Solving the speckle decorrelation challenge in acousto-optic sensing using tandem nanosecond pulses within the ultrasound period

We present a novel acousto-optic (AO) method, based on a nanosecond laser system, which will enable us to obtain AO signals in liquid turbid media. By diverting part of the light in a delay line, we inject tandem pulses with 27 ns separation. The change of the speckle pattern, caused by the ultrasound phase shift, reduces the speckle contrast of the integrated speckle pattern captured in a single camera frame. With these tandem pulses, we were able to perform AO on a 2 cm liquid turbid medium in transmission mode. We show the raw signal and a spatial AO scan of a homogenous water-intralipid sample. This approach is potentially capable of AO probing in vivo, since the acquisition time (of approximately 40 ns) is four orders of magnitude less than the typical time scales of speckle decorrelation found in vivo. The method may eventually enable us to obtain fluence compensated photoacoustic signals generated by the same lase

Towards acousto-optic tissue imaging with nanosecond laser pulses

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

Towards quantitative tissue absorption imaging by combining photoacoustics and acousto-optics

We propose a strategy for quantitative photoacoustic mapping of chromophore concentrations that can be performed purely experimentally. We exploit the possibility of acousto-optic modulation using focused ultrasound, and the principle that photons follow trajectories through a turbid medium in two directions with equal probability. A theory is presented that expresses the local absorption coefficient inside a medium in terms of noninvasively measured quantities and experimental parameters. Proof of the validity of the theory is given with Monte Carlo simulations.Comment: 14 pages, 5 figure

Time domain algorithm for accelerated determination of the first order moment of photo current fluctuations in high speed laser Doppler perfusion imaging

Advances in optical array sensor technology allow for the real time acquisition of dynamic laser speckle patterns generated by tissue perfusion, which, in principle, allows for real time laser Doppler perfusion imaging (LDPI). Exploitation of these developments is enhanced with the introduction of faster algorithms to transform photo currents into perfusion estimates using the first moment of the power spectrum. A time domain (TD) algorithm is presented for determining the first-order spectral moment. Experiments are performed to compare this algorithm with the widely used Fast Fourier Transform (FFT). This study shows that the TD-algorithm is twice as fast as the FFT-algorithm without loss of accuracy. Compared to FFT, the TD-algorithm is efficient in terms of processor time, memory usage and data transport