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J Biomed Opt. 2018 Feb;23(2):1-8. doi: 10.1117/1.JBO.23.2.026009.

Processing methods for photoacoustic Doppler flowmetry with a clinical ultrasound scanner.

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University College London, Department of Medical Physics and Biomedical Engineering, London, United Kingdom.
University of Twente, MIRA Institute for Biomedical Technology and Technical Medicine, Enschede, The Netherlands.
University College London, Department of Mechanical Engineering, London, United Kingdom.


Photoacoustic flowmetry (PAF) based on time-domain cross correlation of photoacoustic signals is a promising technique for deep tissue measurement of blood flow velocity. Signal processing has previously been developed for single element transducers. Here, the processing methods for acoustic resolution PAF using a clinical ultrasound transducer array are developed and validated using a 64-element transducer array with a -6 dB detection band of 11 to 17 MHz. Measurements were performed on a flow phantom consisting of a tube (580  μm inner diameter) perfused with human blood flowing at physiological speeds ranging from 3 to 25  mm  /  s. The processing pipeline comprised: image reconstruction, filtering, displacement detection, and masking. High-pass filtering and background subtraction were found to be key preprocessing steps to enable accurate flow velocity estimates, which were calculated using a cross-correlation based method. In addition, the regions of interest in the calculated velocity maps were defined using a masking approach based on the amplitude of the cross-correlation functions. These developments enabled blood flow measurements using a transducer array, bringing PAF one step closer to clinical applicability.


blood flow; cross correlation; flowmetry; image processing; masking; photoacoustic Doppler effect; transducer array


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