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See the Human Cardiovascular System in a Whole New Way

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Watch this brief video and you might guess you’re seeing an animated line drawing, gradually revealing a delicate take on a familiar system: the internal structures of the human body. But this movie doesn’t capture the work of a talented sketch artist. It was created using the first 3D, full-body imaging device using positron emission tomography (PET).

The device is called an EXPLORER (EXtreme Performance LOng axial REsearch scanneR) total-body PET scanner. By pairing this scanner with an advanced method for reconstructing images from vast quantities of data, the researchers can make movies.

For this movie in particular, the researchers injected small amounts of a short-lived radioactive tracer—an essential component of all PET scans—into the lower leg of a study volunteer. They then sat back as the scanner captured images of the tracer moving up the leg and into the body, where it enters the heart. The tracer moves through the heart’s right ventricle to the lungs, back through the left ventricle, and up to the brain. Keep watching, and, near the 30-second mark, you will see in closer focus a haunting capture of the beating heart.

This groundbreaking scanner was developed and tested by Jinyi Qi, Simon Cherry, Ramsey Badawi, and their colleagues at the University of California, Davis [1]. As the NIH-funded researchers reported recently in Proceedings of the National Academy of Sciences, their new scanner can capture dynamic changes in the body that take place in a tenth of a second [2]. That’s faster than the blink of an eye!

This movie is composed of frames captured at 0.1-second intervals. It highlights a feature that makes this scanner so unique: its ability to visualize the whole body at once. Other medical imaging methods, including MRI, CT, and traditional PET scans, can be used to capture beautiful images of the heart or the brain, for example. But they can’t show what’s happening in the heart and brain at the same time.

The ability to capture the dynamics of radioactive tracers in multiple organs at once opens a new window into human biology. For example, the EXPLORER system makes it possible to measure inflammation that occurs in many parts of the body after a heart attack, as well as to study interactions between the brain and gut in Parkinson’s disease and other disorders.

EXPLORER also offers other advantages. It’s extra sensitive, which enables it to capture images other scanners would miss—and with a lower dose of radiation. It’s also much faster than a regular PET scanner, making it especially useful for imaging wiggly kids. And it expands the realm of research possibilities for PET imaging studies. For instance, researchers might repeatedly image a person with arthritis over time to observe changes that may be related to treatments or exercise.

Currently, the UC Davis team is working with colleagues at the University of California, San Francisco to use EXPLORER to enhance our understanding of HIV infection. Their preliminary findings show that the scanner makes it easier to capture where the human immunodeficiency virus (HIV), the cause of AIDS, is lurking in the body by picking up on signals too weak to be seen on traditional PET scans.

While the research potential for this scanner is clearly vast, it also holds promise for clinical use. In fact, a commercial version of the scanner, called uEXPLORER, has been approved by the FDA and is in use at UC Davis [3]. The researchers have found that its improved sensitivity makes it much easier to detect cancers in patients who are obese and, therefore, harder to image well using traditional PET scanners.

As soon as the COVID-19 outbreak subsides enough to allow clinical research to resume, the researchers say they’ll begin recruiting patients with cancer into a clinical study designed to compare traditional PET and EXPLORER scans directly.

As these researchers, and other researchers around the world, begin to put this new scanner to use, we can look forward to seeing many more remarkable movies like this one. Imagine what they will reveal!


[1] First human imaging studies with the EXPLORER total-body PET scanner. Badawi RD, Shi H, Hu P, Chen S, Xu T, Price PM, Ding Y, Spencer BA, Nardo L, Liu W, Bao J, Jones T, Li H, Cherry SR. J Nucl Med. 2019 Mar;60(3):299-303.

[2] Subsecond total-body imaging using ultrasensitive positron emission tomography. Zhang X, Cherry SR, Xie Z, Shi H, Badawi RD, Qi J. Proc Natl Acad Sci U S A. 2020 Feb 4;117(5):2265-2267.

[3] “United Imaging Healthcare uEXPLORER Total-body Scanner Cleared by FDA, Available in U.S. Early 2019.” Cision PR Newswire. January 22, 2019.


Positron Emission Tomography (PET) (NIH Clinical Center)

EXPLORER Total-Body PET Scanner (University of California, Davis)

Cherry Lab (UC Davis)

Badawi Lab (UC Davis Medical Center, Sacramento)

NIH Support: National Cancer Institute; National Institute of Biomedical Imaging and Bioengineering; Common Fund

A New View of the 3D Genome

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Caption: 3D model of a chromatin “forest.” Each sphere represents a tree-shaped domain of about 10 nucleosomes, the basic structural unit of DNA packaging. Larger domains are green; smaller ones are red. Credit: Northwestern University, Evanston, IL


This lush panoply of color might stir up daydreams of getting away to explore a tropical rain forest. But what you see here is a new model that’s enabling researchers to explore something equally amazing: how a string of DNA that measures 6 feet long can be packed into the microscopic nucleus of a human cell. Fitting that much DNA in a nucleus is like fitting a thread the length of the Empire State building underneath your fingernail!

Scientists have known for a while that that the answer lies in how DNA is folded onto spool-like complexes called chromatin, but many details of the process still remain to be worked out. Recently, an NIH-funded team, led by Vadim Backman and Igal Szleifer, Northwestern University, Evanston, IL, developed this new model of chromatin folding by pairing sophisticated mathematical modeling and optical imaging.In a study published in the journal Science Advances [1], the team found that chromatin is folded into a variety of tree-like domains along a chromatin backbone, which they liken to an aggregation of trees growing from the forest floor. The colorful spheres you see above represent trees of varying sizes.

Earlier models of chromatin folding had suggested that DNA folds into regular and orderly fibers. In the new study, the Northwestern researchers used their own specially designed Partial Wave Spectroscopic microscope. This high-powered system, coupled with electron imaging, allowed them to peer deep inside living cells to “sense” real-time alterations in chromatin packing. What makes their new view on chromatin so interesting is it suggests our DNA is packaged in a way that’s much more disorderly and unpredictable than initially thought.

Chromatin Forest
Caption: Schematic shows the interplay between transcription and chromatin packing. Inactive high DNA density (blue) regions and active low DNA density (red). The horizontal chromatin backbone includes RNA polymerase (green), activating factors (yellow), and repressing factors (purple). Credit: Huang et al., Sci. Adv. 2020

As Backman notes, it is reasonable to assume that a forest would be filled with trees of varying sizes and shapes. But you couldn’t predict the exact location of each tree or its particular size and configuration. The same appears to be true of these tree-like structures within chromatin. Their precise location and size vary, seemingly unpredictably, from cell to cell.

This apparently random DNA packing structure might seem surprising given chromatin’s importance in influencing the expression and function of our genes. But the researchers think such variability likely has its advantages.

Here’s the idea: If all of our cells responded to stressful conditions (such as heat or a toxic exposure) in exactly the same way and that way happened to be suboptimal, the whole tissue or organ might fail. But if differences in chromatin structure lead each cell to respond somewhat differently to the same stimulus, then some cells might be more likely to survive or even thrive under the stress. It’s a built-in way for cells to hedge their bets.

These new findings offer a fundamentally new three-dimensional view of the human genome. They might also inspire innovative strategies to understand and fight cancer, as well as other diseases. And, while most of us probably won’t be venturing off into the rain forest anytime soon, this work does give us all something to think about next time we’re enjoying the great outdoors in our own neck of the woods. 


[1] Physical and data structure of 3D genome. Huang K, Li Y, Shim AR, Virk RKA, Agrawal V, Eshein A, Nap RJ, Almassalha LM, Backman V, Szleifer I. Sci Adv. 2020 Jan 10;6(2):eaay4055.


Deoxyribonucleic Acid (DNA) (National Human Genome Research Institute/NIH)

4D Nucleome (Common Fund/NIH)

Vadim Backman (Northwestern University, Evanston, IL)

Igal Szleifer (Northwestern University, Evanston, IL)

NIH Support: National Cancer Institute

Seeing Coronavirus Replicate in Kidney Cells

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Bernbaum Imaging Post
Credit: NIAID Integrated Research Facility, Fort Detrick, MD

You’ve probably seen pictures of SARS-CoV-2—the novel coronavirus that causes COVID-19—that look alarming. But the high-resolution micrograph above paints a rather different picture, using rich pseudo-colors to show how newly assembled viral particles cause infected cells to bulge, or bleb, and then self-destruct.

This image depicts a common primate kidney cell line (green) infected with SARS-CoV-2. Notice the bulging, spherical cellular blebs, seen best in the upper right and bottom left corners. These badly damaged cells, which are filled to the point of bursting with viral particles, are beginning to self-destruct. Some cells have apparently already burst open, allowing hundreds of viral particles (purple) to spill out and potentially infect other cells.

This stunning picture was taken by John Bernbaum, an electron microscopist with NIH’s National Institute of Allergy and Infectious Diseases (NIAID). Bernbaum works at NIAID’s Integrated Research Facility (IRF), Fort Detrick, MD, a specialized, high-level biocontainment facility equipped with unique medical imaging capabilities. In this special environment, Bernbaum and his colleagues can safely visualize SARS-CoV-2, as well as other viruses and microbes that pose serious risks to human health.

To get this shot of SARS-CoV-2, Bernbaum relied on a conventional scanning electron microscope (SEM). First, a sample of kidney cells that had been exposed to SARS-CoV-2 was dehydrated, chemically preserved, and coated with a thin layer of metal. Once everything was ready, the SEM was used to focus a high-energy beam of electrons onto the sample. As electrons bounced off the metal surface, they revealed spatial variations and properties in the sample that were used to generate this 3D image.

Originally, this image was in gray scale. To better highlight the destructive powers of SARS-CoV-2, Jiro Wada, a skilled graphic illustrator at the IRF, used a computer program to colorize key features in exquisite detail. By studying these 3D images, researchers can learn about things such as the rate of infection and the prodigious number of particles each infected cell produces. They can also learn about how the infection affects the conditions inside cells.

Interestingly, what Bernbaum finds most striking about SARS-CoV-2 is what you don’t see in his images. Uninfected kidney cells look like a flat, delicately interwoven quilt (not pictured). When Bernbaum used SEM to study this sample of kidney cells, about 80 to 90 percent of the cells appeared flat and unremarkable. Yet, as the scan progressed, he came across a small subset of cells that appeared to be deformed by SARS-CoV-2 infection. Those abnormalities include the spherical bulges that I pointed out earlier, along with some worm-like protrusions that you can see in the top left.

Bernbaum has been producing amazing images like this one for 32 years—the last 11 of them at the IRF. If you’d like to see even more of his impressive work and that of the IRF team, check out the NIAID’s image gallery.


Coronavirus (NIH)

Integrated Research Facility (National Institute of Allergy and Infectious Diseases/NIH)

NIH Support: National Institute of Allergy and Infectious Diseases

Capturing Viral Shedding in Action

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Credit: Rocky Mountain Laboratories, National Institute of Allergy and Infectious Diseases, Hamilton, MT

You’ve probably seen some amazing high-resolution images of SARS-CoV-2, the novel coronavirus that causes COVID-19, on television and the web. What you might not know is that many of these images, including the ones shown here, were produced at Rocky Mountain Laboratories (RML), a part of NIH’s National Institute of Allergy and Infectious Diseases (NIAID) that’s located in the small Montana town of Hamilton.

The head of RML’s Electron Microscopy Unit, Elizabeth Fischer, was the researcher who took this portrait of SARS-CoV-2. For more than 25 years, Fischer has snapped stunning images of dangerous viruses and microbes, including some remarkable shots of the deadly Ebola virus. She also took some of the first pictures of the coronavirus that causes Middle East respiratory syndrome (MERS), which arose from camels and continues to circulate at low levels in people.

The NIAID facility uses a variety of microscopy techniques, including state-of-the-art cryo-electron microscopy (cryo-EM). But the eye-catching image you see here was taken with a classic scanning electron microscope (SEM).

SEM enables visualization of particles, including viruses, that are too small to be seen with traditional light microscopy. It does so by focusing electrons, instead of light, into a beam that scans the surface of a sample that’s first been dehydrated, chemically preserved, and then coated with a thin layer of metal. As electrons bounce off the sample’s surface, microscopists such as Fischer are able to capture its precise topology. The result is a gray-scale micrograph like the one you see above on the left. To make the image easier to interpret, Fischer hands the originals off to RML’s Visual Medical Arts Department, which uses colorization to make key features pop like they do in the image on the right.

So, what exactly are you seeing in this image? The orange-brown folds and protrusions are part of the surface of a single cell that’s been infected with SARS-CoV-2. This particular cell comes from a commonly studied primate kidney epithelial cell line. The small, blue spheres emerging from the cell surface are SARS-CoV-2 particles.

This picture is quite literally a snapshot of viral shedding, a process in which viral particles are released from a dying cell. This image gives us a window into how devastatingly effective SARS-CoV-2 appears to be at co-opting a host’s cellular machinery: just one infected cell is capable of releasing thousands of new virus particles that can, in turn, be transmitted to others.

While capturing a fixed sample on the microscope is fairly straightforward for a pro like Fischer, developing a sample like this one involves plenty of behind-the-scenes trial and error by NIAID investigators. As you might imagine, to see the moment that viruses emerge from an infected cell, you have to get the timing just right.

By capturing many shots of the coronavirus using the arsenal of microscopes available at RML and elsewhere, researchers are learning more every day about how SARS-CoV-2 enters a cell, moves inside it, and then emerges to infect other cells. In addition to advancing scientific knowledge, Fischer notes that images like these also hold the remarkable power to make an invisible enemy visible to the world at large.

Making SARS-CoV-2 tangible helps to demystify the challenges that all of us now face as a result of the COVID-19 pandemic. The hope is it will encourage each and every one of us to do our part to fight it, whether that means digging into the research, working on the front lines, or staying at home to prevent transmission and flatten the curve. And, if you could use some additional inspiration, don’t miss the NIAID’s image gallery on Flickr, which includes some of Fischer’s finest work.


Coronavirus (COVID-19) (NIH)

Rocky Mountain Laboratories (National Institute of Allergy and Infectious Diseases/NIH)

Elizabeth Fischer (National Institute of Allergy and Infectious Diseases/NIH)

NIH Support: National Institute of Allergy and Infectious Diseases

Pursuing Safe and Effective Anti-Viral Drugs for COVID-19

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Senior hospital patient on a ventilator
Stock photo/SoumenNath

Right now, the world is utterly focused on the coronavirus outbreak known as COVID-19. That’s certainly true for those of us at NIH. Though I am working from home to adhere rigorously to physical distancing, I can’t remember ever working harder, trying to do everything I can to assist in the development of safe and effective treatments and vaccines.

Over the past several weeks, a mind-boggling array of possible therapies have been considered. None have yet been proven to be effective in rigorously controlled trials, but for one of them, it’s been a busy week. So let’s focus on an experimental anti-viral drug, called remdesivir, that was originally developed for the deadly Ebola virus. Though remdesivir failed to help people with Ebola virus disease, encouraging results from studies of coronavirus-infected animals have prompted the launch of human clinical trials to see if this drug might fight SARS-CoV-2, the novel coronavirus that causes COVID-19.

You may wonder how a drug could possibly work for Ebola and SARS-CoV-2, since they are very different viruses that produce dramatically different symptoms in humans. The commonality is that both viruses have genomes made of ribonucleic acid (RNA), which must be copied by an enzyme called RNA-dependent RNA polymerase for the virus to replicate.

Remdesivir has an affinity for attaching to this kind of polymerase because its structure is very similar to one of the RNA letters that make up the viral genome [1]. Due to this similarity, when an RNA virus attempts to replicate, its polymerase is tricked into incorporating remdesivir into its genome as a foreign nucleotide, or anomalous letter. That undecipherable, extra letter brings the replication process to a crashing halt—and, without the ability to replicate, viruses can’t infect human cells.

Would this work on a SARS-CoV-2 infection in a living organism? An important step was just posted as a preprint yesterday—a small study showed infusion of remdesivir was effective in limiting the severity of lung disease in rhesus macaques [2]. That’s encouraging news. But the only sure way to find out if remdesivir will actually help humans who are infected with SARS-CoV-2 is to conduct a randomized, controlled clinical trial.

In late February, NIH’s National Institute of Allergy and Infectious Diseases (NIAID) did just that, when it launched a randomized, controlled clinical trial to test remdesivir in people with COVID-19. The study, led by NIAID’s Division of Microbiology and Infectious Diseases, has already enrolled 805 patients at 67 testing sites. Most sites are in the United States, but there are also some in Singapore, Japan, South Korea, Mexico, Spain, the United Kingdom, Denmark, Greece, and Germany.

All trial participants must have laboratory-confirmed COVID-19 infections and evidence of lung involvement, such as abnormal chest X-rays, rattling sounds when breathing (rales) with a need for supplemental oxygen, or a need for mechanical ventilation. They are randomly assigned to receive either a round of treatment with remdesivir or a harmless placebo with no therapeutic effect. To avoid bias from creeping into patient care, the study is double-blind, meaning neither the medical staff nor the participants know who is receiving remdesivir.

There is also an early hint from another publication that remdesivir may benefit some people with COVID-19. Since the end of January 2020, Gilead Sciences, Foster City, CA, which makes remdesivir, has provided daily, intravenous infusions of the drug on a compassionate basis to more than 1,800 people hospitalized with advanced COVID-19 around the world. In a study of a subgroup of 53 compassionate-use patients with advanced complications of COVID-19, nearly two-thirds improved when given remdesivir for up to 10 days [3]. Most of the participants were men over age 60 with preexisting conditions that included hypertension, diabetes, high cholesterol, and asthma.

This may sound exciting, but these preliminary results, published in the New England Journal of Medicine, come with major caveats. There were no controls, participants were not randomized, and the study lacked other key features of the more rigorously designed NIH clinical trial. We can all look forward to the results from the NIH trial, which are are expected within a matter of weeks. Hopefully these will provide much-needed scientific evidence on remdesivir’s safety and efficacy in people with COVID-19.

In the meantime, basic researchers continue to learn more about remdesivir and its interaction with the novel coronavirus that causes COVID-19. In a recent study in the journal Science, a research team, led by Quan Wang, Shanghai Tech University, China, mapped the 3D atomic structure of the novel coronavirus’s polymerase while it was complexed with two other vital parts of the viral replication machinery [4]. This was accomplished using a high-resolution imaging approach called cryo-electron microscopy (cryo-EM), which involves flash-freezing molecules in liquid nitrogen and bombarding them with electrons to capture their images with a special camera.

With these atomic structures in hand, the researchers then modeled exactly how remdesivir binds to the polymerase of the novel coronavirus. The model will help inform future efforts to tweak the structure of the drug and optimize its ability to disrupt viral replication. Such detailed biochemical information will be vital in the weeks ahead, especially if data generated by the NIH clinical trial indicate that remdesivir is a worthwhile lead to pursue in our ongoing search for anti-viral drugs to combat the global COVID-19 pandemic.


[1] Nucleoside analogues for the treatment of coronavirus infections. Pruijssers AJ, Denison MR. Curr Opin Virol. 2019 Apr;35:57-62.

[2] Clinical benefit of remdesivir in rhesus macaques infected with SARS-CoV-2. Williamson B, Feldmann F, Schwarz B, Scott D, Munster V, de Wit E et. al. BioRxiv. Preprint posted 15 April 2020.

[3] Compassionate use of remdesivir for patients with severe Covid-19. Grein J, Ohmagari N, Shin D, Brainard DM, Childs R, Flanigan T. et. al. N Engl J Med. 2020 Apr 10. [Epub ahead of publication]

[4] Structure of the RNA-dependent RNA polymerase from COVID-19 virus. Gao Y, Yan L, Liu F, Wang Q, Lou Z, Rao A, et al. Science. 10 April 2020. [Epub ahead of publication]


Coronavirus (COVID-19) (NIH)

Accelerating COVID-19 Therapeutic Interventions and Vaccines (NIH)

NIH Clinical Trial of Remdesivir to Treat COVID-19 Begins (National Institute of Allergy and Infectious Diseases/NIH)

Developing Therapeutics and Vaccines for Coronaviruses (NIAID)


NIH Support: National Institute of Allergy and Infectious Diseases

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