*2.2.1 Point shear wave elastography (pSWE): clinical applications for FLLs evaluation*

Relied on ARFI technique, pSWE is available in different US machines and permits real-time non-invasive tissue stiffness assessment during US B-mode examination. Under US guidance, the operator can place the measurement box in any region of the hepatic parenchyma with no vasculature or in an FLL to a maximum depth of 8 cm from the skin plane, as shown in **Figure 2**. The SWV (m/sec) and depth (cm) of the region of interest (ROI) evaluated will be displayed.

Several meta-analysis focused on the performance of SWE in discriminating benign and malignant FLLs [31–33].

#### **Figure 2.** *pSWE measurement in metastasis using Siemens Acuson-Sequoia US system.*

*The Place of Elastography for Liver Tumors Assessment DOI: http://dx.doi.org/10.5772/intechopen.103777*

A meta-analysis performed by Jiao et al. [31] that included 9 prospective studies with a total of 1046 FLLs (malignant 679) showed a pooled sensitivity and specificity of 82.2% (95% CI: 73.4–88.5) and 80.2% (95% CI: 73.3–85.7), respectively. The positive likelihood ratio negative likelihood ratio and diagnostic odds ratio of SWE in differentiating malignant and benign liver lesions were 4.159 (95% CI: 2.899–5.966), 0.222 (95% CI: 0.140–0.352), and 18.749 (95% CI: 8.746–40.195), respectively. The area under the hierarchical summary receiver operating characteristic (HSROC) curve was 87% (95% CI: 84–90). The authors concluded that SWE complementary to the conventional US could be useful in FLL differentiation [31].

Another meta-analysis that included 8 studies with 590 lesions (228 benign and 362 malignant) showed that the cut-off value of SWV was different across studies, ranging from 1.5 to 2.7 m/sec. The sensitivity and specificity were 0.86 (95% CI 0.74–0.93) and 0.89 (95% CI 0.81–0.94). The HSROC curve was 0.94 (95% CI 0.91–0.96) [32].

Also, a recent meta-analysis of pSWE (12 studies) and 2D-SWE (3 studies) showed promising results for FLL evaluation [33]. The data included a total of 1894 FLLs from a large cohort (1728 patients). Comparing the methods, 2D-SWE had slightly higher sensitivity compared with pSWE (84% vs. 82%, P < 0.01) and no significant difference in the specificity for the two modalities (P = 0.18). SWE evaluation was useful for FLL differentiation with a mean sensibility of 0.72 (95% confidence interval [CI]: 0.59–0.83) and a mean specificity of 0.82 (95% CI: 0.43–0.97). The area under the operating curve (AUC) was 0.89 (95% CI: 0.86–0.91). The accuracy of the SWV ratio for the differentiation of benign and malignant FLLs was also assessed. The pooled sensitivity, specificity, PLR, and NLR, of the SWV ratio (FLL to surrounding liver parenchyma) for the differentiation of malignant and benign FLLs were 0.72 (95% CI: 0.59–0.83), 0.82 (95% CI: 0.43–0.97), 4.08 (95% CI: 0.88–18.89), and 0.33 (95% CI: 0.19–0.60), respectively. Using the Fagan plot demonstrated that SWE is fairly effective for FLL differentiation: 82% probability of malignant disease following a positive measurement, and the probability reduced to 18% when a negative measurement occurred [33].

Some published studies regarding FLL characterization using pSWE showed higher SWV in malignant tumors [34], and others showed similar SWV values in benign and malignant tumors [35–38]. The overlapping results can be explained by the level of fibrous tissue in an FLL and the level of vascularization [34].

The studies demonstrated that malignant FLLs are generally stiffer than benign lesions, reporting the following descending stiffness order: Liver metastases > HCC > FNH (focal nodular hyperplasia) > Hemangioma [17, 32, 34, 39]. In the setting of liver cirrhosis, HCC lesions may appear softer than the surrounding liver parenchyma and also softer than other malignant FLLs (metastases and cholangiocarcinoma) [40–42], with SWV values varying from 2.16 ± 0.75 m/s [43] to 3.07 ± 0.89 m/s in the Guo study [44]. SWE assessment of a lesion must be interpreted, considering the patient's clinical background [17, 33].

**Table 1** shows the SWV mean values (m/sec) for different FLLS (HCC, Metastases, HH, FNH, and HA) and the cut-off values (m/sec) for discriminating between malignant and benign lesions obtained by different studies using pSWE for FLL evaluation.

### *2.2.2 Two-dimensional shear wave elastography (2D-SWE): clinical applications for FLLs evaluation*

2D-SWE is another quantitative elastographic technique used in clinical practice to discriminate between malignant and benign lesions in the prostate [46], thyroid [47, 48],


#### **Table 1.**

*Shear wave velocity values (m/sec, range) for FLLs in different studies using pSWE. Cut-off values (m/sec) for discriminating malignant versus benign FLLs.*

breast [49], and FLLs [50–54]. This method allows real-time visualization of a color quantitative elastogram superimposed on a B-mode image. **Figures 3** and **4** show examples of 2D-SWE FLL evaluation implemented on different US devices.

Grgurevic et al. [52] aimed in a recent study to describe the stiffness of the most common benign and malignant FLLs by means of RT-2D-SWE (real-time

*The Place of Elastography for Liver Tumors Assessment DOI: http://dx.doi.org/10.5772/intechopen.103777*

#### **Figure 4.**

*2D-SWE.GE evaluation for a HCC using Logiq E9, GE Healthcare US system.*

2-dimensional share-wave elastography), to analyze the ratio between the stiffness of FLL and surrounding liver parenchyma, and to determine the accuracy of RT-2D-SWE in differentiating benign and malignant FLLs. The authors developed a liver elastography malignancy prediction score (LEMP) for non-invasive characterization of FLLs that enabled correct differentiation of benign and malignant FLL in 96% of patients. This study concluded that RT-2D-SWE could be a reliable method for differentiating malignant from benign liver lesions with a comprehensive approach.

Two other 2D-SWE studies found no significant differences between malignant and benign FLL stiffness [51, 55]. Both studies showed that FNHs were significantly stiffer than HA. Regarding HCC nodules, studies showed 2D-SWE values that varied from19.6 kPa to 44.8 kPa (range 15.8 kPa–97 kPa) [51, 53]. This variability can be explained by many factors, including lesion dimensions and ROI positioning. Additionally, the background liver can influence the diagnostic capability of 2D-SWE [52, 54].
