Study Uses MRI Sequence to Measure Placental Blood Flow in Pregnant Women
The noninvasive technique shows promise for detecting early aberrations in placental function and fetal development.
The amount of blood flowing through the placenta has a significant impact on the fetal environment, since it determines the quantity of oxygen delivered to the fetus. Typically, placental blood flow is indirectly assessed by examining the uterine arteries using Doppler ultrasound. However, this method can lack reproducibility and sensitivity.
As a possible alternative, researchers from the University of California, Los Angeles have demonstrated the use of a new MRI technique to noninvasively measure placental blood flow in pregnant women. The MRI technique performs perfusion imaging without a contrast agent using single-shot 3-D acquisition, capturing the entire placenta in eight slices. The study was published online Nov. 14 in The Journal of Magnetic Resonance Imaging.
The subjects included 34 normal pregnant women scanned twice in their second trimester, from 14 to 16 weeks and 19 to 22 weeks gestational age. Placental blood flow was measured with a method called pseudocontinuous arterial spin labeling, or pCASL, an MRI technique for measuring tissue perfusion which is commonly used on the brain. The researchers combined pCASL with a fast 3-D hybrid sequence that employed two different types of MRI pulse sequences, known as gradient and spin echo sequences. They also examined the women's arterial blood flow using the traditional Doppler ultrasound method. In particular, any abrupt drop of the waveform at the beginning of diastole—termed notching—was noted, as it indicates impaired perfusion.
Between the two gestational ages, average placental blood flow increased by 10.4 percent. The average placental blood flow as measured by MRI was much lower for subjects that showed notching in the Doppler ultrasound waveform as compared to those without notching, indicating that MRI was able to detect the same blood flow problems identified by traditional ultrasound methods.
While this particular technique remains in early stages, the study demonstrates the potential of using MRI to detect aberrations in placental function and normal fetal development. The hope is for MRI to provide more precision and detail about placental blood flow than the current standard of Doppler ultrasound, since it is able to provide a 3-D image of perfusion rather than a simple waveform.