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    Characterization of Ultrasound Elevation Beamwidth Artefacts for Brachytherapy Needle Insertion

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    Date
    2011-09-01
    Author
    Peikari, Mohammad
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    Abstract
    Ultrasound elevation beamwidth is the out of plane thickness causing image artefacts

    normally appearing around anechoic areas in the medium. These artefacts could also

    cause uncertainties in localizing objects (such as a surgical needle) in the ultrasound

    image slices. This thesis studies the clinical significance of elevation beamwidth artefacts

    in needle insertion procedures. A new measurement device was constructed to

    measure the transrectal ultrasound elevation beamwidth. The beam profiles of various

    lateral and axial distances to the transducer were generated. It is shown that

    the ultrasound elevation beamwidth converges to a point within its focal zone close

    to the transducer. This means that the transrectal ultrasound images have the best

    resolution within the focal zone of the ultrasound close to the transducer. It is also

    shown that the ultrasound device settings have a considerable impact on the amount

    of beamwidth artefacts. Needle tip localization error was examined for a curvilinear

    transrectal ultrasound transducer. Beveled prostate brachytherapy needles were inserted

    through all holes of a grid template orthogonal to the axial beam axis. The

    effects of device imaging parameters were also investigated on the amount of localization

    error. Based on the developed results, it was found that the imaging parameters

    of an ultrasound device have direct impact on the amount of object localization error

    from 0.5 mm to 4 mm. The smallest localization error occurs laterally close to the center of the grid template, and axially within the beam’s focal zone. Similarly, the

    largest localization error occurs laterally around both sides of the grid template, and

    axially within the beam’s far field. Using the ultrasound device with appropriate

    imaging settings could minimize the effects of these artefacts. We suggest to reduce

    the gain setting of the ultrasound device. This will reduce the energies assigned to

    the off-axis beams and as a result, the elevation beamwidth artefacts are minimized.
    URI for this record
    http://hdl.handle.net/1974/6696
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