###### Abstract
Recently, normal values of quantities that were measured by SWE of the liver have been summarized [16] and the official American Gastroenterological Association Institute (AGAI) Guidelines on the Role of Elastography in the Evaluation of Liver Fibrosis have been published [17]. Unfortunately, despite the title of the AGAI guidelines paper, it focuses only on the role of VCTE in the evaluation of liver fibrosis, ignoring the fact that the term elastography covers all of the technologies mentioned above. This approach might indicate to the reader that elastography equates only to one commercially available equipment, the Fibroscan(r), manufactured only by Echosens, which implements VCTE. This is not true. The review also classifies VCTE as an imaging-based fibrosis assessment, which it is not. VCTE as implemented on the Fibroscan(r) does not display an anatomical image, although, interestingly, General Electric has recently announced that the Echosens technology has been integrated into its conventional ultrasound system. Guidelines were introduced in part because of the extremely rapid spread of the use of elastography systems in the clinic once the technology had become commercially available. It is worth mentioning that new methods can be clinically valid and yet are not always (or are rarely) supported by the highest ranking scientific evidence, namely by randomized trials. Often these innovations are so obviously of benefit that randomized controlled trials comparing them with older, less safe or less effective techniques could be deemed unethical. Elastography can be applied to examine almost all organs in the human body. We refer to a variety of clinical papers with practical applications in the thyroid [9; 18; 19; 20; 21; 22], pancreas [13], prostate [10; 23; 24], and endoscopic (endorectal) ultrasound applications [25; 26; 27] including the endobronchial use of elastography [28]. The current special issue of Applied Sciences deals with a wide range of elastography methods from many different points of view including open issues of the liver, thyroid, and magnetic resonance elastography (MRE), as well as applications in selected patient groups, e.g., pediatric patients. MRE is an alternative to ultrasound elastography which has been described in a number of reviews, including [29; 30; 31]. The modern method was originated by the Mayo Clinic in 1995 [32] and, like ultrasound elastography, the technique has evolved with a number of technical variations. As with ultrasound elastography, MRE begins by measuring tissue displacement as a function of time and space. Variations exist both in terms of the motion encoding and displacement readout strategies [33] and with respect to algorithms that are used to reconstruct the viscoelastic properties from the measured displacements [34]. As with ultrasound elastography, considerable technical development continues to take place in a research context. One difference to ultrasound elastography is that although quasistatic MRE has long existed (based on a technique known as MR tagging [35]), and it provides cardiac strain assessment [36; 37], it is dynamic methods that emerged into widespread clinical use, and 3D-SWE is the ultrasound elastography method that is the closest equivalent of most MRE. However, although acoustic radiation force has been tried as a method of generating displacement, MRE routinely employs harmonic vibrations that are generated by a relatively complex external MR-compatible mechanical device. The clinical use of MRE is less widespread than that of ultrasound elastography,which is likely to be due to a combination of factors, including the high entry-cost, the more limited regulatory approval, the relatively few manufacturers, the relative difficulty of patient set-up, the lack of system portability, and the relatively long examination time.