as small as ~30 μm × 70 μm. Space gating allows effective filtering of multiply scattered waves that cannot be filtered out with existing approaches. The researchers demonstrate the power of space-gated microscopy with quantitative phase imaging of cells embedded in scattering medium and skeletal muscle structure in intact zebrafish 30 days post-fertilization.