Resolution of axial shear strain elastography

Abstract

The technique of mapping the local axial component of the shear strain due to quasi-static axial compression is defined as axial shear strain elastography. In this paper, the spatial resolution of axial shear strain elastography is investigated through simulations, using an elastically stiff cylindrical lesion embedded in a homogeneously softer background. Resolution was defined as the smallest size of the inclusion for which the strain value at the inclusion/background interface was greater than the average of the axial shear strain values at the interface and inside the inclusion. The resolution was measured from the axial shear strain profile oriented at 45 degrees to the axis of beam propagation, due to the absence of axial shear strain along the normal directions. The effects of the ultrasound system parameters such as bandwidth, beamwidth and transducer element pitch along with signal processing parameters such as correlation window length (W) and axial shift (DeltaW) on the estimated resolution were investigated. The results show that the resolution (at 45 degrees orientation) is determined by the bandwidth and the beamwidth. However, the upper bound on the resolution is limited by the larger of the beamwidth and the window length, which is scaled inversely to the bandwidth. The results also show that the resolution is proportional to the pitch and not significantly affected by the axial window shift.

Real-time quasi-static ultrasound elastography

“…A more direct way to visualize these patterns is by the axial-shear strain, i.e. the lateral gradient of axial displacement [78,[104][105][106][107], or indeed some combination of axial-and lateral-shear strain [108,109].…”

A 2D strain estimator with numerical optimization method for soft-tissue elastography

“…u x and v y are the lateral strain and axial strain, respectively, and estimated strain directly obtained by NOMPA is denoted as NOMPA-I. The shear strain can be obtained by the other two first order partial differentials u y and v x , denoted as e xy ¼ 0:5ðu y þ m x Þ [18][19][20][21]. The other two components u and v are passed through Savitzky-Golay (SG) smoothing and differentiation filters [22,23] and then the lateral and axial strains can also be obtained.…”

On the Advantages of Imaging the Axial-Shear Strain Component of the Total Shear Strain in Breast Tumors

“…This is due to the well-known US limitation that the estimation of motion along the direction of the US beam axis is significantly more precise than estimation of the motion across the US beam axis. Therefore, the relatively inferior image quality of the lateral component estimate $(\frac{\partial \mathrm{u}}{\partial \mathrm{y}})$ was seen as the primary practical reason for developing ASSE (ThitaiKumar et al 2006, 2007, 2007a, 2008, 2011, Chen et al, 2010, Garcia et al 2011, Xu et al 2010, Varghese 2011). …”