Near field shear wave elasticity imaging with high frequency single element transducers

Abstract

Shear wave elasticity imaging (SWEI) has emerged as a promising technique for tissue stiffness quantification by measuring shear wave speed (SWS) propagating within tissue. High frequency (>=40MHz) ultrasound imaging, which provides higher spatial resolution and better sensitivity for detecting shear wave (SW) displacements, is suitable for pre-clinical small animal studies. In our previous setup, the region of interest (ROI) is imaged through mechanical scanning with single element transducers. In this case, the push transducer is fixed while the imaging transducer performs scanning. Due to attenuation and diffraction, the SNR and accuracy decrease with distance. The speed calculation map tends to be incorrect for large ROI. Thus, we hypothesize that by adopting near field SWEI (i.e., detection transducer and imaging transducer are kept close to each other), SWEI resolution and accuracy can be improved. The imaging system consists of two single element transducers: a 20MHz push transducer for generating acoustic radiation force and inducing shear wave, and a 40MHz transducer for imaging shear wave propagation. The two transducers are fixed by a setup where the lateral distance between the focal points of the two transducers is 0.5 mm. Thus, SWS is calculated as the SW propagation distance divided by the SW arriving time. The B-mode image and the corresponding SWS map of a gelatin phantom with a 2 mm inclusion were acquired. The contrast-to-noise ratio is 1.45 for the previous setup, and 2.0 for near field setup. Ex vivo results from a swine liver also demonstrate advantages of the proposed approach.