Modeling human observer detection for varying data acquisition in undersampled MRI for two-alternative forced choice (2-AFC) and forced localization tasks.

Undersampling in the frequency domain (k-space) in MRI enables faster data acquisition. In this study, we used a fixed 1D undersampling factor of 5x with only 20% of the k-space collected. The fraction of fully acquired low k-space frequencies were varied from 0% (all aliasing) to 20% (all blurring). The images were reconstructed using a multi-coil SENSE algorithm. We used two-alternative forced choice (2-AFC) and the forced localization tasks with a subtle signal to estimate the human observer performance. The 2-AFC average human observer performance remained fairly constant across all imaging conditions. The forced localization task performance improved from the 0% condition to the 2.5% condition and remained fairly constant for the remaining conditions, suggesting that there was a decrease in task performance only in the pure aliasing situation. We modeled the average human performance using a sparse-difference of Gaussians (SDOG) Hotelling observer model. Because the blurring in the undersampling direction makes the mean signal asymmetric, we explored an adaptation for irregular signals that made the SDOG template asymmetric. To improve the observer performance, we also varied the number of SDOG channels from 3 to 4. We found that despite the asymmetry in the mean signal, both the symmetric and asymmetric models reasonably predicted the human performance in the 2-AFC experiments. However, the symmetric model performed slightly better. We also found that a symmetric SDOG model with 4 channels implemented using a spatial domain convolution and constrained to the possible signal locations reasonably modeled the forced localization human observer results.

Optimizing data acquisition in undersampled magnetic resonance imaging (MRI) using two alternative forced choice (2-AFC) and search tasks.

Undersampling in the frequency domain (k-space) in MRI accelerates the data acquisition. Typically, a fraction of the low frequencies is fully collected and the rest are equally undersampled. We used a fixed 1D undersampling factor of 5x where 20% of the k-space lines are collected but varied the fraction of the low k-space frequencies that are fully sampled. We used a range of fully acquired low k-space frequencies from 0% where the primary artifact is aliasing to 20% where the primary artifact is blurring in the undersampling direction. Small lesions were placed in the coil k-space data for fluid-attenuated inversion recovery (FLAIR) brain images from the fastMRI database. The images were reconstructed using a multi-coil SENSE reconstruction with no regularization. We conducted a human observer two-alternative forced choice (2-AFC) study with a signal known exactly and a search task with variable backgrounds for each of the acquisitions. We found that for the 2-AFC task, the average human observer did better with more of the low frequencies being fully sampled. For the search task, we found that after an initial improvement from having none of the low frequencies fully sampled to just 2.5%, the performance remained fairly constant. We found that the performance in the two tasks had a different relationship to the acquired data. We also found that the search task was more consistent with common practice in MRI where a range of frequencies between 5% and 10% of the low frequencies are fully sampled.

Modeling human observer detection in undersampled magnetic resonance imaging reconstruction with total variation and wavelet sparsity regularization.

Purpose: Task-based assessment of image quality in undersampled magnetic resonance imaging provides a way of evaluating the impact of regularization on task performance. In this work, we evaluated the effect of total variation (TV) and wavelet regularization on human detection of signals with a varying background and validated a model observer in predicting human performance. Approach: Human observer studies used two-alternative forced choice (2-AFC) trials with a small signal known exactly task but with varying backgrounds for fluid-attenuated inversion recovery images reconstructed from undersampled multi-coil data. We used a 3.48 undersampling factor with TV and a wavelet sparsity constraints. The sparse difference-of-Gaussians (S-DOG) observer with internal noise was used to model human observer detection. The internal noise for the S-DOG was chosen to match the average percent correct (PC) in 2-AFC studies for four observers using no regularization. That S-DOG model was used to predict the PC of human observers for a range of regularization parameters. Results: We observed a trend that the human observer detection performance remained fairly constant for a broad range of values in the regularization parameter before decreasing at large values. A similar result was found for the normalized ensemble root mean squared error. Without changing the internal noise, the model observer tracked the performance of the human observers as the regularization was increased but overestimated the PC for large amounts of regularization for TV and wavelet sparsity, as well as the combination of both parameters. Conclusions: For the task we studied, the S-DOG observer was able to reasonably predict human performance with both TV and wavelet sparsity regularizers over a broad range of regularization parameters. We observed a trend that task performance remained fairly constant for a range of regularization parameters before decreasing for large amounts of regularization.

Predicting human detection performance in magnetic resonance imaging (MRI) with total variation and wavelet sparsity regularizers.

Two common regularization methods in reconstruction of magnetic resonance images are total variation (TV) which restricts the magnitude of the gradient in the reconstructed image and wavelet sparsity which assumes that the object being imaged is sparse in the wavelet domain. These regularization methods have resulted in images with fewer undersampling artifacts and less noise but introduce their own artifacts. In this work, we extend previous results on modeling of human observer performance for images using TV regularization to also predict human detection performance using wavelet regularization and a combination of wavelet and TV regularization. Small lesions were placed in the coil k-space data for fluid-attenuated inversion recovery (FLAIR) brain images from the fastMRI database. The data was undersampled using an acceleration factor of 3.48. The undersampled data was reconstructed using a range of regularization parameters for both the TV and wavelet regularization. The internal noise level for the sparse difference-of-Gaussians (S-DOG) model observer was chosen to match the average human percent correct in two-alternative forced choice (2-AFC) studies with a signal known exactly with variable backgrounds and no regularization. The S-DOG model largely tracked the human observer results except at large values of the regularization parameter where it outperformed the average human observer. We found that the regularization with either constraint or in combination did not improve human observer performance for this task.

New records of Sabethini (Diptera: Culicidae) from Colombia.

BACKGROUND: In the Neotropical Region, the mosquitoes, grouped in the tribe Sabethini (Arthropoda, Insecta, Diptera: Culicidae) are considered of medical importance by the role that some species may have in arbovirus transmission; also, because they are good bioindicators. More than 400 species are currently recognised and are mainly associated with forest areas. The tribe Sabethini is poorly studied and the information about diversity and distribution for species relating to it is scarce. In Colombia, 54 species of the tribe are known; however, several geographical areas have not been included in the studies for this group and data for recent field collections are not available; therefore, the records are outdated. NEW INFORMATION: This study presents the species list of the Sabethini tribe in Colombia, based on a review of previous publications and recent unpublished data. The list includes 68 species of nine genera and 16 subgenera. The genus Wyeomyia has the highest species number (39), followed by Sabethes (14). A total of 29 new records are registered and actualized information related to the local distribution in some Departments is presented, including geographic coordinates. In this paper, the distribution records of Sabethini for Colombia are updated, revealing the high diversity of this group in the country and providing some useful information for species that may need surveillance or control.

Optimizing constrained reconstruction in magnetic resonance imaging for signal detection.

Constrained reconstruction in magnetic resonance imaging (MRI) allows the use of prior information through constraints to improve reconstructed images. These constraints often take the form of regularization terms in the objective function used for reconstruction. Constrained reconstruction leads to images which appear to have fewer artifacts than reconstructions without constraints but because the methods are typically nonlinear, the reconstructed images have artifacts whose structure is hard to predict. In this work, we compared different methods of optimizing the regularization parameter using a total variation (TV) constraint in the spatial domain and sparsity in the wavelet domain for one-dimensional (2.56×) undersampling using variable density undersampling. We compared the mean squared error (MSE), structural similarity (SSIM), L-curve and the area under the receiver operating characteristic (AUC) using a linear discriminant for detecting a small and a large signal. We used a signal-known-exactly task with varying backgrounds in a simulation where the anatomical variation was the major source of clutter for the detection task. Our results show that the AUC dependence on regularization parameters varies with the imaging task (i.e. the signal being detected). The choice of regularization parameters for MSE, SSIM, L-curve and AUC were similar. We also found that a model-based reconstruction including TV and wavelet sparsity did slightly better in terms of AUC than just enforcing data consistency but using these constraints resulted in much better MSE and SSIM. These results suggest that the increased performance in MSE and SSIM over-estimate the improvement in detection performance for the tasks in this paper. The MSE and SSIM metrics show a big difference in performance where the difference in AUC is small. To our knowledge, this is the first time that signal detection with varying backgrounds has been used to optimize constrained reconstruction in MRI.

Modeling human observer detection in undersampled magnetic resonance imaging (MRI).

Task-based assessment of image quality in undersampled magnetic resonance imaging (MRI) using constraints is important because of the need to quantify the effect of the artifacts on task performance. Fluid-attenuated inversion recovery (FLAIR) images are used in detection of small metastases in the brain. In this work we carry out two-alternative forced choice (2-AFC) studies with a small signal known exactly (SKE) but with varying background for reconstructed FLAIR images from undersampled multi-coil data. Using a 4x undersampling and a total variation (TV) constraint we found that the human observer detection performance remained fairly constant for a broad range of values in the regularization parameter before decreasing at large values. Using the TV constraint did not improve task performance. The non- prewhitening eye (NPWE) observer and sparse difference-of-Gaussians (S-DOG) observer with internal noise were used to model human observer detection. The parameters for the NPWE and the internal noise for the S-DOG were chosen to match the average percent correct (PC) in 2-AFC studies for three observers using no regularization. The NPWE model observer tracked the performance of the human observers as the regularization was increased but slightly over-estimated the PC for large amounts of regularization. The S-DOG model observer with internal noise tracked human performace for all levels of regularization studied. To our knowledge this is the first time that model observers have been used to track human observer detection for undersampled MRI.

Frecuencia de pacientes que consultan con diagnóstico de delirium en el Hospital Nacional Psiquiátrico "Dr. José Molina Martínez", de marzo a agosto 2013 / Frequency of patients consulting with a diagnosis of delirium at the "Dr. José Molina Martínez" National Psychiatric Hospital, from March to August 2013

El delirium es un trastorno que ha sido descrito desde el inicio de la medicina como un cuadro clínico, de inicio brusco y curso fluctuante, caracterizándose por alteraciones de la conciencia, la atención y el pensamiento, y en el que pueden aparecer ideas delirantes y alucinaciones. Es un trastorno que se sitúa en la frontera entre la psiquiatría y el resto de especialidades médicas, puesto que puede aparecer en el curso de diversas enfermedades. Apareciendo con mucha frecuencia en los pacientes hospitalizados, de edad avanzada, y de otras causas médicas. Esta entidad clínica es una complicación médica que se asocia a una elevada mortalidad y a un importante consumo de recursos. El objetivo del presente estudio es indagar la frecuencia de pacientes que consultan con diagnóstico de delirium en el Hospital Nacional Psiquiátrico "Dr. José Molina Martínez", de marzo a agosto 2013

Enfermedad de Kawasaki en un hospital pediátrico en México / Kawasaki disease at a pediatric hospital in Mexico

Resumen: Introducción: La enfermedad de Kawasaki (EK) es una de las vasculitis sistémicas más comunes en niños menores de 5 años de edad. La epidemiología de la enfermedad no está bien establecida en México. El objetivo de este trabajo fue describir la epidemiología, características clínicas y tratamiento de los pacientes con EK atendidos en el Hospital Infantil de México Federico Gómez (HIMFG). Métodos: Se realizó un estudio retrospectivo, descriptivo y analítico de pacientes diagnosticados con EK en el HIMFG en el periodo comprendido entre enero de 2004 y diciembre de 2014. Resultados: Se analizaron 204 casos, la mayoría de sexo masculino (55%), con mediana de edad de 32.5 meses (6-120) y una tasa de hospitalización del 96%. El 20% de los pacientes presentó EK incompleto. No se reportaron diferencias en la somatometría ni signos vitales. La sintomatología más frecuente fue fiebre, conjuntivitis (89%), cambios orales (84%), faringitis (88%) y lengua en fresa (83%). Se encontraron reactantes de fase aguda más elevados en las presentaciones clásicas. Se reportaron alteraciones ecocardiográficas en 60 pacientes (29%), de las cuales el 12% fueron ectasia y el 11% aneurismas coronarios. Por otro lado, 169 pacientes (83%) recibieron inmunoglobulina intravenosa (IGIV), 18 (9%) resistencia a IGIV, 6 (3%) requirieron corticosteroides y 2 (1%) infliximab; todos recibieron ácido acetilsalicílico. Conclusiones: No se encontraron diferencias importantes entre las presentaciones clásicas e incompletas. La incidencia de alteraciones cardiacas es menor a la reportada previamente en México, pero similar a la de otros países.

Abstract: Background: Kawasaki disease (KD) is one of the most common systemic vasculitis in children under 5 years of age. The epidemiology of the disease is not well established in Mexico. The objective of this study was to describe the epidemiology, clinical features and treatment of patients with KD at the Hospital Infantil de Mexico Federico Gomez (HIMFG). Methods: We conducted a retrospective, descriptive and analytical study of patients diagnosed from January 2004 to December 2014 with KD in the HIMFG. Results: We analyzed 204 cases from which 55% were male, with a median age of 32.5 months (6-120) and a rate of hospitalization of 96%. Twenty percent of patients presented incomplete KD. No differences in the somatometric measurements or vitals were reported. The most frequent symptoms were fever, conjunctivitis (89%), oral changes (84%), pharyngitis (88%) and strawberry tongue (83%). We found higher acute phase reactants in the classic presentation. Echocardiographic alterations in 60 patients (29%), of which 12% were ectasia and 11% reported coronary aneurysms. On the other hand, 169 (83%) patients received intravenous immunoglobulin (IVIG), 18 (9%) presented resistance to IVIG, 6 (3%) required corticosteroids, and 2 (1%) infliximab; all received acetylsalicylic acid. Conclusions: There were no important differences between classic and incomplete presentations. The incidence of cardiac alterations is less than previously reported in Mexico, but similar to that of other countries.

[Kawasaki disease at a pediatric hospital in Mexico]. / Enfermedad de Kawasaki en un hospital pediátrico en México.

BACKGROUND: Kawasaki disease (KD) is one of the most common systemic vasculitis in children under 5 years of age. The epidemiology of the disease is not well established in Mexico. The objective of this study was to describe the epidemiology, clinical features and treatment of patients with KD at the Hospital Infantil de Mexico Federico Gomez (HIMFG). METHODS: We conducted a retrospective, descriptive and analytical study of patients diagnosed from January 2004 to December 2014 with KD in the HIMFG. RESULTS: We analyzed 204 cases from which 55% were male, with a median age of 32.5 months (6-120) and a rate of hospitalization of 96%. Twenty percent of patients presented incomplete KD. No differences in the somatometric measurements or vitals were reported. The most frequent symptoms were fever, conjunctivitis (89%), oral changes (84%), pharyngitis (88%) and strawberry tongue (83%). We found higher acute phase reactants in the classic presentation. Echocardiographic alterations in 60 patients (29%), of which 12% were ectasia and 11% reported coronary aneurysms. On the other hand, 169 (83%) patients received intravenous immunoglobulin (IVIG), 18 (9%) presented resistance to IVIG, 6 (3%) required corticosteroids, and 2 (1%) infliximab; all received acetylsalicylic acid. CONCLUSIONS: There were no important differences between classic and incomplete presentations. The incidence of cardiac alterations is less than previously reported in Mexico, but similar to that of other countries.

Estrategia de intervención para el desarrollo de conocimientos sobre sexualidad en adolescentes de una secundaria básica urbana / Intervention strategy for the development of knowledge on sexuality in adolescents of an urban high school

Se llevó a cabo una estrategia de intervención, para elevar el nivel de conocimientos sobre sexualidad en 15 estudiantes, promotores de salud, pertenecientes a la ESBU Espino Fernández de Santiago de Cuba, desde octubre del 2014 hasta febrero del 2015. Se desarrollaron 6 sesiones grupales donde se empleó la metodología cualitativa y el método de investigación-acción participativa. Esta estrategia permitió que los adolescentes desarrollaran sus conocimientos sobre el tema y comprendieran que las personas con una sexualidad sana tienen un mayor equilibrio emocional, son más estables y productivas(AU)

An intervention strategy was carried out to elevate the knowledge level on sexuality in 15 health promoters students, belonging to Espìno Fernández Urban High School in Santiago de Cuba, from October, 2014 to February, 2015. Six groupal sessions were developed, where the qualitative methodology and the participative investigation-action method were used. This strategy allowed the adolescents to develop their knowledge on the topic and to understand that people with a healthy sexuality have a higher emotional balance, they are more stable and more productive(AU)

To bin or not to bin? The effect of CT system limiting resolution on noise and detectability.

We examine the noise advantages of having a computed tomography (CT) detector whose spatial resolution is significantly better (e.g. a factor of 2) than needed for a desired resolution in the reconstructed images. The effective resolution of detectors in x-ray CT is sometimes degraded by binning cells because the small cell size and fine sampling are not needed to achieve the desired resolution (e.g. with flat panel detectors). We studied the effect of the binning process on the noise in the reconstructed images and found that while the images in the absence of noise can be made identical for the native and the binned system, for the same system MTF in the presence of noise, the binned system always results in noisier reconstructed images. The effect of the increased noise in the reconstructed images on lesion detection is scale (frequency content) dependent with a larger difference between the high resolution and binned systems for imaging fine structure (small objects). We show simulated images reconstructed with both systems for representative objects and quantify the impact of the noise on the detection of the lesions based on mathematical observers. Through both subjective assessment of the reconstructed images and the quantification using mathematical observers, we show that for a CT system where the photon noise is dominant, higher resolution in the detectors leads to better noise performance in the reconstructed images at any resolution.

Beyond noise power in 3D computed tomography: the local NPS and off-diagonal elements of the Fourier domain covariance matrix.

PURPOSE: To investigate the correlation and stationarity of noise in volumetric computed tomography (CT) using the local discrete noise-power spectrum (NPS) and off-diagonal elements of the covariance matrix of the discrete Fourier transform of noise-only images (denoted Σ(DFT)). Experimental conditions were varied to affect noise correlation and stationarity, the effects were quantified in terms of the NPS and Σ(DFT), and practical considerations in CT performance characterization were identified. METHODS: Cone-beam CT (CBCT) images were acquired using a benchtop system comprising an x-ray tube and flat-panel detector for a range of acquisition techniques (e.g., dose and x-ray scatter) and three phantom configurations hypothesized to impart distinct effects on the NPS and Σ(DFT): (A) air, (B) a 20-cm-diameter water cylinder with a bowtie filter, and (C) the cylinder without a bowtie filter. The NPS and off-diagonal elements of the Σ(DFT) were analyzed as a function of position within the reconstructions. RESULTS: The local NPS varied systematically throughout the axial plane in a manner consistent with changes in fluence transmitted to the detector and view sampling effects. Variability in fluence was manifest in the NPS magnitude-e.g., a factor of ~2 variation in NPS magnitude within the axial plane for case C (cylinder without bowtie), compared to nearly constant NPS magnitude for case B (bowtie filter matched to the cylinder). View sampling effects were most prominent in case A (air) where the variance increased at greater distance from the center of reconstruction and in case C (cylinder) where the NPS exhibited correlations in the radial direction. The effects of detector lag were observed as azimuthal correlation. The cylinder (without bowtie) had the strongest nonstationarity because of the larger variability in fluence transmitted to the detector. The diagonal elements of the Σ(DFT) were equivalent to the NPS estimated from the periodogram, and the average off-diagonal elements of the Σ(DFT) exhibited amplitude of ~1% of the NPS for the experimental conditions investigated. Furthermore, the off-diagonal elements demonstrated fairly long tails of nearly constant amplitude, with magnitude somewhat reduced for experimental conditions associated with greater stationarity (viz., lower Σ(DFT) tails for cases A and B in comparison to case C). CONCLUSIONS: Volumetric CT exhibits nonstationarity in the NPS as hypothesized in relation to fluence uniformity and view sampling. Measurement of the NPS should seek to minimize such changes in noise correlations and include careful reporting of experimental conditions (e.g., phantom design and use of a bowtie filter) and spatial dependence (e.g., analysis at fixed radius within a phantom). Off-diagonal elements of the Σ(DFT) similarly depend on experimental conditions and can be readily computed from the same data as the NPS. This work begins to check assumptions in NPS analysis examine the extent to which NPS is an appropriate descriptor of noise correlations, and investigate the magnitude of off-diagonal elements of the Σ(DFT). While the magnitude of such off-diagonal elements appears to be low, their cumulative effect on space-variant detectability remains to be investigated-e.g., using task-specific figures of merit.

Prevalencia de demencia y factores asociados en adultos mayores, Aldea Tablones Arriba, Municipio de Yusguare, Choluteca, mayo 2010 – 2011 / Prevalence of Dementia and Associated Factors in Older Adults, Village

Las demencias son un grupo de enfermedades neurológicas y psiquiátricas; que se presentan en adultos mayores sin respetar edad, sexo, y nivel socioeconómico. Según la Organización Mundial de la Salud (OMS), afectan a un billón de personas en el mundo. Presentan una prevalencia de 6.5 en el Continente Americano, y en América Latina hasta de 7.0. Objetivo: Determinar la prevalencia de demencia y la situación general de salud del adulto mayor en la Comunidad de Tablones Arriba, Municipio de Yusguare, Choluteca. Metodología; Diseño: descriptivo-transversal, Universo: 110 adultos mayores; Muestra: 50 adultos de 60 años, Muestreo: probabilístico al azar estratificado; para la recolección de la información se utilizó una encuesta que constó de 32 preguntas, de las cuales 13 eran preguntas cerradas y 19 preguntas abiertas; la encuesta dividida en las siguientes secciones: Datos generales y datos socio demográficos, antecedentes médicos que se enfocaron en condiciones médicas relevantes actuales y pasadas, una lista actual de medicamentos, historia familiar, examen físico dirigido (antropometría, presión arterial, agudeza visual, evaluación cardiovascular y neurológica) y resultados de laboratorio. La encuesta fue validada en una muestra de 6 adultos mayores de 60 años y previo consentimiento informado; aplicada por medio de una entrevista. Se les realizó un examen físico completo, una evaluación cognitiva funcional corta que incluyó instrumentos estandarizados: MMSE, Test de Folstein, Test del Quetzal (adaptación al Lempira), Escala de Depresión Geriátrica, test de Yesavage, y mini-escala de Estado Nutricional de la Organización Mundial de la Salud. Se utilizaron los criterios de Estratificación de Riesgo Cardiovascular Framingham. El procesamiento de datos se realizó con el programa Epi-info 3.3 (versión Windows) y SPSS 17.0; se utilizó un análisis univariado para la estimación de prevalencia...

On the performance of T2* correction methods for quantification of hepatic fat content.

Nonalcoholic fatty liver disease is the most prevalent chronic liver disease in Western societies. MRI can quantify liver fat, the hallmark feature of nonalcoholic fatty liver disease, so long as multiple confounding factors including T(2)* decay are addressed. Recently developed MRI methods that correct for T(2)* to improve the accuracy of fat quantification either assume a common T(2)* (single-T(2)*) for better stability and noise performance or independently estimate the T(2)* for water and fat (dual-T(2)*) for reduced bias, but with noise performance penalty. In this study, the tradeoff between bias and variance for different T(2)* correction methods is analyzed using the Cramér-Rao bound analysis for biased estimators and is validated using Monte Carlo experiments. A noise performance metric for estimation of fat fraction is proposed. Cramér-Rao bound analysis for biased estimators was used to compute the metric at different echo combinations. Optimization was performed for six echoes and typical T(2)* values. This analysis showed that all methods have better noise performance with very short first echo times and echo spacing of ∼π/2 for single-T(2)* correction, and ∼2π/3 for dual-T(2)* correction. Interestingly, when an echo spacing and first echo shift of ∼π/2 are used, methods without T(2)* correction have less than 5% bias in the estimates of fat fraction.

Gemelos monoamnióticos discordantes para cardiopatía / Monochorial-monoamniotic twins discordant for congenital heart disease

Presentamos el caso de una gestación monocorial-monoamniótica, con diagnóstico en uno de los gemelos de defecto auriculoventricular completo, truncus arterioso, atresia de arteria pulmonar y dudoso drenaje venoso anómalo. No se encuentran descripciones de casos similares en la literatura. Tras un seguimiento ecográfico detallado, en la semana 32 se realizan la maduración fetal y la cesárea electiva; se obtienen dos recién nacidos de bajo peso pero ambos con test de Apgar y pH arterio-venoso umbilical normales. El primer gemelo, portador de la cardiopatía, tiene una evolución posnatal desfavorable y fallece a los 16 días de vida. La evolución del segundo gemelo es favorable(AU)

We report a case of monochorial-monoamniotic twin pregnancy, with diagnosis of an atrioventricular defect, complete truncus arteriosus, pulmonary artery atresia and doubtful anomalous venous drainage in one of the twins. There are no descriptions of similar cases in the literature. After detailed ultrasound follow-up, fetal maturation and elective cesarean section were performed at 32 weeks. The two neonates had low birth weight but Apgar tests and umbilical arteriovenous pH parameters were normal in both. The first newborn twin was diagnosed with congenital heart disease and showed unfavorable postnatal development, dying at 16 days old. Outcome in the second twin was favorable(AU)

Noise analysis for 3-point chemical shift-based water-fat separation with spectral modeling of fat.

PURPOSE: To model the theoretical signal-to-noise ratio (SNR) behavior of 3-point chemical shift-based water-fat separation, using spectral modeling of fat, with experimental validation for spin-echo and gradient-echo imaging. The echo combination that achieves the best SNR performance for a given spectral model of fat was also investigated. MATERIALS AND METHODS: Cramér-Rao bound analysis was used to calculate the best possible SNR performance for a given echo combination. Experimental validation in a fat-water phantom was performed and compared with theory. In vivo scans were performed to compare fat separation with and with out spectral modeling of fat. RESULTS: Theoretical SNR calculations for methods that include spectral modeling of fat agree closely with experimental SNR measurements. Spectral modeling of fat more accurately separates fat and water signals, with only a slight decrease in the SNR performance of the water-only image, although with a relatively large decrease in the fat SNR performance. CONCLUSION: The optimal echo combination that provides the best SNR performance for water using spectral modeling of fat is very similar to previous optimizations that modeled fat as a single peak. Therefore, the optimal echo spacing commonly used for single fat peak models is adequate for most applications that use spectral modeling of fat.

Simultaneous segmentation and reconstruction: a level set method approach for limited view computed tomography.

PURPOSE: An iterative tomographic reconstruction algorithm that simultaneously segments and reconstructs the reconstruction domain is proposed and applied to tomographic reconstructions from a sparse number of projection images. METHODS: The proposed algorithm uses a two-phase level set method segmentation in conjunction with an iterative tomographic reconstruction to achieve simultaneous segmentation and reconstruction. The simultaneous segmentation and reconstruction is achieved by alternating between level set function evolutions and per-region intensity value updates. To deal with the limited number of projections, a priori information about the reconstruction is enforced via penalized likelihood function. Specifically, smooth function within each region (piecewise smooth function) and bounded function intensity values for each region are assumed. Such a priori information is formulated into a quadratic objective function with linear bound constraints. The level set function evolutions are achieved by artificially time evolving the level set function in the negative gradient direction; the intensity value updates are achieved by using the gradient projection conjugate gradient algorithm. RESULTS: The proposed simultaneous segmentation and reconstruction results were compared to "conventional" iterative reconstruction (with no segmentation), iterative reconstruction followed by segmentation, and filtered backprojection. Improvements of 6%-13% in the normalized root mean square error were observed when the proposed algorithm was applied to simulated projections of a numerical phantom and to real fan-beam projections of the Catphan phantom, both of which did not satisfy the a priori assumptions. CONCLUSIONS: The proposed simultaneous segmentation and reconstruction resulted in improved reconstruction image quality. The algorithm correctly segments the reconstruction space into regions, preserves sharp edges between different regions, and smoothes the noise within each region. The proposed algorithm framework has the flexibility to be adapted to different a priori constraints while maintaining the benefits achieved by the simultaneous segmentation and reconstruction.

Independent estimation of T*2 for water and fat for improved accuracy of fat quantification.

Noninvasive biomarkers of intracellular accumulation of fat within the liver (hepatic steatosis) are urgently needed for detection and quantitative grading of nonalcoholic fatty liver disease, the most common cause of chronic liver disease in the United States. Accurate quantification of fat with MRI is challenging due the presence of several confounding factors, including T*(2) decay. The specific purpose of this work is to quantify the impact of T*(2) decay and develop a multiexponential T*(2) correction method for improved accuracy of fat quantification, relaxing assumptions made by previous T*(2) correction methods. A modified Gauss-Newton algorithm is used to estimate the T*(2) for water and fat independently. Improved quantification of fat is demonstrated, with independent estimation of T*(2) for water and fat using phantom experiments. The tradeoffs in algorithm stability and accuracy between multiexponential and single exponential techniques are discussed.

Diagnóstico prenatal de un nefroma mesoblástico congénito / Prenatal diagnosis of congenital mesoblastic nephroma

El nefroma mesoblástico congénito es el tumorrenal más frecuente en neonatos. Presentamosel caso de una masa renal fetal detectadaprenatalmente en una ecografía de rutina, asociadaa un polihidramnios. Los hallazgos ecográficos de lamasa eran sugerentes de un nefroma mesoblástico yel estudio histopatológico confirmó el diagnóstico

Congenital mesoblastic nephroma is the mostcommon kidney tumor in neonates. We reporta case of renal mass detected prenatally in aroutine ultrasonographic examination, associatedwith polyhydramnios. Ultrasonographic featuressuggested mesoblastic nephroma. The diagnosis wasconfirmed by histopathological study