title: Pulsed photoacoustic Doppler flowmetry using time-domain cross-correlation: accuracy, resolution and scalability.
abstract: The feasibility of making spatially resolved measurements of blood velocity using a pulsed photoacoustic Doppler technique in acoustic resolution mode has been investigated. Doppler time shifts were quantified via cross-correlation of photoacoustic waveform pairs generated within a blood-simulating phantom using pairs of light pulses. The phantom comprised micron-scale absorbers imprinted on an acetate sheet and moved at known velocities. The photoacoustic waves were detected using PZT ultrasound transducers operating at center frequencies of 20 MHz, 5 MHz and 3.5 MHz; measurements of velocity and resolution were calculated from the mean cross-correlation function of 25 waveform pairs. Velocities in the range ±0.15 to ±1.5 ms(-1) were quantified with accuracies as low as 1%. The transducer focal beam width determines a maximum measurable velocity |V(max)| beyond which correlation is lost due to absorbers moving out of the focal beam between the two laser pulses. Below |V(max)| a measurement resolution of <4% of the measured velocity was achieved. Resolution and |V(max)| can be scaled to much lower velocities such as those encountered in microvasculature (< 50 mms(-1)). The advantage of pulsed rather than continuous-wave excitation is that spatially resolved velocity measurements can be made, offering the prospect of mapping flow within the microcirculation.
authors.affiliation: Department of Medical Physics and Bioengineering, University College London, Gower Street, London WC1E 6BT, UK. joanna.brunker.09@ucl.ac.uk
authors.forename: Joanna
authors.initials: J
authors.lastname: Brunker
authors.forename: Paul
authors.initials: P
authors.lastname: Beard
mesh_terms: D000818:Animals; D001783:Blood Flow Velocity; D004912:Erythrocytes / Q000502:physiology*; D005240:Feasibility Studies; D006801:Humans; D017078:Laser-Doppler Flowmetry / Q000295:instrumentation / Q000379:methods*; D008833:Microcirculation; D008955:Models, Cardiovascular; D019047:Phantoms, Imaging; D061088:Photoacoustic Techniques / Q000295:instrumentation; D015203:Reproducibility of Results; D012815:Signal Processing, Computer-Assisted; D013997:Time Factors; D014159:Transducers