MORSOM: Probing deeper into living tissues

Visualizing biological processes deep within tissue is a continuing challenge for basic and clinical research. Optical microscopy can work only down to a few hundred microns below the surface because biological tissue strongly scatters light. Now, scientists at Helmholtz Zentrum München and the Technical University of Munich, in partnership with Carl Zeiss AG and iThera Medical GmbH, have presented in the journal ‘Light: Science & Applications’ a new class of optoacoustic mesoscopes that push biological microscopy to new depths.


MORSOM image of 21-day-old zebrafish, showing tissue features as deep as 1 mm. Source: Helmholtz Zentrum München/Dr. Murad Omar

"Optical imaging of intact, non-transparent tissue and model organisms is an important and demanding goal of high biological interest", says Professor Dr. Vasilis Ntziachristos, Director of the Institute of Biological and Medical Imaging (IBMI) at Helmholtz Zentrum München and the Chair for Biological Imaging at the Technical University of Munich (TUM). In optical microscopy, the biological sample is illuminated with light, and the light reflected or generated from the sample is used to form an image. While such microscopy has revolutionized biology, it is limited to studying very thin biological samples, since opaque tissues strongly scatter the illuminating light, preventing the formation of a well‑resolved image. As a result, optical microscopy can analyze biological processes only in thin systems such as cell monolayers, very small transparent organisms in embryonic stages of growth, or tissues dissected from larger organisms.

The mesoscopes designed by the Ntziachristos team get around the depth limitation of optical microscopy by using optoacoustic waves rather than light to image biological samples. The new technique, known as multi-orientation raster scan optoacoustic mesoscopy (MORSOM), illuminates the sample with unfocused light pulses. The sample absorbs the light energy and converts it to heat, causing thermo-elastic expansion, which generates ultrasound waves. These waves are detected by sensors that wrap around the sample, and the wave information is processed mathematically to recover structures deep within the tissue. Since biological tissue scatters ultrasound waves much less than it scatters light waves, MORSOM can provide high-resolution images at tissue depths that optical microscopy cannot reach. “MORSOM makes it possible, for the first time, to image intact, living non-transparent organisms, even after they have reached adulthood, without the need for tissue dissection,” said Ntziachristos.

At the moment, MORSOM can image as deep as 2‑3 mm in opaque organisms, making it well suited to studies of developmental biology and experimental genetics especially with model organisms such as zebrafish, and Drosophila melanogaster.

“The high resolution of MORSOM,” says Dr. Murad Omar, senior scientist on Ntziachristos' team, “comes from the use of ultra-broadband detectors, such as in our case from 10 to 160 MHz.” This frequency range has allowed visualization of structures never seen before in intact, living animals, such as the complex branching of blood vessel networks, melanin-rich structures deep within the skin, and the complete boundaries of internal organs of young fish that, because of their opaque bodies, cannot be studied by light microscopy while still alive.

While MORSOM promises to promote the visualization of biological processes deep inside living organisms, it will not make optical microscopy obsolete. Instead, Ntziachristos’ team is collaborating with Carl Zeiss AG and iThera Medical GmbH to combine optical mesoscopy with a particular type of conventional optical microscopy called single plane illumination microscopy (SPIM) in order to create a single system that can visualize organisms from early stages of development to adulthood, on multiple scales of cells, tissues, organs, and whole organisms. “This will allow unprecedented integration of molecular processes with tissue- and organism-wide processes in healthy animals and disease models”, says Omar.

According to the scientists, MORSOM and technologies derived from it are likely to bring substantial advances not only in the basic understanding of biological processes, but also in efforts to improve the treatment of disease. Omar points out, “We will be able to gain significant insights on disease and treatment from model organisms with the aim of translating this knowledge to help patients." Ntziachristos notes that “this work is aligned with the emerging theme of Munich Bioengineering, which aims to accelerate the discovery of effective treatments for cancer, metabolic diseases and other diseases of high human burden”.  

Further Information

The research presented here reflects the successful collaboration of IBMI and TUM scientists with scientists at Carl Zeiss AG and iThera Medical GmbH within the framework of the Federal Ministry of Education and Research (BMBF)-funded project Tech2See. This project, coordinated by Professor Ntziachristos, pursues the goal of developing the first hybrid prototype device combining optoacoustic mesoscopy and SPIM in order to surpass the limitations of optical microscopy.

Original publication :
Murad Omar et al. (2017), “Optical imaging of post-embryonic zebrafish using multi orientation raster scan optoacoustic mesoscopy”. Light: Science & Applications, doi: 10.1038/lsa.2016.186

The Helmholtz Zentrum München, the German Research Center for Environmental Health, pursues the goal of developing personalized medical approaches for the prevention and therapy of major common diseases such as diabetes and lung diseases. To achieve this, it investigates the interaction of genetics, environmental factors and lifestyle. The Helmholtz Zentrum München is headquartered in Neuherberg in the north of Munich and has about 2,300 staff members. It is a member of the Helmholtz Association, a community of 18 scientific-technical and medical-biological research centers with a total of about 37,000 staff members.

The Institute for Biological and Medical Imaging (IBMI) conducts research into in vivo imaging technologies for the biosciences. It develops systems, theories and methods of imaging and image reconstruction as well as animal models to test new technologies at the biological, preclinical and clinical level. The aim is to provide innovative tools for biomedical laboratories, for diagnosis and for the therapeutic monitoring of human diseases.

Technical University of Munich (TUM) is one of Europe’s leading research universities, with more than 500 professors, around 10,000 academic and non-academic staff, and 39,000 students. Its focus areas are the engineering sciences, natural sciences, life sciences and medicine, reinforced by schools of management and education. TUM acts as an entrepreneurial university that promotes talents and creates value for society. In that it profits from having strong partners in science and industry. It is represented worldwide with a campus in Singapore as well as offices in Beijing, Brussels, Cairo, Mumbai, San Francisco, and São Paulo. Nobel Prize winners and inventors such as Rudolf Diesel, Carl von Linde, and Rudolf Mößbauer have done research at TUM. In 2006 and 2012 it won recognition as a German "Excellence University." In international rankings, TUM regularly places among the best universities in Germany.

The ZEISS Group is an international leader in the fields of optics and optoelectronics with 170 years of successful company history.  Tasks of the corporate research and technology division of Carl Zeiss AG are the identification, evaluation and characterization of innovative and emerging technologies and solutions, with the goal of being a key contributor to future, leading-edge products.