ABSTRACT
Elasticity imaging methods have been used to study kidney mechanical properties and have demonstrated that the kidney elastic modulus increases with disease state. However, studies in swine suggest that kidney elastic modulus is also affected by hemodynamic variables. A newly emerging method called Shearwave Dispersion Ultrasound Vibrometry (SDUV) offers a tool to determine renal elasticity and viscosity in vivo. The purpose of this study was directed toward evaluating the feasibility of SDUV for in vivo measurements of healthy swine kidney during acute gradual decease of renal blood flow. In this study in vivo SDUV measurements were made on a group of 5 normal swine kidneys at baseline renal blood flow (RBF) and 25, 50, 75 and 100% decrease in RBF. The shear elastic modulus at full baseline was 7.04 ± 0.92 kPa and 3.48 ± 0.20 kPa at 100% decrease in RBF. The viscosity did not change between baseline (2.23 ± 0.33 Pa•s) and 100% decrease in RBF (2.03 ± 0.32 Pa•s). The data from this study indicates that other variables such as local blood flow, pressure and volume as well as method accuracy need to be measured to illustrate the relationship between shear elasticity and viscosity associated with acute kidney processes.
Métodos de imágenes de elasticidad se han utilizado para estudiar las propiedades mecánicas renales y han demostrado que el módulo elástico de los riñones del aumenta con el estado de enfermedades renales. Sin embargo, estudios en cerdos sugieren que el riñón módulo elástico también se ve afectada por las variables hemodinámicas. Un método emergente llamado Shearwave Dispersion Ultrasound Vibrometry (SDUV) ofrece una herramienta para determinar la elasticidad y la viscosidad renal. El propósito de este estudio se dirige a la evaluación de la viabilidad de SDUV para mediciones las propiedades viscoelasticas del riñón saludable durante variación aguda del flujo sanguíneo renal. En este estudio el método SDUV se realizó en un grupo de 5 riñones porcinos normales al inicio del flujo sanguíneo renal (RBF) basal y 25, 50, 75 y 100% de disminución en el RBF. El módulo elástico basal fue de 7,04 ± 0,92 kPa y 3,48 ± 0,20 kPa a 100% de disminución del RBF. La viscosidad no cambió entre el momento basal (2,23 ± 0,33 Pa • s) y el 100% de disminución del RBF (2,03 ± 0,32 Pa • s). Los datos de este estudio indican que variables tales como el flujo local de sangre, la presión y el volumen así como el método exactitud deben ser medidos para ilustrar la relación entre la elasticidad y la viscosidad asociada con los procesos renales agudos.
ABSTRACT
Elasticity imaging methods have been used to study kidney mechanical properties and have demonstrated that the kidney elastic modulus increases with disease state. However, studies in swine suggests that kidney elastic modulus is also affected by hemodynamic variables. A newly emerging method called Shearwave Dispersion Ultrasound Vibrometry (SDUV) offers a tool to determine renal elasticity and viscosity in vivo. The purpose of this study is directed toward evaluating the feasibility of SDUV for in vivo measurements of healthy swine kidney during acute gradual decease of renal blood flow. In this study in vivo SDUV measurements were made on a group of 5 normal swine kidneys at baseline renal blood flow (RBF) and 25, 50, 75 and 100% decrease in RBF. The shear elastic modulus at full baseline was 7.04 ± 0.92 kPa and 3.48 ± 0.20 kPa at 100% decrease in RBF. The viscosity did not change between baseline (2.23 ± 0.33 Pa·s) and 100% decrease in RBF (2.03 ± 0.32 Pa·s). The data from this study indicates that other variables such as local blood flow, pressure and volume as well as method accuracy need to be measured to illustrate the relationship between shear elasticity and viscosity associated with acute kidney processes.
ABSTRACT
This paper presents a study of the stress field forming of sector array transducers for vibro-acoustography applications. The system point-spread function (PSF) is given in terms of the dynamic radiation stress exerted on a point target by a dual ultrasound beam with slightly different frequencies. The radiation stress is calculated by assuming that the resulting ultrasound beam is a plane wave. The stress is proportional to the product of the velocity potential of each incident ultrasound beam. The beamforming and stress field forming of sector array transducers are analyzed through linear acoustics. An expression for the velocity potential produced by sector array transducers is derived. The vibro-acoustography PSF is evaluated numerically. A comparison between the PSF of a sector array and a confocal transducers is presented. The compared characteristics of the PSF are sidelobe levels, transverse, and in-depth spatial resolution. Indeed, one motivation to study sector transducers is the fact the depth-of-field of these transducers should be smaller than that of same size confocal transducers. An experimental setup was used to validate the theoretical PSF of sector array transducers. Results show that the measured PSF is in good agreement with the theoretical predications. Vibro-acoustography images of a breast-phantom by both transducers are presented and discussed.