Diffusing light modulated by focused ultrasound (FUS) or acousto optic (AO) sensing is a hybrid technique that utilizes ultrasound features, such as, deep penetration, localize and precise spatial resolution, to surpass optical scattering limitations in optical sensing and maintain the original optical contrast. In this paper, we compare the acousto-optic (AO) signal amplitude when using three different light sources; long coherence, laser diode (LD), and light emitting diode (LED). In recent years, there has been a growing trend towards the use of LEDs and laser diode LDs in optical applications because of their compact and small size, ease of use, safety features, and cost-effectiveness. Aim of this paper is to examine the capability of LDs and LEDs to be used in AO sensing. We evaluated differences in the tagging efficiency using detection of AO signal amplitude metrics. The results showed that particularly LDs are also capable of providing acceptable tagging efficiency in AO-based sensing compared with long coherent lasers and can be beneficial option for use in AO based techniques.
The multiwavelength focused ultrasound (FUS)-optic technique in development aims to provide application for spatially accurate measurements of tissue properties in the focus area in real-time. But setting up such a system is quite challenging due to several factors, for instance the integration of different optical sources, positioning of the optical and acoustic beams on the phantom, and synchronization. In this presentation, we present first steps towards designing a multiwavelength FUS-optic system that measures wavelength dependent changes in the focus area. As a test substance, we used intralipid solution, milk, and the mixture with different levels of concentration. The expected signal peak heights of tagged photons intensities of different wavelengths are partly dependent on the concentration due to the wavelength-dependent optical absorbance. Furthermore, detected FUS modulated amplitudes are in relation with the concentration of sample in focus area. The aim of this study is to characterize the relationship between FUS-optic signal peak heights and the different levels of sample concentration at different wavelengths.
Focusing Ultrasound (FUS) can be used to modulate diffusing light in tissue. In this method, diffused photons are modulated in the ultrasound focus area. Detecting these FUS modulated (or tagged) photons can provide spatially accurate information from the focus area. However, probably the biggest challenge in this method is to enable sufficient tagging photons since most of the illuminated and detected photons do not propagate thru the FUS target area resulting in a low number of tagged photons when compared to the background unmodulated light. Therefore, current applications utilizing such hybrid technique are still limited. Our study aims to optimize illumination and detection of photons that propagate through a FUS target area by adjusting the relative position and angle of a light source-detector pair. For the simulations, the K-wave toolbox was utilized to calculate the nonlinear acoustic pressure field in the discretized numerical model from the FUS source. Furthermore, light propagation in the model is simulated using an open-source Monte Carlo algorithm. The model design is a backward detection mode which is suitable for direct application to the human body.
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