In vivo superresolution photoacoustic computed tomography by localization of single dyed droplets

• Published in: Light, science & applications science & applications, 2019-04, Vol.8 (1), p.36-36, Article 36
• Main Authors: Zhang, Pengfei, Li, Lei, Lin, Li, Shi, Junhui, Wang, Lihong V.
• Format: Article
• Language: English
• Subjects: 639/624/1107/510; 639/624/1111/1115; Acoustics; Applied and Technical Physics; Atomic; Blood vessels; Classical and Continuum Physics; Computed tomography; Cortex; Diffraction; Hydrophobicity; Lasers; Localization; Medical imaging; Molecular; Neuroimaging; Optical and Plasma Physics; Optical Devices; Optics; Photonics; Physics; Physics and Astronomy; Spatial discrimination; Tracers
• ISSN: 2047-7538; 2095-5545; 2047-7538
• DOI: 10.1038/s41377-019-0147-9

Photoacoustic (PA) computed tomography (PACT) is a noninvasive hybrid imaging technique that combines optical excitation and acoustic detection to realize high contrast, high resolution, and deep penetration in biological tissues. However, the spatial resolution of PACT is limited by acoustic diffraction. Here, we report in vivo superresolution PACT, which breaks the acoustic diffraction limit by localizing the centers of single dyed droplets that are flowing in blood vessels. The droplets were prepared by dissolving hydrophobic absorbing dye in oil, followed by mixing with water. The dyed droplets generate much higher-amplitude PA signals than blood and can flow smoothly in vessels; thus, they are excellent tracers for localization-based superresolution imaging. The in vivo resolution enhancement was demonstrated by continuously imaging the cortical layer of a mouse brain during droplet injection. The droplets that were flowing in the vessels were localized, and their center positions were used to construct a superresolution image that exhibits sharper features and more finely resolved vascular details. An improvement in spatial resolution by a factor of 6 has been realized in vivo by the droplet localization technique. Dyed droplets improve photoacoustic imaging Dyed droplets improve the resolution of an imaging technique involving laser pulses and ultrasound. Lihong V. Wang of the California Institute of Technology and colleagues demonstrated improved resolution of ‘photoacoustic computed tomography’ (PACT) by a factor of six by injecting dyed droplets into brain blood vessels of live mice. In PACT, tissues receiving short bursts of laser pulses emit ultrasound waves that are detected by an array of sensors. The technique is used for high-spatiotemporal-resolution imaging of biological tissues with super-contrast and deep penetration. The injected dyed droplets acted as a good contrast medium, producing much higher ‘photoacoustic’ signals than the blood background, while also flowing smoothly through the blood vessels. By localizing the centers of the dyed droplets, a higher resolution image can be formed. Further improvements, by using dyed droplets with higher optical absorption, for example, could lead to applications in blood capillary imaging and in monitoring targeted drug delivery.