Freehand 3D ultrasound edges from lab to clinic

Though still in the research stage, freehand 3D ultrasound is showing promise in helping to guide surgery and radiotherapy in the clinical setting, according to researchers at the University of Cambridge in the U.K.

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

Dr. Richard Prager, a reader in information engineering at Cambridge, provided an overview of the technique and explored the most promising clinical applications at the Horizons Seminar meeting held on Oct. 19 at Churchill College in Cambridge.

Since the beginning of 2004, clinicians at Addenbrooke's Hospital in Cambridge have been using freehand 3D ultrasound for a range of applications in conjunction with traditional scanning methods, all the while gathering data on the utility of the relatively new technology. The results of the experiments designed to evaluate new techniques in the clinic will not be published for at least another six months, Prager said.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. With this procedure, tumors are typically located by manual palpation of the patient. Tumors that are not palpable must be located in other ways, such as though the insertion of a guidewire at the location of the tumor. Three-D ultrasound registered to a laser surface scan of the breast offers a noninvasive, interactive alternative way to guide surgery.

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

Research at Cambridge is performed using a high-definition 2D ultrasound machine and 3D software developed at the university and available to download (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. Anatomic structures can be segmented from the 3D data set and visualized using surface rendering techniques.

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

Other potential applications include the assessment of the complex anatomy of the neonatal foot, as anatomic shape and relative locations of bones in the foot can be gained through segmentation of the ultrasound data.

Some unexpected roles for the technique have also emerged. The Cambridge team worked with the company Western Medical to help design a needle-free injection system, increasing 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," he said.

Clinical use of the technology will broaden if researchers find ways to simplify the way the procedure is performed, according to Prager. In the future, they hope to reduce the intrusiveness of the position sensor, which is a challenge from an engineering point of view. Researchers are also looking at ways to improve the quality of images produced on 2D machines and rendered in 3D.

For more infomation from the Diagnostic Imaging archives:

3D ultrasound breaks through to adult indications

Handheld ultrasound taps thoracic trauma

Dedicated lab takes advantage of 3D imaging capacity