A new approach to strain imaging of soft tissue could improve the treatment of cancer and atrial fibrillation. We catch up with UK-based R&D company, The Technology Partnership, once again, to learn about its breakthrough in the field of elastography
Times are often exciting in innovation-centric Cambridge. And now, The Technology Partnership (TTP) has made major advances in the use of elastography – a medical imaging technique that maps the elastic properties of soft tissue to provide vital diagnostic information during surgery. This new breakthrough could be used for surgical procedures such as: treating abnormal heart rhythms caused by atrial fibrillation, killing or removing cancerous or damaged tissue during radiofrequency ablation, or simply navigating around the body during an operation.
The importance of the elastic properties of soft tissue isn’t new and has been recognised since at least 1500BC when the Egyptians described the manual practice of palpation – where the physician uses his hands to feel the stiffness of a patient’s tissues for diagnosis. This included palpation of tumours and wounds, for example, distinguishing solid tumours from aneurysms.
Today, the practice of palpation is widespread. However, manual palpation is limited to tissues accessible to the physician’s hands, can be distorted by intervening tissue, and is a qualitative, not quantitative method of diagnosis. Modern elastography was developed to address these challenges by generating a digital image of elasticity or stiffness throughout the tissue.
Surgeons currently work with ‘blind’ instruments, so they can’t see into lesions and have to rely on their skills to avoid damaging nearby organs when performing procedures such as resections or ablations. Imaging methods such as Optical Coherence Tomography (OCT) and photoacoustics provide good contrast but inadequate imaging depth, while Electrical Impedance Spectroscopy (EIS) doesn’t produce an image, and traditional ultrasound doesn’t always have enough contrast to enable practitioners to tell the difference between live and dead tissue during ablation. Elastography can determine tissue stiffness and be adapted to measure the level of muscle contraction. For example, cancerous tumours will often be palpably stiffer than the surrounding tissue, and diseased livers are ‘stiffer’ than healthy ones.
Traditional elastography relies on creating displacement in the tissue by inducing a distortion when sending a shear wave through it, or by vibrating the surface of the tissue. However, TTP’s patent-pending approach uses a process of passive elastography, which relies on the body’s normal physiological distortions created, for example, by the beating of the heart, the respiration of the lungs, or the expansion and contraction of the blood vessels. In fact, it doesn’t matter what generates the distortion – this technology is even sensitive enough to measure the small mechanical movement caused by natural hand tremor in the surgeon holding the probe.
Using ultrasound frequencies between 5 and 40 MHz, sets of two or three ultrasound images at a time are captured and then the displacement caused by the body’s natural movement – typically around 10 microns amplitude within each set of images – is measured. Ultrasound images all show ‘speckle’ patterns, and each speckle is produced by a ‘scatterer’. Ultrasound elastography evaluates the movement of those scatterers relative to the ultrasound probe. The structural changes visible from the data to map muscle stiffness or contraction is then examined and displayed as a colour-coded map superimposed over the ultrasound image, so the user can see both sets of information. Regions of large deformation can be labelled as low stiffness, while those of low deformation can be labelled as high stiffness. The result looks similar to a heat map, with a resolution of around 0.5mm and up to a depth of around 50mm.
The strain imaging technology is designed for integration with existing ablation instruments or probes, which will enable surgeons to visualise work that would otherwise be done blind. For example, distinguishing calcified crusts and soft lipid plaques inside arteries would help determine a treatment plan for patients at risk of heart attack or stroke.
Elastography can also help with the visualisation of thermal ablation procedures – such as cancer ablation – where the ablation is blind and the end point of the procedure is uncertain, but where the end point determines both the efficacy and safety of the treatment.
‘When we started looking at ultrasound imaging for these surgical applications, it became clear that there is a need for a new imaging solution with enough contrast, resolution and image depth,’ says TTP’s chief researcher Paul Galluzzo. ‘Our new passive elastography approach gives surgeons much greater visibility which, in turn, increases clinical efficacy. Ultimately the goal is to reduce the number of re-interventions, mortality rates and procedure times for all ‘blind’ medical procedures.’
Passive elastography is the latest addition to TTP’s suite of medical imaging tools and technologies. A number of companies are already partnering with TTP to introduce passive elastography into specialist medical fields, and further opportunities are being explored. Recent development has focused on providing an absolute stiffness capability, 2D scanning and enhancing the underlying performance
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