Second-generation optical imaging technique improves upon the first
Optical frequency-domain imaging (OFDI) gives 3D microscopic views of significantly longer segments of coronary arteries and does so at a faster frame rate, necessitating less of a saline purge compared to optical coherence tomography (OCT), according to a study in the Nov. 17 issue of the Journal of the American College of Cardiology: Cardiovascular Imaging.

“This is the first human demonstration of a technique that has the potential to change how cardiologists look at coronary arteries,” said lead author Gary Tearney, MD, of the pathology department and the Wellman Center for Photomedicine at Massachusetts General Hospital (MGH) in Boston.

While OCT examines tissues one point at a time, the authors said that OFDI can look at more than 1,000 points simultaneously using a device developed at MGH-Wellman. Inside a fiberoptic probe, a rotating laser tip emits a light beam with a wavelength. As the probe moves through the structure to be imaged, it measures how each wavelength is reflected back, allowing the acquisition of data required to create microscopic images. Besides providing 3D images of an artery's microstructure, the increased speed reduces signal interference from blood, the researchers said.

(A) Right anterior oblique angiogram after stent deployment, showing stent site (s) and 4.2-cm optical frequency domain imaging (OFDI) pullback segment (ps). (B) Maximum intensity projection and (C) cutaway views of 3-dimensional volume-rendered OFDI data set, showing scattered calcium deposits and a large lipid-rich lesion at the distal portion of the pullback segment (red arrowhead). Color scale for B and C: red = artery wall; green = macrophages; yellow = lipid pool; blue = stent; white = calcium; gray = guidewire. Scale bars in B and C, 5.0 mm. Source: JACC  
The current study enrolled three patients scheduled to have coronary stent implantation at the Lahey Clinic in Burlington, Mass. After the completion of stent placement, OFDI was used to image three- to seven-centimeter-long segments of the patients’ coronary arteries including the stented areas, according to the investigators.

The researchers said that OFDI provided images along the length of the arteries— visualizing lipid or calcium deposits, immune cells that could indicate inflammation and the stents—and fly-through views looking down the artery's interior. More detailed, cross-sectional images of narrowed vascular segments revealed features associated with atherosclerotic plaques that are likely to rupture and cause a heart attack.

Tearney and colleagues noted that the findings need to be duplicated in a larger group of patients, and the time required to process the fly-through images—currently several hours—needs to be reduced to provide the real-time information most useful for clinical applications. Combining OFDI with intravascular ultrasound might help with another of the technique's limitations, the inability to penetrate deep into tissues.

“We expect to see commercial devices available in a one- to two-year time frame," said Brett Bouma, PhD, of the Wellman Center, senior author of the report. "Our goal now is to help put the pieces in place to ensure that this technique will be widely available to interventional cardiologists.”

Terumo has licensed cardiovascular applications of OFDI, according to MGH.