Technology

Imaging optical contrast in high-resolution, at depth

Optoacoustic imaging: light in, sound out

OAI has the unique capability of visualizing optical contrast at high resolution (down to 10 µm) in deep tissue (up to 3 cm) and displaying the image in real time. This capability is made possible by the photoacoustic effect – the conversion of light energy into acoustic signals. 

Depiction of the photoacoustic effect with a handheld detector.

Depiction of the photoacoustic effect with a handheld detector.

The tradeoff between depth and resolution

Bioimaging can be differentiated into three regimes of imaging depth and spatial resolution.

iThera Medical’s product range features imaging systems for preclinical and clinical use, for both the macroscopic and mesoscopic regime (10 vs. 150 µm resolution at 2 mm vs. 3 cm depth penetration). Additional differences in the product portfolio relate to frame rate, field of view and single-wavelength vs. multispectral illumination.

Differentiating chromophores via multispectral OAI

Depiction of the near infrared absorption spectra of different observable chromophores present in tissue.

Acoustic signals generated in OAI are proportional to optical absorption. Exciting tissue with a single wavelength will yield a composite result of tissue absorbance. To analyze the distribution and concentration of different chromophores, tissue needs to be illuminated with multiple wavelengths. The resulting images are then analyzed regarding their intensity change with changes in wavelength.

The optoacoustic imaging chain

Image processing occurs in multiple steps to enhance visualization and quantification.

Following data acquisition, the signals are reconstructed to form images. Fluence correction is applied to account for reduction in light fluence at depth. Spectral analysis then separates the contribution of different chromophores – both intrinsic (e.g., hemoglobin, melanin, lipids) and extrinsic (e.g., fluorescent probes, nanoparticles). Finally, the image is filtered to enhance anatomical features. All steps can be performed in real time.

The complete range of systems

for optoacoustic imaging

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Top Publications

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Razansky D et al., Nat Protoc. 2011 Jul 7;6(8):1121-9.
Buehler A et al., Opt Lett. 2013 May 1;38(9):1404-6.
Omar M et al., Opt Lett. 2014 Jul 1;39(13):3911-4.
Mercep E. et al., IEEE Trans Ultrason Ferroelectr Freq Control. 2015 Sep;62(9):1651-61.