The diagnosis of diseases like cancer almost always needs a biopsy – a procedure where a clinician removes a piece of suspect tissue from the body to examine it, typically under a microscope. Many areas of diagnostic medicine, especially cancer management, have seen huge advances in technology, with genetic sequencing, molecular biology and artificial intelligence all rapidly increasing doctors' ability to work out what’s wrong with a patient. However the technology of medical needles hasn’t changed dramatically in 150 years, and – in the context of cancer management – needles are struggling to provide adequate tissue samples for new diagnostic techniques. Previously, researchers had shown that modifying the biopsy needle to vibrate rapidly at 30,000 times per second not only provides sufficient data for 21st century diagnostic needs, but is also potentially less painful and less traumatic for patients. Now, new research explores if nonlinear ultrasound can be used to overcome the limitations of currently used medical needles, such as the pain experienced by patients, inaccuracy and variable quality of needle biopsy samples.

Using computer models and experimental studies, the researchers at Aalto University (Espoo, Finland) were able to show that oscillations of the needle caused a number of non-linear acoustic phenomena. These include cavitation, the sudden expansion and collapse of air bubbles; the formation of acoustically driven fluid flows; acoustic radiation force, the force exerted by an ultrasonic wave on an object; and the formation of micro-droplets.

“In this study, we used needles to generate transverse-like motions at 30 kHz. This allows the acoustic energy to be amplified towards the needle tip, exactly where the effect is needed. This localized ultrasound energy can be used in a variety of applications, such as improving the quality of needle biopsy samples,” said Professor Heikki Nieminen, who is leading the project. “The investigated approach has the potential to give conventional medical needles new enhanced functions in medical applications not only in needle biopsy but also in drug or gene delivery, cell stimulation, and minimally invasive surgical procedures.” 

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