The aftermath of heart surgery requires several trips back to the doctor to check stents (small mesh tubes that are used to treat narrowed or weakened arteries in the body) and keep track of scar tissue.  In order to do these checks, high-resolution pictures of the interior of a coronary artery need to be taken and this procedure currently causes the heart to have to be kept free of blood for up to thirty seconds.  However, there is a new approach that seems poised to reduce the time required for imaging and this will make it safer and easier for doctors to do their checks.

Optical coherence tomography (OCT), which is a high-resolution medical imaging system, and which has been in use in ophthalmology for more than a decade, forms the base of the new approach. OCT has occasionally been used to scan arteries but is problematic because it cannot see through blood, so any area being scanned has to be flushed with saline. A special balloon is also used during the procedure to block incoming blood and this can cause damage to the tissue.

OCT can deliver much higher resolution because it is based on light and optics, rather than sound or radio frequency radiation. It works as follows: An optical beam is projected into the subject, and light is reflected from the layers and sub-surface artefacts as the beam penetrates. Most of this light is scattered on its way back to the surface. Scattered light has lost its original direction and therefore cannot be used for imaging: this is why scattering material such as tissue appears opaque to the human eye. However, a very small proportion of the reflected light is not scattered. It is this non-scattered light that is detected and used in an OCT microscope.

Work is being done on improving OCT by a number of companies using what is known as the Fourier domain. This allows multiple wavelengths of data to be gathered simultaneously rather than sequentially, which is an improvement on previous generations of the technology, as this method dramatically reduces the time needed to perform a scan.

Thomas Milner, associate professor in the Department of Biomedical Engineering at the University of Texas, says Optical Fourier domain imaging is "a fairly well-established approach in principle and it's just starting to work its way into instruments that will be on the market soon."

An initial application for this technology will be to image stents after insertion to ensure they haven't shifted.  The increased accuracy of OCT technology allows doctors to monitor how well the stent is fusing to the arterial walls and to track small amounts of endothelial re-growth that would go unnoticed by IVUS.  It could also be used to check healing after operations. The resolution of this scan is fine enough to allow doctors to see small but significant plaque deposits that existing technology might overlook. The technology could also be used to carefully target biopsies, as cancerous cells could be identified in much smaller quantities than currently possible.

This technology will be coming into use "in the very near future...by the end of 2009 at the latest," says Craig Kelley, director of marketing for LightLabs, one of the companies exploiting this technology.