This work demonstrates the first measurements of blood flow velocity using photoacoustic flowmetry (PAF) employing a transducer array. The measurements were made in a flow phantom consisting of a tube (580 μm inner diameter) containing blood flowing steadily at physiological speeds ranging from 3 mm/s to 25 mm/s. Velocity measurements were based on the generation of two successive photoacoustic (PA) signals using two laser pulses with a wavelength of 1064 nm; the PA signals were detected using a 64-element transducer array with a -6 dB detection bandwidth of 11-17 MHz. We developed a processing pipeline to optimise a cross-correlation based velocity measurement method comprising the following processing steps: image reconstruction, filtering, displacement detection, and masking. We found no difference in flow detection accuracy when choosing different image reconstruction algorithms (time reversal, Fourier transformation, and delay-and-sum). High-pass filtering and wallfiltering were however found to be essential pre-processing steps in order to recover the correct displacement information. We masked the calculated velocity map based on the amplitude of the cross-correlation function in order to define the region of interest corresponding to highest signal amplitude. These developments enabled blood flow measurements using a transducer array, bringing PAF one step closer to clinical applicability.
T. M. Bücking, P. J. van den Berg, S. Balabani, W. Steenbergen, P. C. Beard, and J. Brunker, "Acoustic resolution photoacoustic Doppler flowmetry using a transducer array: optimising processing for velocity contrast," Proc. SPIE 10064, Photons Plus Ultrasound: Imaging and Sensing 2017, 100642M (Presented at SPIE BiOS: February 01, 2017; Published: 23 March 2017); https://doi.org/10.1117/12.2252939.
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