Point-of-care PET scanner offers interactive imaging

25 Mar 2019 Tami Freeman

Illustration showing the locations of the two PET detectors and the sampling pattern used to image the cylindrical phantom (the red circle). (Courtesy: Med. Phys. 10.1002/mp.13397)

Molecular imaging technologies such as PET are employed for in vivo diagnosis, evaluating disease progression and guiding therapeutic interventions. PET also offers the potential for imaging of novel theranostic ligands currently under development for personalized treatments. Standard whole-body PET systems, however, require installation in a large, dedicated scanning room and may not be the most cost-effective way to support the translation of novel PET ligands. Furthermore, it’s not always feasible to transfer a patient to the scanner.

Einstein’s general theory of relativity passes a supermassive test

25 Mar 2019

Heart of the matter: Sagittarius A* as seen by the Chandra X-ray Observatory. (Courtesy: NASA/CXC/MIT/F K Baganoff et al).

A key aspect of Einstein’s general theory of relativity (GR) has been tested using the strongest gravitational field so far. The measurement was made by observing changes in optical absorption lines of a star orbiting close to Sagittarius A* – the supermassive black hole at the center of the Milky Way.

Since it was first proposed in 1915, GR has stood firm against every experimental challenge that physicists have come up with. Many of these tests have focused on an important tenet of GR called the Einstein equivalence principle (EEP). Detecting a breakdown of the EEP could point towards new physics beyond GR and could provide important clues about how to develop a quantum theory of gravity. The work was done by physicists working on the GRAVITY Collaboration, which uses the Very Large Telescope at the European Southern Observatory in Chile.

Researchers solve magic angle mystery

25 Mar 2019 Belle Dumé

The general concept of flat bands and how they are related to superconductivity. Courtesy: https://www.alexkruchkov.com

Exactly a year ago, researchers at MIT reported on observing superconductivity in twisted bilayer graphene – a new experimental platform engineered on two misaligned graphene layers – at “magic angles” near 1.1°. The origin of these angles was a mystery, however. A team at Harvard University has now shown that they appear to be fundamentally connected to quantum Hall wave functions.

Graphene is a flat crystal of carbon just one atom thick. When two such sheets are placed on top of each other with a small angle misalignment, they form a Moiré pattern. More surprisingly still, at the twist angle of 1.1°, the material becomes a superconductor (that is, it can carry currents with no losses) at 1.7 K. This effect disappears at slightly larger or smaller angle twists.

Stationary digital breast tomosynthesis increases diagnostic accuracy

26 Mar 2019

A mammogram and a stationary digital breast tomosynthesis image. (Courtesy: Yueh Lee)

The addition of digital breast tomosynthesis (DBT) to a 2D mammography exam can significantly improve breast cancer detection by making lesions more conspicuous on a pseudo-3D image. DBT has limitations, however, including image degradation due to focal spot blurring, noise, scatter and motion artifacts, as well as the inability to visualize breast microcalcifications as well as conventional mammographic images.

To overcome these shortcomings, researchers are developing stationary DBT (sDBT) devices. Existing commercial DBT systems work by moving a single X-ray tube — either by continuous motion or a step-and-shoot technique — to collect a series of projection views at multiple angles. In sDBT, the single rotating X-ray tube is replaced by a fixed array of carbon nanotube-enabled (CNT) X-ray sources. This allows for a rapid, motion-free collection of multiple projection views over a wide-angle span.

Billion-volt thunderstorm studied using muons

26 Mar 2019

Particle deflector: the paths of muons are affected by the huge voltages found in thunderclouds. (Courtesy: iStock/prudkov)

A thundercloud with a record-breaking voltage of 1.3 GV has been observed by physicists in India and Japan. Sunil Gupta at the Tata Institute of Fundamental Research in Mumbai and colleagues calculated the voltage from changes in the intensity of atmospheric muons detected by the GRAPES-3 muon telescope. The existence of such high voltages could explain the origin of the mysterious, high-energy gamma-ray flashes, which are occasionally seen in cloud tops during thunderstorms.

Thunderstorm clouds are normally studied by flying weather balloons and airplanes straight through their centers. Indeed, a balloon was used several decades ago to measure the previous record high voltage of 130 MV – which was observed inside a thunderstorm over New Mexico. Such a voltage is high enough to create atmospheric particle accelerators that can generate X-rays and low-energy gamma rays.

LHCb bags another pentaquark

27 Mar 2019 Hamish Johnston

Molecular structure: artist’s impression of how five quarks could bind together. (Image: Daniel Dominguez/CERN)

A new pentaquark – an exotic hadron comprising five quarks – has been discovered by physicists working on the LHCb experiment at CERN. LHCb scientists have also found that a feature in their data that had previously been associated with one pentaquark could be evidence for two pentaquarks with similar masses.

Hadrons are heavy particles that are made of two or more quarks held together by the strong force. Until the early 2000s, physicists had concrete evidence for only two types of hadron: baryons (such as protons and neutrons) containing three quarks and mesons, which contain a quark and antiquark. Preliminary analysis of the three pentaquarks suggests that they have a molecular structure that resembles a meson bound to a baryon (see figure). Gaining a better understanding of how pentaquarks are bound together could provide important insights into the strong force and quantum chromodynamics.

Superconducting nanowires could shed light on dark matter

28 Mar 2019

Nanowire detector: this device (which is about 15 microns wide) detects photons, but similar detectors could soon join the hunt for dark matter. (Courtesy: Baek/NIST)

Superconducting nanowires could be used as both targets and sensors for the direct detection of dark matter, physicists in Israel and the US have shown. Using a prototype nanowire detector, Yonit Hochberg at the Hebrew University of Jerusalem and colleagues demonstrated the possibility of detecting of dark matter particles with masses below about 1 GeV/c2, while maintaining very low levels of noise. The team says it has already used its prototype to set “meaningful bounds” on interactions between electrons and dark matter.

While dark matter appears to make up about 85% of the matter in the universe, it has not been detected directly – despite the best efforts of physicists working on numerous detectors worldwide.

Chiral material reverses Casimir force, say, physicists

21 Mar 2019

The Casimir force can be tuned and even reversed by placing a chiral optical material between two similar surfaces – according to calculations by Qing-Dong Jiang and Frank Wilczek at the University of Stockholm. The duo’s finding gets around a famous “no-go” theorem, which says that the Casimir force between two similar surfaces must always be attractive. The research could be of practical use because the Casimir force can inhibit the operation of nanomechanical devices.

When two uncharged conducting plates are placed nanometres apart in a vacuum, the Casimir force tends to pull them together. This happens because a vacuum is not empty; rather, it bubbles with virtual photons that appear and then vanish. The gap between the plates acts as an optical cavity, which means that the number of virtual photons at wavelengths resonant with the cavity will be enhanced. This tends to increase the radiation pressure in the gap. Photons at non-resonant wavelengths, however, are suppressed and this leads to a drop in the pressure. The overall effect is a lowering of the radiation pressure in the gap – compared to outside the gap – and this tends to pull the plates together.

For two similar plates, calculations show that the Casimir force must always be attractive, drawing the plates towards each other. Recent theoretical and experimental studies have shown that it is possible to create scenarios with repulsive Casimir forces using objects made of different materials or with different shapes.

Chiral loophole

In their study, Jiang and Wilczek identify a loophole in the no-go theorem, which they say would allow for strong repulsive Casimir forces between two isotropic plates. To do this, the duo devised a setup with an optically active material is placed in the gap. This material is chiral, acting differently on photons of opposite circular polarization. The result is that virtual photons with opposite polarization have different velocities in the medium and this means they make different contributions to the overall radiation pressure between the gap.

With the chiral material in place, Jiang and Wilczek, calculate the Casimir force will oscillate between attractive and repulsive – depending on the distance between the plates. What is more, the repulsive force can be up to three times stronger than the regular attractive Casimir force. They also showed that the magnitude of the force can vary in response to an external magnetic field – providing a second way of tuning the force.

Jiang and Wilczek say that optically active chiral materials are relatively common, which could make it easy for physicists to test the idea in the lab.

The calculations are described in Physical Review D.

Sam Jarman is a science writer based in the UK

22/3/2019 physics

Reprogrammable self-assembly makes molecular computer

21 Mar 2019 Belle Dumé

Molecular programming wall. Courtesy: Damien Woods (Maynooth University)

Researchers have designed a tileset of DNA molecules that can carry out robust reprogrammable computations to execute six-bit algorithms and perform a variety of simple tasks. The system, which works thanks to the self-assembly of DNA strands designed to fit together in different ways while executing the algorithm, is an important milestone in constructing a universal DNA-based computing device.

CERN physicists spot symmetry violation in charm mesons

21 Mar 2019 Michael Banks

Charmed physics: The LHCb detector has spotted CP violation in charm mesons for the first time. (Courtesy: CERN)

Particle physicists at CERN have measured charge-parity (CP) violation in the D0 meson for the first time. Announcing the finding today during the annual Rencontres de Moriond conference held in La Thuile, Italy, the result has a statistical significance of 5.3 σ – exceeding the 5σ “gold standard” for discovery in particle physics. It is the first time that CP violation has been seen in charm mesons and opens up the possibility of searching for physics beyond the Standard Model.

According to conventional cosmological models, equal amounts of matter and antimatter should have been created in the aftermath of the Big Bang.

Grooved surface accelerates dew harvesting

20 Mar 2019

Dewdrop: dew forming on a grooved surface. (Courtesy: PB Bintein et al/Phys. Rev. Lett.)

A grooved surface that collects water by encouraging large dew droplets to form rapidly and then trickle away has been created by Pierre-Brice Bintein and colleagues at the Superior School of Industrial Physics in Paris. The researchers say that a square meter of the surface could be used to collect more than 500 ml of water in one night. The team believes their technique could provide people in some arid regions with a reliable source of fresh water.

Researchers have reduced this sticking time using ultra-smooth and micropatterned surfaces. Droplets on these surfaces experience less of a pinning force and are therefore at the shed at smaller sizes. When an inclined surface is left outside overnight in relatively cool temperatures, dew droplets will form and grow.

Evidence for dark matter could be trapped in ancient rocks

18 Mar 2019

Particle detectors: could evidence for dark matter interactions be extracted from rocks? (Courtesy: James Dacey)

Ancient rocks hidden deep underground could hold important clues about the nature of dark matter – according to physicists in Sweden and Poland. The idea is that dark-matter collisions should create nanoscale defects in the crystalline structure of rock – and this damage could be measured using modern microscopy techniques. Indeed, the team estimates that hundreds of thousands of defects could be present in just one cubic centimetre of rock.

While physicists have built a number of WIMPs detectors worldwide, none have managed to observe the elusive particles. These detectors tend to use large volumes of material and run over several years in the hope of seeing just a handful of collisions between WIMPs at atomic nuclei.

Climate change could allow disease-carrying mosquitoes to spread across Western Europe

15 Mar 2019

Invasive species: an Asian tiger mosquito. (Courtesy: James Gathany/CDC)

Climate change could allow disease-carrying Asian tiger mosquitoes to spread across Western Europe, say two independent groups of researchers. The insects are known to spread more than 20 diseases including yellow fever, chikungunya, dengue, and Zika – which could become more common in the region.

According to a new study by Soeren Metelmann of the University of Liverpool and colleagues in the UK, almost all of England and Wales could be warm enough for the species by the 2060s. Meanwhile, an international team including Moritz Kraemer at the University of Oxford has done an independent study that predicts that the mosquito will spread throughout Europe over the next 30 years.

Quantum-computing initiatives worldwide are examined by leading physicists

01 Mar 2019 Hamish Johnston

Global reach: it is a quantum world out there. (Courtesy: iStock/Bellenixe)

Do you wonder how much Canada is spending on the development of quantum science and technologies, or exactly what the European Commission’s Quantum Flagship is? Well, you are in luck because the journal Quantum Science and Technology has put together a special Focus on Quantum Science and Technology Initiatives Around the World.

Written by some of the leading physicists in the field, the first five articles in the collection cover Canada, the EU, Japan, the US, and Australia. Reports from the UK and China will be published later this year.

Machine learning is implemented on an IBM quantum processor

14 Mar 2019 Hamish Johnston

Multidimensional: quantum computers could expand the representation spaces used by machine learning. (Courtesy: Shutterstock/Dmitriy-Rybin)

Machine-learning algorithms have been run on a quantum computer by physicists at IBM. Although the proof-of-concept demonstration did not involve practical tasks, the team hopes that scaling-up the algorithms to run on larger quantum systems could give machine learning a boost.

Many machine learning algorithms are “kernel methods”, which determine similarities between patterns. The strategy is to transform the data – pixels in a digital image, for example – into a higher-dimensional representation that has clear boundaries between classification types. All images of cats, for example, would reside in one region of this higher-dimensional, space whereas all images of dogs reside in another.

Young forests use carbon most effectively

15 Mar 2019

(Image courtesy: iStnock/temmuzca)

For forests, it really does help to be young. British scientists who have identified the vital factor that shows what makes a forest a good carbon sink say young forests use carbon best and absorb it most efficiently.

A new study in the Proceedings of the National Academy of Sciences seems on the face of it to settle an old puzzle with an unsurprising answer. New and young forests make the most efficient and effective carbon sinks.

CT system developers utilize AI to boost patient care

14 Mar 2019

Chest CT scan viewed with the AI-Rad Companion Chest CT software. (Courtesy: Siemens Healthineers)

Disease detection with CT has benefited greatly from advancements in artificial intelligence (AI) software during the past year. To make the case at the ECR 2019 technical exhibition, many vendors dedicated their CT booth presentations to the integration of AI into the modality. The rewards for patient care are visible for all delegates to see during the recent congress.

With its gaze set firmly on combining AI and CT to enhance care, Siemens Healthineershighlighted its AI-Rad Companion Chest CT, a software assistant for radiology powered by AI technology.

This product is reportedly the company’s first application capable of using AI algorithms to automatically differentiate individual structures on chest CT scans. The algorithms can highlight distinct structures in the thorax and also spot potential abnormalities.

Photonic nanojets achieve super-resolution

07 Mar 2019 Lauren Barr

A truncated sphere of titanium dioxide (TiO2) produces a photonic nanojet (PNJ) of electromagnetic radiation (seen in the central plot) that probes two gold spheres. Image credit: Victor Pacheco-Peña.

Ways to break through the diffraction limit and into the regime of subwavelength imaging have been growing ever-more creative. One tool that has proven useful in this endeavor is the photonic nanojet (PNJ) – an extremely narrow and intense beam of radiation at the interface between a dielectric particle and its surrounding medium. Now, a pair of researchers have developed a way to simultaneously minimize the particles and enhance the PNJs, which could benefit many imaging, microscopy and sensing applications, offering a resolution five times better than that of traditional PNJ imaging systems.Advertisement

Multipole magnetic tweezers measure organelle mechanical properties

14 Mar 2019 Belle Dumé
The magnetic bead exerting 50-piconewtons of force on the nuclear envelope caused deformation of the nucleus. Credit: Wang et al., Sci. Robot. 4, eaav6180 (2019)

Being able to directly probe organelles (specialized structures inside biological cells) and measure their properties is important for understanding subcellular activity, diagnosing diseases associated with this activity and developing new therapies. Doing this is no easy task, however. A team of researchers in Canada, China, and the US has now developed a new magnetic tweezer system that can measure the mechanical properties of organelles for the first time. The device makes use of a magnetic bead placed inside the cell that can be used to precisely manipulate intracellular structures at any location in 3D and apply a controllable force of up to 60 piconewtons to them for long periods. By relating the applied force and the amount by which the organelle deforms, as a result, the nanobot can measure properties such as viscoelasticity and plasticity of the cell nucleus, mitochondria, and endoplasmic reticulum.

“The mechanical properties of the biggest organelle inside a cell – the nucleus – are altered in cancer cells, cells with progeria, and cells infected with malaria,” explains lead author of this research study Xian Wang of the University of Toronto. “Directly probing the mechanical properties of the cell nucleus inside single cells would thus help us better understand the structural differences between diseased and healthy cells.”