Gaussian and Gaussian-pulsed-like Fermi velocity graphene structures.

Gaussian and Gaussian-related structures are quite attractive due to its versatility to modulate the electronic transport, including its possibility as electron filters. Here, we show that these non-conventional profiles are not the exception when dealing with Fermi velocity barriers in monolayer graphene. In particular, we show that Gaussian Fermi velocity graphene barriers (G-FVGBs) and Gaussian-pulsed-like Fermi velocity graphene superlattices (GPL-FVGSLs) can serve as electron band-pass filters and oscillating conductance structures. We reach this conclusion by theoretically studying the transmission and transport properties of the mentioned structures. The study is based on the continuum model, the transfer matrix method and the Landauer-Büttiker formalism. We find nearly flat transmission bands or pass bands for G-FVGBs modulable through the system parameters. The pass bands improve as the maximum ratio of Fermi velocities (ξmax) increases, however its omnidirectional range is reduced. These characteristics result in a decaying conductance (integrated transmission) withξmax. The integrated transmission remains practically unaltered with the size of the system due to the saturation of the electron pass band filtering. In the case of GPL-FVGSLs the GPL profile results in regions of high transmission probability that can merge as flat transmission minibands if the pulse fraction and the superlattice parameters are appropriately tuned. The GPL profile also results in conductance (integrated transmission) oscillations that can be multiplied or reduced in number by adjusting the pulse fraction as well as the superlattice parameters.

Biperiodic superlattices and transparent states in graphene.

The transmission and transport properties of biperiodic graphene superlattices are studied theoretically. Special attention is paid to the so-called transparent states of biperiodic superlattices. A Dirac-like Hamiltonian is used to describe the charge carriers in graphene. The transfer matrix method and the Landauer-Büttiker formalism are implemented to obtain the transmittance and conductance, respectively. Similar results to those reported for Schrödinger electrons are obtained. However, in the case of Dirac electrons the splitted bands and the transparent states associated to the biperiodicity depend strongly on the angle of incidence as well as the character of the charge carriers. In fact, the dynamic of the splitted bands and transparent states is inverted for holes. The origin of transparent states is unveiled by obtaining an analytic expression for the transmittance. It is found that resonant transmission through single and double barriers gives rise to transparent states. Regarding the transport properties, it is possible to identify the fundamental changes caused by the biperiodicity. In particular, it is found a splitting, shifting, and diminishment of the conductance peaks with respect to the case of regular periodicity. This opens the door to corroborate experimentally the fundamental characteristics of biperiodic gated graphene superlattices through transport measurements.

Self-similar transport, spin polarization and thermoelectricity in complex silicene structures.

2D materials open the possibility to study Dirac electrons in complex self-similar geometries. The two-dimensional nature of materials like graphene, silicene, phosphorene and transition-metal dichalcogenides allow the nanostructuration of complex geometries through metallic electrodes, interacting substrates, strain, etc. So far, the only 2D material that presents physical properties that directly reflect the characteristics of the complex geometries is monolayer graphene. In the present work, we show that silicene nanostructured in complex fashion also displays self-similar characteristics in physical properties. In particular, we find self-similar patterns in the conductance, spin polarization and thermoelectricity of Cantor-like silicene structures. These complex structures are generated by modulating electrostatically the silicene local bandgap in Cantor-like fashion along the structure. The charge carriers are described quantum relativistically by means of a Dirac-like Hamiltonian. The transfer matrix method, the Landauer-Büttiker formalism and the Cutler-Mott formula are used to obtain the transmission, transport and thermoelectric properties. We numerically derive scaling rules that connect appropriately the self-similar conductance, spin polarization and Seebeck coefficient patterns. The scaling rules are related to the structural parameters that define the Cantor-like structure such as the generation and length of the system as well as the height of the potential barriers. As far as we know this is the first time that a 2D material beyond monolayer graphene shows self-similar quantum transport as well as that transport related properties like spin polarization and thermoelectricity manifest self-similarity.

Tomografía computarizada multicorte para el estudio de complicaciones de la funduplicatura gástrica / Multislice computed tomography for the study of complications of gastric fundoplication

La técnica de imagen tradicionalmente empleada para valorar a los pacientes con cirugía de funduplicatura y sospecha de complicación es el tránsito esofagogastroduodenal con fluoroscopia. En este artículo describimos una nueva técnica mediante tomografía computarizada multicorte, que puede ser una herramienta útil para estudiar las funduplicaturas con sospecha de complicación o fallo tardío (AU)

The traditional approach to the imaging evaluation of patients after gastric fundoplication is an upper gastrointestinal series obtained by fluoroscopy. In this article, we describe a new technique using multislice computed tomography that we think can be useful to evaluate patients with suspected complications or late failure after gastric fundoplication (AU)

Multislice computed tomography for the study of complications of gastric fundoplication.

The traditional approach to the imaging evaluation of patients after gastric fundoplication is an upper gastrointestinal series obtained by fluoroscopy. In this article, we describe a new technique using multislice computed tomography that we think can be useful to evaluate patients with suspected complications or late failure after gastric fundoplication.

Estado actual y tendencia en el desarrollo tecnológico para la reducción de dosis en los equipos de tomografía computarizada / State of the art and future trends in technology for computed tomography dose reduction

La introducción de las adquisiciones helicoidal y multicorte en los equipos de TC y la disminución de los tiempos de reconstrucción de las imágenes han tenido un impacto enorme en la práctica radiológica. El gran desarrollo tecnológico de los últimos 10-12 años ha propiciado la obtención de imágenes de alta calidad en un tiempo muy breve. Con la mejora en la calidad de las imágenes ha aumentado el número de indicaciones. En paralelo con este desarrollo se ha producido un incremento considerable de la exposición a la radiación de los pacientes. La preocupación acerca de los riesgos potenciales para la salud de los exámenes de TC, así como diversas iniciativas y acciones de organismos oficiales y sociedades científicas, constituyen un estímulo para buscar vías de reducción de la exposición a la radiación de los pacientes sin comprometer la eficacia diagnóstica. Con este fin se han establecido recomendaciones de buena práctica, se han desarrollado aplicaciones especiales en los equipos y se han llevado a cabo investigaciones para optimizar el uso clínico de la TC. Entre los desarrollos técnicos incorporados en los equipos cabe destacar los distintos modos de modulación de la intensidad de corriente del tubo, la selección automática de los valores de tensión del tubo, la protección selectiva de órganos, la colimación adaptativa y la reconstrucción iterativa. El uso adecuado de estas herramientas para reducir las dosis precisa de un buen conocimiento sobre su funcionamiento (AU)

The introduction of helical and multislice acquisitions in CT scanners together with decreased image reconstruction times has had a tremendous impact on radiological practice. Technological developments in the last 10 to 12 years have enabled very high quality images to be obtained in a very short time. Improved image quality has led to an increase in the number of indications for CT. In parallel to this development, radiation exposure in patients has increased considerably. Concern about the potential health risks posed by CT imaging, reflected in diverse initiatives and actions by official organs and scientific societies, has prompted the search for ways to reduce radiation exposure in patients without compromising diagnostic efficacy. To this end, good practice guidelines have been established, special applications have been developed for scanners, and research has been undertaken to optimize the clinical use of CT. Noteworthy technical developments incorporated in scanners include the different modes of X -ray tube current modulation, automatic selection of voltage settings, selective organ protection, adaptive collimation, and iterative reconstruction. The appropriate use of these tools to reduce radiation doses requires thorough knowledge of how they work (AU)

[State of the art and future trends in technology for computed tomography dose reduction]. / Estado actual y tendencia en el desarrollo tecnológico para la reducción de dosis en los equipos de tomografía computarizada.

The introduction of helical and multislice acquisitions in CT scanners together with decreased image reconstruction times has had a tremendous impact on radiological practice. Technological developments in the last 10 to 12 years have enabled very high quality images to be obtained in a very short time. Improved image quality has led to an increase in the number of indications for CT. In parallel to this development, radiation exposure in patients has increased considerably. Concern about the potential health risks posed by CT imaging, reflected in diverse initiatives and actions by official organs and scientific societies, has prompted the search for ways to reduce radiation exposure in patients without compromising diagnostic efficacy. To this end, good practice guidelines have been established, special applications have been developed for scanners, and research has been undertaken to optimize the clinical use of CT. Noteworthy technical developments incorporated in scanners include the different modes of X-ray tube current modulation, automatic selection of voltage settings, selective organ protection, adaptive collimation, and iterative reconstruction. The appropriate use of these tools to reduce radiation doses requires thorough knowledge of how they work.

Técnicas de imagen para el estudio de la recuperación funcional tras el ictus: II. Técnicas complementarias / Imaging techniques for studying functional recovery following a stroke: II. Complementary techniques

Resumen. Muchos pacientes que sobreviven a un ictus se enfrentan a serias discapacidades funcionales durante el resto de sus vidas, lo que supone un drama personal para sí mismos y sus allegados, y un elevado coste para la sociedad. Por ello, la recuperación funcional del sujeto tras un ictus debe ser un objetivo esencial que habría que considerar en el desarrollo de nuevas aproximaciones terapéuticas. Éste es el segundo de una serie de dos trabajos en los que revisamos las estrategias y herramientas disponibles hoy en día para la evaluación de múltiples aspectos relacionados con la función cerebral (tanto en humanos como en animales de experimentación), y que están ayudando a los neurocientíficos a entender mejor los procesos de restauración y reorganización de la función cerebral que se inician tras un ictus, partiendo de la premisa de que una aproximación multidisciplinar proporciona una perspectiva más completa de los mecanismos que subyacen bajo los procesos de reparación tisular, de reorganización plástica del cerebro y de los compensatorios que se desencadenan tras un ictus. En el segundo de los trabajos de esta serie nos centramos en una serie de técnicas complementarias basadas en la imagen por resonancia magnética y que no se engloban dentro de los grupos de técnicas discutidos en el primer trabajo de esta serie, bien por abordar aspectos no relacionados directamente con la función cerebral, aunque sí lo hacen de forma indirecta, bien por estar basados en principios fisicoquímicos o fisiológicos diferentes a los ya discutidos (AU)

Summary. Many patients that survive stroke have to face serious functional disabilities for the rest of their lives, which is a personal drama for themselves and their relatives, and an elevated charge for society. Thus, functional recovery after stroke must be a key aspect of the development of new therapeutic approaches. This is the second of a series of two works on which we review the strategies and tools available nowadays for the assessment of multiple aspects related to brain function (both in humans and research animals) and that are helping neuroscientist to better understand the processes of functional restoration and reorganization of the brain, that are triggered following stroke. We have assumed that a multidisciplinary approach is able to provide us with a wider perspective of the underlying mechanisms behind tissue repair, plastic reorganization of the brain and compensatory mechanisms, that can be triggered after stroke. In the second of the works of this series we are focusing in a series of techniques, complementary to the already discussed in the first work, and that are based on MR. These techniques are discussed separately from those ones, because they tackle with aspects not directly related to brain function, although they somehow do in indirect ways, or because they are based on physicochemical or physiological principles different from those discussed on the first work of this series (AU)

El programa de la especialidad como herramienta de formación. Plan individual de formación de cada residente / The specialty program as a training tool: an individual training plan for each resident

El programa formativo oficial de la especialidad en Radiodiagnóstico establece unos mínimos de aprendizaje que deben cumplirse. Cada unidad docente acreditada lo lleva a la práctica mediante un currículo diseñado según sus características, lo que permite cierta flexibilidad. Por lo que respecta al plan individual de formación de cada residente, hay que contemplar varios aspectos: el esquema de las rotaciones según la organización del servicio, los planes de recuperación o refuerzo, la rotación optativa, el aumento del grado de responsabilidad según las competencias adquiridas a medida que avanza en su programa formativo y la adaptación a personas con alguna discapacidad. No obstante, el plan individual debe adecuarse al currículo establecido que debe garantizar el cumplimiento de los objetivos y contenidos del programa oficial y además hay que adaptar los métodos docentes a las características individuales de los residentes, que es el aspecto más importante en la individualización de la formación. Para todo ello es fundamental que los residentes adopten un papel activo en su formación, guiados por el tutor y con la participación de todos los radiólogos de un servicio que deben actuar como docentes, incluyendo en ello a los mismos residentes (AU)

The official training program for the specialty "Diagnostic Imaging" establishes minimum learning objectives that must be fulfilled. Each accredited teaching unit is responsible for designing and carrying out a curriculum to ensure that these objectives are met, and this approach permits a degree of flexibility. Various aspects must be considered in the individual training plans for each resident: the rotation scheme according to the way the department is organized, plans for recovering missed material or reinforcing weak points, optional rotations, increasing degrees of responsibility as skills are acquired during training, and accommodating special needs of handicapped persons. Nevertheless, the individual plan must be fitted to the established curriculum and guarantee that the content of the official program is covered and that the objectives stipulated therein are met. Furthermore, the methods of teaching must be adapted to the individual characteristics of the residents, and this is the most important aspect of the individualization of training. To this end, it is fundamental for residents to take on an active role in their training, guided by their tutor and with the participation of all the radiologists in the department including the other residents, all of whom should act as teachers (AU)

[The specialty program as a training tool: an individual training plan for each resident]. / El programa de la especialidad como herramienta de formación. Plan individual de formación de cada residente.

The official training program for the specialty "Diagnostic Imaging" establishes minimum learning objectives that must be fulfilled. Each accredited teaching unit is responsible for designing and carrying out a curriculum to ensure that these objectives are met, and this approach permits a degree of flexibility. Various aspects must be considered in the individual training plans for each resident: the rotation scheme according to the way the department is organized, plans for recovering missed material or reinforcing weak points, optional rotations, increasing degrees of responsibility as skills are acquired during training, and accommodating special needs of handicapped persons. Nevertheless, the individual plan must be fitted to the established curriculum and guarantee that the content of the official program is covered and that the objectives stipulated therein are met. Furthermore, the methods of teaching must be adapted to the individual characteristics of the residents, and this is the most important aspect of the individualization of training. To this end, it is fundamental for residents to take on an active role in their training, guided by their tutor and with the participation of all the radiologists in the department including the other residents, all of whom should act as teachers.

Association of growth factors with arterial recanalization and clinical outcome in patients with ischemic stroke treated with tPA.

SUMMARY BACKGROUND: Growth factors (GF) such as vascular endothelial growth factor (VEGF), angiopoietin-1 (Ang-1) and granulocyte-colony stimulating factor (G-CSF) have been associated with greater efficacy of tissue plasminogen activator (tPA) in experimental studies. OBJECTIVES: To study the association of these GF with arterial recanalization and clinical outcome in patients with acute ischemic stroke treated with tPA. METHODS: We prospectively studied 79 patients with ischemic stroke attributable to MCA occlusion treated with i.v. tPA within the first 3 h from onset of symptoms. Continuous transcranial color-coded sonography (TCCS) was performed during the first 2 h after tPA bolus to assess early MCA recanalization. Hemorrhagic transformation (HT) was classified according to ECASS II definitions. Good functional outcome was defined as a Rankin scale score of 0-2 at 90 days. GF levels were determined by ELISA. RESULTS: Mean serum levels of VEGF, G-CSF and Ang-1 at baseline were significantly higher in patients with early MCA recanalization (n = 30) (all P < 0.0001). In the multivariate analysis, serum levels of VEGF (OR, 1.03), G-CSF (OR, 1.02) and Ang-1 (OR, 1.07) were independently associated with early MCA recanalization (all P < 0.0001). On the other hand, patients with parenchymal hematoma (PH) (n = 20) showed higher levels of Ang-1 (P < 0.0001). Ang-1 (OR, 1.12; P < 0.0001) was independently associated with PH, whereas patients with good outcome (n = 38) had higher levels of G-CSF (P < 0.0001). G-CSF was independently associated with good outcome (OR, 1.12; P = 0.036). CONCLUSIONS: These findings suggest that GF may enhance arterial recanalization in patients with ischemic stroke treated with t-PA, although they might increase the HT.

[Molecular markers are associated with early computed tomography ischemic changes]. / Marcadores moleculares asociados a signos precoces de isquemia en tomografía computarizada cerebral.

INTRODUCTION: During brain ischemia, neurotoxicity, neuroinflammation and blood-brain barrier (BBB) disruption mechanisms are involved, leading to necrosis, edema and hemorrhagic transformation. Cranial computed tomography (CT) is the most widely used method in the diagnosis of acute stroke, and its early performance may help in the selection of patients for certain treatments. Our objective is to identify molecular markers of neuroexcitotoxicity, neuroinflammation and BBB disruption in the acute phase of stroke that might be associated with early ischemic CT signs. METHODS: 311 patients with ischemic stroke within the first 24 h from symptoms onset were prospectively included. We established tres groups based on the time between symptom onset and hospital arrival: < or = 6 h, between 6 and 12 h and >12 h. Cranial CT was performed at admission to evaluate early ischemic signs according to the Alberta Stroke Program Early CT Score (ASPECTS). Blood samples were taken at admission for the determination of molecular markers of neuroexcitotoxicity (glutamate), neuroinflammation (interleukin [IL]-6) and BBB disruption (metalloproteinase [MMP]-9). RESULTS: Patients with ASPECTS score < or =7 showed a worse early and late prognosis. Glutamate >134.4 microM (OR: 9.7; CI 95%: 4.2-22.5; p<0.001), IL-6>15.5 pg/mL (OR: 4.4; CI 95%: 2.1-9.4; p<0.001) and MMP-9 > 87.2 ng/mL (OR: 18.4; CI 95%: 7.2-47.1; p<0.001) were associated with ASPECTS score < or =7. In the logistic regression model, only glutamate >134.4 microM/l in the first 6 h (OR: 13.2; CI95%: 5.4-31.3; p<0.001), IL-6>15.5 pg/mL from 6 to 12 h (OR: 10.5; CI 95 %: 4.1-26.7; p<0.001) and MMP-9 >87.2 ng/ml after 12 h (OR: 24.2; CI 95%: 4.8- 50.2; p < 0.001) were independently associated with ASPECTS score < or = 7. CONCLUSIONS: The ASPECTS score may be considered as a surrogate marker of early neurological deterioration and final infarct volume, and associated with molecular markers of neuroexcitotoxicity, neuroinflammation and BBB disruption.

La enseñanza de la Radiología en los estudios de la licenciatura de Medicina en España. Informe de la Comisión de Formación de la SERAM / No disponible

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Tratamiento de la patología oclusiva de la arteria femoral superficial con el dispositivo Viabahn / Treatment of occlusive pathologies of the superficial femoral artery with a Viabahn device

Objetivos. Presentamos los resultados del tratamiento de la patología oclusiva de la arteria femoral superficial (AFS) con el stent recubierto autoexpandible Viabahn –grupo endovascular (EV)-. Comparamos dichos resultados con los obtenidos con el bypass (BP) protésico a primera porción de poplítea –grupo BP-. Pacientes y métodos. Diseño retrospectivo. 46 pacientes (46 extremidades) se han intervenido en 5 años. Indicación de tratamiento: claudicación intermitente o isquemia crítica. Lesiones tratadas: B o C de la clasificación TASC (TransAtlantic Inter. Society Consensus) II. Seguimiento clínico y mediante estudio hemodinámico. En el grupo EV también mediante eco-Doppler. Se ha realizado un estudio descriptivo de permeabilidad de la serie y un análisis de factores pronósticos. Resultados. Grupo EV, 20 pacientes (43,5%), y grupo BP, 26 pacientes (56,5%). La indicación clínica fue mayoritariamente (85%) isquemia crítica en ambos grupos. Hubo diferencias en el tipo de lesión intervenida, TASC-B (60%) en el grupo EV y TASC-C (85%) en el grupo BP (p=0,002). En el grupo EV, 3 pacientes presentaron fracaso hemodinámico y 4 oclusiones (1 amputación mayor). En el grupo-BP se ocluyeron 4 injerto (1 amputación mayor). La permeabilidad primaria y secundaria al año para ambos procedimientos ha sido: grupo EV, 50 y 75%; grupo BP, 87 y 91%. Conclusiones. El tratamiento EV con el dispositivo Viabahn en lesiones tipo B en el sector femoropoplíteo ofrece buenos resultados inmediatos durante el seguimiento. Si bien los resultados no son tan favorables en lesiones tipo C, el tratamiento EV podría ser una alternativa al BP supragenicular en estenosis largas o en tándem, especialmente si se precisa recanalización de la AFS

Aim. We present the outcomes of treatment of occlusive pathologies in the superficial femoral artery (SFA) using the Viabahn self-expanding covered stent – the endovscular (EV) group. We compared these results with those obtained using a prosthetic bypass (BP) in the first portion of the popliteal –the BP group. Patients and methods. The study followed a retrospective design. Over a period of 5 years, surgery was performed on 46 patients (46 limbs). Indication for treatment: intermittent claudication or critical ischaemia. Lesions that were treated: B or C on the TASC (TransAtlantic Inter Society Consensus) II classification. Clinical monitoring by means of haemodynamic studies. Doppler ultrasound was also used in the EV group. Both a descriptive study of the patency of the series and an analysis of prognostic factors were carried out. Results. EV group, 20 patients (43,5%), and BP group, 26 patients (56,5%). The clinical indication was mostly critical inchaemia (85%) in the two groups. There were differences in the type of lesion that was treated by surgery: TASC-B (60%) in the EV group and TASC-C (85%) in the BP group (p=0.002). In the EV group, 3 patients presented haemodynamic failure and there were 4 occlusions (1 major amputation). In the BP group 4 grafts became occluded (1 major amputation). Primary and secondary patency at one year for the two procedures was: EV group, 50 and 75%; BP group, 87 and 91%. Conclusions. EV treatment with a Viabahn device in type B lesions in the femoropopliteal segment offers food outcomes, both immediately and during the follow-up. Although the results are not as favourable in type C lesions, EV treatment could be and alternative to above-the-knee BP in long or tandem stenoses, especially if recanalisation of the SFA is required

Aplicación de la proteómica a las enfermedades neurológicas / Application of the proteomic to neurological diseases

La proteómica es un conjunto de técnicas que permiten la separación e identificación de las proteínas expresadas por una célula, tejido u organismo. La técnica central de esta disciplina es la electroforesis bidimensional, que permite llevar a cabo comparaciones cualitativas y cuantitativas de los patrones proteicos entre muestras dadas. El análisis diferencial de los patrones de expresión en distintas patologías neurológicas (ictus, Alzheimer, Parkinson, esclerosis lateral amiotrófica, Hungtington, epilepsia) permite la identificación de biomarcadores de diagnóstico y/o pronóstico. La posterior validación de estos marcadores llevaría a la identificación de nuevas dianas diagnósticas y terapéuticas

Proteomic is a set of tools that allows the separation and identification of proteins expressed by a cell, tissue or organism. Two-dimensional electrophoresis is the central tool that allows qualitative and quantitative comparisons of protein patterns between samples. Differential analysis of protein expression patterns in different neurological diseases (stroke, Alzheimer, Parkinson, amyotrophic lateral sclerosis, Hungtington, epilepsy) allows the identification of diagnostic and/or prognostic biomarkers. Subsequently, validation of these markers may help to identify new diagnostic and therapeutic targets

[Application of proteomics to neurological diseases]. / Aplicación de la proteómica a las enfermedades neurológicas.

Proteomic is a set of tools that allows the separation and identification of proteins expressed by a cell, tissue or organism. Two-dimensional electrophoresis is the central tool that allows qualitative and quantitative comparisons of protein patterns between samples. Differential analysis of protein expression patterns in different neurological diseases (stroke, Alzheimer, Parkinson, amyotrophic lateral sclerosis, Hungtington, epilepsy) allows the identification of diagnostic and/or prognostic biomarkers. Subsequently, validation of these markers may help to identify new diagnostic and therapeutic targets.

Radiología de la vía biliar / Radiology of biliary tract

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