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

Lukasz J. Nowak,Wiendelt Steenbergen

doi:10.1117/1.jbo.25.9.096002

Abstract

.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.

Highlights

Pathological changes in tissues, such as tumors, can often be detected by their distinctive optical properties
Acousto-optic imaging (AOI) is a technique that can potentially overcome the limitations of purely optical and acoustical medical imaging modalities by utilizing the effects of the interaction between focused US and light scattered in a tissue
speckle contrast difference (SCD) values were determined for different phantoms and various probe positions relative to the inclusions

Summary

Introduction

Pathological changes in tissues, such as tumors, can often be detected by their distinctive optical properties. This fact is exploited by various medical imaging techniques for fast and noninvasive diagnostics and therapy guidance If such pathological changes are localized deeper than a few millimeters inside the body, their detection using purely optical means becomes challenging due to the high scattering of light in tissues.[1] Ultrasound (US) imaging can be used to visualize deeper anatomical structures; it is only capable of detecting boundaries of regions with high enough acoustic impedance contrast. It does not provide any information regarding the diagnostically relevant optical properties of the region of interest.

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