Interview with Steffen Tretbar, Fraunhofer Institute for Biomedical Engineering (IBMT)
Underwater sonar images or examinations of the pregnant abdomen – ultrasounds have various applications. To avoid having to develop an entirely new system for each application, researchers at the Fraunhofer Institute for Biomedical Engineering have created a modular ultrasound platform. Their system covers a wide range of applications.
At COMPAMED.de, team leader Steffen Tretbar explains how this is possible and who already uses the platform.
Mr. Tretbar, what exactly is the modular ultrasound platform that you developed with your team?
Steffen Tretbar: We pursue a modular concept with our ultrasound platform. This means we only need to exchange specific parts in the system to quickly and cost-effectively provide customers with a solution that is adapted to their application areas and requirements.
Which components of the platform are interchangeable?
Tretbar: With ultrasound devices, signals are first transmitted, then reflected back by the examined medium and ultimately received. This is how images of an organ are created with medical ultrasounds for example. Both signal generation and data digitization take place in the so-called front-end boards. These boards are the interchangeable components of our ultrasound platform.
How many front-end boards do you have available?
Tretbar: We developed three standard front-end boards. The first one is a high-frequency board that achieves a digitization rate of up in the 500 megahertz range. It is used in molecular imaging, small animal imaging or in materials testing for example.
The second front-end board lends itself to traditional medical applications. Its digitization rate is up in the 80 MHz range and is able to serve ultrasound transducers with an operating frequency, which can range up to 20 MHz. This board is being used in traditional diagnostic applications or in the area of photoacoustic imaging for instance. Thanks to ultrafast repetition rates (several kHz) and the associated novel signal processing (plane-wave compound imaging), it delivers high-resolution images of tissue structures inside the body without producing dangerous radiation exposure like in computed tomography.
The third board handles low-frequency applications and operates in the range between 100 kHz up to several MHz. This solution is aimed at both sonar applications such as underwater positioning systems for instance and therapeutic ultrasound applications.
There are either eight or 16 receiver channels per front-end board. Sixteen of these boards are in turn connected to a mainboard. With it, we can actualize systems with up to 128 or 256 transmission and receiving channels. Altogether, we cover frequencies ranging from 100 kHz up to 100 MHz for various types of ultrasound applications with these boards.
How do you integrate the individual boards into the system?
Tretbar: The boards are integrated into the ultrasound system via connectors. We also provide software interfaces to easily adapt our systems to the customer’s application. If the customer wants to switch to another frequency range later on, he/she doesn’t have to buy a new system, but could simply exchange the front-end board. The basic software and the mainboard always remain identical.
Can you give a concrete example?
Tretbar: We developed a system for a company that registers patient movement during tumor radiation treatment. With this special system, we collect data from inside the patient’s body by four ultrasound transducers aligned parallel to each other. With the algorithms developed by the customers, the operator deduces how strong the movements inside the patient are. This shift data is used to adapt the planning data for the radiation treatment. In doing so, you can significantly minimize extensive radiation exposure and better protect healthy tissue during cancer radiation. Our customer has used the modular ultrasound platform to use his own algorithms and utilize them in his application.
Who else is using the modular ultrasound platform at the moment?
Tretbar: There is a wide range of customers. For one, the platform is used by international universities for research purposes in many different applications. The Fraunhofer IBMT frequently participates as a partner in these research projects. However, there are also small and large companies that test and/or develop new applications with the system – all the way to the finished product.
This doesn’t just pertain to the medical field, but also to materials testing for example. Customers from this industry sector frequently ask us to develop special transducers. We also create complete imaging systems for the sonar industry, which makes underwater applications possible.
Arrays are often used in ultrasound. What is their purpose?
Tretbar: Arrays are made up of many small single-element transducers. Arrays make it possible to electronically focus and direct the ultrasound beam. They also offer a larger transducer surface to have enough energy to transmit and ensure higher sensitivity when receiving signals. Since we know the position of the single elements, it is easy to control the beam – which is another advantage of array technology.
The combination of ultrasound array and multichannel electronics in our system also facilitates raw data acquisition. This makes it possible to calculate a focal point for each pixel you want to display for example. Unlike with traditional ultrasound technology, this in turn makes it possible to produce high-resolution and high-contrast images.
What other possibilities open up by accessing the unprocessed raw signals in an ultrasound array?
Tretbar: The interesting part of this for many of our research partners is not just the image processing, but also the option of signal processing. We are able to provide the user with unprocessed raw data. This is phase and amplitude data received by every single channel, but that is still not subject to any signal processing or reconstruction algorithm yet. The transmitted signals can also be arbitrarily encoded or time-delayed for each channel to use them for a specific application.