New non-invasive imaging method for showing oxygen in tissue

July 28, 2016, Technical University Munich
eMSOT-images show the amount of oxygen in tissue: red marks high levels of oxygen, green marks low levels. Credit: Tzoumas / TUM

Learning how to look inside a body without having to cut it open is still an important part of medical research. One of the great challenges in imaging remains the visualization of oxygen in tissue. A team led by Prof. Vasilis Ntziachristos, Chair for Biological Imaging at the Technical University of Munich (TUM) and Director of the Institute for Biological and Medical Imaging at the Helmholtz Zentrum München , has developed a new approach to this task.

Imaging of tissue oxygenation is not straightforward; different techniques have been considered but each of them has their shortcomings. In recent years, research in this field has focused on optoacoustic methods. These, especially Multispectral optoacoustic tomography (MSOT), form one of the key areas of Vasilis Ntziachristos' research.

Put in simple terms, MSOT turns into sound and then into visual information: First, a weak pulsed is directed at tissue. Absorbing molecules and cells respond with a minuscule vibration, which, in turn, creates sound signals. The sound signals are then picked up by sound sensors and translated into images. The way molecules and cells react to the laser beam offers insight into their optical and thus into their biochemical properties.

Complex tissue is an obstacle to optoacoustic imaging

While MSOT can, in theory, be used to tell how much oxygen can be found in blood, there is one major obstacle: The intensity of light changes with depth, not only because light has been filtered through all the tissue layers that it passed through, but also because different tissue structures may have different properties that affect how light is scattered and absorbed. In the past, there have been several attempts to solve this problem by calculating how the tissue will affect the propagation of light. "However, due to the high optical complexity of tissues, this approach so far could not be flexibly applied in optoacoustic images of tissues of living subjects," says Stratis Tzoumas, first author of a study published in Nature Communications, in which the scientists describe their new method.

A new description of light distribution in tissue

Ntziachristos, Tzoumas, and their colleagues came up with a completely different approach. Instead of describing the spatial distribution of light, their imaging method eMSOT - the e stands for "eigenspectra" - avoids simulating the path of light through complex tissue altogether. Instead the new method is based on the discovery that the spectrum of light propagating in tissue can be described by using a small number of basic spectra. eMSOT uses data from a conventional MSOT-device combined with a new algorithm that is based on this novel way of describing the light spectrum to correct for the effects of light propagation in tissue and obtain accurate of blood oxygenation in tissue.

With eMSOT, the scientists were able to visualize the blood oxygenation level of up to one centimeter below the skin surface. "Theoretically, the imaging depth can be extended to more than that," says Stratis Tzoumas. "There is, however, a limit at about three because at some point, light cannot penetrate the tissue any further." The scientists observed a vastly improved accuracy in eMSOT over previous optical and optoacoustic approaches. Apart from being non-invasive and radiation-free, eMSOT also delivers comparable or higher resolution both spatially and temporally, than other optical imaging methods. "Information about the amount of oxygen in is important when it comes to various fields in research and treatment - for example tumor growth or in measurements of metabolism" says Vasilis Ntziachristos. "It may be that eMSOT becomes the gold standard method, once it is ready for clinical use."

Explore further: Photoacoustic and magnetic resonance imaging visualizes blood flow and oxygenation status in brain tumor tissue

More information: Stratis Tzoumas et al, Eigenspectra optoacoustic tomography achieves quantitative blood oxygenation imaging deep in tissues, Nature Communications (2016). DOI: 10.1038/ncomms12121

Related Stories

New laser gets to the heart of imaging

April 14, 2016

Yale scientists have developed a laser imaging system with the versatility to look at both the structure of biological tissue and the dynamic activity—such as a heartbeat or the movement of blood cells—that goes on inside.

Flipping the switch to better see cancer cells at depths

November 9, 2015

Using a high-tech imaging method, a team of biomedical engineers at the School of Engineering & Applied Science at Washington University in St. Louis was able to see early-developing cancer cells deeper in tissue than ever ...

Recommended for you

Coffee-based colloids for direct solar absorption

March 22, 2019

Solar energy is one of the most promising resources to help reduce fossil fuel consumption and mitigate greenhouse gas emissions to power a sustainable future. Devices presently in use to convert solar energy into thermal ...

Physicists reveal why matter dominates universe

March 21, 2019

Physicists in the College of Arts and Sciences at Syracuse University have confirmed that matter and antimatter decay differently for elementary particles containing charmed quarks.

ATLAS experiment observes light scattering off light

March 20, 2019

Light-by-light scattering is a very rare phenomenon in which two photons interact, producing another pair of photons. This process was among the earliest predictions of quantum electrodynamics (QED), the quantum theory of ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.