# Ultrasound Elastography: Methods, Clinical Applications, and Limitations: A Review Article
## 5 Clinical Applications of Ultrasound Elastography
### Breast
#### 5.3.1 Elastography Techniques in Breast Disease Diagnosis  
Breast cancer screening is usually performed using mammography and ultrasound scans (specifically B-mode US), but both have shown some faulty limitations in the image, such as poor specificity in B-mode and false-negative results in the mammography of dense breasts. However, since the development of USE, it has served as an additional complementary tool to improve the assessment of breast lesions in a non-invasive manner by evaluating the stiffness levels of the mass. Comparative studies have demonstrated that USE exhibits superior accuracy in detecting and determining the extent of breast lesions, regardless of whether they are cancerous or non-cancerous, with a specificity of 95.1% compared to mammography [99]. Radiologists found that the additional usage of USE alongside B-mode US and mammography aids in the diagnostic improvement of the scans, helping with the decision of the appropriate category of the BI-RADS (Breast Imaging Reporting and Data System) categories, which range from category 1 (not cancer) to category 6 (high likelihood of cancer). Category 0 means more tests are needed. Mammogram reports also include four categories for breast density, utilizing both shear wave imaging and strain elastography as their primary USE techniques, but also depending on three main parameters: the Tsukuba score, the EI/B-mode ratio (also called the width or length ratio), and the strain ratio (the fat-to-lesion ratio, FLR) [100]. The Tsukuba score is a five-point scale that visually grades the stiffness of a mass or lesion and possesses high detection accuracy. This makes it easy to distinguish between benign and malignant tissues. The system computes the score based on lesion stiffness relative to the surrounding tissue stiffness. The tissue score is directly proportional to the degree of malignancy; therefore, the higher the score, the more malignant the lesion is. Score 1 shows a lesion with less or equal stiffness to the background tissue; score 2 depicts that the lesion has mixed areas of stiffness; in score 3, the lesion is stiffer than the background tissue and smaller on the elastogram than in B-mode; score 4 shows that the lesion is stiffer than the background tissue and is of equal size on the elastogram compared to B-mode; in score 5, the lesion is stiffer than the background tissue and is of larger size on the elastogram than in B-mode [14]. See Figure 4.  
The EI/B ratio describes a ratio where the size of the lesion is measured on the elastogram image and the B-mode image and then divided by each other. Given that benign lesions appear smaller on the elastogram than in B-mode and malignant lesions are depicted larger on the elastogram than on the B-mode scan, this ratio incorporates findings from both B-mode and the elastogram. The EI/B-mode ratio shows great promise in the differentiation between malignant and benign masses, given its outstanding sensitivity and specificity of 100% and 95%, respectively [104; 105]. Since fat has a constant elastic modulus over a plethora of compressions, the strain ratio ends up being a semi-quantitative measurement that reflects the ratio of the strain in mass to the strain in subcutaneous fat to reflect the relative stiffness of the lesion rather than the absolute tissue stiffness. Researchers have conducted multiple studies of breast lesions using the EI/B-mode ratio and the strain ratio. Radiologists found that pooled sensitivity and specificity were acceptable for the EI/B-mode ratio (98% and 72%, respectively) and strain ratio studies (88% and 83%, respectively) [106]. A quantitative measurement of the shear wave velocity (also known as Young's modulus) in a mass is obtained in shear wave imaging. To obtain a high-quality SWE image, gaining an adequate gray-scale image is necessary before switching to the SWE mode in order to characterize breast lesions correctly [16; 99]. The most commonly used parameters included a variety of quantitative elasticity values, such as mean and maximum stiffness.