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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.

Author information

1
University College London, Department of Medical Physics and Biomedical Engineering, London, United Kingdom.
2
University of Twente, MIRA Institute for Biomedical Technology and Technical Medicine, Enschede, The Netherlands.
3
University College London, Department of Mechanical Engineering, London, United Kingdom.

Abstract

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.

KEYWORDS:

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

PMID:
29488363
DOI:
10.1117/1.JBO.23.2.026009

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