Ultrasonic tracking of shear wave propagation in tissue is a key step in the estimation of tissue shear modulus in several methods of ultrasound elastography. Tracking of shear wave propagation at multiple locations is used to estimate shear wave velocity or phase. We have shown that ultrasound speckle can contribute a significant variance to these measurements, as a consequence of the independent scatterer sets at each location. Preliminary data indicates that techniques which rely on tracking at a single spatial location are relatively immune to this noise source and hold the potential for highe spatial and modulus resolution. Minimizing speckle noise reduces the need for spatial averaging and allows shear modulus or velocity to be estimated with better precision over a smaller sample volume. We hypothesize that, for a given spatial resolution requirement, methods that track at a single location (STL) produce lower modulus estimates than those that track at multiple locations (MTL). We propose experiments to compare the variance of modulus estimates obtained by STL and MTL under matched conditions of SNR, ultrasound parameters, and shear modulus. Measurements will be performed in tissue mimicking phantoms and in a rat model of liver fibrosis to establish the magnitude of noise reduction under in vivo conditions of increasing tissue heterogeneity.
Ultrasound elastography is a technology for imaging the stiffness of tissues, and can provide important diagnostic capability for many diseases not well detected by conventional imaging modalities. We propose to show that a specific method of ultrasound elastography can produce higher quality, lower noise stiffness images, by suppressing the effect of speckle inherent in ultrasound images. The goal of this proposal is to quantify the improvement in image quality by this technique in tissue mimicking phantoms and in rodent liver under healthy and diseased conditions.
