KEYWORDS: Photoacoustic spectroscopy, Photoacoustic tomography, Acquisition tracking and pointing, Switching, Signal detection, Tissues, Color, Temperature metrology, In vivo imaging, Absorption
SignificanceBased on acoustic detection of optical absorption, photoacoustic tomography (PAT) allows functional and molecular imaging beyond the optical diffusion limit with high spatial resolution. However, multispectral functional and molecular PAT is often limited by decreased spectroscopic accuracy and reduced detection sensitivity in deep tissues, mainly due to wavelength-dependent optical attenuation and inaccurate acoustic inversion.AimPrevious work has demonstrated that reversible color-shifting can drastically improve the detection sensitivity of PAT by suppressing nonswitching background signals. We aim to develop a new color switching-based PAT method using reversibly switchable thermochromics (ReST).ApproachWe developed a family of ReST with excellent water dispersion, biostability, and temperature-controlled color changes by surface modification of commercial thermochromic microcapsules with the hydrophilic polysaccharide alginate.ResultsThe optical absorbance of the ReST was switched on and off repeatedly by modulating the surrounding temperature, allowing differential photoacoustic detection that effectively suppressed the nonswitching background signal and substantially improved image contrast and detection sensitivity. We demonstrate reversible thermal-switching imaging of ReST in vitro and in vivo using three PAT modes at different length scales.ConclusionsReST-enabled PAT is a promising technology for high-sensitivity deep tissue imaging of molecular activity in temperature-related biomedical applications, such as cancer thermotherapy.
Optical-resolution photoacoustic microscopy (OR-PAM) can image biological tissues at micrometer level resolution. However, the imaging speed of traditional OR-PAM is often too slow for capturing dynamic information. In this work, we demonstrate a high-speed OR-PAM system using a water-immersible two-axis torsion-bending scanner, in which the fast axis employs the torsion scanning while the slow axis works at the bending mode. The system has achieved a cross-sectional frame rate of 400 Hz, and a volumetric imaging speed of 1 Hz over a field of view of 1.5 × 2.5 mm2. We have demonstrated high-speed OR-PAM of fast hemodynamic changes in vivo.
KEYWORDS: 3D modeling, Photoacoustic imaging, Autoregressive models, Visual process modeling, In vitro testing, Blood, 3D printing, Visualization, Photoacoustic microscopy, Digital Light Processing
Understanding thrombosis formation is necessary for developing safe and effective treatments. We fabricated sophisticated in vitro models of blood vessels with internal microchannels by using digital light processing-based 3D printing method. Photoacoustic microscopy (PAM) offers a useful platform for imaging 3D-printed vascular structures with different patterns of microchannels. Our results show that PAM can provide clear microchannel structures at depths up to 3.6 mm. We further quantified the blood oxygenation in the 3D-printed vascular models, showing that thrombi had much lower oxygenation than the normal blood. Integration of PAM with 3D printing/bioprinting will enable numerous applications in tissue engineering.
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