Artifacts in liver stiffness evaluation

Overview of artifacts in liver shear wave elastography

The use of shear wave elastography techniques proves valuable in providing qualitative and quantitative elasticity maps of the liver. There are, however, common disturbances that can affect the tissue measurements of stiffness. Image artifacts, signals that appear present on the image but are not present in the body, can result in overestimation, underestimation, and highly variable calculations of tissue stiffness maps. Several artifacts can influence stiffness measurements for most techniques, most notably ultrasound-based techniques. These include:

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  Poor acoustic windows that result in both limited push and tracking penetration and cause high variability in elasticity measurement and rib or lung shadowing, which produce further instabilities in elasticity values. Poor signal-to-noise ratio in the shear wave data or the resultant shear wave speed reconstructions is commonly reported on commercial systems through quality metrics and images.

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  Cardiac pulsatility artifacts that result from both the creation of natural shear waves from a high heart rate and the presence of pulsating vessels near the region of interest.

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  Liver boundary, or Glisson capsule, artifacts due to interactions with portal vessels and the distortion of shear wave motion around the liver capsule.

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  Tissue viscosity that causes both vibration-frequency dependent shear wave speeds, especially when comparing measurements between modalities, and overestimation bias due to reconstruction assumptions of pure elasticity.

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  Tissue nonlinearity such that stiffness changes nonlinearly with strain due to extracellular matrix heterogeneity and is underestimated when calculated with linear assumptions.

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  Motion artifacts due to patient motion and natural motion from breathing.

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  Shear wave reflection artifacts due to stiffness gradients within the liver.

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  Nonperpendicular probe placement that results in nonlinear signal decay and liver stiffness overestimation.

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  Compression with the probe/nonlinear tissue response.