Doppler OCT imaging sheds light on health of baby's heart

For the first time, researchers at Case Western Reserve University (Cleveland, OH), using an optical coherence tomography (OCT) method, have been able to visualize in 3D the stresses induced by flowing blood in an embryonic heart. The method is promising for learning how and why heart defects develop.

The researchers, led by Andrew M. Rollins, an associate professor of biomedical engineering at Case Western Reserve University, looked at a particular type of stress in the heart known as shear stress, which is simply the parallel force of one material sliding along another. In the developing heart, shear stress is induced in the heart’s own endocardial cells as blood cells rush past them. Normally, such shear stress helps to control and regulate cellular processes involved in heart development. Even tiny aberrations in the heart beat, however, can alter blood flow patterns and change these developmental forces, leading to congenital heart defects such as abnormal valve formation.

A quail embryo: the bulge on the middle left side of the embryo is its developing heart
A quail embryo: the bulge on the middle left side of the embryo is its developing heart. (Image courtesy of Biomedical Optics Express)

“All previous attempts at shear-stress mapping have been two-dimensional, but the 3D geometry of the embryonic heart is changing hour by hour at these early stages, and the shape of the heart twists and turns as it develops,” says Rollins, “so a 2D projection doesn’t really provide a good approximation.”

Rollins and colleagues used Doppler OCT, which shines a beam of infrared (IR) light on tissue. Then, the reflections of that light produced at varying depths are used to make a high-resolution image. The technique has been used to image the interior of blood vessels and is routinely used by ophthalmologists to examine the retina.

“We can use this technique to figure out just how function or dysfunction fits into normal heart development and the development of heart defects,” Rollins adds. “An understanding of normal and abnormal development is critical for preventing and treating these defects.”

A map of the shear stress on a developing heart at four evenly spaced time points during a heart cycle. Red indicates areas of greater stress
A map of the shear stress on a developing heart at four evenly spaced time points during a heart cycle. Red indicates areas of greater stress. (Image courtesy of Biomedical Optics Express)

In laboratory experiments, Rollins and colleagues directly measured the heart structure and blood flow within the developing hearts of quail embryos. The data was then used to create 4D images, which showed that “locations of high shear correspond with locations of future valve formation,” he says. “Now we are investigating the effects of abnormal shear caused by alcohol exposure on valve development.”

The researchers hope to take what they have learned from these preliminary animal tests and develop a way to apply this method to humans. The ultimate goal is to develop a tool that doctors can use to decide if early intervention could put a developing heart back on the right track, preventing a defect.

The work appears in Biomedical Optics Express; for more information, please visit http://www.opticsinfobase.org/boe/abstract.cfm?uri=boe-3-11-3022.

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