Three-dimensional ultrasound shows utility in fetal lung volume measurements

Three-dimensional ultrasound can be used to measure fetal lung volume (FLV) for up to 30 weeks gestation, and the technique offers good agreement with MRI in cases with congenital diaphragmatic hernia (CDH), according to separate articles in the March issue of the Journal of Ultrasound in Medicine.

With the goal of building a nomogram of normal fetal lung volumes and assessing the reproducibility of measurements using 3-D ultrasound, researchers from Thomas Jefferson University in Philadelphia studied 75 patients over a nine-month period, from which 182 volumes were analyzed (JUM, March 2004, Vol. 23:3, pp. 347-352).

Scans were performed using a Voluson 530D MT scanner (GE Healthcare, Waukesha, WI) with a 3-to-5 MHz transabdominal three-dimensional volume probe.

Of the 182 volumes, 15 (8.2%) were excluded for poor quality. In the remaining 167 volumes, 83 (50%) volumes could not visualize the clavicle landmark.

The researchers found a second-degree polynomial regression curve to be the best fit for total lung volume. Lung volume was 10.28 mL at 20 weeks and 51.49 mL at 30 weeks.

The study team assessed agreement by selecting 40 volumes. Intraobserver variability was 5.48 mL (10.6%) and 3.07 mL (5.96%), respectively. Interobserver variability was 7 mL.

The findings suggest that 3DUS-derived measurements are reliable and reproducible up to 30 weeks, the researchers said.

"As resolution increases and volume acquisition times shorten, one would expect more accurate determination of fetal lung volumes," the authors noted.

The researchers believe that the clinical value of measuring fetal lung volumes needs to be studied further, as there presently is no reliable information that directly links fetal lung volume with fetal lung maturity.

"Although we proved that we could reliably measure the fetal lung volumes up to 30 weeks with 3DUS, how these volumes correlate with lung maturity, lung architecture, respiratory mechanics, respiratory distress syndrome, and standard biometric measurements requires further investigation," the researchers wrote.

Calculation of fetal lung volumes is a quantitative measurement method, and, as such, it does not necessarily provide reliable qualitative information on the status of lung maturity, according to the study team.

"Ultimately, the goal would be to determine what fetal lung volume, when combined with information from other qualitative measurement techniques (i.e., pulmonary flow or oxygenation studies) at any given gestational age, would predict lungs that are mature enough to sustain an early delivery without postnatal complications," the authors said. "Further research is clearly needed to establish the role of 3DUS in the prenatal evaluation of fetal lung maturity."

US/MRI correlation

To assess the agreement of 3-D ultrasound and MRI in estimating FLV in cases with isolated congenital diaphragmatic hernia (CDH), researchers from Hôpital Necker-Enfants Malades in Paris, France prospectively measured fetal lung volume in 11 cases using both modalities (JUM, March 2004, Vol. 23:3, pp. 353-358).

The 3-D ultrasound scans were given using a Voluson 730 system (GE Healthcare), using a 4-to-8 MHz transducer for 3-D volume scanning. For MRI, the entire thorax was sampled via a two-dimensional acquisition with fast-spin-echo sequences. The scans were then reconstructed to obtain a 3-D model of both lungs, with total lung volume and left and right lung volume measured automatically.

The exams were performed during the same week, and the operators were blinded to each other’s results. The researchers employed intraclass correlation to evaluate the agreement between 3-D ultrasound and MRI estimates of the ipsilateral, contralateral, and total FLV. A Bland-Altman graph was also plotted to detect possible discordant observations.

For total lung volume, intraclass correlation was 0.94 (95% confidence interval), with 0.91 (95% confidence interval) for the contralateral lung and 0.93 (95% confidence interval) for the ipsilateral lung volume. The results suggest that FLV can be estimated by either 3-D multiplanar imaging or by MRI in CDH cases, the researchers said.

"In conclusion, there was a significant agreement between MRI and 3DUS for estimating FLV in cases with isolated CDH," the authors wrote. "Further studies are needed to evaluate the clinical interest of 3D-US in predicting the postnatal outcome of fetuses with CDH."

By Erik L. Ridley staff writer
March 18, 2004

Related Reading

Part II: The psychological impact of 3-D ultrasound on pregnant women, December 30, 2003

Part I: The psychological impact of 3-D ultrasound on pregnant women, December 29, 2003

3-D ultrasound shows promise in neonatal, pediatric neurosonography, November 4, 2003

Turf Wars in Radiology IV: Radiologists, ob/gyns sound off on fetal imaging, September 26, 2002

MRI second-guesses fetal ultrasound, April 25, 2001

Copyright © 2004

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