Durham, NC - Engineers at Duke University have developed a new three-dimensional (3D) ultrasound probe for transesophageal echocardiography (TEE) [1]. The new probe, described by E Chris Pua (Duke University, Durham, NC) and colleagues in this month's issue of Ultrasonic Imaging, can capture an image of the entire heart in the time it takes current technology to image a single section of the heart. Should the prototype pass future clinical tests, it will become the first TEE probe capable of delivering real-time 3D images (also known as "4D").

Eric (Chris) Pua and his 3D TEE probe (Source: Duke University Photography)

"Right now there are several companies that offer real-time transthoracic (TTE) echo," senior author Dr Stephen Smith (Duke University) told heartwire. "This is the first probe that's worked for TEE, at least in animal studies. The big companies, Philips and GE, are certainly working on this as well."

Pua, a graduate student working with Smith, built the prototype device—dubbed the Model 1 system (Volumetrics Medical Imaging, Durham, NC)—using the outer casing of a commercially available 2D TEE probe as the housing for the new 3D model. The 3D probe has a dime-sized array of 504 individual ultrasound sensors, each only as wide as a few human hairs. In a press statement, Pua emphasized that keeping the size of the probe the same as currently available models was a key factor, despite the fact that the new design houses cabling for the 504 active channels, nearly eight times the number of transducer elements as in the original 2D probe.

"It took a craftsman to create this probe," Smith said in praise of his student.

As Smith explains, current TEE probes acquire 2D slices and can create a 2D image in about a 30th of a second. These "old-fashioned" probes can create a 3D image by sequentially acquiring 2D slices, which are then used to reconstruct a 3D image. Making one 3D image may take several minutes.

"Ours makes 30 3D images per second," he says.

Existing TEE probes fall into the categories of single plane, biplane, and multiplane transducers. The probe developed by Pua, Smith, and colleagues is a matrix-array probe. As Smith explains, "whereas the old-fashioned transducers might have 64 little sensors in a row to make one plane, ours has roughly 50x50 sensors—that's 2500—in a checkerboard pattern. And because of that, we can scan those sensors in a full pyramid, rather than just in a single plane that's slowly rotated."

Being able to perform 4D TEE would have many advantages over current 2D TEE, Smith said. Right now, much of the excitement over 4D TTE has been due to its ability to accurately assess left-ventricular volumes and ejection fraction, as reported by heartwire. In patients in whom TTE cannot provide quality images—patients with larger body size, postcardiac surgery patients, and patients with intrathoracic diseases, such as chronic obstructive pulmonary disease—TEE must be used instead. "Our probe allows you to accurately determine ejection fraction from inside the body, rather than outside the body," Smith explains. The real-time images from the new probe would also be an asset for lead placement for biventricular pacing and for certain EP procedures, he says.

Commenting on the prospect of a 4D TEE probe for heartwire, Dr Christopher Thompson (St Paul's Hospital, Vancouver, BC) called the development of the prototype a "formidable accomplishment."

"I see a potentially significant role for this technology in guiding interventional valve procedures, including percutaneous valve replacements and repairs and electrophysiological ablation and modification," Thompson said. "Another potential advantage is limiting the duration the probe must remain in the patients; it is theoretically possible to acquire several 3D data sets, then withdraw the probe and complete the generation and analysis of other 2D images from that data set offline."