MRI may better enable physicians to plan care for infants with heart defects

Magnetic resonance imaging (MRI) techniques can provide real-time measurements of volume in a fetal heart, and may better enable physicians to plan care for infants with heart defects, according to a new study. By producing three-dimensional measurements, functional MRIs may represent an advance over the current technology, fetal echocardiography.

"With echocardiography, the heart looks like a shadow. It looks more like a heart with real-time MRI, with excellent soft tissue contrast," said pediatric cardiologist Mark A. Fogel, M.D., director of Cardiac MRI at The Children's Hospital of Philadelphia. A research team led by Dr. Fogel reported preliminary findings based on studies on two fetuses in the September/October 2005 issue of Fetal Diagnosis and Therapy. It was the first example of functional MRI used for cardiac imaging in fetuses.

MRI produces three-dimensional images, whereas echocardiography typically relies on geometric assumptions to measure how big the heart is in the fetus, added Dr. Fogel. One consequence of this capability is that MRI can directly measure the volume of the heart's ventricles.

Echocardiography, which uses reflected ultrasound waves to produce images, may allow physicians to estimate such volumes, but only if the heart has a normal shape. "Many heart diseases involve abnormal shapes, and accurately measuring ventricular volume in such cases is important in assessing how well the heart is working, and in guiding doctors to the most appropriate treatment," said Dr. Fogel.

"For example, if the fetus has poor heart function, a physician might prescribe a drug that improves pumping, or might recommend an earlier delivery," he added. "Better knowledge of specifics of a heart's structure and function could help the physician and parents better prepare for surgery on the infant after birth. This technology may also be useful in determining how the heart becomes malformed in the mother's womb."

Although further studies will be necessary to build on his team's preliminary results, Dr. Fogel suggests that fetal cardiac MRI may be used to complement echocardiography in cases where the latter technology cannot adequately visualize heart structures.

Furthermore, he added, advances in MRI technology may enhance its medical capabilities for fetal medicine. Previously, fetal movement blurred MRI imaging, but as shown in the current study, real-time functional MRI provides usable images in an unsedated, moving fetus. "We expect future MRI technology to provide better resolution and sharper images, produced in shorter times," he said. "Our study is a first step in that direction."