Hepatic fibrosis is final results of a wide variety of types of liver injury and is a consequence of all chronic liver diseases and progresses more or less rapidly towards cirrhosis, and finally cancer.
In terms of the tools used to quantitate fibrosis today, there are three kinds of tools; biochemical markers, conventional imaging, and functional imaging such as elastography (E) or stiffness imaging. Recent imaging tools for evaluation of hepatic fibrosis are US based techniques, MR based techniques, and perfusion imaging.
US Elastography (USE) is classified into strain-based E and SW-based E. Strain-based E is subclassified into Static USE (Manual compression of the tissue) and Quasi-static USE (Physiologic vibrations (heartbeat, blood vessels pulse). SW-based E is subclassified into 1D such as fibroscan (Echosens), Point E such as virtual touch quantification (Siemens). ElastPQ (Philips) and 2D SWE such as supersonic shear imaging (Supersonic Imagine), and shear wave elastography (GE, Toshiba)).
For the liver, USE is divided into 2 categories quasi-static E and shear wave based imaging. Quasi-static E is not popular. Shear wave based imaging is subdivided into two types based on generation method of shear wave: Controlled external vibration with a vibrator and acoustic radiation force impulse. Transient elastography is using mechanical push, and both ARFI imaging and supersonic shear wave elastography are using ARFI. Strengths of 1D SW-based elastography are the most extensively investigated technique with high portability. Limitations are no B-mode imaging, high technical failure rate (2.4-9.4%) and narrow applications outside of liver investigation. Strengths of point SW-based elastography are low technical failure rate (< 1%), very short acquisition time and extensively investigated technique. Limitations are small ROI and greater energy absorption. Strengths of 2D SW-based elastography are larger ROI, which may reduce sampling variability, real time and 2D elastogram. Limitations are 2-3% technical failure, longer acquisition time, hyper sensitivity for tissue attenuation and motion. Then, which elastography technique should be used? Or how to choose? USE is better than MRE in terms of convenience, acquisition time, cost, and availability. But, MRE is better than USE in terms of sample volume, technical failure, and multiparametric evaluation. Limitations of elastography are many confounders in stiffness measurements, such as inflammation, portal pressure, right heart pressure, and cholestasis and so on, and both techniques of USE and MRE need further standardization. Therefore, other comprehensive imaging techniques are needed, such as DWI or DCE ñUS or MR.
In Summary, liver stiffness is determined by matrix deposition (fibrosis) and pressure change (hydrostatic, osmotic). Hepatic fibrosis (HF) is a consequence of all chronic liver diseases and progresses towards cirrhosis and finally cancer. Noninvasive diagnosis and staging is important clinical issue for hepatic fibrosis which is reversible. Elastrography is clinically acceptable for the prediction of liver fibrosis (?F2) and confounders of stiffness measurement (intercostal approach to right lobe (S7/8), 1-3 cm below the liver capsule, biologic confounders can change stiffness values, fasting at least 2 hours, breath-hold at expiration). Elastography is one of important noninvasive methods to quantify HF more sensitively and objectively. USE is the first line examination for the assessment of HF. MRE is the second line examination, especially in cirrhosis. To avoid confounders of liver stiffness, comprehensive other imaging exams are needed.