Researchers use microtomography for the first time, which allows the generation of internal images in 2D and 3D
A study developed by researchers from Unicamp in collaboration with Harvard University (USA) used for the first time x-ray microcomputed tomography (Micro-CT) to describe the detailed anatomy of small marine bivalves, with lengths less than 3 millimeters. The technique allows the generation of internal images (2D and 3D) with high resolution of the analyzed specimens and the consequent virtual dissection of their organs. Thanks to the resource, animals do not need to be destroyed. The work gave rise to an article recently published in one of the main zoology magazines in the world, the Zoological Journal of the Linnean Society.
The research was carried out during the sandwich doctorate of zoologist and researcher Fabrizio Marcondes Machado. At Unicamp, he was supervised by professor Flávio Dias Passos, from the Department of Animal Biology at the Institute of Biology (IB). At Harvard, in the Department of Organismic & Evolutionary Biology (OEB), the advisor was professor Gonzalo Giribet, from giribetgroup.oeb.harvard.edu. According to Machado, the results of the study were very promising. “We conclude that the use of Micro-CT, a non-invasive and non-destructive tool, can replace classical techniques such as dissection and histology that destroy and/or permanently alter the specimens analyzed”, he maintains.
Because of its originality, the work, adds the zoologist, should serve as a basis for the use of Micro-CT to advance even further among researchers, including in areas that study other marine organisms. According to him, there are some points where microtomography needs to be improved, such as the ability to differentiate structures of similar density and the resolution of images of small structures. “The tool does not completely replace some techniques, but it is moving towards that. I imagine that in a maximum of ten years we will no longer need to dissect an individual to describe its internal parts”, he ventures.
Professor Passos highlights the importance of this advance, remembering that, in some cases, the specimens analyzed are very old and, sometimes, unique. “In other words, without the use of Micro-CT this individual would have to be destroyed to be studied from an anatomical point of view. Now, with this new feature, we can dissect it just virtually and preserve it afterwards,” he argues. The microtomography, explains the professor, not only provides volumetric reconstructions in 3D, but also allows the organs of marine molluscs to be analyzed through virtual sections in 2D.
This allows researchers to view slices (sections) of the same individual in three different planes: transversal, sagittal and frontal. “An important fact about this technique is that it allows descriptions to stop being made based on drawings and start being made based on images. The design requires talent on the part of the author and is subject to his interpretation. Not the image. It portrays the real”, argues the thesis advisor.
Depths of the sea
The author of the work says that he analyzed eight species of bivalves. These molluscs receive this classification because their bodies are protected by a shell with two valves, as is the case with oysters, scallops and mussels. Machado selected animals that are difficult to collect, which occur in deep waters, in countries such as Brazil, Argentina and the Caribbean region. “We chose this group because it is made up of species that are little known anatomically. We studied recently collected animals, but also individuals collected more than 50 years ago, as was the case with a specimen that belongs to the Harvard Museum”, explains the zoologist.
A point highlighted by the advisor and mentor is the possibility of building a national virtual repository, which can store and make available the images produced via Micro-CT by researchers from all over the world. “Access to the material will allow interested parties to dissect and reconstruct the individuals analyzed in different ways, in order to eliminate any doubts. To make an analogy with football, this tool has everything it needs to become the VAR [video referee] for anatomists”, compares, in a good-humored tone, the author of the thesis. The researcher also highlights that the tomographic data set of the species studied in the article is available online at Harvard Dataverse, a freely accessible virtual repository, allowing any researcher in the world to reanalyze the anatomy of these bivalves.
Machado says that he chose Harvard University to do his sandwich doctorate for two main reasons. Firstly, because Professor Gonzalo Giribet is one of the world's greatest authorities on invertebrate phylogeny. He is, so to speak, “the guy” when it comes to evolution. Secondly, because in the North American institution the zoologist had greater access to the microtomography. “Here in Brazil, we don’t have that much equipment available”, he explains.
Before submitting his doctoral project to Harvard, the zoologist initially used the microtomography machines at the Piracicaba Dental School (FOP) and also at the Biology Institute (IB), both at Unicamp. “The results were not so good because there were some adjustments needed in the contrast solution and also because I discovered that each equipment has a different level of resolution. In other words, the FOP and IB equipment were not the most suitable for acquiring images of small molluscs”. Subsequently, the researcher used equipment from the Brazilian Nanotechnology National Laboratory, from the National Center for Research in Energy and Materials (CNPEM), located in Campinas, where part of the tomographic images acquired made up the recently published article.
It turns out that the technology is in huge demand from researchers across the country, from the most diverse areas of knowledge. “Those interested must make an appointment. You can use the microtomography machine a maximum of two to three times a year. At Harvard, in Professor Gonzalo's laboratory, I used the equipment countless times. On one occasion, I did this every day for a week”, says Machado, who received a scholarship granted by the Coordination for the Improvement of Higher Education Personnel (Capes), a body linked to the Ministry of Education, and with support from the Museum of Comparative Harvard Zoology. The researcher maintains a page with information about research in your area of expertise.
Read the article No. Zoological Journal of the Linnean Society