Papers by Guillaume Ferrand
HAL (Le Centre pour la Communication Scientifique Directe), Jun 28, 2021
HAL (Le Centre pour la Communication Scientifique Directe), Oct 16, 2021
HAL (Le Centre pour la Communication Scientifique Directe), Oct 16, 2021
Le projet Iseult-Inumac mené au sein d’un consortium franco-allemand vise à développer les techni... more Le projet Iseult-Inumac mené au sein d’un consortium franco-allemand vise à développer les techniques associées à l’imagerie par résonance magnétique à ultra haut champ, notamment à travers la construction d’un imageur à 11,7 teslas. La résolution accrue du nouvel imageur devrait apporter une meilleure compréhension du système nerveux et de ses dysfonctionnements pour aboutir à un dépistage plus précoce des pathologies telles que la maladie d’Alzheimer, les accidents vasculaires cérébraux ou les tumeurs.La principale difficulté technique du projet, en dehors de la construction de l’aimant statique, réside dans la capacité d’émettre une onde électromagnétique d’amplitude uniforme dans tout le cerveau du patient : problème de l’inhomogénéité de B1 (ou radiofréquence). Une solution proposée consiste à utiliser une antenne réseau à transmission parallèle et des séquences d’excitation IRM spécifiques dites de compensation.Cette thèse se concentre sur la conception des antennes réseaux à ...
For many years our Institute CEA IRFU has had a sound experience in VME and EPICS. For the accele... more For many years our Institute CEA IRFU has had a sound experience in VME and EPICS. For the accelerator projects SPIRAL2 at Ganil in Normandy and IFMIF/LIPAc at JAEA/Rokkasho (Japan) the EPICS control systems were based on VME. For 5 years our Institute has been involved in several in-kind collaboration contracts with ESS. For the first contracts (ESS test stands, Source and LEBT controls) ESS recommended us to use VME based solutions on IOxOS boards. Our close collaboration with ESS, their support and the requirements for new projects have led us to develop a standardized hardware and software platform called IRFU EPICS Environment based on microTCA.4 and MRF timing system. This paper describes the advantages of the combination of these recent technologies and the local control system architectures in progress for the SARAF project.
SNRC and CEA collaborate to the upgrade of the SARAF Accelerator to 5 mA CW 40 MeV deuteron and p... more SNRC and CEA collaborate to the upgrade of the SARAF Accelerator to 5 mA CW 40 MeV deuteron and proton beams (Phase 2). This paper presents the reference design of the SARAF-LINAC Project including a four-vane 176 MHz RFQ, a MEBT and a superconducting linac made of four five-meter cryomodules housing 26 superconducting HWR cavities and 20 superconducting solenoids. The first two identical cryomodules house low-beta (βopt = 0.091), 280 mm long (flange to flange), 176 MHz HWR cavities, the two identical last cryomodules house high-beta (βopt = 0.181), 410 mm long, 176 MHz, HWR cavities. The beam is focused with superconducting solenoids located between cavities housing steering coils. A BPM is placed upstream each solenoid.
CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SC... more CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SCL) for SARAF accelerator in order to accelerate 5mA beam of either protons from 1.3 MeV to 35 MeV or deuterons from 2.6 MeV to 40 MeV. The SCL consists in 4 cryomodules. The first two identical cryomodules host 6 half-wave resonator (HWR) low beta cavities ( = 0.09) at 176 MHz. The last two identical cryomodules will host 7 HWR high-beta cavities ( = 0.18) at 176 MHz. Lowbeta and high beta cavities have been optimized to limit electric and magnetic peak fields in the cavity, and to minimize the dissipated power. Manufacturing constraints and helium cooling were taken into consideration to minimize the risk during manufacturing and operation. Preliminary mechanical studies of the cavity, the tuning system, as well as the couplers and pick-up antennas were carried out.
The present invention relates to a multi-way antenna comprising: a first loop resonator (120) com... more The present invention relates to a multi-way antenna comprising: a first loop resonator (120) comprising a radiating element (121) forming a loop; a second resonator (110) juxtaposed to the first loop resonator (120) comprising a radiating element (111); said antenna being characterized in that said radiating element (121) of the first loop resonator (120) has a main surface S1 defined by a first median plane; a secondary surface S2 defined according to a second median plane, second surface defining a projection (122) of said radiating element (121, 221) positioned opposite the second resonator (110) and having an inclination (α) relative to the mean plane of the main surface S1.
SNRC and CEA collaborate to the upgrade of the SARAF accelerator to 5 mA CW 40 MeV deuteron and p... more SNRC and CEA collaborate to the upgrade of the SARAF accelerator to 5 mA CW 40 MeV deuteron and proton beams (Phase 2). CEA is in charge of the design, construction and commissioning of the superconducting linac (SARAF-LINAC Project). The SCL is made up of 4 cryomodules: the first two will host each 6 half-wave resonator (HWR) low beta cavities ( = 0.09) at 176 MHz; the last two will host each 7 HWR high-beta cavities ( = 0.18) at 176 MHz. The fully equipped cavity includes the niobium cavity with a helium tank, an input power couplers and a frequency tuning system. The final RF design of the low and high beta cavities will be presented in this poster, as well as the RF design of the couplers, the expected tuning range of the cavities and the multipactor analysis.
Introduction: Transmit-SENSE gives the opportunity to implement short excitation pulses with good... more Introduction: Transmit-SENSE gives the opportunity to implement short excitation pulses with good flip-angle homogeneity [1]. Commonly, a transmitarray system used for brain imaging at 7 Tesla consists of 8 independently modulated amplifiers in combination with a dedicated 8-channel RF coil. Due to the additional degrees of freedom introduced by the separate transmit-channels, uniform excitation can be achieved with short excitation pulses. On the other hand, including additional transmit-channels is not only financially demanding, it also complicates B1-mapping and optimized pulse design. Considering the basis set of orthogonal birdcage coil modes, inclusion of the anti-circularly-polarized modes only marginally improve transmit-SENSE applications [2]. In this work we explore the possibility to drive an 8-element transmit coil with only 2 independent transmit-channels, while retaining the ability to perform adequate flip-angle (FA) homogenization in the human brain at 7 Tesla.
Magnetic Resonance in Medicine, 2016
Purpose: Specific absorption rate (SAR) calculations in parallel transmission are commonly perfor... more Purpose: Specific absorption rate (SAR) calculations in parallel transmission are commonly performed by using electromagnetic simulations on generic models. In this study, we propose a probabilistic analysis to study the safety factor employed to account for SAR intersubject variability versus risk relationship in head imaging at 7T. Methods: Thirty-three finite-element electromagnetic simulations were conducted to sample the four-dimensional parameter space consisting of the head length, head breadth, and shifts in Z and Y random variables. Based on the SAR matrices for each configuration, a multivariate second-order polynomial of the SAR versus the different parameters was reconstructed for different types of radiofrequency pulses. A Monte Carlo calculation was then performed to compute the probability of occurrence of a given SAR value. Results: By testing a large number of radiofrequency excitation pulses, the SAR calculated for the average model amplified by a safety margin of 1.5 was found to return a probability of less than 1% to be exceeded across the adult Caucasian population given the investigated parameters. Conclusion: The proposed method to study SAR intersubject variability uses a reasonable number of electromagnetic simulations. Look-ahead SAR safety margins can be deduced based on risk/benefit ratio assessments. Magn Reson Med
NeuroImage, 2012
One of the promises of Ultra High Field (UHF) MRI scanners is to bring finer spatial resolution i... more One of the promises of Ultra High Field (UHF) MRI scanners is to bring finer spatial resolution in the human brain images due to an increased signal to noise ratio. However, at such field strengths, the spatial non-uniformity of the Radio Frequency (RF) transmit profiles challenges the applicability of most MRI sequences, where the signal and contrast levels strongly depend on the flip angle (FA) homogeneity. In particular, the MP-RAGE sequence, one of the most commonly employed 3D sequences to obtain T1-weighted anatomical images of the brain, is highly sensitive to these spatial variations. These cause deterioration in image quality and complicate subsequent image post-processing such as automated tissue segmentation at UHF. In this work, we evaluate the potential of parallel-transmission (pTx) to obtain high-quality MP-RAGE images of the human brain at 7 T. To this end, non-selective transmit-SENSE pulses were individually tailored for each of 8 subjects under study, and applied to an 8-channel transmit-array. Such RF pulses were designed both for the low-FA excitation train and the 180° inversion preparation involved in the sequence, both utilizing the recently introduced k(T)-point trajectory. The resulting images were compared with those obtained from the conventional method and from subject-specific RF-shimmed excitations. In addition, four of the volunteers were scanned at 3 T for benchmarking purposes (clinical setup without pTx). Subsequently, automated tissue classification was performed to provide a more quantitative measure of the final image quality. Results indicated that pTx could already significantly improve image quality at 7 T by adopting a suitable RF-Shim. Exploiting the full potential of the pTx-setup, the proposed k(T)-point method provided excellent inversion fidelity, comparable to what is commonly only achievable at 3 T with energy intensive adiabatic pulses. Furthermore, the cumulative energy deposition was simultaneously reduced by over 40% compared to the conventional adiabatic inversions. Regarding the low-FA k(T)-point based excitations, the FA uniformity achieved at 7 T surpassed what is typically obtained at 3 T. Subsequently, automated white and gray matter segmentation not only confirmed the expected improvements in image quality, but also suggests that care should be taken to properly account for the strong local susceptibility effects near cranial cavities. Overall, these findings indicate that the k(T)-point-based pTx solution is an excellent candidate for UHF 3D imaging, where patient safety is a major concern due to the increase of specific absorption rates.
Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment
In order to match the beam exiting the RFQ to the superconducting cavities and to minimize the lo... more In order to match the beam exiting the RFQ to the superconducting cavities and to minimize the longitudinal beam extension, three rebunchers will be installed in the Medium Energy Beam Transport (MEBT) of SARAF-LINAC phase II. CEA is in charge of the design and fabrication of the copper-plated stainless steel, 3-gap rebunchers. Beam dynamic simulation leads to the global MEBT design. The rebuncher was successfully conditioned to the RF power of 4.4 kW required for CW operation, with sufficient power margin. A solid state power amplifier of 10 kW developed by SNRC is used during the RF test. The rebuncher shows a good performance in terms of the dissipated power, peak temperatures and vacuum level.
Status of the CEA desing of the future Saraf linac (title to be revised)
CEA is committed to delivering a Medium Energy Beam Transfer line and a Super Conducting Linac (S... more CEA is committed to delivering a Medium Energy Beam Transfer line and a Super Conducting Linac (SCL) for SARAF accelerator in order to accelerate 5mA beam of either protons from 1.3MeV to 35MeV or deuterons from 2.6 MeV to 40.1MeV. The SCL consists in 4 cryomodules separated by warm section housing beam diagnostics. The two first identical cryomodules hosts respectively 6 and 7 half-wave resonator (HWR) low beta (0.091) cavities 176MHz. In order to test the cavity with its tuner and coupler and validate some design consideration, the Equipped Cavity Test Stand (ECTS) has been designed and will be presented.
CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SC... more CEA is committed to delivering a Medium Energy Beam Transfer line and a superconducting linac (SCL) for SARAF accelerator in order to accelerate 5 mA beam of either protons from 1.3 MeV to 35 MeV or deuterons from 2.6 MeV to 40 MeV. The SCL consists in 4 cryomodules. The first two cryomodules host 6 and 7 half-wave resonator (HWR) low beta cavities (β = 0.09) at 176 MHz. The last two identical cryomodule will host 7 HWR high-beta cavities (β = 0.18) at 176 MHz. The maximal required power to be transmitted to the beam is 11.4 kW for high-beta cavity couplers. This document presents the results of the coupler tests and conditioning.
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Papers by Guillaume Ferrand