CT: Imaging at mesoscale resolution
A navigational map view of a section of a mouse brain. Like the map view of an Earth imaging program, this image of a brain section takes cues from actual imaging performed with highest-energy X-rays at a synchrotron and turns them into a graphic depiction. The imaging concentrates on a mesoscale of the brain analogous to the map view of Google Earth. The scale could be useful in studying how the brain computes.
If brain imaging could be compared to Google Earth, neuroscientists would already have a pretty good satellite view of the brain, and a great street view of neuron details. But navigating how the brain computes is arguably where the action is, and neurosciences navigational map view has been a bit meagre.
Now, a research team led by Eva Dyer, a computational neuroscientist and electrical engineer, has imaged brains at that map-like or meso scale. (Mesoscale is approximately 1ìm3 resolution.) The imaging scale gives an overview of the intercellular landscape of the brain at a level relevant to small neural networks, which are at the core of the brains ability to compute.
Dyer, who recently joined the Georgia Institute of Technology and Emory University, also studies how the brain computes via its signalling networks, and this imaging technique could someday open new windows onto how they work.
Argonne National Laboratory (ANL) generates the highest-energy X-ray beams in the country at its synchrotron, said Dyer, who co-led the study with ANLs Bobby Kasthuri at the Advanced Photon Source synchrotron. Theyve studied all kinds of materials with really powerful X-rays. Then they got interested in studying the brain.
The technique also revealed capillary grids interlacing brain tissues. They dominated the images, with cell bodies of brain cells evenly speckling capillaries like pebbles in a steel wool sponge.
Our brain cells are embedded in this sea of vasculature, said Dyer, an assistant professor in the Wallace H. Coulter Department of Biomedical Engineering at Georgia Tech and Emory.
The study on the new images appeared in the journal eNeuro on 17 October 2017. The team included researchers from Johns Hopkins University, the University of Chicago, Northwestern University, the Argonne National Laboratory, and the University of Pennsylvania. The work was funded by the U.S. Department of Energy, the National Institutes of Health, the Intelligence Advanced Research Projects Activity, and the Defense Advanced Research Projects Agency.
Neural forest for the trees
So, why do researchers even need mesoscale imaging?
FMRIs image at a high level, and with many microscopes, youre zoomed in too far to recognize the forest for the trees, Dyer said. Though you can see a lot with them, you also can miss a lot.
If you look at brain signaling on the level of individual neurons, it looks very mysterious, but if you take a step back and observe the activity of a population of hundreds of neurons instead, you might see simpler, clearer patterns that intuitively make more sense.
In an earlier study, Dyer discovered that hand motion directions corresponded with reliable neural signalling patterns in the brains motor neocortex. The signals did not occur across single neurons or a few dozen but instead across groups of hundreds of neurons. Mesoscale imaging reveals a spatial view on that same order of hundreds of neurons.
We have begun doing X-ray tomography on large brain tissues, then weve gone deeper into specific tiny regions of interest in the same tissue with an electron microscope to see the full connectome there, Dyer said. The connectome refers to the total scheme of the hundreds of individual connections between neurons. The researchers hope to someday be able to switch from a mesoscale view to close-up view, a bit like Google Earth.
Zeroing in then zooming in
We want to be able to tell somebody researching a disease what the underlying anatomy of their lab sample is in an automated way, she said. You could navigate using this mesoscale view to get the context of where the damage is.
Then the user could zoom in on a blocked artery or destroyed tissue analogous to the way satellite imagery can zoom in on traffic jams to see whats causing them.
From X-ray to graphic image
First, the thick section of brain rotated in the high-energy X-ray beam, which was transformed into an image analogous to the output of a CT scanner. Then structures and characteristics were identified by humans and algorithms before they were computed into three-dimensional, colourcoded vasculature and cell bodies.
The details of individual cells were very basic. In neurons, often the nuclei were visible in the X-ray tomography image, and axons wrapped in myelin (white matter) sometimes appeared as well.
By contrast, the researchers need 100 gigabytes of data to compute a one-cubicmillimetre image of brain tissue using mesoscale X-ray tomography scans of thicker brain sections. But the researchers goal is to not have to slice the tissue at all. Eventually, we want to be able to image whole brains, as is, with this method to see the entirety of their neural networks and other structures.
Nano-CT provides 3D images at 100 nanometres resolution
Computed Tomography (CT) is a standard procedure in hospitals, but so far, the technology has not been suitable for imaging extremely small objects. A team from the Technical University of Munich (TUM) describes a Nano-CT device that creates three-dimensional x-ray images at resolutions up to 100 nanometres. To test the application, the researchers analysed the locomotory system of a velvet worm.
During a CT analysis, the object under investigation is x-rayed and a detector measures the respective amount of radiation absorbed from various angles. Threedimensional images of the inside of the object can be constructed based on several such measurements. Up until now, however, the technology reached its limits when it came to objects as small as the tiny, 0.4 millimetre-long legs of the velvet worm (Onychophora).
High-resolution images of this magnitude required radiation from particle accelerators, yet there are only a few dozen such facilities in Europe. Approaches suitable for the typical laboratory still had to struggle with low resolutions, or the samples investigated had to be made of certain materials and could not exceed a certain size. The reason was often the use of x-ray optics. Put simply, x-ray optics focus x-ray radiation similar to the way optical lenses focus light but they also have several limitations.
The TUM Nano-CT system is based on a newly developed x-ray source, which generates a particularly focused beam, without relying on x-ray optics. In combination with an extremely low-noise detector, the device produces images that approach the resolution possible with a scanning electron microscope, while also capturing structures under the surface of the object under investigation.
Our system has decisive advantages compared to CTs using x-ray optics, says TUM scientist Mark Müller, lead author of the article published in PNAS. We can make tomographies of significantly larger samples and we are more flexible in terms of the materials that can be investigated.
In contrast to arthropods, onychophorans do not have segmented limbs, as is also the case with their presumed common fossil ancestors, says one of the researchers. The investigation of the functional anatomy of the velvet worms legs plays a key role in determining how the segmented limbs of the arthropods evolved.
Future applications in medicine
Our goal in the development of the Nano- CT system is not only to be able to investigate biological samples, such as the leg of the velvet worm, says Franz Pfeiffer, TUM Professor for Biomedical Physics, Director of the MSB, and a Fellow at the TUM Institute for Advanced Study (TUM-IAS).
In the future, this technology will also make biomedical investigations possible. Thus, for example, we will be able to examine tissue samples to clarify whether or not a tumour is malignant. A non-destructive and three-dimensional image of the tissue with a resolution like that of the Nano- CT can also provide new insights into the microscopic development of widespread illnesses such as cancer.
Dunlee Maintaining your CTs technical performance
Dunlee has more than 100 years of expertise in the production and integration of innovative components for imaging solutions. Today, we develop and produce highly reliable, quality and technology differentiating components and solutions tailored to our customerfs needs.
For Independent Service Organizations and in-house teams who replace GE CT tubes at Hospitals and Imaging Centers, Dunleefs replacement tubes and support services help reduce total replacement costs and scanner downtime. We do this by quickly delivering quality products to a network of satisfi ed ISOs who rely on Dunlee to help them maintain their customersf CT scanners.
For all our GE replacement tubes, we guarantee a fast and reliable technical support. Additionally, we ensure that all our tubes are OEM equivalent. With a great network of distributors in the Arabic countries, we make sure to provide solutions to our customersf needs locally as well. Next to our Replacement business line, we also strongly focus on our OEM customers. It is important to us to work towards a committed partnership and offer customizable imaging solutions including:
|Date of upload: 15th Jan 2018|
Copyright © 2018 MiddleEastHealthMag.com. All Rights Reserved.