Abstract
We present a way to generate acousto-optical signals in timovssue-like media with nanosecond laser pulses. Our method is based on recording and analyzing speckle patterns formed by interaction of nanosecond laser pulses with tissue, without and with simultaneous application of ultrasound. Stroboscopic application allows visualizing the temporal behavior of speckles while the ultrasound is propagating through the medium. We investigate two ways of quantifying the acousto-optic effect, viz. adding and subtracting speckle patterns obtained at various ultrasound phases. Both methods are compared with the existing speckle contrast method using a 2D scan and are found to perform similarly. Our method gives outlook on overcoming the speckle decorrelation problem in acousto-optics, and therefore brings in-vivo acousto-optic measurements one step closer. Furthermore it enables combining acousto-optics and photoacoustics in one setup with a single laser.
Highlights
Two hybrid techniques that combine optical contrast and the relatively high resolution of ultrasound (US) in turbid media are photoacoustics (PA) and acousto-optics (AO) [1, 2]
Length of 1.5 m and a pulse energy of 350mJ. This system is capable of delivering enough light in a single pulse to generate a speckle pattern at the camera after transmission through a turbid medium and the energy is sufficient for photoacoustic applications
Two synchronized function generators (FG)(Tektronix AFG 3102) give two TTL trigger signals for the laser consisting of flashlamp (FL) and Q-switch (QS) A third trigger is for the camera (CCD)(Allied Vision Technologies Manta G-145B NIR)
Summary
Two hybrid techniques that combine optical contrast and the relatively high resolution of ultrasound (US) in turbid media are photoacoustics (PA) and acousto-optics (AO) [1, 2]. By applying focused ultrasound on the sample the light acquires a modulated phase change in the US focus [5]. The amount of modulation can be detected in several ways These methods require the measurement to be performed within the so-called speckle decorrelation time. We demonstrate a novel method that brings us close to measuring acousto-optic signals far within the speckle decorrelation time of living tissue. To this end we use a laser that combines an adequately long coherence length with short (nanoseconds) high intensity pulses. For we use a laser at a repetition rate of 10 Hz, stable phantoms with long decorrelation time (>100 ms) are used to give a proof-of-principle
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