Freehand 3D ultrasound takes first steps from lab to clinic

Although it is still in research stages, freehand 3D ultrasound shows promise in guiding surgery and radiotherapy in the clinical setting, according to researchers at the University of Cambridge in the U.K.

Freehand 3D ultrasound includes a position sensor that is attached to the probe of a conventional 2D diagnostic ultrasound machine. Using the probe with a free hand, a clinician can capture positional and orientation data to complement conventional 2D ultrasound images. Three-D techniques enable visualization and measurement of complex anatomy during and after imaging.

Dr. Richard Prager, a reader in information engineering at the University of Cambridge, provided an overview of the technique and explored the most promising clinical applications at the Horizon Seminar "Imaging and Healthcare: the Future," held at Cambridge in October.

Clinicians at Addenbrookes Hospital in Cambridge began using freehand 3D ultrasound early this year in conjunction with traditional scanning methods, while gathering data on the usefulness of the new technology for a range of applications.The results of their research will not be published for at least six months, Prager said.

"We are in the middle of trials. Radiotherapy and surgical planning are getting the most attention from clinicians. If studies conclude freehand 3D ultrasound would result in improved treatment for patients, it will be open for clinicians to use," he said.

Prager demonstrated how the technique might be used in patients undergoing breast lumpectomy. In this procedure, tumors are typically located by manual palpation. Tumors that are not palpable must be located by other means, such as insertion of a guidewire at the presumed location. Three-D ultrasound registered to a laser surface scan of the breast offers a noninvasive, interactive alternative for surgical guidance.

Similarly, radiotherapy can be planned more effectively when the location of the tumor bed is determined, which is feasible using ultrasound findings registered to CT data.

Researchers at the University of Cambridge use a high-definition 2D ultrasound machine and 3D software developed at the university and available for download on the Internet (http://mi.eng.cam.ac.uk/~rwp/stradx).

The data set produced using freehand ultrasound can be visualized by any-plane slicing or volume rendering. Anatomical structures can be segmented from the 3D data set and visualized with surface-rendering techniques.

In addition to helping guide surgery and radiotherapy, freehand 3D ultrasound has proved useful for volume measurement of large structures that require more than one sweep of the probe (liver and near-term fetuses) and in cases that require a specialist probe.

Other potential applications include assessment of the complex anatomy of the neonatal foot. Segmentation of the ultrasound data can provide information on the anatomical shape and relative locations of the bones in the foot.

Some unexpected roles for the technique have also emerged. The Cambridge team worked with Western Medical, also in Cambridge, to design a needle-free injection system that increases the reliability of injections.

"We could get better resolution than you could get with MR at a fraction of the cost. It proved a unique tool in designing the needle-free injection system," Prager said.

Clinical use of the technology will expand if researchers find ways to simplify the procedure, he said. In the future, his group hopes to reduce the intrusiveness of the position sensor, which represents something of an engineering challenge. They are also attempting to improve the quality of images produced on 2D machines and rendered in 3D.