Light Scattering Characteristics of Biological Tissues in Coaxial Ultrasound-Modulated Optical Tomography

Photons Plus Ultrasound: Imaging and Sensing 2021

2021

Imaging performance of an acousto-optic system is limited by light fluence rate and acoustic pressure filed distributions characteristics. The system parameters can be shaped by changing relative positions of ultrasound transducer array and optodes. However, in case of many potential clinical applications optimization possibilities in this regard are limited, as a sample is accessible from one side only and using a water tank for coupling is not feasible. We investigate the possibilities of improving performance of an acousto-optic imaging system operating in reflection mode geometry with linear ultrasound array in direct contact with a sample by using plane wave instead of focused ultrasound pulses. Differences in acoustic pressure field distributions for various transducer excitation patterns were determined numerically. Acousto-optic images of phantoms with and without optically absorbing inclusions were acquired by measuring laser speckle contrast decrease due to the light modulation by plane wave and focused ultrasound pulses. The light fluence rate maps reconstructed using plane wave imaging proved more distinct and clear.

Section: Introductionmentioning

confidence: 99%

Plane wave acousto-optic imaging in reflection mode geometry

Photons Plus Ultrasound: Imaging and Sensing 2021

2021

“…In this study, we consider a reflection mode AOI, i.e., configuration in which both optodes and US transducer are positioned on the same side of an investigated sample. Such a configuration was previously investigated by Lev et al, [7][8][9] Hisaka and Saskura, 10 Kim et al, 11 and Hong-Bo et al 12 In all of these investigations, the imaging was performed by physically changing the relative positions of the investigated sample and the probe while keeping the US focus constant. Such an approach allows one to directly link the observed changes of the received signal with changes of optical properties within the region of interest.…”

Section: Introductionmentioning

confidence: 99%

Reflection-mode acousto-optic imaging using plane wave ultrasound pulses

2021

J. Biomed. Opt.

Significance: Performance of an acousto-optic imaging system is limited by light fluence rate and acoustic pressure field distributions characteristics. In optically scattering media, the former determines the achievable contrast, whereas the latter the imaging resolution. The system parameters can be shaped by changing relative positions of ultrasound (US) transducer array and optodes. However, in the case of many potential clinical applications, optimization possibilities in this regard are limited, as a sample is accessible from one side only and using a water tank for coupling is not feasible.Aim: We investigate the possibilities of improving performance of an acousto-optic imaging system operating in reflection mode geometry with linear US array in direct contact with a sample using plane wave instead of focused US pulses.Approach: Differences in acoustic pressure field distributions for various transducer excitation patterns were determined numerically and experimentally. Acousto-optic images of phantoms with and without optically absorbing inclusions were acquired by measuring laser speckle contrast decrease due to the light modulation by plane wave and focused US pulses with different apodization patterns.Results: The residual acoustic pressure field components occupy relatively large volume and contribute to light modulation. Using nonsteered plane wave US pulses instead of focused ones allows one to mitigate their influence. It also allows one to obtain clear two-dimensional reconstructions of light fluence rate maps by shifting transducer apodization along the lateral direction.Conclusions: Using nonsteered plane wave US pulses allows one to achieve better imaging performance than with focused pulses in the assumed system geometry.

“…They have demonstrated that detection of light-absorbing inclusions inside the investigated samples is possible using this approach. Hisaka and Sasakura, 16 Kim et al., 17 and Hong-Bo et al. 18 presented reflection-mode AOI setups with a light source and detector located above the US transducer, all at fixed positions on the same side of the sample.…”

Section: Introductionmentioning

confidence: 99%

“… 18 presented reflection-mode AOI setups with a light source and detector located above the US transducer, all at fixed positions on the same side of the sample. The US focus was also fixed, and the scanning was performed by mechanically moving the sample inside a water tank 17 , 18 (the Hisaka and Sasakura study 16 does not provide details on coupling to the sample). The studies demonstrated that it is possible to detect light-absorbing inclusions inside phantoms and tissue samples using such a measurement configuration.…”

Section: Introductionmentioning

confidence: 99%

Reflection-mode acousto-optic imaging using a one-dimensional ultrasound array with electronically scanned focus

2020

J. Biomed. Opt.

. Significance: Practical implementation of acousto-optic imaging (AOI) encounters difficulties that prevent it from rapid adoption in clinical use. In many practical medical applications, the region of interest may be accessed only from one side, and using a water tank for coupling is not feasible. The solution might be to use reflection-mode imaging with an electronically scanned ultrasound (US) focus. Such an approach, however, entails considerable challenges. Aim: The possibilities of detecting and localizing light-absorbing inclusions inside turbid media by combining reflection-mode AOI conducted using a one-dimensional US array with electronic scanning of the US focus are investigated experimentally and signal processing algorithms that could be used for this purpose are introduced. Approach: We determine the speckle contrast decrease due to the acousto-optic effect as a function of the US focal point coordinates. Different signal postprocessing techniques are investigated. Results: A significant decrease in the determined speckle contrast difference values is observed due to the presence of light-absorbing inclusions. However, local minima occur in the plots only under specific conditions. Subtracting individual distributions and determining symmetry deviations allow for localizing the inclusions. Conclusions: Detection and localization of optically distinct regions are possible using the introduced approach. Signal postprocessing is required in a general case.