Ultrasound elastography was introduced in 1991 and is used to determine the stiffness and elasticity of an organ or structure. Elastography compresses tissue and creates a map of its elastic properties; it is commercially available in two techniques: strain and shear. Both types are useful tools in determining the necessity for biopsy of a mass, and in monitoring existing masses or conditions. This technology is particularly useful in tracking the progression of liver fibrosis and in diagnosing liver conditions that may not typically be seen in gray-scale imaging techniques, as well as in several other areas of the body.
Strain techniques have been available longer than shear, but shear techniques are gaining popularity and usefulness. Many doctors use the two techniques together to prove a positive or negative result. Shear and strain techniques “complete each other”, as one is quantitative, and the other is qualitative. When used together, they can rule disease processes ‘in’ or ‘out’. The more qualitative strain technique is can be influenced by the histotype or lesion size. However, the quantitative shear method finds its limitations in calculating velocities of very stiff lesions but is more accurate in assessing spatial distribution of tissue stiffness.
The shear method is particularly useful for monitoring liver fibrosis, as the velocity in the wave is what determines stiffness. Shear techniques are also more easily reproduced. Some livers can be diagnosed with diseases based on elastography results before they would have been diagnosed on gray scale imaging alone; studies have shown positive elastography results on patients that exhibited only minor signs of irregular contour and no imageable nodularity. Elastography can also be used to noninvasively monitor known disease processes in children and infants. It allows doctors to see how rapidly fibrosis is progressing without performing a biopsy. In addition to monitoring known processes, elastography has also been used to help diagnose new abnormalities within a patient, without an invasive biopsy. The stiffness reading can help determine which stage of disease is present and probability of malignancy.
Elastography is useful in many areas of study, including abdominal organs (liver, spleen, and native or transplanted kidneys specifically), breast screening, prostate screening, and even is useful for MSK studies. This form of imaging allows doctors to predict malignancy based on size and stiffness of the lesion; malignant lesions are typically bigger and don’t allow the elastography waves to penetrate, while benign lesions are typically softer and smaller. Elastography can help predict which stage of disease is present and allows doctors to form a treatment plan that is most beneficial and least invasive for the patient.
Sources:
Hagen-Ansert, Sandra L. Textbook of Diagnostic Sonography. Elsevier, 2018.
Matten, Mary Beth. “Ultrasound Elastography Gaining Clinical Use.” Applied Radiology , 2 Mar. 2016, appliedradiology.com/articles/ultrasound-elastography-gaining-clinical-use.
