On System-Dependent Sources of Uncertainty and Bias in Ultrasonic Quantitative Shear-Wave Imaging

Abstract

Ultrasonic quantitative shear wave imaging methods have been developed over the last decade to estimate tissue elasticity by measuring the speed of propagating shear waves following acoustic radiation force excitation. This work discusses eight sources of uncertainty and bias arising from ultrasound system dependent parameters in ultrasound shear wave speed (SWS) measurements. Each of the eight sources of error are discussed in the context of a linear, isotropic, elastic, homogeneous medium, combining previously reported analyses with Field II simulations, full-wave 2D acoustic propagation simulations and experimental studies. Errors arising from both spatial and temporal sources lead to errors in SWS measurements. Arrival time estimation noise, speckle bias, hardware fluctuations, and phase aberration cause uncertainties (variance) in SWS measurements, while pulse repetition frequency and beamforming errors, as well as coupling medium sound speed mismatch, cause biases in SWS measurements (accuracy errors). Calibration of the sources of bias is an important step in the development of shear wave imaging systems. In a well-calibrated system, where the sources of bias are minimized, and averaging over an ROI is employed to reduce the sources of uncertainty, a SWS error < 3% can be expected.

Strain sonoelastography of inflammatory myopathies: comparison with clinical examination, magnetic resonance imaging and pathologic findings

“…15 Shear wave does not allow sufficient elastogram in proximal thigh muscles, which are the most commonly involved site of IM. 12,[16][17][18][19] Although IM have been previously studied using conventional ultrasonography and MRI, there are only a few studies in the literature that have attempted to use SSE in IM. 12,20 Furthermore, there are no published data available for the pathologic correlation of myositis including muscle stiffness.…”

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

“…Specifically, pSTL-SWEI estimates of shear modulus agree more with those measured with VTQ than the nominal values. Differences between the VTQ measurements and those made with STL-SWEI, MTL-SWEI, and pSTL-SWEI could be due to differences in the frequency content of the shear wave [29], push F-number, transducer, and system dependent variations [30]. …”

Considerations in the application of two dimensional shear wave elastography in muscle

“…Generation and measurement of shear waves differs between manufacturers and these factors have been found to provide significant difference in shear wave speeds in identical mediums . Also dependent on the manufacturer is how the units of elasticity are displayed, with 2D‐SWE measurements being expressed in units of Young's modulus (kPa) or shear wave speed (m/s) . With magnetic resonance elastography typically reporting shear modulus also in kPa, clarity of reported units is important …”

“…5 An alternative to a mechanical push is the use of an acoustic radiation force impulse (ARFI) to generate shear waves. 23 ARFI may be used to produce a single average shear wave speed within a typically small (<10mm 2 ) region within a B-mode image (point shear wave, p-SWE). 24 Alternatively, a 2D-SWE elastogram may be acquired by using multiple ARFIs across the beam width and focused at varying depths.…”

“…6,12,15,28 The Radiological Society of North America (RSNA) and the Quantitative Imaging Biomarker Alliance (QIBA) established an elastography committee in 2011, to standardise techniques for quantitative elastography, with preliminary focus on liver fibrosis assessment. 23,29 If absolute 2D-SWE values are to be used in the assessment of musculoskeletal disorders, issues regarding variability between machines, probes, technical settings and technique need to be explored.…”