**2. Ultrasound and elastographic evaluation of parathyroid disease**

#### **2.1 2B-ultrasonography evaluation**

Gray scale ultrasound (US) has become a very accessible imaging technique in the endocrinology field, especially for thyroid and parathyroid evaluation, becoming the gold standard in these domains. The noninvasive character, the low cost, the repeatability, and especially the real-time assessment are some of the many advantages of this imagistic technique [43, 44].

The ultrasound evaluation of both thyroid and parathyroid glands involves a large ultrasound framework. Anatomical structures must be well observed and identified both in longitudinal and transverse modes [23, 45, 46]. Additional auxiliary techniques, including the rotation of the head to improve the ultrasound framework on the neck structures or swallowing, could improve the correct identification of anatomical structures and of ectopic parathyroid glands [45].

The sensitivity of ultrasound identification of parathyroid tumors varies from 70 to 80% [47] with higher positive identification for parathyroid hyperplasia 30–90% [48], but precision is dependent on the location and size of the tumor [16], by body habitus and gland morphology, and by the experience of the evaluator [46]. Increased false-positive ultrasound results are caused by structures mimicking parathyroid adenomas such as thyroid nodules, lymph nodes, muscles, vessels, and esophagus [16].

#### *2.1.1 Adding color Doppler mode*

Parathyroid adenomas typically present a peripheral vascular rim and an abnormally increased blood flow than the thyroid gland [49]. Therefore, by adding color Doppler mode in the ultrasound evaluation can increase the accuracy and sensitivity of ultrasound by 54% [50].

#### **2.2 Ultrasound elastography: description and method**

Elastography can be a helpful complementary imaging technique in the evaluation of parathyroid disease, adding additional information on tissue stiffness.

Neoplastic, fibrous, or atherosclerotic transformation in tissues is translated by tissue stiffness in elastographic evaluation [38]. The development of neoplastic tissue can be identified even in early stages, as from the physiopathological point of view, we can have an increased production of connective tissue, changes in cell density, and increased blood flow, all these changes determining a change in the tissue matrix, thus a change in the elasticity of the tissue [2]. Elastography can identify the differences between benign and malignant tissues from the early development of the disease, offering high sensitivity and resolution for deep-situated structures [51].

Elastography evaluates tissue stiffness by applying an external stress and calculating the distortion degree. The distortion in elastography is obtained by applying external pressure, manually or via ultrasound transducer. In acoustic radiation force impulse (ARFI), the distortion is induced by using crossing deformation, with converged ultrasound beams or by emitting of short duration focused acoustic beam that will generate shear waves that diffuse transversally through the tissue [52]. It thus determines qualitative information about tissue stiffness through color maps and color codes and quantitative information through numerical values [38].

*Role of Elastography in the Evaluation of Parathyroid Disease DOI: http://dx.doi.org/10.5772/intechopen.105923*

An elastographic evaluation follows a 2B-mode ultrasound evaluation of the parathyroid glands. It can be performed in all patients; it is cost-efficient and adds valuable information. The elastography module is available on multiple ultrasound machines such as Aixplorer Mach 30 machine (SuperSonic Imagine, France), Philips, Fujifilm, Hitachi Preirus (Hitachi Medical Corporation, Tokyo, Japan) machine.

Elastography on the parathyroid is performed using a linear, high-resolution transducer of 15–4, respectively, 18–5 MHz chosen depending on the clarity of the image, profound parathyroid glands being evaluated with 15–4 probe, obtaining better images. The patient was examined in a supine position with neck hyperextension, maintaining regular superficial breathing. The following parathyroid parameters are to be evaluated—localization, form, parathyroid dimensions, and total volume of the gland.

Two elastographic procedures will be discussed in the chapter—2D shear wave elastography and real-time elastography.

The procedure depends on the type of elastography performed, for example, for shear wave elastography, the examiner must maintain a precise adherence for minimal 6 seconds to the probe on the examined area, with careful attention not to apply any manual compression, permitting the transducer to induce the acoustic vibrations in the parathyroid tissue. After image stabilization, a real-time elastogram will overlap on the B-mode image, obtaining an elastogram or color map (**Figure 1**). Afterimage stabilization, quantitative measurements can be performed on a frozen image.

Quantitative information, described as the elasticity index (EI) obtained on the frozen elastogram image, using a quantification box (Q-box), placed in the regions of interest (ROI). After software computing evaluates the mean SWE, minimum SWE, maximum SWE, and standard deviation, the elasticity parameters are displayed. All measurements are numerically expressed in kilopascals (kPa). As there is no scale setting recommended for the parathyroid examination, we recommend using a thyroid scale (0–100 kPa).

Another elastographic technique that requires external pressure in order to induce a deformation of the examined tissue that is further quantified by the machine software. This method is called real-time elastography (RTE) or strain elastography (SE).

#### **Figure 1.**

*(a) 2B-mode ultrasound evaluation of parathyroid adenoma, with complementary color Doppler mode; (b) Elastogram of parathyroid adenoma overlying B mode image and color map of tissue elasticity, with Q-box on the region of interest and quantitative evaluation [53] .*

The examiner must apply controlled external pressure, usually manually pressure, which determines a mechanical deformation. An elastographic map is overlayed on the 2B greyscale that is displayed as a color map (red for liquid, green for soft tissue, blue for hard tissue), permitting the examined to obtain qualitative information about tissue stiffness for the examined area (**Figure 2**) [38].

Semiquantitative values can be obtained using strain elastography by comparing tissue strain in the region of interest (ROI) of the targeted tissue with another adjacent tissue, calculating a strain ratio (SR) ratio.
