Analysis of the Inverse Electroencephalographic Problem for Volumetric Dipolar Sources Using a Simplification / Análisis del Problema Inverso Electroencefalográfico para Fuentes Dipolares Volumétricas por Medio de una Simplificación

Objective: To analyze the parameter identification problem for volumetric dipolar sources in the brain from measurement of the EEG on the scalp using a simplification which reduces the multilayer conductive medium problem to one homogeneous medium problem with a null Neumann boundary condition. Methodology: The minimum squares technique is used for parameter identification of the dipolar sources. The simple case in which the head is modelled by concentric circles is developed. This case was chosen because we were able to obtain the solution of the forward problem in exact form and for the simplicity of the exposition. Results: The parameter of the dipolar sources can be identified from the EEG on the scalp using the simplification. For the theoretical analysis the results developed for one homogeneous region are used. The numerical implementation is simpler than the multilayer case and the numerical computation requires minor computational cost. Conclusion: The feasibility for solving the parameter identification problem using the simplification is shown. These results can be extended to the case of concentric spheres and complex geometries but the solution cannot be found in exact form.

Objetivo: Analizar el problema de identificación de los parámetros para fuentes dipolares volumétricas en el cerebro a partir de la medición del EEG en el cuero cabelludo mediante una simplificación que reduce el problema de un medio conductor de múltiples capas a un problema en un medio homogéneo con una condición de Neumann nula en su frontera. Metodología: Se utiliza la técnica de mínimos cuadrados para identificar los parámetros de las fuentes dipolares. Se desarrolla el caso simple en el que la cabeza está modelada por círculos concéntricos debido a que la solución del problema directo se puede calcular en forma exacta y por la sencillez de la exposición. Resultados: Se identifican los parámetros de la fuente dipolar a partir del EEG sobre el cuero cabelludo usando la simplificación. Para el análisis teórico se utilizan los resultados desarrollados para una región homogénea. La implementación numérica es más simple y el cálculo numérico requiere menor costo computacional. Conclusión: Se muestra la factibilidad para resolver el problema de identificar los parámetros de una fuente dipolar por medio de la simplificación. Los resultados pueden ser extendidos al caso de esferas concéntricas y al de geometrías complejas pero la solución del problema directo no puede hallarse en forma exacta.

Sex differences of high-risk carotid atherosclerotic plaque with less than 50% stenosis in asymptomatic patients: an in vivo 3T MRI study.

BACKGROUND AND PURPOSE: Men have a greater prevalence of high-risk carotid plaque features associated with stroke compared with women who have ≥50% stenosis, but little is known about these features in less significantly stenotic carotid arteries. This study aims to evaluate sex differences in complicated carotid plaque features in asymptomatic patients with <50% stenosis. MATERIALS AND METHODS: Ninety-six patients (50 men, 46 women) with <50% carotid stenosis on MRA who had been referred for analysis of contralateral >50% carotid stenosis were included. The associations between sex and plaque features as identified by 3T MR carotid plaque imaging were examined by using logistic and linear regression models controlling for demographic characteristics, MRA stenosis, and the presence of contralateral plaque features. RESULTS: The presence of a thin/ruptured fibrous cap (16% versus 2%, adjusted odds ratio = 8.57, P = .047), IPH (24% versus 6%, adjusted odds ratio = 4.53, P = .027), and American Heart Association type VI plaque (26% versus 6%, adjusted odds ratio = 5.04, P = .017) was significantly higher in men than in women. These associations remained significant following adjustment for contralateral plaque features. Men demonstrated a larger percentage volume of LR/NC (median, 1.66% versus -0.21%; P < .01). Calcification was not significantly associated with sex. CONCLUSIONS: There is a sex difference of higher risk carotid plaque features during the early stage of disease seen in patients recruited for MR imaging evaluation of contralateral moderate-to-severe stenosis. Given the potential of using LR/NC without or with IPH to monitor therapy, these results indicate the possible importance of sex-based management in patients with asymptomatic carotid atherosclerosis across all stages of carotid stenosis.

Simplificación del problema inverso electroencefalográfico a una sola región homogénea con condición de Neumann nula / Simplification of the Inverse Electroencephalographic Problem to One Homogeneous Region with Null Neumann Condition

Objetivo: Presentar una simplificación del Problema Inverso Electroencefalográfico (PIE) del caso de varias capas conductoras a una región homogénea con condición de Neumann Nula. Metodología: Se divide el PIE en tres problemas, dos de los cuales se resuelven usando el potencial medido en el cuero cabelludo y con estas soluciones y el tercer problema se lleva a cabo la simplificación. Para validar la simplificación se genera un ejemplo sintético usando el modelo de esferas concéntricas. Resultados: Por medio de la simplificación la fuente se determina a partir de la ecuación de Poisson con una condición de Neumann nula y un dato adicional sobre la frontera de la región homogénea, el cual se obtiene de la medición. Esto es válido para regiones generales con fronteras suficientemente suaves. Adicionalmente, para el caso de esferas concéntricas, se plantea el PIE para el caso de una fuente dipolar (que representa a focos epilépticos) usando esta simplificación y la técnica de la función de Green. Conclusión: La simplificación presentada aquí permite analizar el PIE en una región lo cual simplifica su estudio teórico y numérico. En particular, puede ser útil para el análisis del problema de identificación de los parámetros de una fuente dipolar.

Objective: To give a simplification of the Inverse Electroencephalographic Problem (IEP) from the case of multilayer conductive medium to the case of a homogeneous region with null Neumann condition. Methodology: IEP is divided in three problems, two of which are resolved using the measurements of potential on the scalp and with these solutions and the third problem the simplification is carried out. In order to validate the simplification a synthetic example is generated using the model of concentric spheres. Results: Through of simplification, the source is determined from the Poisson equation with null Neumann condition and an additional data on the boundary of the homogeneous region, which is obtained from the measurement. This is valid for regions with smooth boundary. Additionally, in the case of concentric spheres, it is statement the identification problem for dipolar sources (representing epileptic focus) using this simplification and Green function. Conclusion: The simplification presented here allows us to analyze the inverse problem in one region, which simplifies the theoretical and numerical study. In particular it may be useful to analyze the problem of parameter identification of a dipolar source.

MR carotid plaque imaging and contrast-enhanced MR angiography identifies lesions associated with recent ipsilateral thromboembolic symptoms: an in vivo study at 3T.

BACKGROUND AND PURPOSE: Recent research has suggested the importance of plaque composition to identify patients at risk for stroke. This study aims to identify specific plaque features on 3T carotid MR imaging and CE-MRA associated with recent carotid thromboembolic symptoms in patients with mild/moderate versus severe stenosis. MATERIALS AND METHODS: Ninety-seven consecutive patients (symptomatic, 13; asymptomatic, 84) with 50%-99% stenosis by sonography or CT angiography underwent carotid plaque imaging combined with MRA at 3T. The symptomatic carotid artery or the most stenotic asymptomatic carotid artery was chosen as the index vessel to be analyzed. Plaque features were compared by symptomatic status in patients with mild/moderate (30%-70%) versus severe (70%-99%) stenosis on MRA. RESULTS: Ninety (92.8%) patients had sufficient image quality for interpretation. In 50 patients with mild/moderate stenosis, there were significant associations between the presence of the following plaque characteristics and symptoms: thin/ruptured fibrous cap (100% versus 36%, P = .006) and lipid-rich necrotic core (100% versus 39%, P = .022), with marginal association with hemorrhage (86% versus 33%, P = .055). In 40 patients with severe stenosis, only the angiographic presence of ulceration (86% versus 36%, P = .039) was associated with symptoms. CONCLUSIONS: Several plaque components identified on 3T MR imaging are correlated with recent ipsilateral carotid thromboembolic symptoms. These preliminary results also suggest that associations between plaque characteristics and symptom history may vary by degree of stenosis. If confirmed in larger studies, carotid MR imaging may distinguish stable from unstable lesions, particularly in individuals with mild/moderate stenosis in whom the role of surgical intervention is currently unclear.

[Groups of resource utilization in acute care units and average length of stay at geriatrics services]. / Grupos de utilizacion de recursos en Unidades de agudos y media estancia de Servicios de Geriatria.

BACKGROUND: In recent years, Patient Classifications Systems (PCS's) have been implement in Spain for the purpose of gauging the "hospital product". However, the most conventional systems are not very well-suited to the senior citizen population, among whom illness-related disability is a determining factor with regard to explaining the usage of resources and the results of the health care provided. Therefore, the idea was brought forth of implementing a system in units providing senior citizen care which would entail this parameter, that is, the Resource Usage Groups (RUG's), analyzing the characteristics and differences in the RUG-related spread in four Geriatrics Units. METHODS: A cross-sectional study based on consecutive cutoff points in periods longer than the average stay in each unit, the patients admitted in the acute care units and average stay in the Geriatrics Unit of the Hospital Monte Narango (HMN) (n = 318), Hospital Central de la Cruz Roja (HCCR) (n = 384), Hospital General de Guadalajara (HG) (n = 272) and Hospital Virgen del Valle (HVV) (n = 390), with regard to the spread thereof according to the RUG-T18 classification. The possible differences among the hospitals in question were analyzed by means of the chi-square statistical test (SPSS for Windows). RESULTS: For the overall sample, the patients were divided into groups R, S and C of the classification, groups P and B being represented to a very small degree, differences having been found to exist among the different hospitals. Hence, the HCCR is that which handles the largest percentage of patients in the R group (47.64% vs. 23.66% at HMN; 20.57% at HG and 20.53% at HVV) and a smaller percentage of patients in the S Group (3.12% vs. 6.40% at HMN; 9.92% at HG and 9.76% at HVV) and the C Group (48.94% vs. 76.29% at HMN; 66.89% at HG and 68.36% at HVV). Differences were likewise found to exist in the individual analysis for the acute care units and average length of stay. CONCLUSIONS: The resource usage groups can be useful with regard to ascertaining differences in the health care loads in hospital care for senior citizens.

Stenting of a superior mesenteric artery lesion via the right arm approach.

Chronic mesenteric ischemia is rare and commonly presents with abdominal pain and weight loss. Treatment options are limited to surgical or endovascular revascularization. In this report we describe in detail successful stent-supported angioplasty of a high-grade superior mesenteric artery stenosis utilizing a right brachial artery approach. A brief review of the literature is provided.

Subpectoral implantation of ICD generators: long-term follow-up.

A nonthoracotomy surgical approach using an endocardial electrode and combined implantation of a subcutaneous patch and the implantable cardioverter defibrillator (ICD) generator in a subpectoral pocket has been described. We report the long-term follow-up results in patients undergoing implantation using this approach. The patient population consisted of 28 patients (22 men and 6 women) with a mean age of 59 +/- 12 years. The underlying heart disease consisted of coronary artery disease in 20 patients and dilated cardiomyopathy in 8 patients. Sustained ventricular tachycardia was the mode of presentation in 16 patients and sudden cardiac death in 12 patients. The mean left ventricular ejection fraction was 31% +/- 6%. The lead system consisted of an 8 French bipolar passive fixation rate sensing lead positioned at the right ventricular apex, an 11 French spring coil electrode positioned at the superior vena cava-right atrial junction (surface area 700 mm2), and submuscular placement of a large patch (surface area 28 cm2) on the anterolateral chest wall near the cardiac apex via a submammary incision. A defibrillation threshold of < or = 15 joules (J) was required for implantation. This criterion was not satisfied in five patients; thus, a limited thoracotomy was performed via the submammary incision, and the large patch was placed epicardially. The mean R wave amplitude was 12 +/- 3 mV, the mean pacing threshold was 1.0 +/- 0.5 V at 0.5 msec, and the mean defibrillation threshold was 12.6 +/- 3 J. ICD generators implanted were the Ventak-P in 17, PCD-7217 in 5, and the Cadence V-100 in 6 patients.(ABSTRACT TRUNCATED AT 250 WORDS)

[Geriatric emergencies versus adult emergencies: retrospective analysis of medical emergencies at a general hospital]. / La urgencia geriátrica frente a la urgencia en la edad adulta: análisis retrospectivo de las urgencias médicas de un hospital general.

The aim of the study was to evaluate the process of the attention to emergencies in patients older than 65 years and to compare it with the same process in adult patients. To this end, 965 clinical records of medical emergencies from the Hospital Central de la Cruz Roja in Madrid were retrospectively evaluated, and data were obtained regarding age, the cause for consultation, the investigations performed and their yield, the administration of drug therapy, the major diagnosis at the time of discharge from the service and the clinical course. It was found that all evaluated diagnostic investigations were carried out with equal or higher frequency in patients older than 65 years and that their mean clinical effectiveness was also higher. In addition, it was found that the patients older than 65 years were more commonly admitted to the hospital through the emergency service than the rest of the population. It was concluded, therefore, that the process of attention to emergencies has differential characteristics in the elderly population, and that if the number and proportion of old people increase as it will presumably happen during the two next decades, the cost of attention to emergencies and the number of emergency hospital admissions will also increase.