Photoacoustic flow velocity imaging based on complex field decorrelation

Abstract

Photoacoustic (PA) imaging can be used to monitor flowing blood inside the microvascular and capillary bed. Ultrasound speckle decorrelation based velocimetry imaging was previously shown to accurately estimate blood flow velocity in mouse brain (micro-)vasculature. Translating this method to photoacoustic imaging will allow simultaneous imaging of flow velocity and extracting functional parameters like blood oxygenation. In this study, we use a pulsed laser diode and a quantitative method based on normalized first order field autocorrelation function of PA field fluctuations to estimate flow velocities in an ink tube phantom and in the microvasculature of the chorioallantoic membrane of a chicken embryo. We demonstrate how the decorrelation time of signals acquired over frames are related to the flow speed and show that the PA flow analysis based on this approach is an angle independent flow velocity imaging method.

Speckle Variance Photoacoustic Microscopy for Microhemodynamic Imaging

“…For the microcirculatory tissue beds (e.g., retinal vessels) that are almost perpendicular to the photoacoustic detection axis, SV-PAM still can visualize the hemodynamics by interrogating varied photoacoustic signals caused by the flowing RBCs. Unfortunately, inaccurate estimation of the axial component of the flow vector potentially occurs because of a very subtle time shift or phase shift in the photoacoustic signals. ,, Also, SV-PAM can capture the hemodynamic images (Figures –) without determining the voxel sizes of the excitation laser and/or ultrasonic detection − or imposing an additional thermal spot. , …”

“…The flow speed is quantified based on the photoacoustic Doppler effect. − However, it is impossible to accurately estimate the Doppler angle (angle of the flow direction with respect to the axis of the received acoustic wave) due to insufficient photoacoustic imaging resolution, and only the axial component of the flow vector is obtained. Analyzing the slow-time photoacoustic profiles or autocorrelation function of the photoacoustic signal fluctuations allows one to estimate the flow speed, − but the determination of voxel sizes of the excitation laser and/or the ultrasonic detection always suffers from optical and ultrasonic scattering of the biological tissues, possibly compromising the measurement accuracy. Photoacoustic flowgraphy is achieved by high-speed monitoring of thermal tagging. , However, light or ultrasonic irradiation potentially causes tissue damage.…”

Fibre optic intravascular measurements of blood flow: A review

“…Recently there has been significant interest in this modality to perform intravascular imaging with molecular contrast for pathologies in the vessel walls, such as lipid rich plaques [165]. Photoacoustic imaging performed from outside the body has been used to measure and image blood flow with different mechanisms including PA Doppler shifts [166,167], PA Doppler bandwidth broadening [168], the temperature dependence of the Grüneisen parameter [169], and field fluctuations [170]. With all-optical ultrasound imaging, pulsed light is provided to an engineered coating where it generates ultrasound, and reflections are received.…”

Photoacoustic imaging on its way toward clinical utility: a tutorial review focusing on practical application in medicine

“…Thus, the pressure wave principally has a period 2tp and a maximum frequency fmax=12tp. This effect is visible in experiments with relatively longer pulses, small targets, and high detection frequencies 31 …”

“…This effect is visible in experiments with relatively longer pulses, small targets, and high detection frequencies. 31 …”