The Art of Multiwave Ultrasound

The next generation of ultrasound technology, shearwave elastography, promises significant clinical benefits.

The ultrasound market continues to expand, as medical facilities look for accessible, affordable imaging technology to perform evaluations in a range of pathological conditions. The quality of the images ultrasound can produce is growing in parallel to these market demands. Shearwave elastography is the next generation of ultrasound technology, promising significant clinical and imaging management benefits.

Shearwave elastography can generate, capture and quantify shearwave propagation speed, producing a measurement of tissue elasticity. Knowing tissue elasticity is an important step in the process, because tissue elasticity is related to pathology.

However, capturing shearwaves in tissue requires acquisition rates of at least 5,000Hz, while conventional ultrasound acquisitions speeds are nearer 100Hz. The Aixplorer machine, developed by Supersonic, can function at speeds of up to 20,000Hz and one flat insonification, rather than conventional successive emit-receive cycles.

The Aixplorer system, the only system on the market with multiwave technology (longitudinal wave and shear wave), was originally designed for breast imaging professionals to improve their lesion diagnosis. Today, plans are underway to expand this technology to other applications such as the abdomen and beyond.

Shearwave elastography generates low-frequency shearwaves in the body by employing focused beams of acoustic energy. This is done with a conventional transducer and is completely safe and transparent for the patient. As shearwaves travel through the body, their propagation speed is altered by changes in tissue stiffness. If a shear wave passes through stiffer tissue, the propagation speed increases.

Strain elastography versus shearwave elastography

With conventional ultrasound elastography scanning, a region of tissue is subjected to a compression force (stress) and the degree to which it distorts (strain) is assessed. Although there are different techniques to compress the tissue to achieve a strain reading, or strain elastography, the most common method is to use the transducer itself to apply minimal pressure on the tissue being imaged. The tissue is displaced by a few millimetres. Tracking the movement of the tissue is done by comparing single ultrasound lines, A-mode tracking, or by comparing the B-mode images before and after compression.

Shearwave elastography is different in several ways from strain elastography. First of all, the technique does not require manual compression on the tissue being imaged, therefore it is user-skill independent. Secondly, as there is no compression of the transducer required, more than one person can image the same tissue and obtain the same results.

Furthermore, it is based on the speed of the propagation of shearwaves, not the measurement of the displacement of tissue, so it is truly quantifiable. Because shearwave elastography is a quantifiable technology and each point in lesion can have a value in kilopascals, the exams done with this technique are reproducible and can be used over time to monitor tissue changes.

Advantages of shearwave elastography

• Shearwave elastography is user-skill independent with
  no manual compression needed to obtain tissue
  elasticity results
• Results are reproducible and lesions can be
  quantitatively monitored over time
• It is simple to use and generates a colour-coded
  elasticity map, giving local and quantitative information
  at every point in the lesion, in real-time
• As an additional tool in the diagnostic process, it assists
  in the cost-effectiveness of clinical workflow and
  improves patient safety

Future applications

The fast acquisition rates of the Aixplorer ultrasound system present many future imaging possibilities for a variety of clinical applications.

About Supersonic Imagine

Supersonic Imagine is an international company located in the technology pole of Aix en Provence in the Provence-Alpes-Côte d’Azur region of France.