Ultrasound-mediated optical tomography: a review of current methods

Abstract

Ultrasound-mediated optical tomography (UOT) is a hybrid technique that is able to combine the high penetration depth and high spatial resolution of ultrasound imaging to overcome the limits imposed by optical scattering for deep tissue optical sensing and imaging. It has been proposed as a method to detect blood concentrations, oxygenation and metabolism at depth in tissue for the detection of vascularized tumours or the presence of absorbing or scattering contrast agents. In this paper, the basic principles of the method are outlined and methods for simulating the UOT signal are described. The main detection methods are then summarized with a discussion of the advantages and disadvantages of each. The recent focus on increasing the weak UOT signal through the use of the acoustic radiation force is explained, together with a summary of our results showing sensitivity to the mechanical shear stiffness and optical absorption properties of tissue-mimicking phantoms.

Shear Wave Elasticity Imaging Based on Acoustic Radiation Force and Optical Detection

“…This has been utilised in ultrasound modulated optical tomography (also called acousto-optic imaging) to image local tissue optical properties at millimetre to centimetre depth. Recent reviews of this topic can be found in (Wang 2004;3 Tang et al 2010;Daniel S. Elson et al 2011). Simulation results have shown that by using temporally coherent light and detecting the phase change of diffuse photons from tissue, tissue displacement at the level of nanometres can be detected (Li et al 2009).…”

Optical phase conjugation in Nd:YVO_4 for acousto-optic detection in scattering media

“…Tagging photons using ultrasound is a method to map the optical properties of thick scattering media such as biological tissues [1]. In order to detect the ultrasonically tagged photons coming out of a scattering sample, dynamic holographic techniques are frequently used.…”

Fast acousto-optic tissue sensing with tandem nanosecond pulses

“…A major challenge towards quantification of optical absorption is to compensate the signal strength of photoacoustics for local fluence variations. Recently fluence compensation of PA signals was proposed by using acousto-optic (AO) imaging [17,104] in combination with PA [7]. This method relies on the principle that both PA and AO signal strength depend on the local fluence.…”

“…In this review we describe the progress made in AO imaging since the previous review by Wang [1] in 2003: theoretical models, the detection methods to detect the tagged photons, and applications of AO imaging. For further reading, a review by Elson et al [17] is also focusing on the detection methods, scanning and applications. They give however no equations from the models in the modeling section.…”

“…[17,104] Both methods can be combined to achieve fluence compensated PA imaging [7,8]. While PA already has in vivo applications, AO still suffers from so called speckle decorrelation when applied in vivo, which typically results in no or poor signals.…”