We report on the fabrication of a piezoelectric micromachined ultrasonic transducer (pMUT) and its application to photoacoustic imaging. With c-axis orientation, AlN was grown on a 300 nm-thick SiO2 film and a 200 nm-thick bottom electrode at room temperature. The device consists of SiO2, bottom electrode, AlN films, upper electrode, and polyimide protective layer. An area ratio of 0.45 was used between the upper electrode and the vibration area of the pMUT to provide an optimal sensitivity of transducer. Its resonant frequency was measured to be 2.885 MHz, and the coupling coefficient in the range of 2.38%–3.71%. The fabricated pMUT was integrated with a photoacoustic imaging system and photoacoustic image of a phantom was obtained. The resolution of the system was measured to be about 240 μm.
Acupuncture has been a powerful clinical tool for treating chronic diseases. However, there is currently no appropriate method to clarify the therapeutic effect of acupuncture. Here, we use photoacoustic tomography (PAT) to study the effect of acupuncture on mouse brain blood vessels. Ten healthy mice were stimulated with acupuncture needles on two acupoints. PAT images were obtained before and after acupuncture. We report that stimulation of certain acupoints resulted in changes in hemodynamics/blood flow at these points. The results demonstrate that PAT can non-invasively detect blood flow changes in mouse brain under acupuncture. This pilot study shows the potential of PAT as a visualization tool for illuminating the mechanism of acupuncture and promoting its clinical applications.
This paper developed a 4 array transducers photoacoustic endoscopic probe, and based on this, a photoacoustic endoscopic imaging system was build. Phantom experimental imaging was carried out, and the capability of location for endoscopic probe was demonstrated via analyzing the absorption of the light on the 4 sensors position. The in vitro human normal tissues and early colorectal cancer tissues was imaged using photoacoustic endoscopic system. The statistical analysis of the light absorbtion intensity distribution on different position proved that the photoacoustic endoscopic system has the ability to distinguish human normal tissues and early colorectal cancer tissues. This technology is expected to improve the accuracy of early diagnosis of colorectal cancer and has the potential clinical application.
Introduction: Although many piezoelectric micromachined ultrasonic transducers (pMUTs) with different structures have been presented and fabricated for photoacoustic imaging (PAI), most of them are lack of systemic analysis and optimizations of design parameters. It is of important to explore the internal physical mechanisms and corresponding cause-effect relationships of the receive performance of pMUTs with different structures. The purpose of this study is to present a novel numerical method for an efficient design of the AlN-based pMUT for application in PAI system. Methods: A planar and two curved (dome-shaped and concave) structures of pMUTs based on aluminum nitride (AlN) were modeled numerically in this study. For each pMUT, the performance of receive sensitivity was simulated systemically using the finite elements analysis (FEA). Moreover, the physical parameters of three structureswere analyzed in detail, such as the radius of curvature, the height of SiO2, the height of AlN and the height of polyimide. Results: The obtained results show that the receive performance of three structures in water or air could be ordered as: the dome-shaped > the concave > the planar. Further, several valuable findings of this study would be used to design pMUTs so as to achieve better receive performance, such as: (a) for an optimum radius of curvature almost exists for any curved pMUT, (b) a thinner supporting layer means a better receive performance, (c) the piezoelectric layer in three structures have an optimum thickness, and (d) the height of polyimide affects little the receive performance in all structures. Conclusions: For a pMUT-based ultrasound sensor in photoacoustic imaging (PAI), the dome-shaped pMUT has a better receive sensitivity than that of the planar structure and the concave structure, whose physical parameters combining the work frequency could be optimized efficiently with a numerical method.
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