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Back to Surgery Articles

Monday 12th June, 2006


3-D ultrasound probes built by researchers at Duke's Pratt School of Engineering could give surgeons a better view.


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Biomedical engineers in the United States at Duke University's Pratt School of Engineering have created a new three-dimensional ultrasound imaging probe.

In a peer-reviewed report published in the journal Ultrasonic Imaging, issued in late March 2006, researchers at Duke's Pratt School of Engineering discussed the results of the new 3D ultrasound device that they say is poised to advance minimally invasive surgery.

Endoscopy is a minimally invasive diagnostic medical procedure used to evaluate the interior surfaces of an organ by inserting a small scope in the body, often but not necessarily through a natural body opening. Through the scope, one is able to see lesions.

?Endoscopy is an instrument that not only provides an image but also enables taking small biopsies?, says Dr Mihai Mavru, Primary surgeon - Caritas University Hospital, Romania. ?In addition endoscopy allows for foreign object retrieval and even quite sophisticated surgery. Endoscopy is the vehicle for minimally invasive surgery?, says Dr. Mavru.

Endoscopic surgery has the advantage of reduced postoperative pain and a faster recovery. However, the two-dimensional ultrasound imaging now available offers surgeons only a limited view, which can impede their depth perception and make such procedures difficult to master.

Biomedical engineering professor Stephen Smith, who specializes in ultrasound imaging and his team, including biomedical engineering graduate student Chris Pua, developed the probe specifically for use in hospitals and clinics.

The engineers said their demonstration showed that the new 3D ultrasound probes could give surgeons a better view during human endoscopic surgeries in which operations are performed through tiny "keyhole" incisions.

Surgeons now use optical endoscopes or two-dimensional ultrasound when conducting minimally invasive surgery. Optical endoscopes are thin tubes with a tiny video camera that surgeons can insert directly into the abdomen or chest through small incisions.

The current advance relies on 504 tiny cables and sensors. Each sensor is as wide as a few human hairs. The cables and sensors are packed into a tube 12 millimeters in diameter ?- the size required to fit into surgical instruments, called trocars, that surgeons use to allow easy exchange of laparoscopic tools. By comparison, most two-dimensional ultrasound probes use just 64 cables.

Each cable carries electrical signals from the scanner to the sensors at the tip of the tube, which in turn send pulses of acoustic waves into the surrounding tissue. The sensors then pick up the returning echoes and relay them back to the scanner where they produce an image of the moving tissue or organ. The scanner uses parallel processing to listen to echoes of each pulse in 16 directions at once.

The probe generates ultrasound at 5 million vibrations per second, which, combined with the 504 sensors, provides great sensitivity and a sharp image.

More cables translate into better image quality. The scanners achieve a 3D moving image instantaneously, with no reconstruction.

With this scanner, doctors can see the target lesion or a portion of an organ in a real-time three-dimensional scan. They would have the option of viewing the tissue in three perpendicular cross-sectional slices simultaneously or in the same way a camera would see it ?- except that a camera can't see through blood and tissue.

The technology has yet to be tested in human patients, but its success in preclinical experiments makes it ready for clinical trials, according to the researchers.

In order to demonstrate this possible use, the researchers produced real-time 3D images of a dog's right pulmonary veins -? sites that are targeted in treating atrial fibrillation.

The laparoscopic ultrasound probes may be particularly useful for monitoring heart function during minimally invasive cardiac surgery. Current methods often monitor the heart with a 2D ultrasound endoscope probe down the throat, a method known as transesophageal echocardiography (TEE). This procedure requires general anesthesia. The images can reveal the condition of the heart chambers, valves, major blood vessels and heart tissue. TEE is a safe and fast diagnostic technique.

The new probe, when inserted inside the esophagus, creates a picture of the whole heart in the time it takes for current ultrasound technology to image a single heart cross section. This limitation makes it impractical for use in guiding therapeutic treatment devices such as ablation probes that burn off damaged cells that cause an irregular heart beat. In such procedures, cardiologists use catheters to burn specific locations on the surface of the heart in patients with atrial fibrillation, a disorder characterized by an abnormal heart rhythm. Clinicians must repeatedly and painstakingly reposition the 2-D probe during treatments so, instead, they use fluoroscopy (X-ray movies) to guide the placement of the treatment devices. However, the use of X-ray imaging results in radiation exposure for patients and requires bulky lead-shielding garments for clinicians. In addition, such procedures take up to seven hours to complete.

If physicians instead used the new laparoscopic ultrasonography imager, they could monitor function for hours through a tiny incision -? possibly without anesthesia.

Three-D ultrasound is already an established technology in many hospitals. However, the new real-time 3-D transesophageal probe has all the benefits of the 2-D TEE probe and none of the drawbacks. Doctors will be able to generate sharp, high-contrast images of the whole heart and position heart catheters and ablation devices at the same time. This is what the team says it has already achieved in laboratory tests on animals.

Duke developed the first 3D ultrasound scanner in 1987 for imaging the heart 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 image the vasculature and heart from the inside out.

Similar 3D ultrasound devices also hold promise for minimally invasive abdominal and brain surgery applications.

The research is funded by the Heart, Lung and Blood Institute at the National Institutes of Health and by the National Science Foundation.

By: Dr. Tamer Fouad,

Dr. Mihai Mavru,
Caritas University Hospital, Bucharest, Romania.


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