Exploiting blood flow fluctuations to improve visibility in photoacoustic imaging (Conference Presentation)

Abstract

Limited-view and bandwidth-limited acquisition in acoustic–resolution photoacoustic imaging lead to known imaging artifacts. To eliminate these artifacts, it has first been proposed to use fluctuations induced by multiple speckle illuminations to recover otherwise invisible features. However, a very small size of the optical speckle grain at depth in tissue against the acoustic resolution makes this approach unrealistic in practice. Here, we demonstrate experimentally in vitro that fluctuations induced by blood flow at physiological concentration may be exploited to improve visibility in photoacoustic imaging. We first illustrate how our method reveals features otherwise invisible due to the source directivity: a bended capillary tube (inner diameter 100µm) filled with blood flowing at 1.7cm/s was illuminated by 5ns laser pulses (=532nm, fluence=3.0mJ/cm2, PRF=100Hz) and imaged with a linear ultrasound array (128 elements, pitch=0.1mm, fc=15MHz) connected to an acquisition device. Being partially invisible in the conventional image, the whole capillary is reconstructed by means of a second-order analysis of photoacoustic images. Second, we illustrate how our approach allows for visualization of the inside of large objects otherwise invisible due to highpass filtering: we performed a second-order analysis on photoacoustic data resulting from illumination (=800nm, fluence=9.0mJ/cm2, PRF=10Hz/100Hz) of a glass tube (inner diameter 1mm) with blood flowing at 1cm/s. Whether the tube is perpendicular to the imaging plane or is lying inside the imaging plane parallel to the probe, the whole blood volume is visible on the fluctuation-based image, whereas conventional imaging only reveals the blood stream boundaries.