Super-resolution of brain MR images: from research to the clinic through machine learning approaches.
Magnetic Resonance Imaging (MRI) has become a reference modality for diagnosing and monitoring neurological disorders. However, acquiring high-resolution (HR) brain images remains challenging in clinical practice due to limited scan time, patient comfort constraints, and image degradation caused by patient motion. The increased signal enabled by higher magnetic field strengths can be invested to achieve higher spatial resolution within the same acquisition time. This project aims at taking advantage of the unprecedented spatial resolution achievable with the 11.7T Iseult MRI scanner, currently the most powerful MR scanner in the world, to train a machine learning-based super-resolution (SR) model that enhances the spatial resolution of 3T MRI images acquired in clinical practice. Current SR approaches are typically trained on public datasets, using pairs of high- and low-resolution images, with the low-resolution data synthetically generated from the high-resolution images. In this project we will use a real dataset consisting of 3T and 11.7T images acquired from the same cohort, ensuring higher anatomical fidelity and enabling a rigorous assessment of hallucination risks, i.e. of generating anatomically incorrect details that could be misinterpreted by the radiologists. The project will involve the following steps: improving the quality of 11.7T images (through motion correction and artifact reduction), acquiring pairs of images at 3T and 11.7T, developing and validating SR models, and finally assessing their generalizability on public datasets. This work supports the integration of reliable SR methods into clinical practice, allowing conventional MRI scanners to benefit indirectly from Iseult's unique capabilities.
Modeling of a magnonic diode based on spin-wave non-reciprocity in nanowires and nanotubes
This PhD project focuses on the emerging phenomenon of spin wave non-reciprocity in cylindrical magnetic wires, from their fundamental properties, to their exploitation towards realizing magnonic diode based devices. Preliminary experiments conducted in our laboratory SPINTEC on cylindrical wires, with axial magnetization in the core and azimuthal magnetization on the wire surface, revealed a giant non-symmetrical effect (non-symmetrical dispersion curves with different speeds and periods for left- and right-propagating waves), up to an extent of creating a band gap for a given direction of motion, related to the circulation of magnetization (right or left). This particular situation has not been yet described theoretically or modeled, which sets an unexplored and promising ground for this PhD project. To model spin-wave propagation and derive dispersion curves for a given material we plan to use different numerical tools: our in-home 3D finite element micromagnetic software feeLLGood and open source 2D TetraX package dedicated to eigen modes spectra calculations. This work will be conducted in tight collaboration with experimentalists, with a view both to explain experimental results and to guide further experiments and research directions.
III-V semiconductor nanoplatelets
Colloidal semiconductor nanoplatelets (NPLs) are a class of two-dimensional nanostructures that have electronic and optical properties distinct from those of spherical quantum dots (QDs). They exhibit strong quantum confinement in a single dimension, their thickness, which can be controlled on the monolayer level using solution chemistry. As a result, NPLs emit light with an extremely narrow spectral width and at the same time, they have a very high absorption coefficients. These properties make them ideal candidates for various applications (e.g., light-emitting diodes for low-power-consumption displays, photocatalysis, single-photon emitters).
At present, only the synthesis of metal chalcogenide NPLs has been mastered. These materials either contain toxic elements (CdSe, HgTe, etc.) or have a large bandgap (ZnS, ZnSe). For these reasons, the development of synthesis methods for III-V semiconductor NPLs, such as InP, InAs and InSb is currently a major challenge. In this thesis, we will develop new synthetic approaches for the growth of InP NPLs, exploring different avenues and using in situ characterizations as well as machine learning assisted design of experiments. Numerical simulations will be used to determine the reactivity of precursors and to model the mechanisms inducing anisotropic growth.
Fast labeling of antibodies with fluorine-18: toward simplified and efficient processes for medical imaging
The development of innovative tools in medical imaging represents a major lever for the early and accurate diagnosis of cancer. The combination of PET imaging and antibodies as targeting vectors stands among the most specific approaches for tumor detection. This potential is reflected by the widespread use of these tools in preclinical research, but their translation into routine clinical practice remains challenging, mainly due to the non-negligible dosimetry of the positron-emitting isotopes currently used (8?Zr, 64Cu).
This PhD project aims to develop an antibody-labeling technology using fluorine-18, the reference isotope for clinical PET imaging. Labeling antibodies whose biodistribution time is compatible with this isotope represents a significant technical challenge and requires a non-negligible reaction time compared to the short half-life of fluorine-18. The objective of this project is to simplify and accelerate this process through the development of a chemical tag that would enable the direct labeling of antibodies with fluorine-18 produced by the cyclotron, analogously to the longer-lived radiometals classically used. Several challenges will be addressed in developing this tag, including the optimization of its fluorine-18 radiolabeling and its bioconjugation to antibodies, with the ultimate goal of providing a simple, fast, and clinically translatable tool.
A new altermagnetic material with remarkable properties for spintronics
Altermagnets represent a new class of magnetic materials that uniquely combine the advantages of ferromagnets (spin polarization of electric currents) and antiferromagnets (robustness against magnetic fields and ultrafast spin dynamics). As part of an international collaboration, we have experimentally discovered one of the very first and still rare altermagnets, Mn5Si3, thereby opening the way for new fundamental and applied research. Until now, Mn5Si3 has mainly been synthesized by molecular beam epitaxy, a high-precision technique but one that presents limitations for broader studies. Our goal is to develop the growth of Mn5Si3 using high-temperature sputtering, a more versatile and industry-compatible method, in order to explore and demonstrate its exceptional spin properties.
STUDY OF THE NUCLEAR COLLECTIVE PROPERTIES OF 232TH WITH THE AGATA SPECTROMETER
The study of so-called ‘deformed’ atomic nuclei with a non-spherical charge distribution is essential for testing nuclear interactions and structural models. These deformed nuclei exhibit a very particular pattern of excited states, known as ‘rotational bands’. These bands can be constructed on states with different deformations or different intrinsic structures (shape coexistence). The subject of the thesis is the experimental study of the macroscopic and microscopic properties of the nucleus 232Th. This nuclide exhibits a wide variety of rotational bands that are thought to be due to vibrations of the nuclear surface known as quadrupole and octupole vibrations. In particular the latter have attracted a great deal of interest recently, as octupolar deformed nuclei can be used to determine nuclear electric dipole moments, a fundamental question in physics in general. In our particular case, the aim is to characterise for the first time the quadruplet of octupole bands expected in a strongly deformed nucleus. Furthermore, this nucleus is the only example with a rotational band built on a double quadrupole vibration.
We will study these various shapes using the powerful technique of Coulomb excitation, which is the most direct method for determining the shape of nuclei in their excited states. The experiment will be carried out using AGATA, a new-generation gamma spectrometer consisting of a large number of finely segmented germanium crystals, which can identify each point of interaction of a gamma ray inside the detector and then, using the innovative concept of ‘gamma-ray tracking’, reconstruct the energies of all the gamma rays emitted and their emission angles with unprecedented precision. A complementary experiment will be carried out at HIL Warsaw, which will enable better interpretation of the highly complex data provided by AGATA.
The MINI-BINGO demonstrator: advancing the quest to unveil the neutrino nature
BINGO is an innovative neutrino physics project designed to lay the groundwork for a large-scale bolometric experiment dedicated to the search for neutrinoless double beta decay. The goal is to achieve an extremely low background index—on the order of 10^-5 counts/(keV·kg·yr)—while delivering excellent energy resolution in the region of interest. These performance levels will enable the exploration of lepton number violation with unprecedented sensitivity.
The project relies on scintillating bolometers, which are particularly effective at rejecting the dominant background caused by surface alpha particles. It focuses on two highly promising isotopes, 100Mo and 130Te, whose complementary properties make them both strong candidates for future large-scale investigations.
BINGO introduces three major innovations to the well-established heat-light hybrid bolometer technology. First, the sensitivity of the light detectors will be enhanced by an order of magnitude through the use of Neganov-Luke amplification. Second, a novel detector assembly design will reduce surface radioactivity contributions by at least an order of magnitude. Third, and for the first time in a macrobolometer array, an internal active shield made of ultrapure BGO scintillators with bolometric light readout will be implemented to suppress external gamma background.
As part of this thesis work, the student will take part in the assembly and installation of the MINI-BINGO demonstrator within the cryostat recently installed at the Modane Underground Laboratory. He/she will be involved in data acquisition and analysis, and will contribute to evaluating the final background rejection enabled by the performance of the detector's final configuration.
Optimization of gamma radiation detectors for medical imaging. Time-of-flight positron emission tomography
Introduction
Innovative functional imaging technologies are contributing to the CEA's ‘Medicine for the Future’ priority. Positron emission tomography (PET) is a nuclear medical imaging technique widely used in oncology and neurobiology. The decay of the radioactive tracer emits positrons, which annihilate into two photons of 511 keV. These photons are detected in coincidence and used to reconstruct the distribution of tracer activity in the patient's body.
We're proposing you to contribute to the development of an ambitious, patented technology: ClearMind. The first prototype is in our laboratories. This gamma photon detector uses a monolithic scintillating crystal of high density and atomic number, in which Cherenkov and scintillation photons are produced. These optical photons are converted into electrons by a photoelectric layer and multiplied in a MicroChannel plate. The induced electrical signals are amplified by gigahertz amplifiers and digitized by SAMPIC fast acquisition modules. The opposite side of the crystal will be fitted with a matrix of silicon photomultiplier (SiPM).
Today we have our first prototype, and we are preparing two more.
The proposed work
You will work in an advanced instrumentation laboratory in a particle physics environment .
The first step will be to optimize the "components" of ClearMind detectors, in order to achieve nominal performance. We'll be working on scintillating crystals, optical interfaces, photoelectric layers and associated fast photodetectors (MCP-PMT and SiPM), and readout electronics.
We will then characterize the performance of the prototype detectors on our measurement benches, which are under continuous development. The data acquired will be interpreted using in-house analysis software written in C++ and/or Python.
Finally, we will compare the physical behavior of our detectors to Monté-Carlo simulation software (Geant4/Gate).
A particular effort will be devoted to the development of ultra-fast scintillating crystals in the context of a European collaboration.
Supervision
The successful candidate will work under the joint supervision of Dominique Yvon and Viatcheslav Sharyy (DRF/IRFU & BIOMAPS). The CaLIPSO group at IRFU & BIOMAPS specializes in the development and characterization of innovative PET detectors, including detailed detector simulation. As part of the project, we are working closely with IJCLabs in Orsay, which is developing our readout and acquisition electronics, CEA/DM2S, which is working in particular on trusted AI algorithms, CPPM in Marseille, which is evaluating our detectors under PET imaging acquisition conditions, and UMR BIOMAPS (CEA/SHFJ), working on image calculation algorithms.
Requirements
Knowledge of the physics of particle-matter interaction, radioactivity and the principles of particle detectors is essential. A strong interest in instrumentation and laboratory work is recommended. Basic programming skills, e.g. C++, Gate/Geant4 physics simulation software, are important.
Skills acquired
Good knowledge of state-of-the-art particle detector and positron emission tomography technologies. Simulation principles and techniques for particle-matter interaction and detection systems. Analysis of complex data.
Contact
Dominique Yvon, dominique.yvon@cea.fr
Viatcheslav Sharyy, viatcheslav.sharyy@cea.fr
CUPID-Stage I: Detector optimization and analysis in the context of a next generation 0nbb search
The CUPID experiment (CUORE Upgrade with Particle IDentification) aims to achieve unprecedented sensitivity for the detection of neutrinoless double beta decay (0nßß) using an array of 1596 lithium molybdate (Li2MoO4) crystals of ~450 kg mass. If detected this process would be a direct observation new physics in the lepton sector: in example it violates lepton number by 2 units. Dependent on the model it can provide valuable insight into the neutrino mass-scale and possbily to matter generation in the Universe through leptogenesis.
The use of lithium molybdate for this study is particularly advantageous due to their scintillation properties and the high Q-value of the decay process, which lies above most environmental gamma backgrounds. The CUPID experiment employs this material as cryogenic calorimetric detectors, where the heat signal from particle interactions of O (100 microK/MeV) are registered in a sensitive thermistor at a temperature of ~10 mK. Thanks to the high Q-value Mo-100 features a particularly high sensitivity in terms of large phase space factor and nuclear transition matrix element. This will also allow for precision studies and tests of the standard model, through analyses of the shape of another process: the so-called 2 neutrino double beta decay (2nbb), which is a standard model allowed process. However, this rare process (half-life of 7x10^17yr) is not only an interesting particle/nuclear physics target, it is also expected to contribute the most important background in CUPID: the random coincidence of two events adding up in energy to the Q-value of the 0nßß search.
CUPID aims to deploy its new detector array in two phases: An initial detector array with 1/3 of the mass will be deployed by 2030. In the mean time several tower scale measurement and optimization campaigns during the time of this thesis project will allow to analyze and optimize the detector performance of the CUPID detector modules. The further suppression of this so called pile-up background through detector optimization (acting on the sensor attachment of the light detector with a robotic assembly station developed at CEA) and advanced analysis techniques within this thesis will allow to enhance the sensitivity and science reach of CUPID. A further extension of the analysis techniques developed in this thesis to the processing of an array of O(1000) detectors will be tested with the existing TeO2 detecor array of CUORE. In the context of this process the developed analysis techniques will contribute to the final science analyses of CUORE, the leading experiment for 0nßß search with Te-130.
Drug therapy for the management of radiation-induced hematopoietic and gastrointestinal syndromes
Nuclear technology is widely used in industry, army and medicine (diagnosis, radiotherapy and conditioning for transplants). Circumstances in which high-dose radiation exposure occurs can result in a considerable number of injuries and deaths in the absence of therapeutic intervention. These circumstances may include terrorism, accidents caused by nuclear reactor malfunctions, or radiotherapy accidents involving ionising radiation (IR) overdose. There are also medical cases of high-dose irradiation for the purpose of conditioning the patient for transplantation to treat certain diseases (acquired bone marrow failure, acute myeloblastic leukemia (AML) or hereditary aplastic anemia).
Exposure to high levels of radiation can quickly lead to acute radiation syndrome (ARS), which mainly affects hematological (blood, bone marrow) and gastrointestinal tissues in the hours, days and weeks that follow.
Hematopoietic syndrome (HS) is a major component of ARS. It develops after total body irradiation (TBI) at doses > 1 Gy and is characterized by partial or total destruction of bone marrow stem cells and their environment. The therapeutic management of HS is based on medical treatments using growth factors to stimulate residual hematopoiesis, but these may prove ineffective in cases of severe bone marrow damage. Hematopoietic stem cell transplantation is then the best treatment, but it is invasive, not always feasible due to a lack of donors, and its success rate remains extremely low, particularly due to severe side effects (risk of graft-versus-host disease).
Gastrointestinal syndrome (GIS) develops after a dose > 10 Gy (whole body or localized). It is characterized by weight loss, diarrhea and increased susceptibility to developing bacterial infections leading to septicemia. Death occurs within 5 to 12 days after irradiation. Current management is based solely on symptomatic treatments (antibiotics, anti-diarrhea drugs, anti-emetics).
It is therefore essential to develop new therapeutic methods to treat severely irradiated patients as quickly as possible after radiation exposure and with minimal side effects.
In this project, we propose to develop, through industrial and clinical collaborations, new drug therapies involving the administration of specific molecules to be tested in order to improve hematopoietic and/or intestinal recovery after irradiation.