The research — assisted by a £730,000 EPSRC grant — will use ultrasonic arrays contained within ultrasound transducers, capable of producing ultra-high resolution medical images. This will provide a far clearer view of organ boundaries and considerably superior diagnostic information.
A fifteen-strong team from the universities of
An ultrasound transducer produces sound waves that bounce off body tissues, creating echoes. The transducer also receives the echoes and sends them to a computer that uses them to create a picture called a sonogram. The transducer may be passed over the surface of the body or inserted into an opening, such as the rectum.
Existing ultra-high resolution systems are based on mechanically scanned, single-element transducers. These systems demonstrate the need for increased resolution, but at the same time limit progress because they cannot be used in real time.
The team will develop a technique to produce both ultra-high resolution and real-time images. Initially, the system will be based on single-element, mechanically- scanned transducers, but the project will move into a second phase and develop a multi-element, electronically scanned system, which will improve the uniformity of the scanning process. For this, ultrasound transducers are needed, which can operate at frequencies higher than the present maximum of 30MHz. The team propose to reach frequencies as high as 100MHz.
Ultrasound imaging is measured in millimetres and microns. Achieving 100MHZ frequencies should enable the team to reach the sub-millimetre range. McDicken said: ‘When we look at the layers of a cavity wall we will be able to see much more detail at sub-millimetre range.
‘Improved resolution helps with clarity of lines and boundary definitions. Users may be able to see boundaries they could not see before. We know these boundaries exist from looking at them histologically. If we can improve the imaging equipment we can start seeing these boundaries.’
To achieve ultra-high resolution, the team will reduce the size of piezocomposite material used in ultrasound transducers. Piezocomposites are widely used in underwater sonar and biomedical imaging, but the resolution of the images that can be obtained in medical applications is limited by the maximum frequency.
Usually, the higher the frequency the greater the attenuation. Where a high-resolution image is less important, attenuation is less of an issue. However, where an ultrahigh resolution is desirable — as it is in medical diagnostics — attenuation becomes a serious hurdle.
The maximum frequency is limited by the minimum size of piezocomposite, and the team is focusing on producing micron-scale components that have the dimensions of around 10 microns. To date, attempts to manufacture material with micron-scale dimensions have been unsuccessful. The smallest available is around 20 microns.
in the first instance the researchers will aim at halving the size of the piezocomposite dimensions. But they eventually hope to reduce the present size by a quarter, thus reaching ultra-high levels of frequency.
The three universities each have a discipline to develop. ‘Paisley translates
The technology will particularly benefit cardiovascular diagnostics where it will enable operators to see how plaques slowly build up over time on the arterial walls. Explained McDicken: ‘The main benefits of this system are when we need to look within a few millimetres of the tissue. If we can improve the image quality, then we can begin to see the progression from early disease level. We will also see what is causing disease and how it is responding to therapy.’
The system is claimed to be as safe and as inexpensive as present real-time ultrasonic imaging, which accounts for approximately 20 per cent of all hospital imaging examinations.
‘It will have the all the advantages of ultrasonic — it will be safe, inexpensive and in real-time. But it will be better for certain applications particularly opthamology, dermatology and intravascular applications,’ said Cochran.
The team hopes to carry out pre-clinical trials by the end of the three-year project, where they will use ‘phantom’ (mimicked tissue) material as an alternative to testing on animals or humans.