Optoacoustic

Optoacoustic is a term that denotes the combination of optical (Greek, oπτικός) and acoustic (Greek, ακουστικός) energy (or components) in a single modality, which distinguishes optoacoustic imaging from optical imaging. Photoecho denotes the combination of light (Greek, Φως <phos>) and sound ( Ήχος <echos>) or reflection of sound Hχώ <echo>). The term photoacoustic is also widely used, and it denotes the generation of acoustic energy by light. Photoecho and photoacoustic are to optoacoustics what photon is to optics: optical methods rely on photons, whereas optoacoustic methods rely on photoechoes or photoacoustic responses.

Usage: Multi-spectral Optoacoustic Tomography (MSOT)

Multi-spectral optoacoustic tomography (MSOT) is an imaging technology that generates high-resolution optical images in scattering media, including biological tissues. MSOT illuminates tissue with light of transient energy, typically light pulses lasting 1-100 nanoseconds. The tissue absorbs the light pulses, and as a result undergoes thermo-elastic expansion, a phenomenon known as the optoacoustic or photoacoustic effect. This expansion gives rise to ultrasound waves (photoechoes) that are detected and formed into an image. Image formation can be done by means of hardware (e.g. acoustic focusing or optical focusing) or computed tomography (mathematical image formation). Unlike other types of optoacoustic imaging, MSOT involves illuminating the sample with multiple wavelengths, allowing it to detect ultrasound waves emitted by different photoabsorbing molecules in the tissue, whether endogenous (oxygenated and deoxygenated hemoglobin, melanin) or exogenous (imaging probes, nanoparticles). Computational techniques such as spectral unmixing deconvolute the ultrasound waves emitted by these different absorbers, allowing each emitter to be visualized separately in the target tissue. In this way, MSOT can allow visualization of hemoglobin concentration and tissue oxygenation or hypoxia. Unlike other optical imaging methods, MSOT is unaffected by photon scattering and thus can provide high-resolution optical images deep inside biological tissues [1].

References

[1] V. Ntziachristos, D. Razansky, Molecular imaging by means of multispectral optoacoustic tomography (MSOT), Chem. Rev. 110 (2010) 2783-2794.