Photoacoustic Imaging (PAI) is an emerging non-ionizing and non-invasive biomedical imaging method in the past few years. PAI can effectively obtain both structural and functional information of bio-tissues, providing an important method for studying the morphological structure and physiological characteristics of bio-tissues, especially suitable for early-stage cancer diagnosis. As one important subtype of PAI, optical resolution photoacoustic microscopy (ORPAM) has the advantages of high spatial resolution and imaging contrast. ORPAM has been proved to be an effective and powerful method in hemodynamic and micro-circulation studies. However, due to the low scanning speed over a large field of view (FOV), the application of existing ORPAM systems has been greatly limited. In order to overcome these limitations, we report an ultrafast ORPAM (U-ORPAM) system in this research. By combining our novel rotary scanning protocol with a 200 kHz ultrafast pulsed laser, U-ORPAM has the ability to image an 8-mm-diameter FOV in 5 seconds. Both phantom and in vivo experiments were carried out to demonstrate the performance of the image system. These results indicate that U-ORPAM has equivalent imaging qualities with other ORPAM systems with a much higher imaging speed. These advantages make U-ORPAM a promising tool for the investigation of rapid hemodynamic research and clinical biomedical research.
In this work, we employed a micro-electro-mechanical system (MEMS) mirror as the scanner to reduce the size of the opto-acuostic-fludic system. To evaluate the performance of this system, we imaged flowing droplets generated by Tjunction and flow focusing configurations. The results demonstrate the feasibility of this method in the study of droplet formation dynamics. We also imaged flowing magnetic microspheres to verify the influence of magnetic field. In the end, cancer cells were successfully detected in the microchannel to demonstrate the potential of this method in clinical applications.
This paper reports a novel method, opto-acousto-fluidic microscopy, for label free detection of droplets and cells in microfluidic networks. Leveraging the optoacoustic effect, the microscopic system possesses capabilities of visualizing flowing droplets, analyzing droplet contents, and detecting cell populations encapsulated in droplets via the sensing of acoustic waves induced by intrinsic light-absorbance of matters. The opto-acousto-fluidic chip was fabricated using standard soft-lithography with a channel width of 200 μm and height of 120 μm. Fluid samples were injected into chips using syringe pumps via plastic tubings. A T-junction was used to produce aqueous droplets which consisted of light-absorbing molecule species or cells and buffer fluids. A pulse laser beam (repetition rate 50 kHz) steered by a galvanometer mirror and focused by an objective (4X) transmits through and converges with a focal spot size of 3.2μm in the microfluidic channels. For each scanning line, 250 sampling was made with a spatial interval of 1 μm across the channel with a width of 200 μm in the experiment, and thus the 50kHz repetition rate of the laser provides a 200Hz B-scan rate. In the cell research, arterial blood was draw from a rat and buffered with saline. Droplets with different volumes but same density of red blood cell population were generated, and the cytometric measurement shows that the number of detected RBCs increases proportionally with the volume of the droplet.
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