Improved Ultrasound Device Makes Images of Carotid Artery in Real Time

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Maysam Shabanimotlagh of TU Delft has developed a special ultrasound transducer (converter) with built-in electronics which can be used to make echocardiograms of moving parts of the carotid artery, among other things. What is special about this transducer is that it can make three-dimensional images in rapid succession (up to 1000 per second), for example to visualise the flow of blood in the carotid artery. ‘This could become an important tool for non-invasive screening of cardiovascular diseases,’ says Dr Martin Verweij of TU Delft, one of the promotors.

The work was conducted as part of the STW project, a collaboration between TU Delft and Erasmus MC, and describes a piezo-electric matrix array on an integrated circuit (ASIC). ‘The technology will be integrated in a future generation of ultrasound devices to make real-time three-dimensional images of various organs. For this PhD research, we considered two specific applications: carotid artery imaging and ‘miniaturised transoesophageal echocardiography’ (TEE). The latter application involves conducting cardiac examinations through the oesophagus.’

Integrating the ASIC in the probe makes it possible to use more than 1000 transducer elements, despite the limited number of electrical connections (most ultrasound devices have 256 connections). The foundation of a properly functioning transducer is a well-designed transducer element. In the best-case scenario, where the width of the transducer is small relative to its thickness, the transducer surface will vibrate evenly. However, the disadvantage of a small width is that the element generates less power. ‘To resolve this, we divided the elements into smaller sub-elements. Simulations revealed that dividing an element into smaller parts improves performance.’

One of the specific goals of the research was to design a transducer that can make images of the carotid artery. To this end, a matrix transducer was developed with elements that can be divided into one, two or three sub-elements. Measurements of this transducer in a water tank closely replicated the simulations with each of the different elements. The results revealed that dividing an element into two sub-elements works best for this application.

The researchers developed a piezo-electric matrix transducer on an ASIC for making the three-dimensional images of the carotid artery. The ASIC is designed for 24 × 40 elements, each 150 micrometres in size. The individual ASICs can be combined into groups to make a larger matrix transducer. The 960 elements are connected to the mainframe by 24 transmitting and 24 receiving channels. Each element has a set of switches that enable the transmitting and receiving modes to be switched on and off independently of each other. Each row of 40 elements has a low noise amplifier (LNA) with 20 dB amplification that can be switched on or off by a signal. The measurement results demonstrated that this design of a large matrix transducer is suitable for making three-dimensional images of the carotid artery in real time.

The research also described a prototype that can serve as a proof of concept for a miniature 3D TEE transducer. The acoustic performance of the prototype was tested in a water tank. The tests demonstrated that this prototype is suitable for use in a 3D TEE application.

Verweij emphasises that this new transducer is still very much in the development phase: ‘We have not built a complete transducer yet, but we have certainly demonstrated that our approach could have some very interesting applications.’