Single- and Multiple-Track-Location Shear Wave and Acoustic Radiation Force Impulse Imaging: Matched Comparison of Contrast, Contrast-to-Noise Ratio and Resolution

Abstract

Acoustic radiation force impulse (ARFI) imaging and shear wave elasticity imaging (SWEI) use the dynamic response of tissue to impulsive mechanical stimulus to characterize local elasticity. A variant of conventional, multiple track location SWEI (MTL-SWEI), denoted single track location SWEI (STL-SWEI) offers the promise of creating speckle-free shear wave images. This work compares the three imaging modalities using a high push and track beam density combined acquisition sequence to image inclusions of different sizes and contrasts. STL-SWEI is shown to have significantly higher CNR than MTL-SWEI, allowing for operation at higher resolution. ARFI and STL-SWEI perform similarly in the larger inclusions, with STL-SWEI providing better visualization of small targets ≤2.5 mm in diameter. The processing of each modality introduces different trade-offs between smoothness and resolution of edges and structures; these are discussed in detail.

Plane-Wave Imaging Improves Single-Track Location Shear Wave Elasticity Imaging

“…1b ). The another approach is to create elastograms by only translating the push beams with a fixed tracking beam [15]. Shear waves attenuates less in the first approach because the distance between push and track beams is smaller.…”

“…We can potentially reduce the number of push beams in STL-SWEI by keeping tracking location fixed while translating the push beams as mentioned in [15], but the increasing distance between the push and tracking beams would increase shear wave attenuation noticeably. For example, the second and the third push beams in Fig.…”

“…We defined SNR e as follows [15]: $$SN{R}_e=\frac{\mu }{\sigma },$$ where μ represents the mean SWS in an elastically homogeneous region of the tissue, and σ represents the variance of SWS values within the region.…”

“…The stiffness values reported by the manufacturer of the calibrated phantoms differed from elastographic measurements and are well reported in the literature [15], [24]; therefore, we used the Virtual Touch Quantification (VTQ) method implemented on the Siemens Acuson 300 scanner (Siemens-Acuson, Mountain View, CA, USA) to provide independent estimates of the SWS of the phantoms. We performed all measurements on the Siemens scanner with a 8 MHz 9L4 probe.…”

“…Hollender et al [15] were the first to develop STL-SWEI based on plane wave imaging, which they implemented on a partially parallel receive ultrasound system. Our approach differs from this early work in two ways.…”