Table 4.

Strengths and limitations of US elastography and MR elastography techniques for staging of liver fibrosis

Modality	Implementations	Strengths	Limitations
Ultrasound	1D Transient elastography (TE)	Relatively inexpensive Highly portable Widely available Independently validated worldwide Used by clinicians at point of service Shear wave frequency controlled at 50 Hz Little energy absorption by tissues	Failure and unreliable results due to obesity, narrow intercostal space, ascites Potential classification discrepancies between M, XL, and S probes No anatomic images captured No recording of exact measurement location Narrow applications outside of liver investigation
	Point shear-wave elastography (pSWE)	Permits selection of a ROI on B-mode ultrasound images ROI is saved and may be selected in follow-up studies to permit reliable monitoring pSWE more robust than 1D TE Generates shear waves inside the liver (more robust) Diagnostic performance similar to that of 1D TE Low incremental cost of adding required software to an existing scanner	More expertise required than 1D TE (requires a radiologist or sonographer) Not suitable for point of service Less validated than 1D TE Greater energy absorption by tissue than 1D TE
	Shear Wave Elastography (SWE)	Same strengths as pSWE techniques Fast imaging permits generation of quantitative elastograms Numerous ROIs may be positioned on the elastograms May reduce sampling variability that can occur with 1D TE and pSWE	Same limitations as pSWE Limited availability of this ultrasound system Fewer studies on its diagnostic performance for staging liver fibrosis than 1D TE and pSWE
Magnetic resonance imaging	Magnitude of complex shear modulus	Same hardware and software adopted across MR vendors, which potentially will provide reproducible results High diagnostic accuracy for advanced fibrosis Robust (feasible in larger patients or with ascites) Images a larger proportion of the liver, potentially reducing sampling variability for longitudinal monitoring Incremental cost of hardware and software lower than cost of new 1D TE device Low power output and energy absorption by tissues	Quality may be degraded in patients with marked iron deposition Requires post-processing and offline analysis Limited availability outside of academic centers Some subjectivity in selecting regions of interest Additional time required for positioning the transducer Acquisition with different breatholds Large ROIs not always obtainable due to shear wave attenuation in normal liver
	Complex (G′, G″)	Multifrequency approach permits calculation of elasticity and viscosity	Currently in research domain

Note—G′ = storage modulus. G″ = loss modulus. ROI = region of interest.