Diagnostics & Imaging Week National Editor
As we get older, our arteries develop plaque, building up and clogging these vessels and sometimes and traveling to other parts of the body in troublesome, often fatal, ways.
Plaque can be removed from body and examined microscopically, but that provides little information concerning the source of the problem, or plaque growth and physiological characteristics within the body. And current scanning procedures provide only flat, 2-D views of obstructed arteries.
Now, researchers at the Wellman Center for Photomedicine of Massachusetts General Hospital's (MGH-Wellman; Boston) say they can get a highly detailed look at the interior of the coronary arteries using an advanced form of optical coherence tomography (OCT), called optical frequency-domain imaging (OFDI).
The researchers say that OFDI can provide microscopic 3-D views of inflammation and plaque in these arteries, providing significant information that would be highly helpful in both research and clinical applications.
In terms of research, the study indicates that this technique could assist in tracking the "natural history" of plaque development.
In clinical application, an important use would be to allow an earlier look, and providing guidance, to interventional treatment of plaque build-up.
OCT can examine tissues "one point at a time," according to the MGH-Wellman researchers, but OFDI can look at more than 1,000 points simultaneously using an imaging device that they have developed.
Inside a fiber-optic probe, a constantly rotating laser tip emits a light beam with an ever-changing wavelength. As the probe moves through the structure to be imaged, the measurement of how each wavelength is reflected back allows rapid acquisition of the data required to create the more detailed microscopic observation.
The technique can provide these 3-D images of an artery's microstructure in seconds though final processing takes awhile and this increased speed reduces signal interference from blood, which had plagued the first-generation technology.
The technique has been used to create detailed retinal images, and in 2006 members of the MGH-Wellman team reported the successful use of OFDI to image the esophagus and the coronary arteries of pigs.
The current research enrolled three patients receiving coronary stents at the Lahey Clinic (Burlington, Massachusetts). After stent placement, OFDI was used to image 3-cm to 7-cm-long segments of the patients' coronary arteries including the stented areas.
OFDI provided detailed images along the length of the arteries visualizing lipid or calcium deposits, immune cells that could indicate inflammation, and the stents and what the researchers characterized as "dramatic fly-through" views looking down the artery's interior. More detailed, cross-sectional images of narrowed vascular segments revealed features associated with the type of atherosclerotic plaques that are likely to rupture and cause a heart attack.
"This is the first human demonstration of a technique that has the potential to change how cardiologists look at coronary arteries," said Gary Tearney, MD, PhD, of the MGH Pathology Department and MGH-Wellman, the study's lead author. "The wealth of information that we can now obtain will undoubtedly improve our ability to understand coronary artery disease and may allow cardiologists to diagnose and treat plaque before it leads to serious problems."
Tearney and his colleagues acknowledge that their findings need to be duplicated in a larger group of patients and that 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. They say that a combination of OFDI and intravascular ultrasound might help with another of the technique's limitations, the inability to penetrate deep into tissues.
Brett Bouma, PhD, associate professor of pathology at Harvard Medical School (also Boston) and senior author of the report, said, "While more work remains, the technology is advancing at a rapid pace. We expect to see commercial devices available in a one- to two-year time frame."
The primary goal, he said, "is to help put the pieces in place to ensure that this technique will be widely available to interventional cardiologists."
The study, supported by a grant from the National Institutes of Health, is reported in the current issue of the journal JACC: Cardiovascular Imaging.
MGH-Wellman describes its mission as a focus on light applications in biomedicine, its studies ranging from laser surgery and in vivo microscopy to optical diagnostics and the use of photodynamic therapy.
In September, MSG-Wellman researchers hosted the first International Conference on Intracoronary OCT Standardization and Validation in Prague, Czech Republic, the conference emphasizing the need for standardization of intracoronary OCT and other processes for validating new imaging modalities, and additionally, gathering information from users of the technology.