RESUMO
BACKGROUND: In phase-contrast (PC) MRI, several dual velocity encoding methods have been proposed to robustly increase velocity-to-noise ratio (VNR), including a standard dual-VENC (SDV), an optimal dual-VENC (ODV), and bi- and triconditional methods. PURPOSE: To develop a correction method for the ODV approach and to perform a comparison between methods. STUDY TYPE: Case-control study. POPULATION: Twenty-six volunteers. FIELD STRENGTH/SEQUENCE: 1.5 T phase-contrast MRI with VENCs of 50, 75, and 150 cm/second. ASSESSMENT: Since we acquired single-VENC protocols, we used the background phase from high-VENC (VENCH ) to reconstruct the low-VENC (VENCL ) phase. We implemented and compared the unwrapping methods for different noise levels and also developed a correction of the ODV method. STATISTICAL TESTS: Shapiro-Wilk's normality test, two-way analysis of variance with homogeneity of variances was performed using Levene's test, and the significance level was adjusted by Tukey's multiple post hoc analysis with Bonferroni (P < 0.05). RESULTS: Statistical analysis revealed no extreme outliers, normally distributed residuals, and homogeneous variances. We found statistically significant interaction between noise levels and the unwrapping methods. This implies that the number of non-unwrapped pixels increased with the noise level. We found that for ß = VENCL /VENCH = 1/2, unwrapping methods were more robust to noise. The post hoc test showed a significant difference between the ODV corrected and the other methods, offering the best results regarding the number of unwrapped pixels. DATA CONCLUSIONS: All methods performed similarly without noise, but the ODV corrected method was more robust to noise at the price of a higher computational time. LEVEL OF EVIDENCE: 4 TECHNICAL EFFICACY STAGE: 1.
Assuntos
Algoritmos , Processamento de Imagem Assistida por Computador , Humanos , Processamento de Imagem Assistida por Computador/métodos , Estudos de Casos e Controles , Imageamento por Ressonância Magnética/métodos , Imagens de Fantasmas , Velocidade do Fluxo Sanguíneo , Reprodutibilidade dos TestesRESUMO
Mosquitoes represent a threat to human health and animals because they act as vectors of several diseases. Native fish species are potential candidates to be considered for biological control populations of mosquitoes. Tests of half-hour and 24-hour consumption of Culex pipiens (Linnaeus, 1758) larvae by Cnesterodon decemmaculatus (Jenyns, 1842) and Jenynsia multidentata (Jenyns, 1842) were carried out, measuring the standard length, mouth width and weight in individuals of the two species of fishes. In both tests J. multidentata consumed more C. pipiens than C. decemmaculatus, being C. decemmaculatus female consumption higher than male consumption (and equal than both sexes of J. multidentata in the 24-hour test). These results remained unchanged when making comparisons of absolute or relative consumption in the half-hour test, but when consumptions relative to weight were compared no difference between species was found in the 24-hour test. Regression analysis between morphometric variables and weight vs. consumption rates showed low explanatory value for the half-hour test, while in the 24-hour test these variables had higher explanatory value, especially for the mouth width. Finally, a half-hour test was performed over C. decemmaculatus females using C. pipiens and Aedes aegypti (Linnaeus, 1742) larvae and it showed a strong preference for the latter ones. This work allowed us to observe that there are large differences in consumption rates of C. pipiens larvae between the fish species under study in short periods. Differences are attenuated when consumption times are longer and may even disappear when weight is taken into account.(AU)
Los mosquitos representan una amenaza para la salud del hombre y de los animales debido a que actúan como vectores de distintas enfermedades. Especies de peces nativos son potenciales candidatos a tenerse en cuenta para control biológico de poblaciones de culícidos. Experiencias de consumo de media hora y de 24 horas por Cnesterodon decemmaculatus (Jenyns, 1842) y Jenynsia multidentata (Jenyns, 1842) se llevaron a cabo con larvas de Culex pipiens (Linnaeus, 1758), midiéndose longitud estándar, ancho de boca y peso en individuos de las dos especies. En ambas pruebas, J. multidentata consumió más C. pipiens que C. decemmaculatus, consumiendo las hembras de esta última especie más que los machos (e igual a ambos sexos de J. multidentata en la prueba de 24 horas de duración). Estos resultados no variaron cuando se compararon tantos consumos absolutos o relativos para las pruebas de media hora, sin embargo cuando se compararon los consumos relativos al peso no se encontraron diferencias entre las especies para las pruebas de 24 horas. Análisis de regresión entre las tasas de consumo versus las variables morfométricas y el peso mostraron poco valor explicativo en las pruebas de media hora de duración, mientras que en las pruebas de 24 horas de duración los análisis de regresión tuvieron un mayor valor explicativo, especialmente con el ancho de la boca. Por último, pruebas de media hora de duración fueron llevadas a cabo exponiendo a hembras de C. decemmaculatus con larvas de C. pipiens y Aedes aegypti (Linnaeus, 1742) observándose una fuerte preferencia por las últimas. Este trabajo permitió evidenciar que las especies de peces en estudio presentan grandes diferencias en las tasas de consumo de C. pipiens en periodos cortos. Estas diferencias se atenuaron cuando las tasas de consumo se prolongaron y hasta llegar a desaparecer cuando el peso se tuvo en cuenta.(AU)
Assuntos
Animais , Larva/classificação , Peixes/classificação , Controle Biológico de Vetores/métodosRESUMO
Mosquitoes represent a threat to human health and animals because they act as vectors of several diseases. Native fish species are potential candidates to be considered for biological control populations of mosquitoes. Tests of half-hour and 24-hour consumption of Culex pipiens (Linnaeus, 1758) larvae by Cnesterodon decemmaculatus (Jenyns, 1842) and Jenynsia multidentata (Jenyns, 1842) were carried out, measuring the standard length, mouth width and weight in individuals of the two species of fishes. In both tests J. multidentata consumed more C. pipiens than C. decemmaculatus, being C. decemmaculatus female consumption higher than male consumption (and equal than both sexes of J. multidentata in the 24-hour test). These results remained unchanged when making comparisons of absolute or relative consumption in the half-hour test, but when consumptions relative to weight were compared no difference between species was found in the 24-hour test. Regression analysis between morphometric variables and weight vs. consumption rates showed low explanatory value for the half-hour test, while in the 24-hour test these variables had higher explanatory value, especially for the mouth width. Finally, a half-hour test was performed over C. decemmaculatus females using C. pipiens and Aedes aegypti (Linnaeus, 1742) larvae and it showed a strong preference for the latter ones. This work allowed us to observe that there are large differences in consumption rates of C. pipiens larvae between the fish species under study in short periods. Differences are attenuated when consumption times are longer and may even disappear when weight is taken into account.
Los mosquitos representan una amenaza para la salud del hombre y de los animales debido a que actúan como vectores de distintas enfermedades. Especies de peces nativos son potenciales candidatos a tenerse en cuenta para control biológico de poblaciones de culícidos. Experiencias de consumo de media hora y de 24 horas por Cnesterodon decemmaculatus (Jenyns, 1842) y Jenynsia multidentata (Jenyns, 1842) se llevaron a cabo con larvas de Culex pipiens (Linnaeus, 1758), midiéndose longitud estándar, ancho de boca y peso en individuos de las dos especies. En ambas pruebas, J. multidentata consumió más C. pipiens que C. decemmaculatus, consumiendo las hembras de esta última especie más que los machos (e igual a ambos sexos de J. multidentata en la prueba de 24 horas de duración). Estos resultados no variaron cuando se compararon tantos consumos absolutos o relativos para las pruebas de media hora, sin embargo cuando se compararon los consumos relativos al peso no se encontraron diferencias entre las especies para las pruebas de 24 horas. Análisis de regresión entre las tasas de consumo versus las variables morfométricas y el peso mostraron poco valor explicativo en las pruebas de media hora de duración, mientras que en las pruebas de 24 horas de duración los análisis de regresión tuvieron un mayor valor explicativo, especialmente con el ancho de la boca. Por último, pruebas de media hora de duración fueron llevadas a cabo exponiendo a hembras de C. decemmaculatus con larvas de C. pipiens y Aedes aegypti (Linnaeus, 1742) observándose una fuerte preferencia por las últimas. Este trabajo permitió evidenciar que las especies de peces en estudio presentan grandes diferencias en las tasas de consumo de C. pipiens en periodos cortos. Estas diferencias se atenuaron cuando las tasas de consumo se prolongaron y hasta llegar a desaparecer cuando el peso se tuvo en cuenta.