Method principle and evaluated parameters
Shear wave elastography (Shear wave elastography, SWE) is characterized by high reproducibility and provides the physician with objective quantitative data. The ultrasound transducer generates laterally propagating shear waves passing through the area of interest. The system analyzes their behavior and calculates stiffness (stiffness).
The result is displayed on the monitor as a color or black-and-white map, which is overlaid on top of a standard grayscale B-mode scan.
Key parameters measured by the diagnostician:
- Quantitative elasticity index expressed in kilopascals (kPa).
- The ratio of the size of the altered stiffness zone on the elastogram to the size of the lesion visualized in B-mode.
Differential diagnosis of tumors
Stiffness analysis is an essential tool for differentiating between benign and malignant processes.
- Benign lesions and healthy tissues are characterized by high elasticity and remain relatively soft. Their values typically do not exceed 80 kPa.
- Malignant tumors possess high stiffness.
A characteristic sign of invasive carcinoma is the formation of a dense zone whose area exceeds the visible boundaries of the anomaly on baseline B-mode. This phenomenon is believed to be caused by a pronounced stromal reaction associated with the development and invasion of the tumor node.
Clinical and prognostic significance
The introduction of SWE into clinical practice significantly increases the specificity of ultrasound examination. According to the multi-center BE1 study, ultrasound specificity increased from 61.1% to 78.5%. This allows for more accurate differentiation of neoplasms and avoids prescribing unjustified invasive procedures (biopsies).
In addition to diagnostics, tissue stiffness has prognostic value. It has been proven that ultra-stiff malignant nodes correlate with high process aggressiveness. This is manifested by a high grade of malignancy, a tendency to metastasize to regional lymph nodes, and resistance to neoadjuvant chemotherapy.
For example, on the elastogram of invasive ductal carcinoma, a heterogeneous irregular area with values ranging from 108 to 180 kPa is detected, which is displayed on the color scale by a spectrum from yellow to red.
Basics of ultrasound scanning and anatomical landmarks
To obtain a high-quality image, proper patient positioning is necessary: lying on her back with her arm placed behind her head. This allows the tissues to flatten against the chest wall and reduces the thickness of the scanned layer. The outer quadrants are examined by turning the patient into an oblique position.
Examination is always performed in two perpendicular planes:
- Standard combination: transverse (transverse) and sagittal (sagittal).
- Alternative combination: radial (radial) and anti-radial (anti-radial).
Rationale for radial access: the main ductal system converges radially toward the central nipple-areolar complex, resembling spokes of a wheel. Since most carcinomas originate precisely within the ducts, tumors with intraductal spread are visualized much better when scanned along their axis.
During the examination, macroscopic anatomy is assessed: the superficial and deep breast fasciae, Cooper’s ligaments (Cooper’s ligaments), as well as lobules consisting of Terminal Duct Lobular Units (Terminal Duct Lobular Units - TDLUs), the number of which depends on age and hormonal status.
Impact of radiological density
Breast density is subject to age-related dynamics: in young individuals, a dense glandular background prevails, which over time is replaced by adipose tissue and loses lobular units.
In clinical practice, high radiological density is considered an independent risk factor for the development of cancer. The risks are associated not only with a higher probability of tumor onset but also with its aggressive characteristics. It is hypothesized that this reflects an increased cell population and cellular turnover, leading to high mutational load. Meanwhile, stromal cells, which play a key role in carcinogenesis, remain active precisely in dense glands.
In addition, dense tissue creates a masking effect on mammography, concealing pathological nodes. Therefore, in some countries (e.g., the USA), indicating density in screening reports is mandatory. In such cases, ultrasound with elastography acts as a crucial supplementary method.
Briefly: answers to topical questions
What types of elastography are used in ultrasound breast diagnostics in addition to shear wave elastography?
In addition to shear wave elastography, compression elastography is used in breast ultrasound diagnostics. This ultrasound technique provides additional information on tissue density based on the clinical fact that malignant formations feel harder to the touch than surrounding tissue.
- Compression elastography (strain elastography) is a method where the operator manually and gently compresses the breast tissue with the transducer.
Which colors on the shear wave elastogram correspond to soft tissues and which to stiff tissues?
In the presented elastogram example of invasive ductal carcinoma, the high-stiffness zone is displayed in colors ranging from yellow to red (108–180 kPa). Color coding for soft tissues is not specified in the sources. It is only indicated that benign lesions and normal tissue are softer and have an elasticity of less than 80 kPa.
To understand radial scanning, imagine a bicycle wheel: the nipple is the central hub, and the ducts are the spokes. To trace the path of cancer growing along a duct, the transducer must be guided along the "spoke" (radially).
Class and exam questions
Why is the stiffness zone larger than the tumor itself in invasive cancer?
This is due to a pronounced stromal reaction that thickens around the malignant node and forms a stiff contour exceeding the dimensions of the visible anomaly on B-mode.
How does radiological density affect the risk of developing oncology?
High density is an independent risk factor. In dense tissue, stromal cells are more active, cellular turnover and mutational load are higher, which promotes carcinogenesis and masks tumors on radiographs.
What else to study on this topic
- Structure of the nipple-areolar complex: Montgomery glands and Morgagni tubercles.
- Macroscopic anatomy: Cooper’s suspensory ligaments, fascial leaves, and retromammary space.
- Terminal Duct Lobular Units (TDLUs) and their age-related evolution.
- Methods for assessing breast radiological density (visual and automated).
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