Scientists have published the most comprehensive analysis to date of ultrasound detectors underpinning photoacoustic tomography (PAT) - a fast-emerging medical imaging technology capable of revealing blood vessels, tumours, and tissue function deep inside the body.
Published in Nature Reviews Methods Primers , researchers at the University of Birmingham and UCL reveal that large ceramic detectors are currently best for deep imaging, while optical ultrasound sensors may be the future for high-resolution imaging of tiny structures.
The authors reviewed published data on 82 ultrasound detectors used in photoacoustic imaging, establishing the first standardised 'noise-equivalent pressure' (NEP) landscape – a performance map showing which detectors can hear the faintest biological signals across four main types:
- Ceramic piezoelectric detectors;
- Polymer piezoelectric detectors;
- CMUTs (capacitive ultrasound detectors); and
- Optical ultrasound sensors that detect sound using light rather than electricity.
PAT works by shining short pulses of laser light into tissue. When tissues absorb the light, they produce tiny ultrasound waves which researchers can detect – using them to create images of blood vessels, tumours, and other structures inside the body. However, sound waves originating from deep tissues are extremely weak - the deeper the target, the weaker the signal.
The researchers found that:
- Large ceramic detectors are the most sensitive to low frequency ultrasound waves that arrive head-on, making them well-suited to deep-tissue imaging, such as breast cancer imaging;
- Optical sensors excel when detectors need to be tiny – these detectors can be made extremely small, often under 100 micrometres across, while remaining highly sensitive;
- Polymer detectors provide broader frequency coverage – this can help capture more image detail, particularly for superficial structures; and
- CMUT detectors showed sensitivity comparable to some of the best technologies, but published measurements lacked detail, making it difficult to assess true performance.
Lead author Dr James Guggenheim, from the University of Birmingham, said: "There is no single 'best' ultrasound detector for all photoacoustic imaging applications. Deep tissue imaging, such as breast cancer detection, currently benefits from very sensitive ceramic detectors. However, optical ultrasound sensors which are already best for high-resolution imaging of tiny blood vessels might one day come to dominate even in deep tissue imaging as their sensitivity increases."
"Our study provides researchers and manufacturers with a practical guide to selecting the right detector technology for specific clinical challenges now. It also highlights where future innovation is needed, for example, to develop dense, small-element detector arrays capable of delivering both deep-tissue and high-resolution imaging."
Until now, comparing detector technologies has been difficult because researchers used inconsistent definitions and measurement approaches. The study concludes that future improvements in photoacoustic imaging will depend on creating more sensitive detectors. There also needs to be improvement in detector arrays, standardisation of how performance is measured, and development of practical high-channel-count systems for clinical use.
