"It's the first time, to our knowledge, that anyone has used the information in a 3D ultrasound scan to actually guide a robot", stated Stephen Smith, professor of biomedical engineering at Duke's Pratt School of Engineering. Stephen Smith and Eric Pua, a Pratt graduate student who participated in the research, reported the findings in the cover article of the November 2006 issue of the journal IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control. The work was supported by the National Institutes of Health and the National Science Foundation.
In their demonstration, the researchers used 3D ultrasound images to pinpoint in real time the exact location of targets in a simulated surgical procedure. That spatial information then guided a robotically controlled surgical instrument right to its mark. The scanner could be coupled to the surgeon-operated robots that are being increasingly used for performing minimally invasive "laparoscopic" surgeries on the heart or other organs, according to Stephen Smith. In such operations, surgeons work through tiny "keyhole" incisions, and the new scanner would provide surgeons a more realistic view of the organ they are working on.
"All the technology is available", Stephen Smith stated. "We just need to make the connections between the ultrasound scanner and the robots now in use by surgeons. There are no technological barriers to doing that right away."
Among other applications, surgeons could use the 3D scanner to spot potential tumours in real time during biopsy procedures, making a diagnosis of cancer harder to miss, according to the engineers. Physicians today must rely on still images, such as CT scans, of a patients' organs captured prior to biopsy to locate lesions suspected to be cancer.
As artificial intelligence technology improves in the coming decades, the scanner might even be able to guide surgical robots without the help of a surgeon, according to the researchers. The 3D ultrasound probe has yet to be tested in human patients, Stephen Smith stated, but he added that his team believes the technology is ready for clinical trials.
The Duke team in 1987 developed the first-ever 3D ultrasound scanner for imaging the heart in real time from outside the body. As technology enabled ever smaller ultrasound arrays, the researchers engineered probes that could fit inside catheters threaded through blood vessels to view the vasculature and heart from the inside.
Earlier this year, the team reported another advance: a 3D ultrasound device including 500 tiny cables and sensors packed into a tube 12 millimeters in diameter - small enough to be inserted through the incisions required for laparoscopic surgeries. The researchers then showed that the device can produce actual 3D images of the beating hearts in animals. The team has since demonstrated that the scanner also can be used to laparoscopically image other organs, including the spleen, liver and gall bladder.
In the current study, the researchers used the scanner to identify co-ordinates denoting the precise location of an artificial lesion inside a type of artificial organ, or "phantom", commonly used for testing imaging technologies. The researchers then entered the co-ordinates into a simple robot that controlled a biopsy needle, and the robot did the rest.
The researchers also have used the scanner to guide the biopsy robot toward a designated target in the gall bladder of an animal that had died. An ultrasound video of the needle traveling toward and then precisely puncturing the animal's organ can be downloaded at http://transducers.bme.duke.edu/movies.php. "Once the robot takes over, it sends the needle to within about 1,5 millimeters of the centre of the target", Stephen Smith stated. "That's pretty good accuracy."
The 3D ultrasound scanner also has the advantage of seeing the interior of organs, according to Stephen Smith. Optical laparoscopes, in contrast, provide surgeons only a view of organs' outer surfaces. "Two-dimensional laparoscopic ultrasound has seen increased use as a surgical aide in general, gynaecological and urological procedures", Eric Pua added. "Our results show that the application of real-time 3D ultrasound to these surgical procedures may increase information available to the surgeon and serve as an additional guidance tool."
Other researchers in the study were Matthew Fronheiser, Joanna Noble, Edward Light and Patrick Wolf, who work in Duke's biomedical engineering department, and Daniel von Allmen, chief of the division of paediatric surgery at the University of North Carolina, Chapel Hill. A copy of the article is available at the web site of IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control.