Triple vision

Cambridge team plans to combine best of existing 3D imaging technologies

A ‘hybrid’ 3D ultrasound system designed to provide data so detailed it could replace CT or MRI scans for certain applications is being developed at Cambridge University, in collaboration with an industrial partner.

In the case of CT scans, it would give doctors the option of reducing a patient’s exposure to ionising radiation, and would be a cheaper alternative to MRI, saving the NHS money.

The resulting system would allow doctors a clear view of any enlargement of a diseased organ such as the liver, and would also allow them to accurately measure the size and shape of tumours during treatment.

It could be used during procedures such as local anaesthesia, when doctors must ensure they avoid certain veins and arteries. ‘Research has found that in up to 30 per cent of the population, their arrangement differs from that found in standard anatomy textbooks,’ said lead researcher Dr Richard Prager.

The researchers, based in the university’s engineering department, said most ultrasound machines in hospitals work in two dimensions, sending high-frequency sound pulses into the body and displaying the echoes that come back as a two-dimensional or 2D picture.

The resulting image therefore shows the sound reflections in one slice through the body. However, in some areas of medicine doctors would like to be able to gather ultrasound data as a three-dimensional (3D) block rather than a two-dimensional slice, particularly when there is a need to measure the volume of an organ or tissue, or if complex geometry must be analysed.

At present, 3D scanning is possible using two different methods. The first involves a probe that can record a fixed block of data, either by having an internal sweeping mechanism or by using electronic beam steering.

The second uses a conventional 2D ultrasound machine. During this method, called freehand 3D ultrasound, an optical or magnetic position sensor is attached to a conventional probe and the precise 3D trajectory of it, including the angles of the sound, is recorded as the doctor performs the scan. Complex computer processing allows the positional information from the sensor to be combined with the 2D ultrasound slices from the ultrasound machine, displaying this as a 3D image.

The new Cambridge system will combine the benefits of the existing 3D technologies and offer some additional, unique advantages. It will record dense regular data such as the integrated 3D probe, but will also acquire large data-sets as is possible with the freehand approach.

However, there will be no need for an inconvenient external position sensor to be attached to the probe as much of the information required to calculate its trajectory will be discovered by matching the 3D blocks of recorded data. A miniature inertial orientation sensor will be used to guide the matching algorithms, increasing their speed and reliability. Such a sensor could eventually be incorporated in the probe housing.

The project is being carried out in partnership with ultrasound company Dynamic Imaging, based in Livingstone, and Addenbrooke’s Hospital and the Royal Marsden Hospital.

It will focus on tracking the trajectory of the probe based on the acquired data and the output of the inertial position sensor. It will determine calibration of the hybrid system and how to correct artefacts in the data caused by variations of the pressure from the probe being applied to the skin during the scan. The team will also look at development and evaluation of software tools to enable the system to be used effectively in a hospital environment.

As part of the research, a complete version of the system will be mounted on a trolley and used to explore the range of applications in which this type of scanner could offer benefits to doctors. Researchers will also study the problems caused during real-life use, measuring the size and precision of scans than can be reliably acquired using the system in a busy ultrasound clinic.