A recent publication by UCLouvain’s Prof. Greet Kerckhofs reports on a new method for observing mouse placentas during growth: a three-dimensional, non-invasive and quantitative virtual histology(1). This is a breakthrough that makes Prof. Kerckhofs a pioneer of 3D histology of biological tissues.
From the ancient Greek ‘ἱστός’, ‘tissue’, and ‘λόγος’, ‘discourse’, histology is the branch of biology that deals with the structure of living tissues. At the crossroads of cell biology, anatomy, biochemistry and physiology, the discipline explores the microstructure of living organisms and the renewal of their tissues.
‘Still today, histology is a leading imaging method for analysing and quantifying at cellular and microstructural scale the changes induced by diseases and pathologies in living tissues’, explains Greet Kerckhofs, associate professor in the Department of Mechatronic, Dynamic and Electrical Energy Systems (MEED) of the UCLouvain Institute of Mechanics, Materials and Civil Engineering (IMMC). ‘But to study non-solid and soft tissues, such as the placenta, the standard technique in histology is to extract a sample, dissect it, dye the sections and then observe it under a microscope. This widespread technique has its limits: it’s destructive and only allows 2D observations.’
An engineering technique that inspires biomedical scientists
Having earned her PhD in 2009, Prof. Kerckhofs now studies an engineering technique that could extend to biology. ‘The goal was to optimise the use of microfocus X-ray tomography(2) (microCT), that is, the use of a very specialised technique in medical imaging processes, at higher resolution only in hospitals. Since microCT is not applicable to soft tissue imaging, we developed our own non-invasive, tissue-specific, X-ray-opaque dyes, which now give us the unprecedented capacity to visualise in 3D not only hard biological tissues, but also soft biological tissues. This technique is called contrast-enhanced microfocus computed tomography (CE-CT).’ The technique makes it possible to visualise the entirety of the internal structure of a material without destroying it, unlike the current technique.
In an article in the June issue of the journal PNAS, Prof. Kerckhofs, in close collaboration with the professor and biomedical scientist Joris Vriens and the PhD student Katrien De Clercq, who studies at KU Leuven’s Endometrium, Endometriosis & Reproductive Medicine Laboratory, developed CE-CT for analysing a mouse’s placenta during pregnancy. Via this innovative method and the interdisciplinary approach adopted by pioneering engineers, chemists and biomedical scientists, they are leading the field of evaluating the morphology of the placenta and its development in three dimensions (3D).
A two-cubic-metre cutting-edge machine
To benefit from 3D observations in virtual histology, a two-cubic-metre machine bombards the sample with X-rays. The resulting detail can reach a precision of less than a micrometre. Coupled with the new dyes they developed, the new high-resolution CE-CT approach allowed the teams of the two researchers to visualise with extreme precision mouse placenta characteristics during pregnancy: volumes, ratio of different layers, volumes of different cell populations, vessels – parameters crucial to ensuring thorough statistical evaluation of the tissue in order to decipher developmental changes and disease-induced changes as well as their effects on embryonic development.
In this study, the samples are ex vivo and taken from animals. With this new imaging methodology, it has been possible to study early stages of embryonic development in a mouse uterus. But the goal is to develop the technique to prevent embryonic problems at the earliest possible moment. Observing placenta vascularisation and the fractions and compositions of layers makes it possible to understand whether a disease has developed. In an ongoing study, human placenta tissues are being evaluated.
‘But our new methodology could have many other applications’, Prof. Kerckhofs says. ‘It could be applied to other complex biological tissues such as cardiovascular tissues (arteries, valves) or organs, such as the lungs, kidneys, liver, and many others.’ She very much hopes to be able to generalise this process in hospitals within the next ten years.
How did you manage to reconcile engineering and biology?
Originally in 2004, as a materials engineer, I was studying biomaterials to understand how to introduce this as yet undeveloped 3D observation technique in this field, microCT, into new fields of application. Over time, the data accumulated and allowed for translating the results for biological tissues and refining the interdisciplinary aspect of the research, which combines highly technical and chemical aspects with pure biology. Interdisciplinarity allows us to take giant steps. Without it, the publication wouldn’t have been possible.
This PNAS article makes you and your interdisciplinary team pioneers in the technique.
The methodology is brand new: many researchers are interested in the subject while having increased the level of interdisciplinarity in the research. This is our strength: a rich multidisciplinary environment. Only two or three groups in the world work on the subject in an equivalent way. This interdisciplinarity is very rare. As engineers, we can only advance these types of techniques when we have a clear biological issue to resolve and have the full support of biomedical scientists and our clinical colleagues.
LEXIQUE (1) Branch of biology that deals with the microstructure of living tissues. Since its birth two centuries ago, histology has experienced three revolutions: the founding revolution born of optical microscopy and cell theory; the revolution engendered by electron microscopy; the decisive revolution of molecular biology. These three crucial periods in the discipline’s history drove increasingly fine scales of observation that in turn revealed elementary levels of biological organisation. (2) Tomography is an imaging technique, widely used in medical imaging, as well as in geophysics, astrophysics and materials science/mechanics. The technique makes it possible to reconstruct an object’s volume from a series of measurements taken from outside the object. It provides an image not of the entire organ but of horizontal, vertical or oblique cross-sections.
A glance at Greet Kerckhofs' bio
Prof. Greet Kerckhofs received her PhD in materials engineering from KU Leuven in 2009. She is a member of Prometheus, which focuses on tissue and skeletal analysis (imaging, biomaterials and bioprocessing). She is now actively contributing to the interdisciplinary nature of research. Since 2017, Prof. Kerckhofs has served as assistant professor in the UCLouvain Biomechanics Laboratory in the Institute of Mechanics, Materials and Civil Engineering. During her PhD, she developed the ‘contrast-enhanced microfocus computed tomography (CE-CT)’, a method that displays the entire internal structure of a material, without destroying it, unlike the current technique. A pioneer in the field, she is developing international collaborations and her research team, currently composed of six PhD students, two postdocs and a laboratory technician, which will determine the future of 3D histology..