Pallás Lodeiro, Eduardo

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Simultaneous imaging of hard and soft biological tissues in a low-field dental MRI scanner
(Nature Publishing Group, 2020-12-08) Algarín Guisado, José Miguel; Díaz-Caballero, Elena; Borreguero Morata, José; Galve, Fernando; Grau-Ruiz, Daniel; Rigla, Juan P.; Bosch Esteve, Ruben; González-Hernández, José Manuel; Pallás Lodeiro, Eduardo; Corberán, Miguel; Gramage, Carlos; Aja-Fernández, Santiago; Ríos, Alfonso; Benlloch Baviera, Jose María; Alonso, Joseba; Instituto de Instrumentación para Imagen Molecular; European Commission; Generalitat Valenciana; Agencia Estatal de Investigación; European Regional Development Fund
[EN] Magnetic Resonance Imaging (MRI) of hard biological tissues is challenging due to the fleeting lifetime and low strength of their response to resonant stimuli, especially at low magnetic fields. Consequently, the impact of MRI on some medical applications, such as dentistry, continues to be limited. Here, we present three-dimensional reconstructions of ex-vivo human teeth, as well as a rabbit head and part of a cow femur, all obtained at a field strength of 260 mT. These images are the first featuring soft and hard tissues simultaneously at sub-Tesla fields, and they have been acquired in a home-made, special-purpose, pre-medical MRI scanner designed with the goal of demonstrating dental imaging at low field settings. We encode spatial information with two pulse sequences: Pointwise-Encoding Time reduction with Radial Acquisition and a new sequence we have called Double Radial Non-Stop Spin Echo, which we find to perform better than the former. For image reconstruction we employ Algebraic Reconstruction Techniques (ART) as well as standard Fourier methods. An analysis of the resulting images shows that ART reconstructions exhibit a higher signal-to-noise ratio with a more homogeneous noise distribution.
Estudio comparativo del método de los elementos finitos y de la norma VDI 2230 en el cálculo de uniones atornilladas de uso de la industria ferroviaria
(Universitat Politècnica de València, 2016-09-15) Pallás Lodeiro, Eduardo; Suñer Martinez, Josep Lluis; Escuela Técnica Superior de Ingeniería Aeroespacial y Diseño Industrial; Departamento de Ingeniería Mecánica y de Materiales; Instituto Universitario de Investigación Concertado de Ingeniería Mecánica y Biomecánica
Consulta en la Biblioteca ETSI Industriales (Riunet)
Prepolarized MRI of Hard Tissues and Solid-State Matter
(John Wiley & Sons, 2022-08) Borreguero Morata, José; González Hernández, José Manuel; Pallás Lodeiro, Eduardo; Rigla, Juan P.; Algarín Guisado, José Miguel; Bosch Esteve, Ruben; Galve, Fernando; Grau-Ruiz, Daniel; Pellicer, Rubén; Rios, Alfonso; Benlloch Baviera, Jose María; Alonso, Joseba; Instituto de Instrumentación para Imagen Molecular; GENERALITAT VALENCIANA; Agencia Estatal de Investigación; European Regional Development Fund; Agència Valenciana de la Innovació
[EN] Prepolarized MRI (PMRI) is a long-established technique conceived to counteract the loss in signal-to-noise ratio (SNR) inherent to low-field MRI systems. When it comes to hard biological tissues and solid-state matter, PMRI is severely restricted by their ultra-short characteristic relaxation times. Here we demonstrate that efficient hard-tissue prepolarization is within reach with a special-purpose 0.26 T scanner designed for ex vivo dental MRI and equipped with suitable high-power electronics. We have characterized the performance of a 0.5 T prepolarizer module, which can be switched on and off in 200 mu s. To this end, we have used resin, dental and bone samples, all with T1$$ {\mathbf{T}}_{\mathbf{1}} $$ times of the order of 20 ms at our field strength. The measured SNR enhancement is in good agreement with a simple theoretical model, and deviations in extreme regimes can be attributed to mechanical vibrations due to the magnetic interaction between the prepolarization and main magnets.
Magneto-stimulation limits in medical imaging applications with rapid field dynamics
(IOP Publishing, 2022-02-21) Grau-Ruiz, Daniel; Rigla, Juan P.; Pallás Lodeiro, Eduardo; Algarín Guisado, José Miguel; Borreguero Morata, José; Bosch Esteve, Ruben; López-Comazzi, Guillermo; Galve, Fernando; Díaz-Caballero, Elena; Gramage, Carlos; González Hernández, José Manuel; Pellicer, Rubén; Rios, Alfonso; Benlloch Baviera, Jose María; Alonso, Joseba; Instituto de Instrumentación para Imagen Molecular; Agencia Estatal de Investigación; Generalitat Valenciana; European Commission
[EN] Objective. The goal of this work is to extend previous peripheral nerve stimulation (PNS) studies to scenarios relevant to magnetic particle imaging (MPI) and low-field magnetic resonance imaging (MRI), where field dynamics can evolve at kilo-hertz frequencies. Approach. We have constructed an apparatus for PNS threshold determination on a subject's limb, capable of narrow and broad-band magnetic stimulation with pulse characteristic times down to 40 mu s. Main result. From a first set of measurements on 51 volunteers, we conclude that the PNS dependence on pulse frequency/rise-time is compatible with traditional stimulation models where nervous responses are characterized by a rheobase and a chronaxie. Additionally, we have extended pulse length studies to these fast timescales and confirm thresholds increase significantly as trains transition from tens to a few pulses. We also look at the influence of field spatial distribution on PNS effects, and find that thresholds are higher in an approximately linearly inhomogeneous field (relevant to MRI) than in a rather homogeneous distribution (as in MPI). Significance. PNS constrains the clinical performance of MRI and MPI systems. Extensive magneto-stimulation studies have been carried out recently in the field of MPI, where typical operation frequencies range from single to tens of kilo-hertz. However, PNS literature is scarce for MRI in this fast regime, relevant to small (low inductance) dedicated MRI setups, and where the resonant character of MPI coils prevents studies of broad-band stimulation pulses. This work advances in this direction.
Portable magnetic resonance imaging of patients indoors, outdoors and at home
(Nature Publishing Group, 2022-07-30) Guallart-Naval, Teresa; Algarín Guisado, José Miguel; Pellicer-Guridi, Rubén; Galve Conde, Fernando; Vives-Gilabert, Yolanda; Bosch Esteve, Ruben; Pallás Lodeiro, Eduardo; González, José M.; Rigla, Juan P.; Martínez, Pablo; Lloris, Francisco J.; Borreguero Morata, José; Marcos-Perucho, Álvaro; Negnevitsky, Vlad; Martí-Bonmatí, Luis; Rios, Alfonso; Benlloch Baviera, Jose María; Alonso-Otamendi, Joseba; Instituto de Instrumentación para Imagen Molecular; Generalitat Valenciana; Agencia Estatal de Investigación; European Regional Development Fund; Agència Valenciana de la Innovació
[EN] Mobile medical imaging devices are invaluable for clinical diagnostic purposes both in and outside healthcare institutions. Among the various imaging modalities, only a few are readily portable. Magnetic resonance imaging (MRI), the gold standard for numerous healthcare conditions, does not traditionally belong to this group. Recently, low-field MRI technology companies have demonstrated the first decisive steps towards portability within medical facilities and vehicles. However, these scanners' weight and dimensions are incompatible with more demanding use cases such as in remote and developing regions, sports facilities and events, medical and military camps, or home healthcare. Here we present in vivo images taken with a light, small footprint, low-field extremity MRI scanner outside the controlled environment provided by medical facilities. To demonstrate the true portability of the system and benchmark its performance in various relevant scenarios, we have acquired images of a volunteer's knee in: (i) an MRI physics laboratory; (ii) an office room; (iii) outside a campus building, connected to a nearby power outlet; (iv) in open air, powered from a small fuel-based generator; and (v) at the volunteer's home. All images have been acquired within clinically viable times, and signal-to-noise ratios and tissue contrast suffice for 2D and 3D reconstructions with diagnostic value. Furthermore, the volunteer carries a fixation metallic implant screwed to the femur, which leads to strong artifacts in standard clinical systems but appears sharp in our low-field acquisitions. Altogether, this work opens a path towards highly accessible MRI under circumstances previously unrealistic.
A Fast 0.5 T Prepolarizer Module for Preclinical Magnetic Resonance Imaging
(Institute of Electrical and Electronics Engineers, 2022-02) Rigla, J. P.; Borreguero Morata, José; Gramage, Carlos; Pallás Lodeiro, Eduardo; González-Hernández, José Manuel; Bosch Esteve, Ruben; Algarín Guisado, José Miguel; Sanchez-Andres, Juan V.; Galve, Fernando; Grau-Ruiz, Daniel; Pellicer, Rubén; Rios, Alfonso; Benlloch Baviera, Jose María; Alonso, Joseba; Instituto de Instrumentación para Imagen Molecular; Universitat Jaume I; GENERALITAT VALENCIANA; Agencia Estatal de Investigación; European Regional Development Fund; Agència Valenciana de la Innovació; European Commission
[EN] We present a magnet and high power electronics for Prepolarized Magnetic Resonance Imaging (PMRI) in a home-made, special-purpose preclinical system designed for simultaneous visualization of hard and soft biological tissues. The sensitivity of MRI systems grows with field strength, but so do their costs. PMRI can boost the signal-to-noise ratio (SNR) in affordable low-field scanners by means of a long and strong magnetic pulse. However, this must be rapidly switched off prior to the imaging pulse sequence, in timescales shorter than the spin relaxation (or T1) time of the sample. We have operated our prepolarizer at up to 0.5 T and demonstrated enhanced magnetization, image SNR and tissue contrast with PMRI of tap water, an ex vivo mouse brain and food samples. These have T1 times ranging from hundreds of milli-seconds to single seconds, while the preliminary high-power electronics setup employed in this work can switch off the prepolarization field in tens of milli-seconds. In order to make this system suitable for solid-state matter and hard tissues, which feature T1 times as short as 10 ms, we are developing new electronics which can cut switching times to ~ 300 ¿s. This does not require changes in the prepolarizer module, opening the door to the first experimental demonstration of PMRI on hard biological tissues.