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Aperture Effect

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Lihong V. Wang – One of the best experts on this subject based on the ideXlab platform.

  • High-NA-based virtual point detectors for photoacoustic imaging
    Photons Plus Ultrasound: Imaging and Sensing 2009, 2009
    Co-Authors: Lihong V. Wang

    Abstract:

    We demonstrated the focal point of a high-numerical-Aperture (NA) ultrasonic transducer can be used as a
    virtual point detector. This virtual point detector detects omnidirectionally over a wide acceptance angle. It
    also combines a large active transducer surface and a small Effective virtual detector size, thus the sensitivity is
    high compared with that of a real point detector, and the Aperture Effect is small compared with that of a finite
    size transducer. Phantom experiments are provided to demonstrate the applications of high-NA-based virtual
    point detectors in photoacoustic tomography and thermoacoustic tomography. The virtual point detector is also
    used to image the cerebral cortex of mice.

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  • Photoacoustic tomography of the mouse cerebral cortex with a high-numerical-Aperture-based virtual point detector.
    Journal of Biomedical Optics, 2009
    Co-Authors: Lihong V. Wang

    Abstract:

    The mouse cerebral cortex was imaged in situ by photoacoustic tomography (PAT). Instead of a flat ultrasonic transducer, a virtual point detector based on a high numerical Aperture (NA), positively focused transducer was used. This virtual point detector has a wide omnidirectional acceptance angle, a high sensitivity, and a negligible Aperture Effect. In addition, the virtual point detector can be located much more closely to the object during the detection. Compared with a finite-size flat transducer, images generated by using this virtual point detector have both uniform signal-to-noise ratio (SNR) and resolution.

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  • High-numerical-Aperture-based virtual point detectors for photoacoustic tomography.
    Applied Physics Letters, 2008
    Co-Authors: Lihong V. Wang

    Abstract:

    The focal point of a high-numerical-Aperture (NA) ultrasonic transducer can be used as a virtual point detector. This virtual point detector detects omnidirectionally over a wide acceptance angle. It also combines a large active transducer surface and a small Effective virtual detector size. Thus the sensitivity is high compared with that of a real point detector, and the Aperture Effect is small compared with that of a finite size transducer. We present two kinds of high-NA-based virtual point detectors and their successful application in photoacoustic tomography. They can also be applied in other ultrasound-related fields.

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Xinmai Yang – One of the best experts on this subject based on the ideXlab platform.

  • Ring-based ultrasonic virtual point detector with applications to photoacoustic tomography
    Applied Physics Letters, 2007
    Co-Authors: Xinmai Yang, Lihong V. Wang

    Abstract:

    An ultrasonic virtual point detector is constructed using the center of a ring transducer. The virtual point detector provides ideal omnidirectional detection free of any Aperture Effect. Compared with a real point detector, the virtual one has lower thermal noise and can be scanned with its center inside a physically inaccessible medium. When applied to photoacoustictomography, the virtual point detector provides both high spatial resolution and high signal-to-noise ratio. It can also be potentially applied to other ultrasound-related technologies.

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  • Photoacoustic tomography of a rat cerebral cortex with a ring-based ultrasonic virtual point detector.
    Journal of Biomedical Optics, 2007
    Co-Authors: Xinmai Yang, Lihong V. Wang

    Abstract:

    We image a rat cerebral cortex in situ by using a ring-based ultrasonic virtual point detector developed previously. Compared to the image generated by a finite-Aperture detector, the image generated by the virtual point detector has a uniformly distributed resolution throughout the imaged area, owing to the lack of Aperture Effect of the ultrasonic detector. At the periphery of the image, the signal-to-noise ratio of the image obtained by the virtual point detector is also better than that of a finite-Aperture detector. Furthermore, the virtual point detector can be scanned inside the brain to improve the local signal-to-noise ratio.

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Olaf. Kolditz – One of the best experts on this subject based on the ideXlab platform.

  • Toward physical aspects affecting a possible leakage of geologically stored CO_2 into the shallow subsurface
    Acta Geotechnica, 2014
    Co-Authors: Ashok Singh, Jens Olaf Delfs, Uwe Jens Görke, Olaf. Kolditz

    Abstract:

    In geological formations, migration of CO_2 plume is very complex and irregular. To make CO_2 capture and storage technology feasible, it is important to quantify CO_2 amount associated with possible leakage through natural occurring faults and fractures in geologic medium. Present work examines the fracture Aperture Effect on CO_2 migration due to free convection. Numerical results reveal that fracture with larger-Aperture intensify CO_2 leakage. Mathematical formulation and equations of state for the mixture are implemented within the object-oriented finite element code OpenGeoSys developed by the authors. The volume translated Peng–Robinson equation of state is used for material properties of CO_2 and water.

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  • Toward physical aspects affecting a possible leakage of geologically stored CO2 into the shallow subsurface
    Acta Geotechnica, 2013
    Co-Authors: Ashok Singh, Jens Olaf Delfs, Uwe Jens Görke, Olaf. Kolditz

    Abstract:

    In geological formations, migration of CO2 plume is very complex and irregular. To make CO2 capture and storage technology feasible, it is important to quantify CO2 amount associated with possible leakage through natural occurring faults and fractures in geologic medium. Present work examines the fracture Aperture Effect on CO2 migration due to free convection. Numerical results reveal that fracture with larger-Aperture intensify CO2 leakage. Mathematical formulation and equations of state for the mixture are implemented within the object-oriented finite element code OpenGeoSys developed by the authors. The volume translated Peng–Robinson equation of state is used for material properties of CO2 and water.

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