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Technology advances improve imaging for paediatric patients

New techniques for imaging paediatric patients, including a hybrid imaging sequence that may make abdominal MRI exams easier for children to undergo, were among the topics presented in a virtual scientific session at the recent European Congress of Radiology (ECR 2021).

Conventional abdominal MRI exams can be challenging to perform on children. The procedure involves a series of differently weighted imaging sequences executed during repeated breath-hold manoeuvres. Because of this, the exam is complex, time-inefficient and sensitive to artefacts related to incomplete suspension of respiration.

A team at UKBB, the University Children’s Hospital of Basel, is currently evaluating a new radial volumetric encoding (RAVE) hybrid T2/T1 imaging technique that enables free-breathing abdominal MRI scans. The sequence follows a multi-parametric approach that enables the acquisition of both a T2-weighted and a T1-weighted image in a single scan.

Speaking at ECR 2021, Katja Glutig of the Universitäts Klinikum Jena described an initial feasibility study to determine whether this sequence is feasible for use in paediatric patients. She believes that the sequence will be particularly favourable for children and adolescents with cystic fibrosis.

The study included 15 patients aged between one and 19 years who had abdominal MRI scans at UKBB during 2019. Patients underwent a standard MRI exam using routine sequences on a 3T scanner, followed by an axial RAVE T2/T1 hybrid sequence at the end of the exam. The sequence, developed at New York University School of Medicine’s Center for Advanced Imaging Innovation and Research (CAI²R) in 2017, is described in detail in Magnetic Resonance in Medicine.

Two paediatric radiologists independently assessed images acquired from basic T2- and T1-weighted MR images and those of the hybrid sequence. They ranked the overall image quality, respiratory motion artefacts, clarity of portal vein wall delineation, sharpness of the hepatic margin and the quality of fat suppression.

“Our results indicate that the quality of the T2-weighted component of the RAVE-T2/T1 aspect was significantly higher than the standard T2 HASTE FS sequence in all categories except the quality of fat suppression,” Glutig reported. “Similarly, the quality of the T1 RAVE acquired aspect compared to the standard T1 DIXON sequence aspect was significantly higher for respiratory motion artefacts, clarity of portal vein wall delineation and sharpness of hepatic margin.”

“There will be several advantages to this sequence when it can be implemented in clinical practice,” Glutig tells Physics World. “It will help improve analysis of very small lesions, such as those in the kidney. The radial acquisition allows a patient to breathe freely during the measurement. In spite of free breathing, the MR images are almost free of artefacts and are of good diagnostic quality, corresponding to a standard sequence or better. This will be beneficial when imaging cystic fibrosis patients, who often suffer from constant coughing, causing motion during a scan.”

Glutig advises that data from a pilot study being conducted in Jena evaluating a RAVE hybrid sequence for cystic fibrosis patients are currently being analysed, and that the researchers hope to publish their findings later in 2021.

Decreasing the radiation dose

Speaking in the same session, Lütfiye Özlem Atay from Gazi University Faculty of Medicine described a technique to reduce radiation exposure when scanning paediatric cancer patients, who may require multiple ionizing radiation-based imaging exams during their course of treatment. Replacing PET/CT with PET/MRI, using hybrid PET/MRI scanners, can reduce radiation exposure by up to 70%. Atay and colleagues are working to reduce radiation exposure even more, by decreasing the injected radiotracer dose.

Atay presented a study suggesting that a third-dose of radiotracer can produce diagnostic-quality images in paediatric oncologic PET/MRI, with only a small relative percentage change in quantitative parameters. The study included 54 patients, aged between two and 18 years, with 12 different types of cancer. The patients underwent whole-body PET/MRI scans performed on a 3T scanner with a time-of-flight PET detector, roughly one hour after injection of 1.9 MBq/kg of ¹⁸F-FDG – half of the recommended tracer dose, and currently used as standard at Gazi University Hospital.

To investigate whether the injected tracer activity could be reduced further, the researchers used the acquired list-mode data sets from 77 PET/MRI exams to retrospectively simulate images acquired at one third (1.2 MBq/kg) and one quarter (0.9 MBq/kg) dose. They placed volumes-of-interest within organs and around FDG-avid lesions to examine the influence of dose reduction on quantification.

Atay reported that signal-to-noise ratios differed significantly among PET data sets, showing gradually increasing image noise with decreased tracer dose. However, image quality and lesion detectability were comparable, for both visual assessment and quantitative contrast-to-noise analysis.

Dose reduction — PET images of a 17-year-old girl with newly diagnosed Hodgkin’s lymphoma. From left to right: the original data set (1.9 MBq/kg), simulated activities of 1.2 and 0.9 MBq/kg. While there was no significant difference in the detectability of ¹⁸F-FDG-avid lesions, image noise and granularity increased with decreasing tracer activity. (Courtesy: Lutfiye Özlem Atay)

“We’ve been using half-dose tracer since September 2017, and wanted to determine the effect of even lower tracer doses,” explained Atay. “When considered with the elimination of CT-related radiation dose, using injected radiotracer activity of third dose allows a radiation dose reduction of more than 80% in PET/MRI exams compared to PET/CT. This situation provides a significant reduction in the cumulative ionizing radiation dose, especially in paediatric patients who require repeated PET imaging during treatment and follow-up.”

Physics of dopant emission to harness the rainbow emission of nanocrystals

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The physics of Mn emission in nanocrystals is one of the most intriguing emissions and its origin has been debated for several decades. Being a spin and orbital forbidden excitation, its intensity has befuddled many researchers. However, this intense emission also gives rise to several interesting properties, especially upon understanding the mechanism of excitation and emission, and is hence the subject topic of discussion even in recent literature, specifically in the context to storing the spin information.

In this seminar, Ranjani Viswanatha will discuss the various anomalous manifestations of the optical properties of Mn emission, like polarized emission, extensive back transfer. Although the hosts were initially thought to be non-consequential, we demonstrate that the host indirectly plays a critical role in the emission. Thus, with the introduction of Mn in perovskites, they have given a whole new dimension that is previously not observed in II-VI semiconductor quantum dots. We further discuss the origin of these anomalous properties and thus can be utilized in several devices, specifically playing a key role in quantum computing.

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Dr Ranjani Viswanatha is an associate professor at the Jawaharlal Nehru Centre for Advanced Scientific Research (JNCASR), Bangalore, India. She graduated from the Indian Institute of Science, Bangalore, with MS and PhD degrees. After several postdoctoral stints at the University of Arkansas, US, and Los Alamos National Lab, she joined JNCASR as an assistant professor. Dr Viswanatha’s research interests include optical, magnetic, magneto-optical, and electronic structure studies of nanocrystals with an emphasis on II-VI semiconductors and perovskite nanomaterials. Her research has been published and cited in international journals, and she holds several patents in the field. She is a member of the editorial advisory board of ChemPhotoChem. Her work has been recognized through several awards and honours.

Switching career from particle physics to nuclear power

Troels Schönfeldt is a physicist who has had an innate curiosity about how and why things work since childhood. However, his career path into physics “took quite a big detour” thanks to his decision to leave school at the age of 16 and travel around Europe. “I was not the typical career guy,” he says. “I started off as a dropout but then I got back on track.” Today, he is the chief executive of Copenhagen, Denmark-based start-up company Seaborg Technologies, which is working towards manufacturing and commercializing a safer, cheaper and cleaner nuclear reactor – a Compact Molten Salt Reactor (CMSR) – that cannot be weaponized, or result in a nuclear disaster.

Schönfeldt’s interest in physics was piqued after he returned to school and found it gave him the deep understanding and knowledge he longed for. He had spent five years working as a laboratory assistant at Danish company Coloplast, which manufactures medical devices, before returning to his studies. “I still wanted to know how and why,” he recalls. His initial goal was to earn a chemistry degree but he soon realized that for him physics was “the king of science”. He graduated from the Niels Bohr Institute of the University of Copenhagen in 2011, with a Master’s degree in particle physics, in collaboration with CERN in Geneva, Switzerland.

Schönfeldt continued his studies at the Technical University of Denmark (TUD) and the European Spallation Source (ESS) in Lund, Sweden, and earned his PhD in neutron physics in 2015. “I worked on advanced neutron moderators, so I had to design the ESS moderator system to slow down the fast neutrons the source produced, and make them useful for neutron scattering experiments,” he explains, adding that “The moderator now actually has a specific shape – the so-called butterfly moderator – which I came up with as part of my PhD.”

Talking nuclear

During his PhD, Schönfeldt occasionally met up with two fellow physicists he had known through his Master’s to brew beer and discuss nuclear power. “We called it the Beer Nuclear Power Club,” he recalls. Each meet-up concluded with them complaining about how nuclear was not being used as a solution for the climate-change crisis. One night in 2014 they decided to take matters into their owns hands and start a company, becoming “impact entrepreneurs” – those who start companies with the aim to generate change in society, and improve lives. “We didn’t even know what a company was, but nobody was reacting; sometimes you cannot expect other people to do it, you have to do it yourself,” Schönfeldt says.

At first, Seaborg Technologies – named after US nuclear chemist and Nobel laureate Glenn T Seaborg – started as an ambitious volunteer project, where the three worked on the technology in their spare time. “We were trying to pick up from where the Molten Salt Reactor Experiment was shut down in the 1960s. They didn’t have the computers to calculate the advanced calculations they needed to handle neutronics in a liquid,” says Schönfeldt. In the meantime, Schönfeldt finished his PhD in 2015 and had several postdocs lined up. “My plan was to take one of those offers, but I was so much in love with Seaborg Technologies that I actually said no and went full time with no salary.”

The company designed its compact molten salt reactor that same year, aiming to provide electricity, clean water, heating and cooling to around 200,000 households with renewable energy. The liquid salt is used as a neutron moderator that acts as a catalyst to improve the chain reaction – similar to what Schönfeldt had previously worked on. “My PhD geared me very well to work on nuclear reactors,” he says. Soon after, two other physicists and a serial entrepreneur joined the team, became co-founders and helped set up the company properly. Schönfeldt points out that having an entrepreneur on the team really helped with the business side of things. “The mindset you have as a physicist is valuable in business, but you cannot do everything as a physicist.”

Power barges — **Change is afloat** Seaborg Technologies is hoping to get its first commercial reactors running on power barges in south-east Asia in the next four years. (Courtesy: Seaborg Technologies)

Learning business

Schönfeldt unintentionally became chief executive after his co-founders nominated him for the role. “I was 10 minutes late for that meeting,” he recalls, “I had no interest in being the CEO, I wanted to do physics.” Over the next few years, Schönfeldt learned the ins and outs of business, licensing processes, commercialization, management and human resources. “I started to love and understand being the CEO. It turned out it was a really lucky choice.”

I started to love and understand being the CEO. It turned out it was a really lucky choice.
Troels Schönfeldt

After refining the business plan, Seaborg Technologies found its first investors in 2018, and since then has received numerous funding from venture capital funds, grants and private investors. “We started off really small, but we have grown to about 30 people from five continents – including physicists, nuclear engineers, chemists, safety experts and business developers – and we’re now in the process of hiring 50 more. We also receive a couple of handfuls of interns every year,” he says.

Ten years after Fukushima: could new fuels make nuclear power safer?

In 2019 Seaborg Technologies built its own small-scale laboratory, enabling on-site experimental research. “We are well under way to license the next generation of nuclear reactors to save the world,” Schönfeldt says. Despite setbacks due to coronavirus, he explains their goal still remains to have the first commercial nuclear power source up and running by 2025. “To make it truly impactful we will place our reactors on power barges and mass produce them at Korean shipyards, and then tow them to seaside cities in south-east Asia.”

Maintaining company culture

As Seaborg Technologies’ chief executive, Schönfeldt’s job involves lots of meetings, navigating opinions and stakeholders, and ensuring everyone is happy. “Culture is fundamental for any company, and building it requires a lot of nurturing and a lot of work,” he says. He often misses doing physics, but at the same time, he enjoys the varied challenges. “We have a lot of clever heads here and my main role is to ensure that they have the framework to solve problems – not solve them myself,” says Schönfeldt.

Having ended up in a career that he never expected, Schönfeldt pauses before giving advice to today’s physics graduates. “It has been a hardcore transition – founding a company is the best thing you will ever do, but it’s also the worst,” he says. Even so, he encourages them to think outside the box to create change in the world. “Please start a company. The world needs young creative people and new ways of thinking. But don’t expect to know and solve everything from the beginning, your physics skills might not be where you end up.”

Standing up for science in difficult times

Every minute of every day some 300 hours of video is uploaded to YouTube and millions of stimulating but unregulated discussions occur daily on forum sites. While the Internet allows instant access to information and each other, the bias of algorithms favour suggestions that appeal to the user. Alongside media sensationalism and political corruption, the Internet has cultivated an insurgence of anti-science ideology, fuelled by misinformation, under-representation and angered passion. In a world where nearly 60% of the population has access to the Internet, scientists are needed more than ever to safeguard facts, reliability, global peace and health.

Anti-science rhetoric has nucleated in the past decade, especially when it comes to the climate. Despite the worst-case scenario showing a global temperature increase of 8 °C and a sea level rise of 1 m by 2100 – well within the lifetime of our youngest generation – many opt to ignore it or challenge the underlying evidence. In the wake of COVID-19, ignorance and a failure to listen to scientists has exacerbated the problem. Onlookers watch as countries guided by science slowly return to a cautious normality, while other countries suffer painful death rates, long-term lockdowns and frustration at U-turns in policies.

As people seek to find a balanced view of hyperbolized news, scientists appear a good first point of contact for their trained critical thinking

In the UK, prime minister Boris Johnson initially shook hands with hospitalized COVID-19 patients, then prioritized economics over health, overlooked members of his government breaching COVID laws and changed his mind haphazardly regarding education, free school meals and Christmas celebrations. When scientists extensively modelled the outcomes for COVID and detailed the steps required to prevent the worst, a compliant government should have listened. Banging pots and pans for under-funded, over-worked NHS and other stressed keyworkers is not the answer. And in the US we’ve seen a similar COVID rebellion, with its former president Donald Trump calling for protests against mask-wearing and lockdowns, as well as promoting the ingestion of bleach and hydroxychloroquine, giving false statistics and highlighting vaccine cynicism. Thankfully, new US president Joe Biden is taking a different approach.

When influential people show such disregard, disrespect and suspicion regarding science, it’s easy to understand how conspiracies are formed and cultivated in communities, giving rise to the dangerous anti-science crusade. The role of a scientist is to be the elective voice of reason against absurdity and tunnel-visioned proclamations. It is vital then that figures of authority trust scientific judgement and act correspondingly. The trust of politicians and the media can help to combat anti-science rhetoric and some of the most pressing issues faced by humanity. With the obvious need for visible scientists, it should be our duty to speak up about our concerns about certain policies.

Putting yourself out there

Scientists are trained over many years to sift through jargon and data to establish facts, spot flaws and – mostly – set aside their personal convictions should evidence deem them unlikely. After all, even Einstein could not fault quantum mechanics despite his deep, philosophical trouble with the theory. Scientists are approached with complex and detailed situations sometimes falling beyond the scope of their field. As people seek to find a balanced view of hyperbolized news, scientists appear a good first point of contact for their trained critical thinking.

Although rewarding, being the fact-finding, jargon-juggling rock of reason is often taxing as it not only requires time and effort but mental gymnastics to produce a satisfactory response. Being the go-to for factual concerns can add a different, sometimes unwanted complexity. Alternatively, constant mental stimulation and problem solving is a thriving point for some scientists who use such interesting conversations as a break – or indeed, procrastination – from their day-to-day work.

The demand for and of scientists is high. But we know that for every scientist who chooses to be vocal, there is another who is loathe to fill such an open role, not least because they do not have the time. Indeed, speaking up and putting yourself out there is not always easy. The response from those outside of the community is sometimes ostracizing and offputting: rife with misogyny for women, judgemental towards people of colour, and filled with the misconception that scientists believe they’re better than the general public.

This, in combination with an often unrelatable day job, can lead scientists to reduce their social ties to non-scientists, ultimately removing an indispensable connection with most of the population. Part of being vocal is to also break down stereotypes and defy stigma. Doing so demonstrates the “normality” lying behind the graphs, liquid nitrogen and serious statistics; behind every scientist is a unique person with distinct interests, families and stories. This is crucial to portray if today’s young people are to grow up with trust and passion in science and if minorities are going to feel welcomed into the scientific community.

People are often taken aback should a scientist have unexpected hobbies – be it bodybuilder, pro-chef, sommelier, artist or musician. When the outside world only sees “scientist” as one’s identity, it inadvertently belittles talents and hobbies that have taken decades to master. A scientist may, in their eyes, then transform from a boring person who sits behind a computer all day to someone who does science but also runs ultra-marathons or produces their own music.

Demonstrating that science is accessible for anybody and everybody is not just about improving the image of scientists. It is also a pivotal step in dousing the anti-science fire and drowning out conspiracies – both vital if we are to continue the global advance towards a more peaceful, safe and healthy future.

Soft robot dives 10 km under the ocean

A soft, self-powered robot, capable of swimming in the deepest regions of Earth’s oceans has been created by researchers in China. Inspired by the hadal snailfish, the team led by Guorui Li at Zhejiang University designed its device to feature flapping fins, and decentralized electronics encased in a deformable silicone body. Having successfully demonstrated the design in the Mariana Trench, their innovations could lead to new ways of exploring some of the most remote regions of the oceans.

The scope of human exploration has extended to even the most inhospitable environments on land, but the deepest regions of Earth’s oceans remain almost entirely unexplored. At depths below 3000 m, extreme pressures experienced by exploration vessels make it very difficult to design robust electronic components required for onboard power, control, and thrust. If these components are closely packed together on a rigid circuit board, pressure-induced shear stresses can cause them to fail at their interfaces.

To overcome these challenges, researchers seek inspiration from the many organisms that thrive at such depths. In their study, Li’s team considered the hadal snailfish, which was recently discovered at depths exceeding 8000 m in the Pacific Ocean. These strange creatures have several features that give them high adaptability and mobility, even at extreme pressures: including a distributed, highly deformable skull, and flapping pectoral fins.

Decentralized electronics

Imitating these features, the researchers designed a pressure-resilient electronics system, which could be fully encased in a soft silicone body. Like the skull of a snailfish, the team decentralized the components of this system – either by increasing the distances between components, or by separating them into several smaller circuit boards. This allowed them to reduce maximum shear stresses at component interfaces by 17%, making them far more resilient to extreme pressures.

To imitate the bird-like flapping fins of the snailfish, Li and colleagues designed artificial muscles using dielectric elastomers: rubber-like materials that convert electrical energy into mechanical work. By sandwiching a compliant electrode between two dielectric elastomer membranes, the researchers could generate flapping in two silicone films, which they supported using elastic frames.

Li’s team tested the performance of their robot at the bottom of the Mariana Trench, some 10,900 m beneath the ocean surface. Their device was powered by an onboard lithium-ion battery, and fitted with a high-voltage amplifier, video cameras, and LED lights. Even at pressures exceeding 1000 atmospheres, it maintained a flapping motion for 45 min. Further tests in the South China Sea (see video), alongside experiments in a pressure chamber, demonstrated that the device could swim freely and resiliently at speeds exceeding 5 cm/s.

Li and colleagues now hope that their design could be extended to enable more complex tasks, including sensing and communications. They will now focus on developing new materials and structures to enhance the intelligence, versatility, and efficiency of soft robots – further improving their ability to operate in extreme conditions.

The robot is described in Nature.

Mantis shrimp inspires hyperspectral and polarimetric light sensor

A novel hyperspectral and polarimetric optical sensor that’s small enough to fit on a smartphone has been developed by researchers in the US and Korea. The device consists of an alternating stack of polarization-sensitive organic photovoltaics (P-OPVs) and folded polymer retarders, and can detect four spectral and three polarization channels. However, the researchers claim that the design could ultimately sense 15 spectral channels over the visible spectrum.

Hyperspectral and polarization imaging has the potential to revolutionize many fields, from biomedicine to astronomy. Hyperspectral imaging allows visible light to be sensed in more narrow bands than are visible to the human eye. This can be useful, for example, for determining the chemical composition of objects, identifying hazardous gases, or detecting subtle differences in tissue composition for medical diagnosis. Polarimetry, on the other hand, measures polarization in light, providing useful information on surface geometry and subsurface detail of objects.

Current devices for measuring spectral and polarimetric information simultaneously, known as spectral polarization imaging, are large and expensive, and have image quality issues. To build a smaller, more user-friendly sensor, Ali Altaqui of North Carolina State University and his colleagues turned to the mantis shrimp.

Mantis shrimp can detect 12 different spectral channels, or colours, a huge step up from the three – red, green and blue – that humans can see. They can also analyse the polarization of light. These marine crustaceans use this advanced vision as a tool for navigation, communication, object separation and predator evasion.

The compound eye of mantis shrimp contains 12 spectrally selective photoreceptors – with sensitivity ranging from ultraviolet to far-red – and four elements that are sensitive to circular polarization, vertically stacked along a single optical axis. As light propagates into the stack, the mantis shrimp extracts spectral and polarization information.

Taking inspiration from these crustaceans, Altaqui and his colleagues’ sensor is comprised of spectrally selective elements, the folded polymer retarders, and P-OPVs vertically stacked along a single optical axis.

The device simultaneously detects spectral and polarization information in a similar way to the mantis shrimp’s eye. The first two P-OPVs detect the light’s polarization state; then an alternating arrangement of folded retarders and P-OPVs provides the spectral analysis.

Altaqui tells Physics World that when broadband light enters the device it is vertically polarized, by a polarizer. Then the first folded retarder rotates red light by 90°, polarizing it horizontally while leaving the other colours polarized vertically. Next, the light hits a P-OPV element. As this is polarized vertically, it absorbs the red light, while transmitting all other wavelengths.

The next folded retarder only rotates yellow light by 90°. And the following P-OPV element absorbs this yellow light, while transmitting the other colours. “This process is repeated where different folded retarders will rotate different colours by 90 degrees, allowing different P-OPVs to absorb the rotated colours,” Altaqui explains.

Pratik Sen, a co-author of the paper, published in Science Advances, says: “Organic semiconductors are interesting materials because they are semi-transparent and can be fabricated to induce intrinsic sensitivity to polarized light. This means we can integrate them into new and exciting device architectures that would not be possible with some of the more traditional semiconductor materials like silicon.”

Altaqui says that the sensor could have a wide range of applications, including in fields such as biomedical imaging, agriculture and food safety, defence, astronomy, atmospheric monitoring and machine vision. For example, it could be used for the early diagnosis of skin cancer, to assess the quality of crops or to characterize aerosols for climate modelling, he explains.

According to the researchers, modelling shows that their technique could be used to create detectors that measure more than 15 spectral channels with wavelengths from 400 to 750 nm. But Altaqui notes that they do not currently have the required retarder materials to produce 15 spectral bands. They are now working to further shrink the sensor and incorporate additional mantis shrimp eye features.

Has a new particle called a ‘leptoquark’ been spotted at CERN?

A hint of the possible existence of a hypothetical particle called a leptoquark has appeared as an unexpected difference in how beauty quarks decay to create electrons or muons. Measured by physicists working on the LHCb experiment on the Large Hadron Collider (LHC) at CERN, the difference appears to violate the principle of “lepton universality”, which is part of the Standard Model of particle physics. The measurement has been made at a statistical significance of 3.1σ, which is well below the 5σ level that is usually considered a discovery. If the violation is confirmed, it could provide physicists with important clues about physics beyond the Standard Model – such as the existence of leptoquarks.

When high-energy protons are smashed together at the LHC large numbers of exotic particles are created, including some containing the beauty quark. These exotic particles quickly decay, and beauty quarks can follow decay paths that involve the production of either electrons or muons, which are both leptons. According to the Standard Model of particle physics, the interactions involved in producing leptons do not discriminate between lepton type, so the rates at which electrons and muons are created by beauty-quark decays are expected to be the same.

Starting in 2014, physicists working on LHCb noticed hints of the violation of this lepton universality. Now, after analysing collision data collected between 2011 and 2018, the researchers have found that the beauty quark appears to favour the electron decay chain over the muon decay chain.

New particle

The decay process involves the conversion of a beauty quark into a strange quark with the production of an electron and antielectron or a muon and antimuon. The Standard Model predicts that this occurs via electroweak bosons and the W⁺ and Z⁰ particles. However, violation of lepton universality suggests that there may be other ways for this to happen. One tantalizing explanation is the existence of a hypothetical particle called a leptoquark, which is a massive boson that couples to both leptons and quarks. In principle, leptoquarks could have different coupling strengths to electrons and muons.

While a new particle is an exciting proposition, physicists will have to wait until LHCb gathers more data in upcoming runs of the LHC to confirm the violation of the Standard Model. Team member Nicola Serra of the University of Zurich says “it is too early to draw a final conclusion. However, this deviation agrees with a pattern of anomalies that have manifested themselves over the last decade. Fortunately, the LHCb collaboration is well placed to clarify the potential existence of new physics effects in these decays. We just need many more related measurements in the future.”

The research is described in a preprint on arXiv.

End-to-End QA with the QUASAR™ Multi-Purpose Body Phantom: TPS and SBRT

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The QUASAR™ Multi-Purpose Body Phantom is a flexible QA tool designed to perform comprehensive testing recommended by AAPM TG 53/66/76 and IAEA TECDOC- 1583.

The phantom incorporates a wide variety of test objects in a solid body oval. Designed to perform end-to-end QA on Simulation, Treatment Planning and Treatment Delivery Systems; the Multi-Purpose Body Phantom is a comprehensive solution for today’s physicist. Users can also increase testing versatility by adding motion to the phantom with the addition of a QUASAR™ Respiratory Motion Assembly or Motion Platform.

This webinar, presented by Joanne Tang, will provide an overview of the advanced features and added motion capabilities of the QUASAR™ Multi-Purpose Body Phantom, highlighting both its versatile testing applications and its value to the SBRT workflow.

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Joanne Tang is an application specialist at Modus QA. Having joined Modus QA after completing her BSc and MSc in medical biophysics at the University of Western Ontario, she is currently involved in customer application support of the QUASAR™ Multi-Purpose Body Phantom.

Proton radiography: one step closer to clinical use

Protons. Destroying cancer cells more precisely than X-rays. Depositing less dose in healthy tissues. Verifying treatment plans and improving patient alignment?

Christina Sarosiek, a graduate student at Northern Illinois University, is working on that.

“The goal of our project is to make proton therapy safer and more effective using an imaging modality called proton radiography,” she explains. “We’re able to take a picture of the tumour directly before treatment and therefore know that we’re irradiating the tumour and not healthy tissues.”

Creating radiographs with protons

Like all medical therapies, proton therapy has some uncertainties. Changes in patient anatomy between treatments, small misalignments of the patient, or errors in the calibration from a planning CT scan to a proton treatment plan, for example, can all lead to underdosing a tumour or delivering dose to healthy tissues, neither of which are optimal.

Sarosiek is part of an interdisciplinary team that is developing and characterizing a prototype proton radiography system that not only improves upon methods used today, but also may help scientists and clinicians tackle all of these other challenges.

For example, medical physicists can verify proton range in vivo using a range probe, which works by passing a low-dose, high-energy proton pencil beam (a very thin beam) through a patient and comparing the measured integral Bragg peak with that from a planning CT. But a range probe is limited because it doesn’t provide any spatial information and can’t improve patient alignment.

Proton radiography, on the other hand, works by sending very high-energy but low-intensity protons through a patient and then reconstructing an image based on the resulting data, which represents, pixel-by-pixel, the water-equivalent thickness – basically, how far a proton would have travelled if it were in water. The source of image contrast in a proton radiograph is the energy loss of the transmitted protons (the integrated stopping powers of protons in the patient).

“We’re getting an image of the integrated energy through an entire patient,” Sarosiek says. “If the anatomy changes or the [electron] density changes on the way to the tumour, we would see that appear as a difference in the full integration through the patient.”

To put this another way, a proton radiograph would tell a medical physicist or clinician if, but not precisely where, there was a difference from what was planned.

“Proton radiographs can alert us to range discrepancies in the plane perpendicular to the beam, but a single proton radiograph cannot inform us about exactly where along the beam path (that is, proximal or distal to the tumour) that discrepancy lies,” Sarosiek explains.

Image quality sufficient for pre-treatment range verification

Sarosiek and the team characterized their prototype proton radiography system using several different phantoms. They published the results of these studies in Medical Physics.

The proton radiography system and the team’s reconstruction algorithm produced images with high enough spatial resolution and image quality to help align a patient better right before their proton treatment starts.

Results also illustrated that the system could be used to help clinicians with quality assurance, by detecting errors in treatment plans resulting from changes in patient density between a treatment planning CT and the proton treatment plan. These applications might ultimately help clinicians and medical physicists reduce margins in treatment planning.

Sarosiek says that their results are comparable to those in other studies, which rely on custom proton radiograph systems. One advantage of the system studied by Sarosiek and the rest of the team is that it is currently being optimized and commercialized by an industry collaborator.

An integrated proton imaging and treatment delivery system

“In the short term, we know [our proton radiography system] works. The long-term impact, I think, is that we may be able to use the same modality for imaging and therapy,” Sarosiek says.

Currently, proton therapy treatments are planned using an X-ray-based CT scan. CT images are displayed in Hounsfield units, which represent a transformation of the X-rays’ attenuation coefficients. Protons interact with tissue and deposit dose differently, and this presents an additional source of error for proton therapy.

Researchers are also working on limiting these errors. Several proton radiographs may be used to create patient-specific curves comparing CT dose to relative proton stopping power (RSP). The downside, though, is that thus far, studies looking into this are based on simulated data, Sarosiek says.

Another avenue being pursued is proton CT. Proton CT would allow medical physicists and clinicians to create a treatment plan directly using the proton CT and avoid a calibration curve like the CT-to-RSP curve examined by other groups. Sarosiek’s collaborators will be investigating this in the future.

For now, though, Sarosiek and the rest of the research team are focused on one of the immediate limitations of proton radiography before it can transition into clinical use.

“One of the major limitations [of this approach] is that for proton radiography, we require a high-energy, low-intensity proton beam. But clinical proton treatment beams have much higher intensity with lower energy,” Sarosiek says. That means that any integrated proton imaging and treatment delivery system would need onboard beam monitoring systems that analyse low-intensity imaging beams, ensuring that dose to the patient remains low.

Once this problem is solved, proton radiography can enter clinical practice, she says.

Porous carbon aerogels might power future Mars missions

Lightweight composite materials containing more than 99% air could prove key to powering future space missions. The materials, known as porous carbon aerogels, make up the electrodes of a supercapacitor developed by researchers at the NASA-sponsored Merced nAnomaterials Center for Energy and Sensing, the University of California, Santa Cruz (UCSC), the University of California, Merced, and the Lawrence Livermore National Laboratory. The device’s ability to operate at extremely cold temperatures could also make it a good power source for polar expeditions on Earth.

Many spacecraft require heating systems to operate in their inhospitable environment. NASA’s Perseverance Rover, for example, recently began a two-year mission to look for signs of ancient microbial life on Mars, where the average temperature is –62 °C, dropping below –125 °C in the winter. Onboard heaters keep the electrolytes in the rover’s batteries from freezing, but the heaters and the energy sources required to power them add weight to the spacecraft payload.

In-between capacitors and batteries

In the trade-off between charge/discharge speed and energy storage capacity, supercapacitors – or, more accurately, electric double-layer or electrochemical capacitors – fall somewhere between batteries and conventional (dielectric) capacitors. Though less good at storing charge than batteries, supercapacitors are better than conventional capacitors in this respect thanks to their porous electrodes, which have surface areas as large as several square kilometres. The double layer that forms at the electrolyte-electrode interface of such devices when a voltage is applied further increases the amount of charge they can store.

Supercapacitors also have some advantages over batteries. They can charge and discharge in minutes – unlike batteries, which take hours. They also have a much longer lifespan, lasting for millions of cycles rather than thousands. And unlike batteries, which work through chemical reactions, supercapacitors store energy in the form of electrically charged ions that assemble on the surfaces of their electrodes.

Hierarchical channels

Building on their previous work, the researchers, led by Jennifer Lu of UC Merced and Yat Li of UCSC, used a 3D printing technique called direct ink writing to make their supercapacitor electrodes. They made the ink by combining cellulose nanocrystals (which provide carbon) with a suspension of silica microspheres. The latter serve as a hard template for creating macropores in the lattice structure of the aerogel once it has been freeze-dried.

The pores in the aerogel lattice vary in size from 500 microns to just nanometres, creating a hierarchical structure of channels. These channels significantly increase the rate at which the ions in an electrolyte diffuse through the material, while also minimizing the distance they need to travel.

Advantages over other supercapacitors

The team’s 3D multiscale porous carbon aerogel has a surface area of around 1750 m²/g, and tests show that an electrode made from the material has a capacitance of 148.6 F/g when a voltage of 5 mV/s is applied. The researchers say that this is higher than most other low-temperature supercapacitors.

The team also demonstrated that a device containing this electrode allows for ion diffusion and charge transfer at temperatures as low as –70 °C. To compare, the lowest working temperatures of commercial lithium-ion batteries and supercapacitors are typically around –20 °C to –40 °C – values that are limited, as mentioned, by the freezing point of the electrolytes.

The team will now collaborate with scientists at NASA to further characterize the devices’ low-temperature performance. “We will do this by testing them in environments that mimic those of the Moon, Mars and international space stations,” Lu tells Physics World.

The present research is detailed in Nano Letters.

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