P2B-14 Real-Time Indication of Acoustic Window for Phased-Array Transducers in Ultrasound Imaging

In ultrasound imaging, the transducer aperture may be partly obstructed due to a lack of acoustic contact with the patient skin, or from objects close to the transducer surface such as a patient's ribs. For phased-array operation, such a reduction of imaging aperture results in a gradual degradation in image quality in terms of a reduced lateral resolution and a loss in penetration. This loss in image quality is not always obvious and may result in that inferior images are used in further diagnosis. A method for real-time feedback of the acoustic contact along phased-array transducers has been developed. The method is based on the Fraunhofer approximation, which implies that the lateral power spectrum close to focus is bandlimited by the convolution of the transmit and receive aperture functions. By estimating and visualizing the lateral power spectrum, an image of the acoustic contact can be produced. Using data from a tissue-mimicking phantom, we show that the lateral power spectrum closely corresponds to the effective aperture used for 0-100% acoustic contact. The method was further evaluated for in vivo cardiac imaging, where we show that the obstruction of sound caused by the human sternum similarly can be observed in the lateral spectrum, and therefore indicate that a more suitable probe position should be sought.