Photoacoustic imaging

Last revised by Andrew Murphy on 15 Mar 2021

Citation, DOI, disclosures and article data

Citation:

Botz B, Murphy A, Bell D, Photoacoustic imaging. Reference article, Radiopaedia.org (Accessed on 25 Apr 2024) https://doi.org/10.53347/rID-87647

DOI:

https://doi.org/10.53347/rID-87647

Permalink:

https://radiopaedia.org/articles/87647

rID:

87647

Article created:

10 Mar 2021, Bálint Botz ◉

Disclosures:

At the time the article was created Bálint Botz had no recorded disclosures.

View Bálint Botz's current disclosures

Last revised:

15 Mar 2021, Andrew Murphy ◉

Disclosures:

At the time the article was last revised Andrew Murphy had no recorded disclosures.

View Andrew Murphy's current disclosures

Revisions:

3 times, by 3 contributors - see full revision history and disclosures

Sections:

Imaging Technology

Synonyms:

Optoacoustic imaging
Optoacoustic tomography
Photoacoustic imaging (PAI)

Photoacoustic or optoacoustic imaging (PAI) is an emerging imaging modality that utilises a hybrid approach by using optical illumination of endogenous materials or administered fluorescent tracers, and consequent detection of the ultrasound waves released due to thermoelastic expansion.

During photoacoustic imaging, a typically nanosecond, narrow bandpass laser or LED illumination is used to excite biological tissues. Molecules absorb the optical energy and convert it to heat, which in turn results in thermoelectric expansion of the investigated tissue. This expansion generates acoustic waves that can be detected by US transducers. Clinical use of optical imaging has been hampered by the limited penetration of light in biological tissues. Photoacoustic imaging partially overcomes this limitation by using the emitted US waves for detection, increasing the maximum depth of the imaging to several centimetres.

The most promising aspect of photoacoustic imaging in clinical imaging is its ability to selectively detect naturally occurring chromophores with distinct optical absorption spectra, such as haemoglobin, lipids, melanin, and water ¹.

Current use and potential future applications

Label-free photoacoustic imaging is a non-invasive method similar to the conventional US, and can be readily utilised in a variety of tasks. It can differentiate deoxyhaemoglobin and haemoglobin, thereby directly visualising ischaemia/hypoxia. Superficial, pigmented lesions (e.g. melanoma) can also be visualised directly. Label-free photoacoustic imaging of tissue vascularity has been successfully employed in e.g. imaging of breast cancers, skin tumours, psoriatic skin lesions, wound healing, and inflammation of the small joints ^2-5. PAI has been also proposed as a tool to image disease activity in Crohn disease ⁶. With the light source easily integrated into a linear array, US transducer photoacoustic imaging can be readily utilised as an adjunct in sonography.

The clinically approved fluorophores indocyanine green, and methylene blue can also be depicted with photoacoustic imaging as can most other fluorescent tracers ¹. Selective labelling with these chromophores (e.g. labelled peptides or antibodies) can open up new perspectives in clinical molecular imaging.