Adding a dimension to ultrasound

In the context of medical imaging, ultrasound technology enables scanning of the inside of the human body in a cheap, quick and patient-friendly manner. Most ultrasound probes on the market use a one-dimensional array of transducing elements to obtain a two-dimensional image. Recently, probes have been developed to acquire 3D scans.

However, they are not suitable for high frame rate applications, and their dimensions limit them mainly to external use, two factors that make imaging diagnostics for cardiovascular disorders challenging. In fact, imaging blood is problematical due to the fast-dissipating flow phenomena that occur in vessels. And scanning the heart is sometimes only possible by means of a swallowed probe (Transo Esophageal Echocardiography or TEE), which can prove extremely uncomfortable for the patient.

Recently, Dr. Maysam Shabanimotlagh successful completed his doctoral thesis, under the supervision of Prof. de Jong and Dr. Verweij, on the development of a new type of transducer that can scan fast enough to obtain motion pictures and is small enough to be used internally (the transducer is only 1 cm across). They mainly focused on the design of such a probe for carotid artery imaging; its miniaturization improves the patient’s comfort during TEE and enables continuous monitoring of the heart.

The array is built of piezoelectric materials and mounted directly on top of an Application Specific Integrated Circuit (ASIC), which allows for direct processing of the signal, thus avoiding cable losses. Dr. Shabanimotlagh also found that by performing micron-thick cuts on the matrix, the signal-to-noise ratio could be increased to obtain higher-quality images and stabilize the vibration of the elements during operation.

One of the main challenges with building a two-dimensional matrix transducer is to handle the connections of the single elements to the computer. It is not an option to wire out all signals at once, due to the excessive number of wires needed. Dr. Verweij explains how, together with Dr. Shabanimotlagh, they studied a few scanning techniques that swipe through the array elements to collect their signals hundreds of times per second. Using these techniques, it is also possible to direct the sound waves to particular regions by forming the beam into a specific shape.

These results do not stand alone. At the Faculty of Applied Physics, Prof. de Jong and Dr. Verweij are conducting extensive research on various applications of matrix transducers in collaboration with the Erasmus Medical Centre in Rotterdam. Dr. Verweij stresses how this technology could be used to continuously monitor blood flow in the brain of prematurely born babies, or to produce real-time 3D observations of the status of the patient during surgical procedures. These devices are still in the research and development stage, but Dr. Verweij expects ultrasound technology to be used in the future for an increasing number of applications.

• Mayam Shabanimotlagh, Ultrasound Matrix Transducers for High Frame Rate 3D Medical Imaging, PhD supervisors Dr Marcel Verweij (Applied Sciences,TU Delft) and Prof. N. de Jong (Erasmus MC), 12 September 2018.

Giulio Dacome / Stagiair