We propose a dual-parameter detection method to realize the simultaneous optical absorption and viscoelasticity imaging based on photoacoustic lock-in measurement. Both optical absorption and viscoelasticity properties can be obtained simultaneously by analyzing the amplitude and phase of photoacoustic signals. This method is experimentally verified by imaging of gelatin phantoms with different absorption coefficients and viscoelastic coefficients. Furthermore, pilot experiments were performed on an in vivo murine EMT6 tumor from the back of a BALB/c mouse. Results demonstrate that the method can be used to measure the optical absorption and viscoelasticity of different biological tissues.

Photoacoustic viscoelasticity imaging (PAVEI) is a technique that directly provides the morphology of biological tissues with correlative mechanical information. In this Letter, we demonstrate the use of PAVEI to successfully characterize early-stage atherosclerotic plaques. Lipid, as the main material in early plaque lesions, embedded in gelatin was imaged to test the feasibility of PAVEI. Atherosclerosis of rabbits was studied ex vivo, and the rabbit arteries were imaged to show the intrinsic contrast of PAVEI. Our results demonstrate that PAVEI can provide valuable viscoelasticity information for early detection of atherosclerotic plaques, which yields new insights into biomechanical diagnosis of cardiovascular diseases.

In this letter, we proposed a method for viscoelastic characterization of biological tissues based on time-resolved photoacoustic measurement. The theoretical and experimental study was performed on the influence of viscoelasticity effects on photoacoustic generation. Taking the time delay between the photoacoustic signal and the exciting laser, the viscoelasticity distribution of biological tissues can be mapped. To validate our method, gelatin phantoms with different densities were measured. We also applied this method in discrimination between fat and liver to confirm the usefulness of the viscoelastic evaluation. Furthermore, pilot experiments were performed on atherosclerosis artery from an apolipoprotein E-knockout mouse to show the viscoelastic characterization of atherosclerotic plaque. Our results demonstrate that this technique has the potential for visualizing the biomechanical properties and lesions of biological tissues.

In this letter, we proposed a photoacoustic (PA) method for noninvasively detecting blood viscosity in subcutaneous microvasculature with the frequency-resolved measurement. The influence of viscosity on PA generation was investigated theoretically, and a negative correlation was shown between the viscosity and the full width at half maximum (FWHM) of the PA frequency spectrum, which can be utilized to reflect the viscosity distribution. To test the feasibility and accuracy of this method, water mixed with different concentrations of glycerol was measured. FWHM of the PA frequency spectrum was also obtained in vivo in the mouse ear to characterize the blood viscosity from different vessel bifurcations, and the metabolism-induced viscosity changes were dynamically monitored in the microvasculature. Experimental results demonstrate that this technique has future potential clinical applications for real-time monitoring the viscosity changes in subcutaneous microvasculature.

In this paper, a novel photoacoustic viscoelasticity imaging (PAVEI) technique that provides viscoelastic information of biological tissues is presented. We deduced the process of photoacoustic (PA) effect on the basis of thermal viscoelasticity theory and established the relationship between the PA phase delay and the viscoelasticity for soft solids. By detecting the phase delay of PA signal, the viscoelasticity distribution of absorbers can be mapped. Gelatin phantoms with different densities and different absorption coefficients were used to verify the dependence of PAVEI measurements. Moreover, tissue mimicking phantoms mixed with fat and collagen at different concentrations were used to testify the feasibility of this technique with reliable contrast. Finally, the PAVEI was successfully applied to discrimination between biological tissue constituents. Our experimental results demonstrate that this novel technique has the potential for visualizing the anatomical and biomechanical properties of biological tissues.

In this Letter, we propose a novel triplex-parameter detection method to realize simultaneous radiometric, photoacoustic, and ultrasonic imaging based on single-pulse excitation. The optical attenuation, optical absorption, and acoustic impedance properties can be obtained simultaneously by analyzing the photoacoustic signals and the ultrasonic echo signals. To test the feasibility and accuracy of this method, agar phantoms with different absorption coefficients and elastic coefficients were measured. Then, this method was experimentally verified by imaging a leaf skeleton piece embedded in an agar cylinder. Furthermore, pilot experiments were performed by triplex imaging of pig ear tissue ex vivo to characterize the cartilage and surrounding tissue. Experimental results demonstrated that this technique has future potentials for visualizing and providing the functional and structural information of biological tissues.