This episode of the Physics World Weekly podcast features an interview with Charalampos (Harry) Tsoumpas at the University of Leeds, who explains why the development of ultrafast gamma-ray detectors could be a boon for medical imaging.
Also appearing this week is the soft-matter physicist Carmen Lee at McMaster University, who talks about an online programme called Ask A Scientist that answers questions about physics from school children who are learning at home. Lee also chats about her research into the Cheerios effect.
Participants in this webinar will learn how RadCalc’s 3D platform can improve efficiency, accuracy, and safety in the QA process for treatment plans.
The webinar, presented by Dana Cooper, will give the audience information on:
The workflow of the 3D platform.
Commissioning process and analysis tools.
Most popular benefits of using RadCalc 7.1.
Dana Cooper is a certified medical dosimetrist/technical sales representative with LifeLine Software, Inc, part of the LAP Group. She has more than 25 years of experience in radiation oncology, having held positions such as radiation therapist, dosimetrist and department manager. Dana joined LSI in 2016 and has been connecting radiation therapy departments with software that increases productivity and safety ever since.
Anomalies in the radioactive decay of beryllium-8 and helium-4 point to the existence of a new force of nature. That is the conclusion of a group of theorists in the US, who have scrutinized data from experiments carried out by nuclear physicists in Hungary over the past five years. Results from the two different isotopes agree on both the mass and interaction strength of the hypothetical boson that would carry the long-sought fifth force, the team found.
The Standard Model of particle physics tells us that matter particles interact with one another via four forces: electromagnetic; strong; weak; and gravity. But theorists have long hypothesized the existence of other forces, including “dark photons” that might mediate interactions between particles of dark and ordinary matter.
It was just such a particle that Attila Krasznahorkay of the Institute of Nuclear Research (ATOMKI) in Hungary and colleagues were hunting when carrying out experiments on beryllium. As they reported in a little-noticed paper in 2015, they fired protons at targets made from lithium-7 to create nuclei of beryllium-8. They then measured the angles between the trajectories of each electron and positron given off in the subsequent decays of the unstable beryllium isotope.
Mystery particle
If the Standard Model correctly describes such decays, the number of emitted electron-positron pairs should gradually drop off as the angle between the two particles increases. But Krasznahorkay and colleagues instead found an increase, or bump, in the distribution at an angle of about 140°. They interpreted this as due to beryllium-8 decaying to a previously unknown particle in a tiny fraction of its decays (before that particle then disintegrates into an electron and positron), calculating the mass of the new particle to be about 17 MeV/c2.
It was only a year later when Jonathan Feng and colleagues at the University of California, Irvine, published a theoretical analysis of Krasznahorkay’s team’s results that others took notice. Feng’s group concluded that the particle in question, if it exists, is not a dark photon but what they called a “protophobic” gauge boson – a force carrying particle that interacts more readily with electrons and neutrons than it does protons.
For other theorists, such unusual interactions cast doubt on the claimed discovery. More importantly, no other experimental group has since reproduced the anomalous results. In fact, the NA64 experiment at the CERN laboratory in Switzerland has narrowed down the range of such a particle’s possible interaction strengths by looking for evidence of its coupling to electrons and finding nothing.
Similar bump
Undeterred, Krasznahorkay and colleagues have pressed on. They rebuilt their detector between 2017 and 2018, and found that the bump at 140° remains. More strikingly, they found a similar bump at 115° in the decay of helium-4. Remarkably, they calculated that the particle responsible for this anomaly would also have a mass of about 17 MeV/c2.
That result was reported in autumn 2019 via a preprint on arXiv and prompted sensationalist headlines declaring that a Nobel prize might be in the offing. However, Feng realized that more could be done to establish whether the latest data really do stack up consistently against the old. In a new preprint, also on arXiv, he and a couple of theorist colleagues at Irvine, Chris Verhaaren and Tim Tait, not only check whether the two results agree on the mass of a putative new boson but also calculate what the particle’s interaction strength would be in each case.
Feng, Tait and Verhaaren point out that beryllium-8 and helium-4 decay at similar rates within the two experiments. But they say that that does not necessarily imply similar interaction strengths between the new boson and the quarks in each nucleus, noting that the excited states in each case have different quantum numbers and different excitation energies. They add that the beryllium-8 measurement was done on resonance while that of helium-4 was carried out between two resonances.
Remarkable agreement
After factoring all these things in, the trio concluded that the new particle does indeed interact with the same strength in both cases. Specifically, they find that the helium-4 decay rate calculated using the properties of the protophobic boson from their analysis of the beryllium-8 data agrees with the rate from the helium data. What is more, they say that such close agreement is not possible with any other type of hypothetical force carrier. “For other new particles proposed to explain the beryllium data, the predicted helium rate can be orders of magnitude off,” says Feng. “So, this concordance is, frankly, remarkable.”
To settle the issue once and for all, Feng and colleagues say that other experimentalists must try to reproduce the results. But they also propose several new measurements that could provide additional confirmation. Requiring only simple modifications of the existing experimental set-up, these include gathering data to better understand background processes as well as measuring decays from carbon-12 – whose rate they predict precisely. “If the predictions are confirrmed, these measurements will provide overwhelming evidence that a fifth force has been discovered,” they write.
Other theorists welcome the new analysis. Rouven Essig of Stony Brook University agrees it is important to establish consistency of interaction strength, while Jesse Thaler of the Massachusetts Institute of Technology also encourages other experimentalists to enter the fray. Indeed, he believes it is vital. “Only a confirmation from an independent experiment would give me significant confidence in the ATOMKI result,” he says.
One collaboration planning to test the anomalous result is DarkLight, based in the US. This will look for evidence of the 17 MeV/c2 boson by firing electrons from the Jefferson Lab’s CEBAF injector at a tantalum target. According to co-spokesperson Richard Milner of MIT, the experiment should produce results within the next couple of years – assuming that scientific approval and funding are forthcoming.
Researchers from France have shown that hepatobiliary MR contrast agent uptake can predict survival in patients with resectable hepatocellular carcinoma (HCC) as well as 18F-FDG PET/CT can. They published their findings in European Radiology.
Sébastien Mulé, a radiologist from Henri Mondor University Hospital in Créteil, south-east of Paris, and colleagues found that in 32 patients with 35 surgically proven HCCs, the quantitative analysis of the hepatobiliary phase (HBP) tumour enhancement in gadobenate dimeglumine (Gd-BOPTA)-enhanced MRI (lesion-to-liver contrast enhancement ratio, LLCER) accurately identifies moderately to poorly differentiated and/or microvascular invasion (MVI)-positive HCCs.
Compared with dual-tracer 18F-FDG and 18F-fluorocholine PET/CT, the contrast-enhanced MRI method performed well for the prediction of tumour aggressiveness and recurrence-free survival (RFS). Gd-BOPTA-enhanced MRI with delayed HBP images deserves consideration as part of pre-surgery workup in patients with resectable HCC, the authors noted.
MR and dual-tracer PET/CT imaging in a 41-year-old man with poorly differentiated 90-mm HCC lesion in the right liver lobe. (Courtesy: European Radiology)
“The findings confirm our impressions in clinical routine. Indeed, we noted that HCC without significant enhancement at the hepatobiliary phase had higher histological grades than the other ones. Therefore, we were not surprised that the HBP tumour enhancement may also help predict recurrence-free survival,” Mulé told AuntMinnieEurope.com in an email.
However, he added that the strength of that predictive ability surprised the team in part, particularly because 18F-FDG PET/CT is of such well-established prognostic value in patients with HCC.
“PET/CT using 18F-FDG allows the identification of poorly differentiated HCCs at the expense of a relatively lower sensitivity for the detection of well-differentiated HCCs. 18F-FDG has also been shown to negatively correlate with tumour differentiation,” the authors wrote, emphasizing that 18F-FDG positivity may help predict both MVI and early recurrence after surgical resection, while PET/CT with radiolabelled choline – i.e., 11C-acetate or 18F-fluorocholine (18F-FCH) – is of great interest to detect well-differentiated HCCs.
Study details
All patients with untreated HCC who underwent 18F-FDG PET/CT as part of workup before liver resection or orthotopic liver transplantation at Henri Mondor University Hospital between October 2013 and January 2018 were considered eligible for the study (n = 71), and patients were included if they also underwent preoperative liver MRI with HBP imaging. A total of 36 people met the inclusion criteria.
All patients underwent Gd-BOPTA-enhanced MRI including delayed HBP images, 18F-FDG PET/CT, and (for 29/32 patients) 18F-FCH PET/CT during the two months prior to surgery. For each lesion, the authors calculated the LLCER on MRI HBP images and the SUVmax tumour-to-liver ratio (SUVT/L) for both tracers. They analysed and compared the predictive value for aggressive pathological features, including the histological grade and MVI, as well as the RFS.
The areas under receiver operating characteristics for the identification of aggressive HCCs on pathology with LLCER, 18F-FDG SUVT/L and 18F-FCH SUVT/L were 0.92 (95% confidence interval [CI] 0.78, 0.98), 0.89 (95% CI 0.74, 0.97; p = 0.70), and 0.64 (95% CI 0.45, 0.80; p = 0.035).
LLCER was identified as an independent predictor of RFS (HR [95% CI] = 0.91 [0.84, 0.99], p = 0.022). LLCER of -4.72% or less also accurately predicted moderate to poor differentiation grade (sensitivity = 100%, specificity = 92.9%) and MVI (sensitivity = 93.3%, specificity = 60%) and identified patients with poor RFS after surgical resection (p = 0.030).
After surgical resection for HCC, patients with an LLCER of -4.72% or less had significantly poorer recurrence-free survival than patients with an LLCER superior to -4.72%, according to the authors.
“HBP tumour enhancement after Gd-BOPTA injection may help identify aggressive HCC pathological features, and patients with reduced recurrence-free survival after surgical resection,” they wrote.
Impact of research
Based on the study findings, senior author and radiologist Alain Luciani and the rest of the team have changed their routine practice by integrating Gd-BOPTA-enhanced MRI with delayed HBP images as part of pre-surgery workup in all patients with resectable HCC.
Sébastien Mulé.
“PET/MRI with 18F-FDG is now performed in our institution as part of HCC pre-treatment workup,” Mulé noted. “Improving lesion characterization and prognostic prediction by systematically performing acquisitions at the hepatobiliary phase may be an interesting next step. Further studies will evaluate whether hepatobiliary MR contrast agent uptake may help optimize therapeutic management strategy in patients with HCC.”
Staff at the Henri Mondor University Hospital have been and still are involved in the care of COVID-19 patients, and the pandemic has had a significant impact on the organization and the clinical activity of the radiology department, he said.
“Notably, the management of patients with HCC was significantly altered, as patients were more likely to wait before they consult, and thus to present with more advanced stages of disease,” Mulé added.
00:00–00:08
It’s fair to say there has been confusion about how ultraviolet light can help in the COVID-19 pandemic.
00:09–00:17
Sadly, it’s obscured some of the genuine science, which could actually be very significant. So let’s try to clear up some of the misinformation.
00:19–00:30
Now, when it comes to UV light, we are most familiar with UVA and UVB – the bands of sunlight that filter through the atmosphere and make it to the Earth’s surface.
00:31–00:35
In moderate doses it’s good for us in a number of ways.
00:36–00:44
But overexposure can cause sunburn – or even cancer – so that’s why we slap on the suncream, or shelter under parasols.
00:45–01:00
Fortunately, the ozone layer filters out an even more dangerous band of sunlight known as UVC. If you exposed yourself to UVC, you would experience serious burns and damage to DNA.
01:01–01:12
But UVC is a double-edged sword. As well as damaging skin, it can also mangle the genetic material of viruses and bacteria, preventing them from reproducing.
01:13–01:27
Scientists have known for over a century about UV’s ability to disinfect. And for many years, UVC lamps have been used for sterilization in medical settings, food production and a number of other places.
01:28–01:37
During the COVID-19 outbreak in China, buses were even bathed in UV light overnight, to leave them clinically clean for the next day.
01:38–01:53
For these applications, UVC lamps are great. But they’re often big and unwieldy. And because of the high risk to humans, operators need to wear really hardcore safety equipment and go through specialized training.
01:53–02:02
But now, emerging research could prove to be a game-changer for UVC sterilization. Making it much more accessible.
02:03–02:16
Researchers have discovered that a specific wavelength of UVC light – 222 nm – could be much less dangerous to humans, while still lethal for viruses and bacteria.
02:17–02:21
Now think about that for a second. The implication is huge.
02:22–02:32
In theory, we could deploy 222 nm lights across the world to shield ourselves from coronaviruses, and a bunch of other invisible enemies.
02:34–02:49
But before you get too excited, there is a long way to go and many questions still remain. Crucially, this far-UVC light has so far only been tested on mice at short exposure times and single doses.
02:50–03:01
So clearly, much more research is needed to check its safety for humans, and its ability to damage SARS-CoV-2, the virus behind COVID-19 disease.
03:02–03:11
And even if it does work, we would still to develop new lighting technologies, that are practical for a variety of applications.
03:11–03:24
The most promising approach seems to be light-emitting diodes – LEDs. And several groups of physicists are already experimenting with different materials to develop far-UVC LEDs.
03:25–03:36
Even the most optimistic researchers would admit that it is unlikely the technology could be ready in time for the COVID-19 pandemic, even if there is a second wave.
03:36–03:51
But the number of zoonotic diseases – that’s diseases passing from animals to humans – has been on the increase in recent times. So these far-UVC LEDs could come to play a vital role in the next serious pandemic.
03:52–03:59
Find out more about UV light and sterilization in the June 2020 issue of Physics World.
Light diffracts as it travels around objects. If it didn’t, designing quantum optics devices and getting optical microscopy to resolve nanoscale images would be heaps easier. Now an international collaboration of researchers has shown that dispersion- and diffraction-free propagation is possible, with a resolution that beats the diffraction limit by more than an order of magnitude, in twisted layers of 2D molybdenum trioxide. These photonic effects mirror the behaviour of electrons in twisted bilayer graphene, where reports of electrons travelling with no resistance kicked off a rich new field of 2D materials research known as “twistronics”.
In 2018 Pablo Jarillo-Herrero and colleagues observed that electrons in pristine bilayer graphene – layers of a honeycomb-shaped carbon atom lattice – could be made to superconduct, or exist in Mott insulator states (depending on whether an electric field is applied or not) when one layer is twisted by a “magic angle” with respect to the other. Following this announcement, reports of other twisted 2D systems exploded in number. But while scientists with a penchant for curious electron antics pondered how electrons racing through magic-angle graphene could couple strongly enough to form the Cooper pairs behind superconductivity, this so-called “flat band” behaviour was also stimulating new ideas for researchers in photonics.
Photonic flat bands
Andrea Alù, a researcher at City University of New York and senior author of the latest report (which is published in Nature) notes that in magic-angle twisted bilayer graphene, the term “flat band” refers to a state in which electron energies flatten as their momentum increases, rather than increasing linearly with momentum (as they would in a single layer of graphene). This behaviour arises because when the two carbon-lattice layers are twisted ever so slightly out of sync with each other, electrons tunnelling between them experience a potential field with a new periodic variation, like the beating of two musical tones.
Photonics, of course, is concerned with light rather than electron transport. However, Alù and his collaborators realized that similar flat-band behaviour can also occur in photonic “metasurfaces” – that is, materials with a composition and structure engineered to support unusual photonic effects at their surface.
Normally, light emanates from a point source in circular wavefronts, like the rings round a pebble dropped in a pond. In metasurfaces engineered to have anisotropic photonic responses, however, these rings become squashed into ellipses. At their extreme, these ellipses can even take on a hyperbolic shape, like the trajectory of a rocket reaching escape velocity. The photonic flat bands Alù and colleagues observed appeared at the transition between elliptical and hyperbolic responses to light, which occurs at the resonance frequency of a metasurface made from a grid of graphene nanoribbons.
Inspired by developments in twistronics, the researchers decided to investigate whether the photonic flat-band behaviour in two layered metasurfaces would change if the metasurfaces were twisted relative to each other. They calculated that they could shift the flat band away from the resonance frequency simply by controlling the relative angle between the two surfaces. This would be a huge bonus, because the metasurface strongly absorbs light at its resonant frequency, which would make it hard to exploit the flat-band effect. However, for this effect to work without suffering from large nonlocalities, they found that they needed to make the nanoribbons in their metasurface very densely spaced, with features that are prohibitively small for even the most sophisticated nanofabrication techniques.
Natural flat bands
These stringent nanofabrication requirements posed a serious challenge to the researchers’ effort to experimentally validate their results. The breakthrough came with reports that a natural (that is, non-structured) 2D material known as α-molybdenum trioxide (α-MoO3) exhibits unusual dispersion behaviour in quasiparticles known as phonon-polaritons, which arise when incident photons and vibrations of the material’s lattice oscillate in unison. “Interestingly, MoO3 naturally supports hyperbolic polariton propagation in plane, which is exactly what we needed for our concept to work, without any complicated fabrication requirements,” Alù tells Physics World.
He and his collaborators took two layers of 2D α-MoO3 rotated with respect to each other and used a nanoscale metallic tip to excite the phonon-polaritons. They then used the same tip as a scanning near-field optical microscopy (SNOM) probe, which measures the non-propagating near-field, to achieve non-diffraction-limited polariton images.
These experiments revealed the existence of an all-important flat band at magic-angle twists of the two α-MoO3 layers, where phonon-polaritons propagate as rays with no diffraction. While diffraction limits the resolution of propagating light to around half its wavelength, the researchers clocked the full-width half maximum of the ray near the defect at 1/40th of its free-space wavelength. The ray’s decay length was also almost eight times the phonon-polariton decay length at the flat band resonance in a single layer of α-MoO3. The effects were observed even when the thicknesses of the layer varied, indicating they were not easily perturbed – a robustness typical of topological phenomena.
“To me, the most exciting part is the beauty of how you can predict this phenomenon to arise from purely geometric formulae,” explains Alu. “Overlaying the hyperbolic shapes associated with each of the isolated layers and gradually increasing the twist between the layers will lead to crossing points where the hyperbolic dispersion curves intersect. At first there will be just two intersections, but when the other sides of the hyperbolae intersect as well, there will be four, and it is at this ‘magic angle’ for which the number of intersections changes that the flat band and associated effects occur. Because the shape the hyperbola makes with respect to the lattice for a given frequency is known, it is possible to predict the magic angle just by counting the intersections. You can then tune the flat band to any frequency of interest within the hyperbolic band of α-MoO3 by twisting.”
Frank Koppens, a researcher at the Institute for Photonic Science in Spain who was not involved in the paper, notes that twisted two-dimensional materials “have opened a completely new era in material science as a completely new way to design correlated matter in a controlled fashion.” Koppens, who works at the frontiers of both 2D materials and nanophotonics, adds that this latest work “has taken twistronics into the realm of twist-nanophotonics, and demonstrated completely new ways of working with optical fields at the nanoscale.”
The researchers expect their effects to have important implications for nano-imaging, unusual resonant features, quantum optics, low-energy optical signal processing and computing.
My degree was in physics with astrophysics, and it has been hugely valuable to me throughout my career. Although I have never worked as a professional scientist, the ability to understand complex mathematics and scientific concepts has made me better at my job. In order to communicate a subject, you have to understand what you are communicating. By having a scientific background, I am equipped with the skills needed to ask the right questions of scientists and understand what they are talking about. My degree has also added to my credibility when communicating science.
But studying physics has also provided me with many other skills, which I still use to this day. These include team work – developed through years of group work and doing labs at university – as well as the ability to communicate complex scientific topics and ideas to others, a skill I developed thanks to group work during my undergraduate studies.
What do you like best and least about your job?
What I love most about my job is the opportunity I have to inspire as many people as possible about space. Be that through social media, partnership with organizations and companies, hosting events, television shows, radio shows or books. My audience is a mix of people who are interested in space and want to learn more, and those who don’t necessarily know a huge amount, but who I get to inspire about how space is shaping their lives. It is a privilege to help explain to as many people as possible the importance of space exploration.
The second thing I love about what I do is the travel and the opportunity to work with incredible people. I have travelled the world filming and giving talks about space exploration and I have worked with the likes of Buzz Aldrin, Jeff Bezos, Chris Hadfield to name but a few. I have appeared on screen in Times Square, New York, hosted events in countless countries and been fortunate enough to see several space launches.
However, what I do involves long hours and extended periods of time away from home. It also involves being a self-starter and an element of hustle, developing new ideas and projects, which may not be for everyone. Added to that is rejection; it’s a natural part of working in the media and you need to have thick skin in order to be able to deal with this element. Overall, though, I think that I have the best job in the world, and am always exited to be playing my small part in helping humanity continue to explore space.
What do you know today, that you wish you knew when you were starting out in your career?
I wish I had known to aim higher. One of the phrases that frustrates me the most is “manage your expectations” – I heard it a lot in my early career. My advice to anyone starting out in their careers is to follow their dreams. However, don’t do so blindly – think about what you want to achieve and the skills you need, and work towards developing them. Have a plan in place, but don’t stick to it rigidly. Early in my career I also didn’t really know of anyone who did the type of job I wanted to do, but it is really important to find mentors and look at what other people are doing. I wish I had known more about how to find a mentor. It is so important to research who is doing the type of work you want to do and then reach out to them and ask questions. The worst that can happen is that they will say no, but most people are keen to help.
The other thing I wish I had known when I was starting out is that time is your friend. It can sometimes be frustrating; you don’t think you are getting where you hoped you would be. Nothing happens overnight. You have to be patient and keep working consistently hard, that is the key to success. And sometimes you will fail, but failing or getting rejected isn’t always a bad thing. Instead, the most important thing to do is to embrace failure and learn from it. Failure doesn’t define us, but how we react to things not going as planned does.
A day of action: The logo of the #ShutDownAcademia and #ShutDownSTEM campaign. (Courtesy: #ShutDownAcademia)
Today – Wednesday 10 June – will not be a normal day in the physics calendar. That’s because, at the time of writing, more than 3000 physicists around the world have agreed to take part in a “Strike for Black Lives”.
Organized in the wake of the death of George Floyd – part of a wider pattern of police killings of black Americans that has now been condemned by several US scientific societies – the strike is not intended to be a “day off” for non-black people. Instead, participating physicists have pledged to use the time they would have spent teaching classes or doing research to explore what practical actions they can take to support black physicists.
If you’re wondering what you can do, the Strike for Black Lives organizers have compiled a list of suggested steps and actions. Staff at the arXiv pre-print server have already agreed not to announce new papers on the day of the strike, while staff at the Institute of Physics (Physics World‘s parent organization) plan to suspend normal work in favour of “reflect[ing] on the role that we can take as individuals and as an organization”. If you wish, you can pledge your personal support too.
Here at Physics World, we’re highlighting – on our home page and on social media – relevant stories we’ve published by or about black physicists and the issues they face.
Some physicists, I am sure, will question the need for this initiative or feel it has no relevance to them. But we all harbour unconscious biases, myself included – as I discovered while writing this feature on diversity in physics.
If there’s only one thing you do, read this powerful open letter by Nord and Prescod-Weinstein, who explain far better than I can precisely why the Strike for Black Lives is so vital.
Posted on behalf of the Physics World editorial team
What is the point of a first-year physics lab? As lab instructors, we had to grapple with that question when we learned that the summer term at McMaster University would be done online because of the COVID-19 pandemic. We had to consider not just what we could accomplish with the lab assignments we gave, but also, what we wanted our students to accomplish
Traditionally, our course (1A03) included eight hours of in-lab work, done in groups of 2-3 under the close supervision of teaching assistants. Students also did one major at-home experiment of their choice. When it was announced that the summer term would be online, me and my colleagues Sara Cormier and Kari Dalnoki-Veress decided to develop a kit that students could use to do all the experiments for the course at home.
For our cohort, who are mainly life science students (and in many cases not excited to be taking physics), we thought that a more pragmatic approach focusing on building experiments, collecting good data, and developing a physical intuition for the concepts in the course would better suit their needs. However, the COVID-19 shelter-in-place order was going to make obtaining materials and performing experiments difficult for students. Our solution was to mail each student a tiny “At-Home Lab Kit”.
The contents of the kits were simple by design (see figure). Using household items, we wanted to reinforce the connection between the real world and what they learn in class. Additionally, the labs focused on determining what they can measure with limited tools, and how those measurements can be turned into reproducible data that can be used to test a theory. Indeed, the skills developed by doing these experiments go well beyond what we usually teach in this first year course.
Exceptional accuracy
Students were surprised by the kind of results that can be obtained with such simple items. In the first lab session, students collected data that allowed them to measure the acceleration due to gravity with exceptional accuracy. Another lab used a clear plastic box, protractor, and some pins to measure the index of refraction of water. Further experiments with diffraction were done and students investigated total internal reflection, which is crucial to the operation of optical fibres for telecommunication.
With a bouncy ball, students measured the time between successive bounces to investigate energy transfer, energy loss, and the validity of concepts like conservation of energy and momentum. And of course, no first-year course would be complete without dealing with frictional forces. In pre-COVID times, students would use a digital force-transducer to make precise measurements. This year, they were given a spring (a coiled-plastic keychain). An example of how students had to calibrate their spring and make measurements is shown in the video below.
Early action and planning were crucial to the success of this project. Despite the simplicity of the kits, we first had to obtain approval from the university’s Crisis Management Group, convincing them the kits were safe to be sent to students. Perhaps misunderstanding our intentions, we were asked to provide Workplace Hazardous Materials Information System assessments for each object to be shipped. In the end, we all agreed students already understood how to safely handle and store rulers and elastic bands.
More difficult were dealing practical issues like shipping over 200 kits across the world. For students who were unable to receive packages (including several undergoing a 21-day hotel-based quarantine), we offered one-on-one advice on scavenging for materials — a skill that, as an experimental physicist, I take pride in. In only two cases could students not perform the labs themselves. For them, we provided videos that they could make measurements from.
At the time of writing, we are releasing the final lab exercise for the course, and early feedback from students has been very positive. Though we wish we could be back in our labs in September, we are thrilled to share these labs with 900 more students in the fall term. We are confident that we are not simply making the best of a bad situation; we are providing a unique experience for our students that will hopefully compliment whatever path they take at McMaster.
Echo-planar images from rat brains implanted with GF (top row) and platinum–iridium (PtIr) electrodes; and (right) magnetic field distortions observed in rats with GF and PtIr electrodes. Red and blue arrows point to GF and PtIr implants, respectively. (Courtesy: CC BY 4.0/Nat. Commun. 10.1038/s41467-020-15570-9)
The ability to perform functional MRI (fMRI) during deep brain stimulation (DBS) is important for understanding the effects of DBS therapies. DBS, which involves electrical stimulation of neural tissues via implanted electrodes, is used for treatments of movement disorders such as Parkinson’s disease and essential tremor. But the therapeutic mechanisms and neuromodulatory effects of DBS are not well understood.
While fMRI provides a powerful tool for mapping brain activity, strong magnetic field interference from conventional metal DBS electrodes creates artefacts in the MR images. Such artefacts preclude functional and structural mapping of large volumes of brain tissues surrounding the electrodes and impede visualization of local responses at the stimulation site during simultaneous DBS and fMRI.
A team in China has now shown that use of novel graphene fibre (GF) DBS microelectrodes can enable full activation pattern mapping during DBS–fMRI in a rat model of Parkinson’s disease. The GF electrodes caused minimal interference with the magnetic field of a 9.4 T MRI scanner, enabling significantly better, artefact-free or near artefact-free, images than those created when using tungsten wire or platinum–iridium electrodes.
The researchers, at Peking University and the Institute of Neuroscience, Chinese Academy of Sciences, fabricated GF electrodes with a charge-injection-capacity 70 times greater than DBS electrodes made of platinum–iridium, the material most commonly used in clinical neural stimulation devices. This high charge-injection-capacity is desirable to decrease MRI artefact size and improve stimulation resolution.
Xiaojie Duan (left) and Zhifeng Liang.
Co-principal investigators Xiaojie Duan and Zhifeng Liang created the GFs from aqueous graphite oxide suspensions injected into a glass pipeline. They baked the pipeline at 230°C to produce a GF matching the pipe geometry, with a fibre diameter of about 75 µm.
To fabricate a GF-stimulating microelectrode, they pasted together two parallel-aligned insulated GFs, with one end soldered to a custom MRI-compatible copper connector that interfaces with the stimulation pulse generator. The GFs were then mechanically cut to expose their cross sections as electrically active sites. These GF electrodes showed a higher charge-injection limit than most available electrode materials.
Activity of a Parkinsonian rat before, during and after DBS with a GF electrode. (Courtesy: CC BY 4.0/Nat. Commun.)
The researchers tested the DBS capability of the GF electrodes by using them to stimulate the subthalamic nucleus in Parkinsonian rats, with stimulation parameters replicating a clinical DBS setting. They observed significant improvement in the rats’ mobility, confirming the therapeutic efficacy of subthalamic nucleus-DBS with GF electrodes.
Comparing MRI artefacts generated by the GF microelectrodes with those created by platinum-iridium microelectrodes of the same diameter showed that the GF electrodes exhibited much smaller artefacts in both anatomical images and functional (echo planar imaging) scans. The GF electrodes also showed high stability under continuous overcurrent pulsing.
“The GF electrodes caused minimal interference to the magnetic field, and their presence would not cause significant attenuation in fMRI signals, thus enabling a full and unbiased mapping of the activation pattern under DBS–fMRI studies,” write the researchers. “Such advantage is critical for exploring the neuromodulatory effects and mechanisms of DBS therapies.”
“With the unique capability for full and unbiased mapping of the entire circuit and network connectivity without obstructing brain nuclei, future DBS–studies with the GF electrodes at different targets and with varied stimulation frequency and strength could provide important insights into brain circuitries and network connections, as well as the therapeutic mechanisms underlying various DBS therapies,” they write.
The team now hopes to use the GF electrodes for DBS–fMRI studies on other neurological disorders, such as treatment-resistant depression.
Dana Cooper is a certified medical dosimetrist/technical sales representative with LifeLine Software, Inc, part of the LAP Group. She has more than 25 years of experience in radiation oncology, having held positions such as radiation therapist, dosimetrist and department manager. Dana joined LSI in 2016 and has been connecting radiation therapy departments with software that increases productivity and safety ever since.
