**1. Introduction**

Elastography has surfaced in the early 1990s as a new noninvasive technique capable of offering new diagnostic opportunities for malignant diseases [1]. Initially, considered for superficial organs such as the breast [2, 3] or thyroid [4], elastography became to have an upward trend by covering most of the parenchymatous organs from the digestive system [5]. Over the years, new elastography techniques were integrated into ultrasound devices trying to create a foundational stage and to develop new standards by enhancing the spectrum of the available techniques [6]. However, the pancreas still stands as a challenge as it is hard to reach by elastography measurements.

When compared with other organs, the pancreas has by far a more limited number of studies. Due to its' retroperitoneal position, transabdominal ultrasound elastography may be rather difficult to be properly executed, and it may lead to an inaccurate or imprecise examination. The evolving field of evidence-based medicine has then focused on more precise imaging techniques used for the pancreas examination such as endoscopic ultrasound (EUS) [7]. This enhanced the spectrum of available techniques that might enable pancreatic disease diagnosis and lead to a pathbreaking development along with the endoscopic ultrasound fine-needle aspiration

(EUS-FNA) implementation as a standard and necessary method [8]. While EUS-FNA has laid the grounds for the current therapeutic techniques for pancreatic disease complications, it has also contributed to the elastography imaging, mainly by providing a pathological result, which is helped as the standard method for the elastography evaluation.

In the evolutionary steps of elastography, the first introduced method was strain elastography [9]. This technique measures the strain developed during external pressure, and its' results are considered inversely related, meaning that the tissue stiffness will be softer if the strain will be greater. The manual compression is acknowledged as a limitation in a pancreatic setting thus, it requires strain to be obtained from nearby structures. However, several limitations are encountered, as measurements may be obtained usually at the level of the pancreatic body, provided that no vascular elements are in the elastography region of interest.

Further on, other elastography techniques have tried to enlarge the current spectrum and to extend elastography to a more precise tool. Shear-wave elastography [10], which is based on a different principle, was then proposed to outcome the flaws of strain elastography. By generating shear waves from the transducer, pancreatic tissue is measured and its stiffness becomes more evident as the shear wave velocity is faster. This technique was recently introduced to a EUS setting and might strengthen the available data [11].

As part of ongoing technical developments, artificial intelligence methods have also been introduced in pancreatic elastography assessment [12]. Their potential is nonetheless beneficial, as they may avoid the human factor in some situations, thus covering new grounds in pancreatic elastography.

With this chapter, we try to explore the potential of elastography in different pancreatic diseases and try to answer some of the available questions about the future of elastography.

## **2. Endoscopic ultrasound elastography (EUS-E) techniques**

Probably the major outcome of EUS-E is that it may reach structures that are rather hard to examine, such as the pancreas or adjacent lymph nodes. As mentioned above, there are two elastography techniques available on EUS systems that have been tested on pancreatic diseases: strain elastography and the recently introduced shear wave method [11].

#### **2.1 Strain elastography**

This technique was first considered a qualitative technique, with the elastography region of interest (ROI), which covered the ultrasound image showing a pattern of green and blue colors in correspondence to the tissue stiffness [12, 13]. Green areas were considered benign, whereas blue areas were related to a possible malignant tissue. Since this method requires the transducer to be placed near the examination tissue, it is recommended to cover up at least 50% of the targeted tissue. Also, since the compression will be performed with the echoendoscope, it is important not to produce too strong compressions, so that reproducible types of elastograms may be achieved. The targeted lesion should be in the center of the transducer so that the elastography image should cover it and avoid adjacent tissue as much as possible [14, 15].

#### *Endoscopic Ultrasound Elastography: New Advancement in Pancreatic Diseases DOI: http://dx.doi.org/10.5772/intechopen.103890*

Semiquantitative analysis was introduced by determining strain ratio [16, 17]. This concept allows the practitioner to select an ROI by highlighting a round-shaped area in the targeted tissue and a smaller ROI within the nearby normal tissue, which might be either the normal parenchyma or the gastrointestinal tract wall. Then, the strain ratio has resulted from the two selected areas, with a value displayed by the ultrasound software.

Another method is represented by the strain histogram, which is based on the hue histograms averaged over several compression cycles [18, 19]. The results are usually described by mean values and standard deviation, as well as other parameters characteristic to histograms (Kurtosis, skewness, etc.). This strain histogram will cover a scale of 256 colors, being now embedded in the software of most ultrasound systems.

#### **2.2 Shear-wave elastography**

Shear-wave elastography (SWE) also became recently available in the EUS setting [11]. While the concept of SWE is similar to strain elastography, it does not use a transducer to create pressure, but it creates an elasticity map by measuring shear wave parameters. Directed by the ultrasound beam, the tissue is targeted by a perpendicular "push-pulse," which generates shear waves. SWE is capable of providing direct stiffness measurements, which are translated either in kilopascal (kPa) or meter/second (m/s). This technique might be easier to use, as it may be performed much easier, and most of all since will directly provide quantitative values. However, it will require establishing cutoff values for every organ, which will be examined.
