Magnetic particle imaging (MPI) is an emerging medical imaging modality with the potential for high sensitivity and spatial resolution. Since its introduction back in 2005, researchers have built numerous preclinical MPI systems for small-animal studies. But human-scale MPI remains an unmet challenge. Now, a team headed up at the Athinoula A Martinos Center for Biomedical Imaging has built a proof-of-concept human brain-scale MPI system and demonstrated its potential for functional neuroimaging.
MPI works by visualizing injected superparamagnetic iron oxide nanoparticles (SPIONs). SPIONs exhibit a nonlinear response to an applied magnetic field: at low fields they respond roughly linearly, but at larger field strengths, particle response saturates. MPI exploits this behaviour by creating a magnetic field gradient across the imaging space with a field-free line (FFL) in the centre. Signals are only generated by the unsaturated SPIONs inside the FFL, which can be scanned through the imaging space to map SPION distribution.
First author Eli Mattingly and colleagues propose that MPI could be of particular interest for imaging the dynamics of blood volume in the brain, as it can measure the local distribution of nanoparticles in blood without an interfering background signal.
“In the brain, the tracer stays in the blood so we get an image of blood volume distribution,” Mattingly explains. “This is an important physiological parameter to map since blood is so vital for supporting metabolism. In fact, when a brain area is used by a mental task, the local blood volume swells about 20% in response, allowing us to map functional brain activity by dynamically imaging cerebral blood volume.”
Rescaling the scanner
The researchers began by defining the parameters required to build a human brain-scale MPI system. Such a device should be able to image the head with 6 mm spatial resolution (as used in many MRI-based functional neuroimaging studies) and 5 s temporal resolution for at least 30 min. To achieve this, they rescaled their existing rodent-sized imager.
Proof-of-concept system The back of the MPI scanner showing the opening for the patient head. (Courtesy: Lawrence Wald)
The resulting scanner uses two opposed permanent magnets to generate the FFL and high-power electromagnet shift coils, comprising inner and outer coils on each side of the head, to sweep the FFL across the head. The magnets create a gradient of 1.13 T/m, sufficient to achieve 5–6 mm resolution with high-performance SPIONs. To create 2D images, a mechanical gantry rotates the magnets and shift coils at 6 RPM, enabling imaging every 5 s.
The MPI system also incorporates a water-cooled 26.3 kHz drive coil, which produces the oscillating magnetic field (of up to 7 mTpeak) needed to drive the SPIONs in and out of saturation. A gradiometer-based receive coil fits over the head to record the SPION response.
Mattingly notes that this rescaling was far from straightforward as many parameters scale with the volumeof the imaging bore. “With a bore about five times larger, the volume is about 125 times larger,” he says. “This means the power electronics require one to two orders of magnitude more power than rat-sized MPI systems, and the receive coils are simultaneously less sensitive as they become larger.”
Performance assessment
The researchers tested the scanner performance using a series of phantoms. They first evaluated spatial resolution by imaging 2.5 mm-diameter capillary tubes filled with Synomag SPIONs and spaced by between 5 and 9 mm. They reconstructed images using an inverse Radon reconstruction algorithm and a forward-model iterative reconstruction.
The system demonstrated a spatial resolution of about 7 mm with inverse Radon reconstruction, increasing to 5 mm with iterative reconstruction. The team notes that this resolution should be sufficient to observe changes in cerebral blood volume associated with brain function and following brain injuries.
To determine the practical detection limit, the researchers imaged Synomag samples with concentrations from 6 mgFe/ml to 15.6 µgFe/ml, observing a limit of about 1 µgFe. Based on this result, they predict that MPI should show grey matter with a signal-to-noise ratio (SNR) of roughly five and large blood vessels with an SNR of about 100 in a 5 s image. They also expect to detect changes during brain activation with a contrast-to-noise ratio of above one.
Next, they quantified the scanner’s imaging field-of-view using a G-shaped phantom filled with Synomag at roughly the concentration of blood. The field-of-view was 181 mm in diameter – sufficient to encompass most human brains. Finally, the team monitored the drive current stability over 35 min of continuous imaging. At a drive field of 4.6 mTpeak, the current deviated less than 2%. As this drift was smooth and slow, it should be straightforward to separate it from the larger signal changes expected from brain activation.
The researchers conclude that their scanner – the first human head-sized, mechanically rotating, FFL-based MPI – delivers a suitable spatial resolution, temporal resolution and sensitivity for functional human neuroimaging. And they continue to improve the device. “Currently, the group is developing hardware to enable studies such as application-specific receive coils to prepare for in vivo experiments,” says Mattingly.
At present, the scanner’s sensitivity is limited by background noise from the amplifiers. Mitigating such noise could increase sensitivity 20-fold, the team predicts, potentially providing an order of magnitude improvement over other human neuroimaging methods and enabling visualization of haemodynamic changes following brain activity.
Lia Merminga has resigned as director of Fermilab – the US’s premier particle-physics lab. She stepped down yesterday after a turbulent year that saw staff layoffs, a change in the lab’s management contractor and accusations of a toxic atmosphere. Merminga is being replaced by Young-Kee Kim from the University of Chicago, who will serve as interim director until a permanent successor is found. Kim was previously Fermilab’s deputy director between 2006 and 2013.
Tracy Marc, a spokerperson for Fermilab, says that the search for Merminga’s successor has already begun, although without a specific schedule. “Input from Fermilab employees is highly valued and we expect to have Fermilab employee representatives as advisory members on the search committee, just as has been done in the past,” Marc told Physics World. “The search committee will keep the Fermilab community informed about the progress of this search.”
The departure of Merminga, who became Fermilab director in August 2022, was announced by Paul Alivisatos, president of the University of Chicago. The university jointly manages the lab with Universities Research Association (URA), a consortium of research universities, as well as the industrial firms Amentum Environment & Energy, Inc. and Longenecker & Associates.
“Her dedication and passion for high-energy physics and Fermilab’s mission have been deeply appreciated,” Alivisatos said in a statement. “This leadership change will bring fresh perspectives and expertise to the Fermilab leadership team.”
Turbulent times
The reasons for Merminga’s resignation are unclear but Fermilab has experienced a difficult last two years with questions raised about its internal management and external oversight. Last August, a group of anonymous self-styled whistleblowers published a 113-page “white paper” on the arXiv preprint server, asserting that the lab was “doomed without a management overhaul”.
The document highlighted issues such as management cover ups of dangerous behaviour including guns being brought onto Fermilab’s campus and a male employee’s attack on a female colleague. In addition, key experiments such as the Deep Underground Neutrino Experiment suffered notable delays. Cost overruns also led to a “limited operations period” with most staff on leave in late August.
In October, the US Department of Energy, which oversees Fermilab, announced a new organization – Fermi Forward Discovery Group – to manage the lab. Yet that decision came under scrutiny given it is dominated by the University of Chicago and URA, which had already been part of the management since 2007. Then a month later, almost 2.5% of Fermilab’s employees were laid off, adding to portray an institution in crisis.
Born in Greece, Merminga, 65, earned a BSc in physics from the University of Athens before moving to the University of Michigan where she completed an MS and PhD in physics. Before taking on Fermilab’s directorship, she held leadership posts in governmental physics-related institutions in the US and Canada.
Signals from the global navigation satellite system can be jammed and spoofed, so a Google spinout is working on an alternative positioning and navigation system that uses the Earth’s magnetic field.
CERN’s ALICE Collaboration has found the first evidence for antihyperhelium-4, which is an antimatter hypernucleus that is a heavier version of antihelium-4. It contains two antiprotons, an antineutron and an antilambda baryon. The latter contains three antiquarks (up, down and strange – making it an antihyperon), and is electrically neutral like a neutron. The antihyperhelium-4 was created by smashing lead nuclei together at the Large Hadron Collider (LHC) in Switzerland and the observation has a statistical significance of 3.5σ. While this is below the 5σ level that is generally accepted as a discovery in particle physics, the observation is in line with the Standard Model of particle physics. The detection therefore helps constrain theories beyond the Standard Model that try to explain why the universe contains much more matter than antimatter.
Hypernuclei are rare, short-lived atomic nuclei made up of protons, neutrons, and at least one hyperon. Hypernuclei and their antimatter counterparts can be formed within a quark–gluon plasma (QGP), which is created when heavy ions such as lead collide at high energies. A QGP is an extreme state of matter that also existed in the first millionth of a second following the Big Bang.
Exotic antinuclei
Just a few hundred picoseconds after being formed in collisions, antihypernuclei will decay via the weak force – creating two or more distinctive decay products that can be detected. The first antihypernucleus to be observed was a form of antihyperhydrogen called antihypertriton, which contains an antiproton, an antineutron, and an antilambda hyperon It was discovered in 2010 by the STAR Collaboration, who smashed together gold nuclei at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC).
Then in 2024, the STAR Collaboration at Brookhaven National Laboratory’s Relativistic Heavy Ion Collider (RHIC) reported the first observations of the decay products of antihyperhydrogen-4, which contains one more antineutron than antihypertriton.
Now, ALICE physicists have delved deeper into the word of antihypernuclei by doing a fresh analysis of data taken at the LHC in 2018 – where lead ions were collided at 5 TeV.
Using a machine learning technique to analyse the decay products of the nuclei produced in these collisions, the ALICE team identified the same signature of antihyperhydrogen-4 detected by the STAR Collaboration. This is the first time an antimatter hypernucleus has been detected at the LHC.
Rapid decay
But that is not all. The team also found evidence for another, slightly lighter antihypernucleus, called antihyperhelium-4. This contains two antiprotons, an antineutron, and an antihyperon. It decays almost instantly into an antihelium-3 nucleus, an antiproton, and a charged pion. The latter is a meson comprising a quark–antiquark pair.
Physicists describe production of hypernuclei in a QGP using the statistical hadronization model (SHM). For both antihyperhydrogen-4 and antihyperhelium-4, the masses and production yields measured by the ALICE team closely matched the predictions of the SHM – assuming that the particles were produced in a certain mixture of their excited and ground states.
The team’s result further confirms that the SHM can accurately describe the production of hypernuclei and antihypernuclei from a QGP. The researchers also found that equal numbers of hypernuclei and antihypernuclei are produced in the collisions, within experimental uncertainty. While this provides no explanation as to why there is much more matter than antimatter in the observable universe, the research allows physicists to put further constraints on theories that reach beyond the Standard Model of particle physics to try to explain this asymmetry.
The research could also pave the way for further studies into how hyperons within hypernuclei interact with their neighbouring protons and neutrons. With a deeper knowledge of these interactions, astronomers could gain new insights into the mysterious interior properties of neutron stars.
The observation is described in a paper that has been submitted to Physical Review Letters.
The Electrochemical Society (ECS) is an international non-profit scholarly organization that promotes research, education and technological innovation in electrochemistry, solid-state science and related fields.
Founded in 1902, the ECS brings together scientists and engineers to share knowledge and advance electrochemical technologies.
As part of that mission, the society publishes several journals including the flagship Journal of the Electrochemical Society (JES), which is over 120 years old and covers a wide range of topics in electrochemical science and engineering.
Someone who has seen their involvement with the ECS and ECS journals increase over their career is chemist Trisha Andrew from the University of Massachusetts Amherst. She directs the wearable electronics lab, a multi-disciplinary research team that produces garment-integrated technologies using reactive vapor deposition.
Trisha Andrew from the University of Massachusetts Amherst. (Courtesy: Trisha Andrew)
Her involvement with the ECS began when she was invited by the editor-in-chief of ECS Sensors Plus to act as a referee for the journal. Andrew found the depth and practical application of the papers she reviewed interesting and of high quality. This resulted in her submitting her own work to ECS journals and she later became an associate editor for both ECS Sensors Plus and JES.
Professional Opportunities
Physical chemist Weiran Zheng from the Guangdong Technion – Israel Institute of Technology China, meanwhile, says that due to the reputation of ECS journals, they have been his “go-to” place to publish since graduate school.
Physical chemist Weiran Zheng from the Guangdong Technion – Israel Institute of Technology China. (Courtesy: Weiran Zheng)
One of his papers entitled “Python for electrochemistry: a free an all-in-one toolset” (ECS Adv. 2 040502) has been downloaded over 8000 times and is currently the most-read ECS Advances article. This led to an invitation to deliver an ECS webinar — Introducing Python for Electrochemistry Research. “I never expected such an impact when the paper was accepted, and none of this would be possible without the platform offered by ECS journals,” adds Zheng.
Publishing in ECS journals has helped Zheng’s career advance through new connections and becoming more involved with ECS activities. This has not only boosted his research but also professional network and given these benefits, Zheng plans to continue to publish his latest findings in ECS journals.
Highly cited papers
Battery researcher Thierry Brousse from Nantes University in France, came to electrochemistry later on in his career having first carried out a PhD in high-temperature superconducting thin films at the University of Caen Normandy.
Battery researcher Thierry Brousse from Nantes University in France. (Courtesy: Thierry Brousse)
When he began working in the field he collaborated with the chemist Donald Schleich from Polytech Nantes, who was an ECS member. It was then that he began to read the JES finding it a prestigious platform for his research in supercapacitors and microdevices for energy storage. “Most of the inspiring scientific papers I was reading at that time were from JES,” notes Brousse. “Naturally, my first papers were then submitted to this journal.”
Brousse says that publishing in ECS journals has provided him with new collaborations as well as invitations to speak at major conferences. He emphasizes the importance of innovative work and the positive impact of publishing in ECS journals where some of his most cited work has been published.
Brousse, who is an associate editor for JES, adds that he particularly values how publishing with ECS journals fosters a quick integration into specific research communities. This, he says, has been instrumental in advancing his career.
Long-standing relationships
Robert Savinell’s relationship with the ECS and ECS journals began during his PhD research in electrochemistry, which he carried out at the University of Pittsburgh. Now at Case Western Reserve University in Cleveland, Ohio, his research focusses on developing a flow battery for low-cost long duration energy storage primarily using iron and water. It is designed to improve the efficiency of the power grid and accelerate the addition of solar and wind power supplies.
Robert Savinell at Case Western Reserve University in Cleveland, Ohio. (Courtesy: Robert Savinell)
Savinell also leads a Department of Energy funded Emerging Frontier Research Center on Breakthrough Electrolytes for Energy Storage. This Center focuses on fundamental research on nano to meso-scale structured electrolytes for energy storage.
ECS journals have been a cornerstone of his professional career, providing a platform for his research and fostering valuable professional connections. “Some of my research published in JES many years ago are still cited today,” says Savinell.
Savinell’s contributions to the ECS community have been recognized through various roles, including being elected a fellow of the ECS and he has previously served as chair of the ECS’s electrolytic and electrochemical engineering division. He was editor-in-chief of JES for the past decade and most recently was elected third vice president of the ECS.
Savinell says that the connections he has made through ECS have been significant, ranging from funding programme managers to personal friends. “My whole professional career has been focused around ECS,” he says, adding that he aims to continue to publish in ECS journals and hopes that his work will inspire solutions to some of society’s biggest problems.
Personal touch
For many researchers in the field, publishing in ECS journals has brought with it several benefits. That includes the high level of engagement and the personal touch within the ECS community and also the promotional support ECS provides for published work.
The ECS journals’ broad portfolio also ensure that researcher’s work reaches the right audience, and such a visibility and engagement is a significant factor when it comes to advancing the careers of scientists. “The difference between ECS journals is the amount of engagement, views and reception that you receive,” says Andrew. “That’s what I found to be the most unique”.
Melted plastic pipes and drastic water-pressure drops are potentially leaching toxic chemicals and contaminants into local supplies. Multiple water authorities in north Los Angeles have issued Do Not Drink notices.
A recently-discovered class of magnets called altermagnets has been imaged in detail for the first time thanks to a technique developed by physicists at the University of Nottingham’s School of Physics and Astronomy in the UK. The team exploited the unique properties of altermagnetism to map the magnetic domains in the altermagnet manganese telluride (MnTe) down to the nanoscale level, raising hopes that its unusual magnetic ordering could be controlled and exploited in technological applications.
In most magnetically-ordered materials, the spins of atoms (that is, their magnetic moments) have two options: they can line up parallel with each other, or antiparallel, alternating up and down. These arrangements arise from the exchange interaction between atoms, and lead to ferromagnetism and antiferromagnetism, respectively.
Altermagnets, which were discovered in 2024, are different. While their neighbouring spins are antiparallel, like an antiferromagnet, the atoms hosting these spins are rotated relative to their neighbours. This means that they combine some properties from both types of conventional magnetism. For example, the up, down, up ordering of their spins leads to a net magnetization of zero because – as in antiferromagnets – the spins essentially cancel each other out. However, their spin splitting is non-relativistic, as in ferromagnets.
Resolving altermagnetic states down to nanoscale
Working at the MAX IV international synchrotron facility in Sweden, a team led by Nottingham’sPeter Wadley used photoemission electron microscopy to detect the electrons emitted from the surface of MnTe when it was irradiated with a polarized X-ray beam.
“The emitted electrons depend on the polarization of the X-ray beam in ways not seen in other classes of magnetic materials,” explains Wadley, “and this can be used to map the magnetic domains in the material with unprecedented detail.”
Using this technique, the team was able to resolve altermagnetic states down to the nanoscale – from 100-nm-scale vortices and domain walls up to 10-μm-sized single-domain states. And that is not all: Wadley and colleagues found that they could control these features by cooling the material while a magnetic field is applied.
Potential uses of altermagnets
Magnetic materials are found in most long-term computer memory devices and in many advanced microchips, including those used for Internet of Things and artificial intelligence applications. If these materials were replaced with altermagnets, Wadley and colleagues say that the switching speed of microelectronic components and digital memory could increase by up to a factor of 1000, with lower energy consumption.
“The predicted properties of altermagnets make them very attractive from the point of view of fundamental research and applications,” Wadley tells Physics World. “With strong theoretical guidance from our collaborators at FZU Prague and the Max Planck Institute for the Physics of Complex Systems, we realised that our experience in materials development and magnetic imaging positioned us well to attempt to image and control altermagnetic domains.”
One of the main challenges the researchers faced was developing thin films of MnTe with surfaces of a sufficiently high quality that allowed them to detect the subtle X-ray spectroscopy signatures of the altermagnetic order. They hope that their study, detailed in Nature, will spur further interest in these materials.
“Altermagnets provide a new vista of predicted phenomena from unconventional domain walls to unique band structure effects,” Wadley says. “We are exploring these effects on multiple fronts and one of the major goals is to demonstrate a more efficient means of controlling the magnetic domains, for example, by applying electric currents rather than cooling them down.”
Metals usually become less conductive as they get thinner. Niobium phosphide, however, is different. According to researchers at Stanford University, US, a very thin film of this non-crystalline topological semimetal conducts electricity better than copper even in non-crystalline films. This surprising result could aid the development of ultrathin low-resistivity wires for nanoelectronics applications.
“As today’s electronic devices and chips become smaller and more complex, the ultrathin metallic wires that carry electrical signals within these chips can become a bottleneck when they are scaled down,” explains study leader Asir Intisar Khan, a visiting postdoctoral scholar and former PhD student in Eric Pop’s group at Stanford.
The solution, he says, is to create ultrathin conductors with a lower electrical resistivity to make the metal interconnects that enable dense logic and memory operations within neuromorphic and spintronic devices. “Low resistance will lead to lower voltage drops and lower signal delays, ultimately helping to reduce power dissipation at the system level,” Khan says.
The problem is that the resistivity of conventional metals increases when they are made into thin films. The thinner the film, the less good it is at conducting electricity.
Topological semimetals are different
Topological semimetals are different. Analogous to the better-known topological insulators, which conduct electricity along special edge states while remaining insulating in their bulk, these materials can carry large amounts of current along their surface even when their structure is somewhat disordered. Crucially, they maintain this surface-conducting property even as they are thinned down.
In the new work, Khan and colleagues found that the effective resistivity of non-crystalline films of niobium phosphide (NbP) decreases dramatically as the film thickness is reduced. Indeed, the thinnest films (< 5 nm) have resistivities lower than conventional metals like copper of similar thicknesses at room temperature.
Another advantage is that these films can be created and deposited on substrates at relatively low temperatures (around 400 °C). This makes them compatible with modern semiconductor and chip fabrication processes such as industrial back-end-of-line (BEOL). Such materials would therefore be relatively easy to integrate into state-of-the-art nanoelectronics. The fact that the films are non-crystalline is also an important practical advantage.
A “huge” collaboration
Khan says he began thinking about this project in 2022 after discussions with a colleague, Ching-Tzu Chen, from IBM’s TJ Watson Research Center. “At IBM, they were exploring the theory concept of using topological semimetals for this purpose,” he recalls. “Upon further discussion with Prof. Eric Pop, we wanted to explore the possibility of experimental realization of thin films of such semimetals at Stanford.”
This turned out to more difficult than expected, he says. While physicists have been experimenting with single crystals of bulk NbP and this class of topological semimetals since 2015, fabricating them at the ultrathin film limit of less than 5 nm at a temperature and using deposition methods compatible with industry and nanoelectronic fabrication was new. “We therefore had to optimize the deposition process from a variety of angles: substrate choice, strain engineering, temperature, pressure and stoichiometry, to name a few,” Khan tells Physics World.
The project turned out to be a “huge” collaboration in the end, with researchers from Stanford, Ajou University, Korea, and IBM Watson all getting involved, he adds.
The researchers says they will now be running further tests on their material. “We also think NbP is not the only material with this property, so there’s much more to discover,” Pop says.
Three exotic new species of superconductivity were spotted last year, illustrating the myriad ways electrons can join together to form a frictionless quantum soup.
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