Introduction:
Breast cancer is one of the most widespread cancers affecting females. Their incidence is mounting globally despite increasing awareness and efficient screening measures. The plausible reason for this surge in cases could be that not all breast lumps may be palpable in their initial stages. Also, the lesion could be small enough to be missed in the diagnostic screening. Such neglected lesions could potentially prove grave and may result in advanced stages of the disease requiring more intricate therapies.
Imaging techniques such as sonography and mammography are the gold standard in diagnosing breast lumps. However, both techniques present certain limitations. Though sonography is sensitive in diagnosing solid breast lesions, its specificity is poor. Mammography is not efficient for examining dense breasts. Also, reduced accessibility, pricey equipment, and high technicalities make it challenging to use mammography, particularly in lower economic settings. Hence to overcome these limitations and for a more precise diagnosis, a novel technique was introduced known as sonoelastography.
What Is Sonoelastography?
Sonoelastography is a form of sonographic imaging technique that uses the mechanical properties of tissue to establish a diagnosis. It is also known as ultrasound elastography. It is a non-invasive technique that employs tissue elasticity and deformability to assess and characterize the lesions. Sonoelastography, though novel, has proved beneficial in lesions of various organs such as the breast, thyroid, prostate, and lymph nodes. However, breast sonoelastography has revolutionized the field of diagnostic oncology.
What Is the Working Principle of Sonoelastography?
Sonoelastography is based on the principle of tissue elasticity. Elasticity is a mechanical property of any substance that enables it to deform when subjected to external force or mechanical strain and return to its original form when the strain is removed. The response of the tissue varies depending on its inherent elasticity.
Deformation of the tissue is inversely proportional to tissue elasticity. Normal tissues, such as fatty tissues, are more easily deformed; however, fibrous tissue tends to deform more slowly as they are stiffer. A tumor (cancerous or non-cancerous) is more rigid than its corresponding normal tissues. Hence, they deform less when a mechanical strain is applied. The difference in the soft tissue elasticity from the standard scale helps diagnose any underlying anomalies.
What Is the Importance of Sonoelastography in Breast Lesions?
Breast elastography is most commonly used to characterize a lump in the breast as a benign (non-cancerous) or malignant (cancerous) tumor. It can be used to detect multiple lesions, which may usually appear as a single lesion on conventional ultrasound. It can also diagnose a fat lobule or a benign breast cyst. Screening elastography can also help identify non-palpable lesions, initiating early diagnosis and prompt treatment. Sonoelastography can also be used to assist in the biopsy, and this procedure is known as an image-guided biopsy. Image-guided biopsy is beneficial as sonoelastography can help to identify the abnormal tissue precisely and thus remove it, resulting in negligible scaring and quick recovery.
How Is Sonoelastography for Breasts Performed?
Sonoelastography works similarly to conventional sonography by using sound waves with additional tissue compression. No radiation is involved, and hence it is incredibly safe for pregnant women. The high-frequency sound waves are transmitted into the body using a device known as a transducer. These sound waves strike various internal structures within the body and bounce back, which is again captured by the transducer. The computer then processes these returning sound waves into images that can be visualized as real-time images on the screen.
Tissue compression can be achieved in various ways. One is manual compression using a conventional transducer or by using respiratory movements. However, the sonographic equipment may not comprehend the force and degree of compression, and the result may be variable. However, an alternative and more precise method to apply mechanical strain or force is to use an acoustic impulse to deform the tissue. Acoustic impulses are high-intensity vibrations generated as pressure waves deform the tissues. Another quantitative method of elastography is known as real-time shear velocity, which can quantify the accurate tissue stiffness in kilopascals (kPa), thereby reducing interobserver variability.
What Is an Elastographic Score?
Breast elastography focuses on two essential aspects: the size and stiffness of the breast lesions. Stiff nodules seem more significant in sonoelastography than in a conventional ultrasound. The lesions are evaluated in the following methods:
1. Numerical Method-
Lesions with elasticity less than 20 kPa are considered benign, and those greater than 20 kPa are deemed malignant.
2. Dimensional Difference-
A dimensional difference indicates the ratio between the diameters of the lesion on the sonoelastogram to that in the ultrasonogram. A value greater than or equal to 1 is indicative of malignancy.
3. Tissue Deformation-
- Score 1- Entire lesion is deformable.
- Score 2- Most of the lesion is deformable with some stiff areas.
- Score 3- Peripheral lesion is deformable, whereas the center is stiff.
- Score 4- Entire lesion is stiff.
- Score 5- Entire lesion, along with the surrounding tissue, is stiff.
This scoring criterion was given by Itoh et al. Scores 1, 2, and 3 are considered benign, whereas scores 4 and 5 are considered malignant.
4. Encoding Method-
This method gives a color coding representative of the deformation changes. They are as given below:
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Score 1- Indicates greatest intensity deformation changes such as that found in necrotic tissue, hemorrhagic lesion, or lesions containing necrotic debris, liquids, or exudate. They are color-coded as red-yellow.
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Score 2- Indicates high-intensity deformation such as normal breast parenchyma. They are color-coded green.
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Score 3- Indicates inelastic tissues such as fibrosis that are depicted as blue.
What Are the Benefits and Risks of Sonoelastography?
Benefits:
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The procedure is non-invasive.
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Painless and well tolerated by the patients.
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No use of radiation.
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Superior and accurate results.
Risks:
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Sonoelastographic examination has no known risks.
Conclusion:
Breast sonoelastography has proved to be a powerful diagnostic tool in evaluating breast lesions. The precision, easy accessibility, and noninvasive technique make it superior to conventional ultrasound. Considering the high specificity and sensitivity of sonoelastography, biopsies of benign lesions can be drastically reduced. Sound technical knowledge and the ability to interpret the results accurately can help apply elastography to daily practice.
