MRI catches beating fetal heart

Researchers from The Children's Hospital of Philadelphia have performed real-time functional cardiac MRI in two fetuses. It is the first time this technique has been reported, and it may represent an advance over the current gold standard of fetal echocardiography.

Quantitatively, fetal echocardiography relies on geometric assumptions to determine ventricular volume. This can be problematic with odd-shaped hearts found in congenital heart disease patients. MRI, on the other hand, produces 3D images and can directly measure ventricular volume, said lead investigator Dr. Mark A. Fogel, director of cardiac MRI at CHOP.

In one case, fetal echocardiography could not differentiate between true extracardiac compression of a normal heart and hypoplastic left-heart syndrome. With real-time TrueFISP cine MRI, physicians determined the fetus suffered from the latter.

The second fetus had ductus arteriosus constriction and right ventricular dilation and hypertrophy. Measurement of the ductus arteriosus and descending aorta by MRI (5 mm) was within 1 mm of the value obtained by fetal echocardiography (6 mm).

MRI functional data came within 15% of the value calculated by Doppler echocardiography in the great arteries, according to the study published in the September/October issue of Fetal Diagnosis and Therapy. Fetal echocardiography yielded a cardiac index of 153 cm3/kg/min, while MRI produced a cardiac index of 127 cm3/kg/min. Researchers suggest the lower MRI cardiac index could be due in part to the sedation of one fetus during MRI but not at echocardiography. (The average gestational age of the fetuses at MRI was 33 weeks.)

"In time, temporal and spatial resolution will only improve, making this technique even more clinically valuable," Fogel said.