A microscopy scheme is proposed to simultaneously achieve optical scattering-absorption dual-contrast imaging of a transparent or semi-transparent specimen. This scheme is based on a transmission-mode photoacoustic microscope. We find that two peaks exist in the detected photoacoustic signal. One peak is caused by the optical absorption of the specimen, and the other is related to both the optical scattering and absorption of the specimen. Therefore, both the absorption and scattering information can be simultaneously extracted by analyzing the same photoacoustic signal excited by a single-shot laser pulse. After the microscope is validated by imaging a binary mixture consisting of particles with different optical properties, it successfully acquires dual images of red blood cells with different contrasts. Quantitative analysis reveals that the optical absorption and scattering properties of the specimen can be derived from the two images. The proposed dual-modal imaging method would be useful in revealing the structural and functional properties of tissues at the cell level or the clinical assessment of pathological sections.
Quasi-periodic scanning combined with a register-fusion algorithm is proposed to realize tunable spatiotemporal resolution photoacoustic microscopy. Quasi-periodic scanning involves an irrational number ratio for the periods of scanning signals in two directions. It can provide sub-pixel spatial sampling. The proposed method can adjust the temporal and spatial resolutions by changing the data length for image reconstruction. For moving targets, the method can obtain a series of low-resolution images with a high imaging frame rate. A high-spatial-resolution image can be fused from these images using the register-fusion algorithm. The proposed method can acquire both motion and structural details of moving target
Quantitative images of multiple molecular components in tissues have significance in understanding tissue functions. However, most imaging methods of quantifying a multicomponent mixture often rely on multiple excitations with different wavelengths or intensities. In this study, a transmission-mode photoacoustic microscope is developed to achieve quantitative images of two components in specimen slices. Different from other methods, the proposed method only scans the specimen one time by using a single-wavelength laser. After each laser excitation, the ultrasound transducer detects two signals: One is only related to optical absorption and the other is associated with both absorption and scattering. A linear equation system is proposed to describe the relationship between the signal magnitude and the molecular concentrations of thin-specimen. Solving these equations, we extract quantitative images of components in the thin-specimen from the two signals excited by a single-wavelength laser. Experiments demonstrate that the scheme accurately quantifies the concentrations of various mixtures of sterile sheep blood and milk, moreover, correctly revealing the concentration gradient due to molecular diffusion along the boundary between different components. This method could overcome the limitations induced by multiple excitations, and it will be helpful in developing a quantitative multiple-molecular imaging system.
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