Ultra-small ultrasound

Listening has always been one of the most important tools for doctors. The sounds the body makes can give all sorts of information about what is going on inside, and the stethoscope is the iconic piece of medical equipment. But using sound to look inside the body also has a long history, and now the portability of the stethoscope and the pictures of ultrasound may be combined.

Siemens’ Acuson P10, now about to make its debut in the NHS, is the smallest ultrasound system available on the market, and is claimed to be the first pocket-sized ultrasound system. The company says it is as handy as a stethoscope, could save lives in emergency situations, and change the way doctors examine patients.

Portable ultrasound systems have been available for almost 10 years, but they are only portable up to a point.

‘If we look back at the past eight years or so, a handful of systems smaller than the historical size ultrasound have been brought to market,’ said Kirsten Woitovich, senior marketing manager for the P10. ‘They’ve been described as hand-carried, compact, convertible and/or portable, but they are associated with laptop-based devices and weigh anything from 6-25lb (3-12.5kg).

‘Some, if not all, of these devices make them more luggable than portable and in the vast majority of cases, they end up on a cart and are wheeled around, just like their predecessors.’

The P10, in contrast, will fit easily in the pocket of a doctor’s white coat. It weighs 700g and is about a fifth the size of a laptop. While its separate probe is used to examine patients, the main unit displays images on a 9.2cm flip-up black-and-white screen and the operator can navigate menus and use the device’s various functions via an iPod-style control pad. ‘We refer to it as a video stethoscope,’ said Klaus Hambüchen, president of Siemens Medical Solutions.

The size of the device was a definite goal in the development. ‘It was very important for the device to be light and easy to carry around, such as in a lab coat, a small hip-pocket or carrying bag,’ said Woitovich. ‘The design was specifically targeted to be a personal device, for use at the point of care, such as in triage, a physical exam, or general assessment.’

Making a device as complex as an ultrasound imager that small involved innovation and compromise. The transducer — the probe that produces the ultrasound signal and is in contact with the body — is about the same size as any other ultrasound transducer; its size is limited by the physics of the process. The device itself is another matter.

‘Everything has been miniaturised,’ said Woitovich. Helped by the development of smaller batteries and compact display screens, the Siemens team took several years to develop custom integrated circuits and optimised software, rather than adapting existing ultrasound technologies. ‘The analogue and digital signal processing had to be minimised to reduce power consumption, and the software architecture was developed to avoid the cost and power required by more complex systems.’

The probe, or transducer, of the system provides ultrasound in a relatively low frequency, 2-4MHz. Larger ultrasound systems which, Siemens insists, the P10 is not designed to displace, use frequencies up to 18MHz. There is a trade-off between frequency, resolution and imaging depth: high-frequency ultrasound provides the best resolution, but lower frequencies can penetrate deeper into the body.

Because of this, the device is designed for emergency medicine. This was an important factor in designing the user interface, and Siemens used simulators and hardware mock-ups to test configurations with potential users of the device. ‘The primary feedback we received was that boot-up time and speed of exam type selection were the most important,’ said Woitovich. ‘Under typical conditions, a person has the transducer in one hand and the display in the other, so the primary controls had to be operated with the thumb.’

One of the first users of the device, Eyal Herzog, director of cardiac care at St Luke’s-Roosevelt Hospital Centre in New York, says this could be invaluable in emergencies. ‘Instead of having to rush the patient to the technology, the P10 system brings the technology to the patient,’ he said. ‘This can save critical minutes, especially when a patient is in cardiac distress or with trauma patients who have multiple injuries.’

The device is particularly suited to detecting internal bleeding in trauma patients, said Siemens, and can also be used in emergencies with pregnant women to gather information on the position of the foetus, the volume of amniotic fluid and the foetal heartbeat.

The imaging provided by the P10 makes it more useful than a stethoscope in emergencies, according to Bruce Kimura, director of non-invasive cardiology at Scripps Mercy Hospital in San Diego. ‘Hearing is difficult, even in ideal situations, but it is arduous and almost an impossibility in a busy trauma centre or even an intensive care unit, when various monitors and equipment are buzzing,’ he said.

One of the most important applications for the P10 is in cardiology. According to Kimura, several cardiovascular conditions, including narrowing of the arteries in the neck, malfunctions of the contraction of the left side of the heart, and weaknesses in the main blood vessels leaving the heart, are hard to detect in a routine examination. An examination with handheld ultrasound would add 10 minutes to a standard outpatient appointment, but could add years to the patient’s life.

Woitovich claimed all this ability makes the P10 disruptive technology, opening up a new way of practising medicine. ‘This makes ultrasound available for the first time to people who would traditionally not have access to its usages and/or capabilities, such as nurses, midwives, interns, neurologists, GPs and emergency clinicians and paramedics,’ she said. ‘Today, these people will primarily listen to the heart and lungs. The P10 allows them to immediately see what they have only been able to listen to for the past 200 years.’

This immediate visual readout could also change the way patients regard their health, said Kimura, especially those with cardiac problems. Using the device to scan arteries will give an instant image of cholesterol deposits narrowing the blood vessel, which start to build up years before any cardiovascular symptoms appear. This image will have much more effect than the abstract numbers of cholesterol levels and ratios of weight and waist measurement to height, Kimura believes. Faced with such an image, patients are more likely to switch to a healthier diet and lifestyle.

St Thomas’ Hospital in London is certainly convinced of the advantages, and has ordered three of the systems for its cardiology department, where it hopes it will speed up diagnosis, eliminate unnecessary tests and help with patient review.

Woitovich said the P10 is not intended to replace the traditional fixed ultrasound; the small size of the display, the limited battery power for signal processing, and the compact-optimised user interface mean it will not be as versatile or capable of producing highly-detailed images.

‘But its cost, power capabilities and portability support the ideal usage for looking at things on the fly, anywhere, anytime — something the world of healthcare has never been able to do until now.’

And in future, she is sure advances in display and power technologies will allow subsequent versions of the device with better image quality and a longer battery life.