Spatial localization of mechanical excitation affects spatial resolution, contrast, and contrast-to-noise ratio in acoustic radiation force optical coherence elastography.

Nichaluk Leartprapun,Steven G Adie,Colin D Mackey,Rishyashring R Iyer

doi:10.1364/boe.10.005877

Abstract

The notion that a spatially confined mechanical excitation would produce an elastogram with high spatial resolution has motivated the development of various elastography techniques with localized mechanical excitation. However, a quantitative investigation of the effects of spatial localization of mechanical excitation on the spatial resolution of elastograms is still lacking in optical coherence elastography (OCE). Here, we experimentally investigated the effect of spatial localization of acoustic radiation force (ARF) excitation on spatial resolution, contrast, and contrast-to-noise ratio (CNR) of dynamic uniaxial strain elastograms in dynamic ARF-OCE, based on a framework for analyzing the factors that influence the quality of the elastogram at different stages of the elastography workflow. Our results show that localized ARF excitation with a smaller acoustic focal spot size produced a strain elastogram with superior spatial resolution, contrast, and CNR. Our results also suggest that the spatial extent spanned by the displacement response in the sample may connect between the spatial localization of the mechanical excitation and the resulting elastogram quality. The elastography framework and experimental approach presented here may provide a basis for the quantitative analysis of elastogram quality in OCE that can be adapted and applied to different OCE systems and applications.

Highlights

Biomechanical interactions between cells and their surroundings play an important role in both physiological and pathological processes across a wide range of length scales [1,2,3,4]
In Experiment 2, we found that localized acoustic radiation force (ARF) excitation with a smaller region of excitation (ROE) produced a uniaxial strain elastogram with superior spatial resolution, contrast and contrast-to-noise ratio (CNR) compared to a larger ROE in all three side-by-side samples (Fig. 8)
We presented a dynamic ARF-optical coherence elastography (OCE) experimental investigation of the conjecture that in order to obtain an elastogram with high spatial resolution, the applied mechanical excitation must be spatially localized to a small region in the sample such that the response it produces is confined to a smaller spatial range

Summary

Introduction

Biomechanical interactions between cells and their surroundings play an important role in both physiological and pathological processes across a wide range of length scales [1,2,3,4]. The ability to resolve microscopic mechanical properties in nano- or micro-indentation testing with AFM has been attributed to the applied stress that is highly localized in 3D space underneath the indenter tip [21,22,23,24] This has motivated the development of numerous elastography techniques with localized mechanical excitation over the past two decades, including acousto-vibrography [17], acoustic radiation force impulse imaging (ARFI) [18,20], as well as various implementations of OCE [14,24,25,26,27,28]. The notion that a more spatially localized mechanical excitation would improve the spatial resolution of the elastogram remains relatively under-investigated, both theoretically and experimentally, despite having had a significant influence on the field of elastography

Methods

Results

Discussion

Conclusion