Breast Ultrasound :  The New Wave

Worldwide, breast cancer has the highest incidence of all cancers in women and has a mortality rate in developed countries of 25%.

X-ray mammography is the “Gold Standard” primary exam used to detect breast cancers.  It has a sensitivity (probability that the test indicates a potential abnormality ) of about 80%. However, this sensitivity decreases significantly when imaging dense breasts.  Mammography, however, has some limits.  For example, low mammography specificity (probability that the test provides better characterization) often leads to unnecessary biopsies.

Other imaging techniques, such as ultrasound and MRI also have limiting factors.  MRI machines have a very high sensitivity but have only a moderate specificity.  The MRI machine is an expensive imaging modality and not readily available in all hospitals and clinics. 

Ultrasound has a higher specificity than mammography but has the disadvantages of being user skill dependent and having varying results based on the quality of the system used.

Breast lesions that are detected by mammography, ultrasound or MRI can be classified following the American College of Radiology standards named BI-RADS®.  This classification takes into account different semiological criteria and scales them 1 to 6 (from benign to malignant).

Adding criteria to the classification could help refine diagnosis.  As it is common knowledge that tissue elasticity is related to pathology, tissue elasticity could be one of these parameters.

 

Associated with Ultrasound, Elastography assists in characterizing the differences in tissue elasticity.

In the case of Static Elastography, the transducer is used to compress the tissue and the strain is calculated.  This calculation gives a superimposed color map, on top of the B mode or black and white image, which represents tissue elasticity.  This technique largely depends on the compression that is applied to the transducer and is difficult to reproduce and not quantitative but qualitative.

The Elastography technology created by SuperSonic Imagine is very different.

ShearWave™ Elastography (transient) is reproducible, quantifiable and user-independent.

An ultrasound shear wave is generated by the transducer (instead of a manual compression) and then the propagation speed in the tissue of this shear wave is measured.  The speed at which the shear wave propagates is proportional to the square root of the tissue elasticity. In order to follow the shear wave propagation (speed of 1 to 2 m/s) it is mandatory to have an Ultrafast™ ultrasound system that can acquire images at a speed greater than 1000 per second. 

This « New Wave » in ultrasound, using Ultrafast™ imaging creates a totally different Elastography imaging technique for the breast.  Today, only ShearWave™ Elastography is capable of measuring true tissue elasticity in a reproducible and user-independent manner.