Estimation of fetal lung volume using enhanced 3-dimensional ultrasound: a new method and first result

Fetal lung maturity assessment: A historic perspective and Non - invasive assessment using an automatic quantitative ultrasound analysis (a potentially useful clinical tool)

Immature fetal lung is associated with many adverse outcomes including respiratory distress syndrome and transient tachypnoea of the newborn. Several methods/tools have been used over several decades to assess fetal lung maturity prior to delivery. Some of the methods that have been used to assess fetal lung maturity include amniocentesis for the biochemical markers, lecithin and sphingomyelin, lamellar body counts, gray scale ultrasound scan and magnetic resonance imaging. Amniocentesis an invasive procedure which carries a small risk of miscarriage has almost become obsolete. Magnetic resonance imaging on the other hand is expensive and not very practical. Quantitative ultrasound fetal lung maturity (quantusFLM) assessment is a new technique aimed at assessing fetal lung texture using ultrasound. The technique depends on visualization of fetal lungs at the level of the 4- chamber view. Images obtained are then uploaded via a web page application and these are analyzed remotely and results generated in minutes. The analysis depends on studying changes in the texture of lung images that depend on changes at histological level especially of collagen, fat and water. These changes are undetectable to the human eye. Randomized clinical trials have shown this technique to be accurate, reproducible, and completely non - invasive. The aim of this review was to take a historic look at methods/tools for assessing fetal lug maturity and discuss further advances and a potential non-invasive tool/method especially the non-invasive assessment that combines ultrasound scan and machine learning to accurately assess lung maturity.

Prenatal assessment of pulmonary maturity on 3-D ultrasound

AIM

The aim of this study was to assess the feasibility and accuracy of 3-D ultrasound indices to evaluate fetal lung maturity, and to establish a normal reference for fetal lung volume (FLV) and fetal lung-to-liver intensity ratio (FLLIR) in a Chinese population.

METHODS

A total of 1022 pregnant women with singleton pregnancy were prospectively studied between June 2008 to June 2011. Ultrasound examination was performed. The breathing-related nasal fluid flow (BRNFF) spectrum, FLV, pulmonary artery blood flow parameters, and echo intensity of the lung were calculated. Phosphoglycerides in the amniotic fluid were measured on thin layer chromatography.

RESULTS

FLLIR and FLV were positively and linearly correlated with gestational age (F = 0.915, 0.846). Indicators of fetal lung maturity included FLLIR >1.1, FLV >50 mL, and regular BRNFF spectrum, with positive likelihood ratios of 12.28, 11.78, and 11.63, independently.

CONCLUSION

Ultrasound indices, including FLLIR, FLV and BRNFF may serve as useful alternatives to amniotic fluid phospholipids in analyzing fetal lung maturity in Chinese patients.

Recent advances in sonographic imaging of fetal thoracic structures

Recent ultrasonographic methods applied in the evaluation of fetal thoracic structures and anomalies are presented. Fetal lung volumetric assessment by 3D ultrasonography, analysis of the thoracic wall by 3D-rendered image and 3D skeletal-mode imaging, intrathoracic vessel evaluation by 3D power Doppler ultrasonography, analysis of heart anatomy and abnormalities by 4D spatiotemporal image correlation, identification of normal and abnormal intrathoracic almost isoechogenic structures by volume contrast imaging and evaluation of the heart and great vessels by 3 and 4D inverse mode will be reviewed.

A review of fetal volumetry: the need for standardization and definitions in measurement methodology

Volume charts of fetal organs and structures vary considerably among studies. This review identified 42 studies reporting normal volumes, namely for fetal brain (n = 3), cerebellum (n = 4), liver (n = 6), femur (n = 2), lungs (n = 15), kidneys (n = 3) and first-trimester embryo (n = 9). The differences among median volumes were expressed both in percentage form and as standard deviation scores. Wide discrepancies in reported normal volumes make it extremely difficult to diagnose pathological organ growth reliably. Given its magnitude, this variation is likely to be due to inconsistencies in volumetric methodology, rather than population differences. Complicating factors include the absence of clearly defined anatomical landmarks for measurement; inadequate assessment and reporting of method repeatability; the inherent difficulty in validating fetal measurements in vivo against a reference standard; and a multitude of mutually incompatible three-dimensional (3D) imaging formats and software measuring tools. An attempt to standardize these factors would improve intra- and inter-researcher agreement concerning reported volumetric measures, would allow generalization of reference data across different populations and different ultrasound systems, and would allow quality assurance in 3D fetal biometry. Failure to ensure a quality control process may hamper the wide use of 3D ultrasound.

MR volumetry of brain and CSF in fetuses referred for ventriculomegaly

OBJECTIVE

The purpose of this study was to validate the method of performing fetal brain volumetry. In particular, our objectives were to assess which imaging plane is most reproducible for the performance of brain volumetry measurements and to ascertain inter- and intraobserver variability in determining brain volume in fetuses referred for ventriculomegaly (VM).

SUBJECTS AND METHODS

In this prospective study, 50 consecutive fetuses at 17-37 weeks of gestational age referred for MRI for VM underwent fast spin-echo T2-weighted imaging. Supratentorial brain parenchyma, lateral ventricles, and extraaxial and cerebellar volumetric measurements were manually obtained in three planes by three radiologists. Inter- and intraobserver variability were assessed. The relationship between volumes and gestational age, and lateral ventricular diameter were assessed.

RESULTS

Volumes increased with gestational age. The presence of VM correlated with increased lateral ventricle diameter. The effect of imaging plane was negligible. Inter- and intraobserver variability were low.

CONCLUSION

Supratentorial parenchyma and lateral ventricular volumes can be reliably measured on fetal MRI, and imaging plane was not an important factor in measurement. Further studies are needed to correlate these indexes with long-term postnatal outcomes.

Predicting pulmonary hypoplasia using the sonographic fetal lung volume to body weight ratio--how precise and accurate is it?

OBJECTIVES

To determine the precision and accuracy of ultrasound in estimating the fetal lung to body weight ratio (FLB ratio) using two-dimensional (2D) and three-dimensional (3D) ultrasound by comparison with postmortem measurements, and to evaluate its potential to diagnose pulmonary hypoplasia.

METHODS

Lung volumes were estimated by 3D ultrasound (rotational technique) and fetal weights were measured by 2D ultrasound (Hadlock equation) in 35 fetuses immediately before termination of pregnancy at 15-38 weeks. Sonographic estimates of FLB ratio were compared with postmortem values. Based on the pathological definition of pulmonary hypoplasia, the accuracy of sonographic estimation of the FLB ratio was analyzed.

RESULTS

The mean gestational age at termination of pregnancy was 26.7 (range, 15-38) weeks. The mean FLB ratios were 0.018 (SD, 0.006) on ultrasound and 0.019 (SD, 0.007) at autopsy (P = 0.730). Bias and precision of sonographic FLB ratio were - 0.001 and 0.003 (absolute limits, - 0.007 to + 0.006), respectively. Pulmonary hypoplasia was diagnosed in 12 (34.3%) cases at autopsy. The sonographic FLB ratio was significantly lower in fetuses with pulmonary hypoplasia at autopsy (median, 0.011; range, 0.004-0.014) than it was in those without pulmonary hypoplasia (median, 0.022; range, 0.013-0.045, P < 0.001). The sensitivity and specificity of the sonographic FLB ratio for diagnosing pulmonary hypoplasia were 91.7% (11/12) and 91.3% (21/23), respectively, the positive and negative predictive values were 84.6% (11/13) and 95.5% (21/22), and the accuracy was 91.4% (32/35).

CONCLUSION

FLB ratio can be estimated precisely on ultrasound examination, albeit with wide limits of agreement. The sonographically estimated FLB ratio may be useful in the prediction and diagnosis of pulmonary hypoplasia.

Fetal pulmonary artery diameter measurements as a predictor of morbidity in antenatally diagnosed congenital diaphragmatic hernia: a prospective study

OBJECTIVE

The objective of the study was to examine the size and growth of fetal pulmonary artery diameters in congenital diaphragmatic hernia and assess their correlation with postnatal survival and morbidity outcomes.

STUDY DESIGN

Prospective antenatal echocardiographic examination of fetal branch pulmonary arteries were correlated with postnatal survival and respiratory morbidity in cases of congenital diaphragmatic hernia. Receiver operator curves were developed to assess their utilization as predictors of respiratory morbidity and survival.

RESULTS

Twenty-one cases were diagnosed antenatally over 3 years. Fifteen subjects survived postnatally. The ipsilateral fetal branch pulmonary artery diameter was smaller throughout gestation in left-sided congenital diaphragmatic hernia (P = .008). The small left pulmonary diameter did not correlate with survival but correlated strongly with morbidity outcomes. Progressive ipsilateral fetal pulmonary artery hypoplasia was demonstrated throughout gestation in subjects who died or had severe morbidity.

CONCLUSION

Fetal pulmonary artery diameter measurements correlate with respiratory morbidity in postnatal congenital diaphragmatic hernia and may assist with prediction of outcome. Survival has improved, possibly because of improved postnatal management of congenital diaphragmatic hernia, limiting this measurement in assessing survival.

A nomogram of fetal lung volumes estimated by 3-dimensional ultrasonography using the rotational technique (virtual organ computer-aided analysis)

OBJECTIVE

The purpose of this study was to build a nomogram of normal fetal lung volumes throughout gestational age estimated by 3-dimensional ultrasonography using the rotational technique (Virtual Organ Computer-Aided Analysis [VOCAL]; GE Healthcare, Kretztechnik, Zipf, Austria).

METHODS

Fetal lung volume was assessed in 146 healthy fetuses by 3-dimensional ultrasonography using the technique of rotation of the multiplanar imaging (VOCAL). Inclusion criteria were healthy women with singleton normal pregnancies, normal fetal morphologic ultrasonographic findings, reliable dating established by dates and by ultrasonographic measurement of the crown-lump length in the first trimester, and gestational age from 20 to 37 weeks. Exclusion criteria were discordance between clinical and ultrasonographic dating, patients lost to follow-up, and birth weight disorders. Each patient was scanned once during pregnancy.

RESULTS

The right, left, and total mean pulmonary volumes ranged, respectively, from 5.37, 4.66, and 9.95 cm3 at 20 weeks to 46.06, 37.34, and 84.35 cm3 at 37 weeks. The logistic transformation analysis yielded the following formulas: right lung volume = exp(4.07/[1 + exp(21.90 - gestational age/5.44)]); left lung volume = exp(3.82/(1 + exp[22.03 - gestational age/5.17)]); and, total lung volume = exp(4.72/[1 + exp(20.30 - gestational age/6.05)]).

CONCLUSIONS

A new nomogram of fetal lung (right, left, and total) volumes throughout gestational age using the rotational technique (VOCAL) is described, and reference values have been generated.

Normal fetal lung volume measured with three-dimensional ultrasound

OBJECTIVES

To construct reference intervals for fetal lung volumes measured longitudinally using three-dimensional (3D) ultrasound, and to evaluate the effect of gender on lung size.

METHODS

This was a prospective, longitudinal study in the obstetric outpatient department of the VU University Medical Center, Amsterdam. Seventy-eight women with uncomplicated pregnancies were scanned three to four times at gestational ages of 18-34 weeks. 3D models of the lung were constructed using the ultrasound machine's software. After the infants were delivered the entire group was reanalyzed with regard to fetal gender. Centiles for the lung volumes of the entire group and for each gender separately were estimated using multilevel modeling.

RESULTS

Charts and tables of right and left fetal lung volumes, using gestational age and estimated fetal weight as the independent variables, are presented. There was a significant difference in lung volume between male and female fetuses at each gestational age. Charts and tables of right and left fetal lung volumes for each gender at gestational ages of 18-34 weeks are also presented.

CONCLUSIONS

We present valid references for volumetric measurements of the right and left fetal lungs in male and female fetuses. The feasibility and reliability of fetal lung volume measurements using 3D ultrasound is good.

Lung and heart volumes by three-dimensional ultrasound in normal fetuses at 12-32 weeks' gestation

OBJECTIVE

To establish reference intervals for the fetal right, left and total lung volumes and heart volume between 12 and 32 weeks of gestation.

METHODS

Fetal lung and heart volumes were measured using three-dimensional (3D) ultrasound in 650 normal singleton pregnancies at 12-32 weeks. The VOCAL (Virtual Organ Computer-aided AnaLysis) technique was used to obtain a sequence of six sections of each lung and the heart around a fixed axis, each after a 30 degrees rotation from the previous one. The rotation axis for the lungs extended from the apex to the upper limit of the diaphragm dome, and the rotation axis for the heart extended from its apex to its connection to the great vessels. The contour of each of these organs was drawn manually in the six different rotation planes to obtain the 3D volume measurement. In 60 cases the fetal lungs and heart volumes were measured by the same sonographer twice and also by a second sonographer once in order to compare the measurements and calculate intra- and interobserver agreement.

RESULTS

The total lung volume and heart volume increased with gestation, from respective mean values of 1.6 and 0.6 mL at 12 weeks to 10.9 and 4.3 mL at 20 weeks and 49.3 and 26.6 mL at 32 weeks. The right to left lung volume ratio did not change significantly with gestation (median, 0.7), whereas the heart to total lung volume ratio increased with gestation from about 0.3 at 12 weeks to 0.5 at 32 weeks. In the Bland-Altman plot, the difference between paired measurements by two sonographers was, in 95% of the cases, less than 0.05, 0.5 and 1.9 mL for each lung at 12-13, 19-22 and 29-32 weeks, respectively, and the corresponding values for the heart volumes were 0.04, 0.4 and 2.3 mL.

CONCLUSIONS

In normal fetuses the lung and heart volumes increase between 12 and 32 weeks of gestation. The extent to which in pathological pregnancies possible deviations in these measurements from normal prove to be useful in the prediction of outcome remains to be determined.

Prenatal prognosis of congenital diaphragmatic hernia using magnetic resonance imaging measurement of fetal lung volume

OBJECTIVES

To investigate the correlation between fetal lung volume (FLV), measured with magnetic resonance imaging (MRI), and postnatal mortality in newborns with prenatally diagnosed isolated congenital diaphragmatic hernia (CDH).

METHODS

In a 4-year prospective multicenter study, 77 fetuses with isolated CDH diagnosed between 20 and 33 weeks' gestation underwent fast spin-echo T2-weighted lung MRI. These MRI-FLV measurements were compared with a previously published normative curve obtained in 215 fetuses without thoracoabdominal malformations and with normal ultrasound biometric findings. FLV measurements were correlated with postnatal survival. The mean gestational age at MRI was 31.3 weeks.

RESULTS

The measured/expected FLV ratio was significantly lower in the newborns with CDH who died compared with those who survived (23.6 +/- 12.2 vs. 36.1 +/- 13.0, P < 0.001). When the ratio was below 25%, there was a significant decrease in postnatal survival (19% vs. 40.3%, P = 0.008). Survival was significantly lower for neonates when one lung could not be seen by fetal MRI compared with those fetuses with two visible lungs on MRI (17.9% vs. 62.1%, P < 0.001).

CONCLUSION

In isolated CDH, FLV measurement by MRI is a good predictor of postnatal mortality due to pulmonary hypoplasia.

Accuracy of fetal lung volume assessed by three-dimensional sonography

OBJECTIVE

To determine the accuracy and precision of prenatal three-dimensional (3D) ultrasound in estimating fetal lung volume using the rotational multiplanar technique (VOCAL) by comparing it to postmortem volume measurements.

METHODS

Fetal lung volume was measured during 3D ultrasound examination using a rotational multiplanar technique in eight cases of congenital diaphragmatic hernia (CDH) (six left and two right-sided) and in 25 controls without pulmonary malformation, immediately before termination. Prenatal 3D sonographic estimates of fetal lung volume were compared with postmortem measurement of fetal lung volume achieved by water displacement.

RESULTS

The intraclass correlation coefficient of fetal lung volume estimated by 3D ultrasound and measured at postmortem examination was 0.95 in CDH cases and 0.99 in controls. Based on Bland-Altman analysis, the bias, precision and limits of agreement were, respectively, 0.35 cm(3), 1.46 cm(3) and between -2.51 and + 3.21 cm(3) in cases with CDH and 0.08 cm(3), 2.80 cm(3) and between -5.41 and + 5.57 cm(3) in controls. The mean relative error of 3D ultrasound fetal lung volume measurement was -7.19% (from -42.70% to + 18.11%) in CDH cases and -0.72% (from -30.25% to + 19.22%) in controls, while the mean absolute error of 3D ultrasound fetal lung volume measurement was 1.40 (range, 0.71-2.52) cm(3) and 2.12 (range, 0.05-4.98) cm(3), respectively. Accuracy of 3D ultrasound for measuring fetal lung volumes was 84.86 (range, 57.30-99.48)% in cases with CDH and 91.38 (range, 69.75-99.45)% in controls. The mean intraobserver variability for lung volume estimated by 3D ultrasound was 0.28 cm(3) in controls and 0.17 cm(3) in CDH cases.

CONCLUSION

Prenatal 3D ultrasound can estimate accurately fetal lung volume using the rotational multiplanar technique for volume measurements (VOCAL), even in fetuses with very small lungs, such as cases with isolated CDH.

Fetal lung volumetry using two- and three-dimensional ultrasound

OBJECTIVES

To compare methods of measuring fetal pulmonary volume and to establish nomograms of fetal pulmonary volume according to gestational age for the accurate diagnosis of pulmonary hypoplasia.

METHODS

Three methods of measuring fetal pulmonary volume in 39 normal fetuses were compared: two-dimensional (2D) ultrasound measurement assuming that the lung is a geometrical pyramid, three-dimensional (3D) ultrasound using the VOCAL rotational method, and the conventional multiplanar 3D mode. Linear regression was used to construct an equation for 3D volume calculation from 2D measurements (the re-evaluated pulmonary volume equation (RPVE)). Lung volume measurements were recorded from 622 singleton fetuses in order to construct nomograms.

RESULTS

There was no statistically significant difference between the lung volume values obtained using the two 3D modes. However, in comparison with the 2D measurements the volumes obtained were larger (mean difference = 11.99, P < 0.1 x 10(-6)). The relationship between the 2D and 3D volumes was determined using a statistical linear regression method: RPVE (mL) = 4.24 + (1.53 x 2DGPV), where 2DGPV (2D geometric pulmonary volume) = (surface area right lung base (cm2) + surface area left lung base (cm2)) x 1/3 height right lung (cm). Two nomograms were constructed, one for use with 2D and one for 3D technology.

CONCLUSION

2D pulmonary volume assessment can be used in clinical situations where fetal prognosis depends on lung volume and its growth potential. It is routinely available and easy to perform particularly when repeat measurements are required in evaluation of lung growth. We therefore propose this method as an alternative to magnetic resonance imaging or 3D ultrasound.

Quantitative and Qualitative Evaluations of Fetal Lung with MR Imaging

PURPOSE

To measure both volume and signal intensity of the fetal lung at magnetic resonance (MR) imaging and to evaluate the clinical use of this method to predict fetal pulmonary hypoplasia.

MATERIALS AND METHODS

A total of 87 fetuses evaluated with MR imaging at 24-39 weeks of gestation were classified into a control group with good respiratory outcome (group A, n = 58) or a poor outcome group with severe respiratory disturbance after birth (group B, n = 29). Planimetric measurement of total lung volume and calculation of the ratio of lung signal intensity to spinal fluid signal intensity (L/SF) were performed on MR images by using region-of-interest analysis. Regression analysis, analysis of covariance, analysis of variance, and receiver operating characteristic (ROC) analysis were performed.

RESULTS

The best fit for group A lung volume was represented by the regression line V = (2.41 x G) - 37.6 (r = 0.537, P <.001), in which V is lung volume and G is gestational weeks; that for group B, by V = (0.97 x G) - 14.0 (r = 0.378, P <.05). Results of analysis of covariance with gestational weeks used as a covariate showed a significant difference in lung volume between the two groups (P <.001). Mean +/- SEM for L/SF ratio was 0.817 +/- 0.013 and 0.598 +/- 0.019 in groups A and B, respectively (P <.001). For prediction of postnatal respiratory outcome, the area under the ROC curve for lung volume and L/SF ratio combined was 0.990, significantly higher than that for lung volume alone (P <.05).

CONCLUSION

Simultaneous measurement of fetal lung volume and signal intensity on MR images is a promising method for predicting fetal pulmonary hypoplasia.

Three-dimensional ultrasonographic assessment of fetal lung volume as prognostic factor in isolated congenital diaphragmatic hernia

OBJECTIVE

To evaluate the potential of three-dimensional ultrasound to predict outcome in congenital diaphragmatic hernia.

DESIGN

Prospective observational study.

SETTING

Tertiary care centre.

POPULATION

Twelve cases of isolated congenital diaphragmatic hernia (11 left-sided, 1 right-sided) and 109 controls.

METHODS

Fetal lung volume was assessed by three-dimensional ultrasound using the technique of rotation of the multiplanar imaging. In the control fetuses, a logistic transformation was performed to correlate fetal lung volume with gestational age, and the confidence interval was obtained with a bootstrap resampling. A mathematical equation was then obtained allowing calculation of the expected fetal lung volume as a function of gestational age. In fetuses with congenital diaphragmatic hernia, the observed/expected lung volume ratio was compared with postnatal outcome.

MAIN OUTCOME MEASURES

Neonatal mortality and pulmonary hypoplasia, which was defined as lung/body weight ratios less than 0.012.

RESULTS

The expected fetal lung volume was derived from the mathematical equation: Fetal lung volume (mL) = exp (4.72/(1 + exp ((20.32 - gestational age in weeks)/6.05))). The observed/expected fetal lung volume ratio was significantly lower in the congenital diaphragmatic hernia group (median: 0.34, range: 0.16-0.66), than in the control group (median: 1.02, range: 0.62-1.97, P < 0.0001). The distribution of this ratio was significantly downshifted in the infants with congenital diaphragmatic hernia who died (median: 0.19, range: 0.18-0.66) compared with survivors (median: 0.44, range: 0.36-0.66, P= 0.04). The observed/expected fetal lung volume ratio was also correlated with the postmortem lung/body weight ratio.

CONCLUSION

In isolated congenital diaphragmatic hernia, fetal lung volume measurement by three-dimensional ultrasound is a potential predictor for pulmonary hypoplasia and postnatal outcome.

Three-dimensional ultrasound fetal lung volume measurement: a systematic study comparing the multiplanar method with the rotational (VOCAL) technique

OBJECTIVES

This study was designed to compare a conventional multiplanar technique for three-dimensional (3D) ultrasound measurement of fetal lung volume with a rotational method using VOCAL trade mark (Virtual Organ Computer-aided AnaLysis).

METHODS

Thirty-two fetuses with a variety of conditions at risk for pulmonary hypoplasia were studied. 3D volume data sets of the fetal lungs were acquired using a commercially available ultrasound system. The right and left lung volumes were calculated separately using VOCAL and the multiplanar technique. The level of agreement between two independent observers in categorizing the 3D volume data set as measurable or non-measurable was determined. The interobserver and intermethod variabilities were also evaluated for both methods.

RESULTS

The intermethod variability was excellent (correlation r = 0.93 and r = 0.96 for the left and right lung, respectively), and there was substantial agreement between the results of both approaches (limits of agreement - 4.4 to 8.9 and - 3.4 to 4.8 mL for the right and left lung, respectively). Fetal lung estimation with VOCAL had a significantly higher interobserver variability than the multiplanar technique. Interobserver agreement in categorizing lung volume data sets as measurable or non-measurable was lower when VOCAL was used.

CONCLUSION

Fetal lung volume measurements can be undertaken interchangeably using the multiplanar technique or the rotational method with VOCAL. However, the latter was less reproducible (lower degree of agreement and significantly higher interobserver variability) than the former.

Prenatal prediction of lethal pulmonary hypoplasia: the hyperoxygenation test for pulmonary artery reactivity

OBJECTIVE

The purpose of this study was to determine the predictive accuracy of a test for neonatal death from pulmonary hypoplasia by measuring changes in fetal pulmonary artery blood flow on room air and during maternal hyperoxygenation.

STUDY DESIGN

Women who were carrying fetuses with congenital anomalies that may cause pulmonary hypoplasia were offered participation in the study as part of a comprehensive fetal echocardiogram. Each fetus at > or =30 weeks of gestation underwent Doppler measurement of the blood flow pattern in the first branch of either the right or the left pulmonary artery before and again during exposure to maternal breathing of 60% oxygen by mask. An increase in the fetal pulmonary blood flow with oxygen (a decrease of > or =20% of the pulsatility index) was considered a reactive test. A change of <20% in the flow pattern during maternal hyperoxygenation was a nonreactive test and suggested pulmonary hypoplasia. The primary outcome for this study was neonatal death from pulmonary hypoplasia.

RESULTS

Twenty-nine pregnancies met the criteria for inclusion in our study. Of the 14 fetuses who had a nonreactive hyperoxygenation test, 11 fetuses (79%) died of pulmonary hypoplasia. Of the 15 fetuses who had a reactive hyperoxygenation test, only one fetus (7%) died in the neonatal period. Sensitivity, specificity, and positive and negative predictive values were 92%, 82%, 79%, and 93%, respectively, with an odds ratio of 51 (95% CI, 4.6-560).

CONCLUSION

Testing fetal pulmonary vascular reactivity with maternal hyperoxygenation is highly predictive of pulmonary hypoplasia. A reactive test predicted 92% of surviving infants; a nonreactive test predicted 79% of fetal deaths from pulmonary hypoplasia.

Application of lung volume measurement by three-dimensional ultrasonography for clinical assessment of fetal lung development

OBJECTIVE

To prepare nomograms for normal fetal lung volume using three-dimensional ultrasonography and to evaluate the possibility of clinical applications of this procedure.

METHODS

One hundred twenty-five healthy neonates with birth weights within +/-1.5 SD (group A), 9 neonates with intrauterine growth restriction (birth weight less than -1.5 SD) but no severe respiratory disturbance at birth (group B), and 10 neonates with severe respiratory disturbance but no intrauterine growth restriction (group C) were studied. With the use of a three-dimensional ultrasonographic device, continuous B-mode images centering on the fetal thorax were acquired as volume data. Analytical software was used to repeatedly trace the contours of bilateral fetal lungs on transverse slices to calculate the lung volume.

RESULTS

In group A, the total volume of normal fetal lungs can be expressed by the second-degree regression equation: 0.08 x (gestational week - 30.1)2 + 3.28 x gestational week - 67.2 (R = 0.909; P < .001). The lung volumes of groups B and C were below the 25th and 2.5th percentiles, respectively, of this regression curve. For the same case, the lung volume increased with gestational week in group B but remained unchanged or even decreased in group C. The total volume of normal fetal lungs can also be expressed by the linear regression equation: 0.02 x estimated fetal weight + 0.29 (R = 0.902). The lung volumes of groups B and C were distributed below and above, respectively, the 2.5th percentile of the regression line.

CONCLUSIONS

This analytical method may be applied to evaluate lung development.

Development of three-dimensional power Doppler ultrasound imaging of fetoplacental vasculature

To develop an off-line system for three-dimensional (3-D) ultrasound (US) reconstruction of fetoplacental vasculature using colour segmentation and reconstruction software and to determine sources of error in fully freehand ultrasound image acquisition. US images were acquired freehand with the Acuson Sequoia (5C 2-MHz transducer) using power Doppler. After digital transfer to a personal computer, CQ Analysis software (Kinetic Imaging Ltd, Liverpool, UK) was used to segment the colour information from these images, and the resulting 8-bit grey-scale images were used for 3-D rendering using commercial software (VoxBlast, Vaytek Inc., Fairfield, IA, USA). 2-D scanning, software and freehand acquisition accuracy were assessed using a linear test rig and distance and volume phantoms (Dansk Phantom Service Ltd); 2-D scanning accuracy was within 1.3%, and software reconstruction accuracy within 1% for x and y planes and up to 3% for the z plane. Fully freehand acquisition was associated with a 12% to 18% mean percentage error in distance measurement in the plane of acquisition. Volumetric reconstruction inaccuracy was between 1.5% and 19.7% for precisely separated images and between 16.2% and 39.2% for fully freehand image acquisition. Rendered 3-D US vascular images clearly delineated vascular anatomy within the placenta and cord. Fully freehand 3-D US does have a role in off-line reconstruction of vascular anatomy, although variability in the z plane precludes its use for volumetric measurement. (E-mail: a.welsh@ic.ac.uk)

The importance of ventilation to effective resuscitation in the term and preterm infant

Although resuscitation at birth often has a successful outcome, there is very little data available on the optimal method. Face mask/bag resuscitation is relatively ineffective, rarely producing adequate alveolar ventilation before lung expansion has occurred, probably depending on the Head's Paradoxical Reflex to stimulate inspiratory efforts The T-piece/face mask technique is easier to use and more effective as the inflation pressure can be maintained for longer. Standard T-piece/endotracheal tube resuscitation produces inflation volumes of less than half of those generated by spontaneously breathing infants, and the functional residual capacity is not formed for several breaths. This can be overcome by maintaining the first inflation for 3 s. More studies are urgently required in very preterm infants as these are particularly vulnerable to volutrauma immediately after delivery.

Fetal lung volume: estimation at MR imaging-initial results

PURPOSE

To plot normal fetal lung volume (FLV) obtained with fast spin-echo magnetic resonance (MR) images against gestational age; to investigate the correlation between lung growth and fetal presentation, sex, and ultrasonographic (US) biometric measurements; and to investigate its potential application in fetuses with thoracoabdominal malformations.

MATERIALS AND METHODS

In a prospective multicenter study, 336 fetuses suspected of having central nervous system disorders underwent fast spin-echo T2-weighted lung MR imaging. Data obtained at 21-38 weeks gestation in 215 fetuses without thoracoabdominal malformations and with normal US biometric findings were selected for an FLV normative curve. FLV measurements obtained at pathologic examination with an immersion method were compared with MR FLV measurements in 11 fetuses. MR FLV values in 16 fetuses with thoracoabdominal malformations were compared with the normative curve.

RESULTS

Normal FLV increased with gestational age as a power curve; the spread of values increased with age. Interobserver correlation was excellent (R(2) = 0.96). FLV measurements at MR imaging were 0.90 times those at pathologic examination. A constant ratio (0.78) between FLV on the left and right sides was observed. No significant difference in FLV was observed between fetal presentations. Normal FLV was observed in all fetuses with cystic adenomatoid malformations and in four of six with oligohydramnios. Lowest FLV values were observed in fetuses with diaphragmatic hernia.

CONCLUSION

In fetuses with normal lungs, FLV distribution against gestational age is easily assessed in utero with fast spin-echo T2-weighted MR imaging. These preliminary findings illustrate the potential for comparing FLV measurements in fetuses at risk of lung hypoplasia with normative values.

Fetal and placental volumetric and functional analysis using echo-planar imaging

Recent and past work using echo-planar imaging (EPI) in pregnancy has allowed important anatomic and physiological information to be obtained, giving advantages over conventional radiological methods such as ultrasound. EPI is a quick, convenient method of measuring organ volumes. The volumetric estimates throughout gestation correlate well with known fetal weight at these gestations. Relaxation time measurements also can be made in the placenta and lungs. By combining the changes in relaxation and volume with gestation in the future, it may be possible to develop an "index of maturity." This could be used to accurately reflect lung maturation. T1 and T2 parameters in the placenta decreased with gestational age and with abnormal placentation. EPI can be used to assess perfusion in the placenta and flow in the uterine arteries because of its rapid acquisition times. These techniques have been applied to assess perfusion within the fetal brain.

The fetal lung. 2: Pulmonary hypoplasia

This review describes the pathogenesis of pulmonary hypoplasia and highlights its clinical, radiological and pathologic features, with emphasis on oligohydramnios-related pulmonary hypoplasia. Since pulmonary hypoplasia may lead to severe respiratory distress immediately after birth and even to neonatal death, an accurate and patient-friendly prenatal test for early detection and distinction between lethal and non-lethal pulmonary hypoplasia is still highly desirable. An extended overview of the proposed methods for the prenatal prediction of pulmonary hypoplasia is presented.

Serial fetal lung volume measurement using three-dimensional ultrasound

OBJECTIVE

To establish reference intervals for fetal lung growth.

DESIGN

Longitudinal observational study.

SUBJECTS

Fifty-eight women with initially uncomplicated singleton pregnancies were recruited from the antenatal population of a teaching hospital. Four women were excluded from the final analysis because of complications arising in their pregnancy.

METHODS

Each subject was serially scanned at monthly intervals. At each visit lung volume was measured using an ultrasound-based computerized three-dimensional imaging system. Multilevel models were used to determine conditional and unconditional reference intervals.

RESULTS

Reference intervals for fetal lung growth were derived. Fetal lung volume increases in a non-linear way with gestation.

CONCLUSIONS

Our computerized system has the capacity to be used in conjunction with any standard two-dimensional ultrasound scanner in order to measure volume. Lung volume measurement may be useful in predicting pulmonary hypoplasia.

Lung volume measurements in childhood

Although less commonly used in clinical practice than spirometry, lung volume measurements are helpful in assessing progress and response to therapy in situations where lung volume is likely to be increased, as in asthma or cystic fibrosis, or reduced secondary to pulmonary hypoplasia, pulmonary fibrosis, or musculoskeletal abnormalities. Their contribution to research has been considerable. The techniques most commonly used are those of inert gas dilution on rebreathing, applicable to children of all ages but tending to under-record in the presence of gas trapping. The gold standard is body plethysmography. This is relatively expensive and requires more technical skill, but will measure all the gas within the chest. Computer programmes have been developed to obtain a reasonable estimate of lung volume from chest X-rays alone. More accurate results are obtained by echo-planar imaging but this is only available in highly specialized units. Information on fetal lung volumes can be obtained using digitized ultrasound images and position sensors attached to the ultrasound probe.

Prenatal sonographic chest and lung measurements for predicting severe pulmonary hypoplasia

Pulmonary hypoplasia was diagnosed sonographically in 32 fetuses from 20 to 33 weeks of gestation. In addition to standard biometry, transverse thoracic diameter (TTD), sagittal thoracic diameter (TSD), thoracic circumference (TC) and lung diameter (LD) were measured in all cases and compared with known nomograms. The fetuses were divided into five groups according to the main sonographic findings: group 1-skeletal dysplasia; group 2-renal agenesis; group 3-diaphragmatic hernia; group 4-hydrothorax; and group 5-others. Severe pulmonary hypoplasia (PH) was diagnosed prenatally in all cases on the basis of LD measurements. In 17 (53.1 per cent) out of 32 cases TTD was below the 5th percentile while lower TSD measurements were recorded in 15 (46.8 per cent) fetuses. A thorax circumference below the 5th percentile for the respective gestational age was found in 15 cases (46.8 per cent) and a decreased LD/TC ratio in 25 cases (78.1 per cent). In 13 out of 32 fetuses pulmonary hypoplasia was diagnosed before, and in 19 cases after 24 weeks of gestation. Pulmonary hypoplasia was confirmed by autopsy in all cases.

CONCLUSION

pulmonary hypoplasia can be sonographically detected before 24 weeks of gestation. In cases of skeletal dysplasia and renal agenesis pulmonary hypoplasia can be diagnosed by chest and lung measurements, whereas in diaphragmatic hernia and hydrothorax diagnosis of pulmonary hypoplasia is possible only by lung measurement.

The changes in magnetic resonance properties of the fetal lungs: a first result and a potential tool for the non-invasive in utero demonstration of fetal lung maturation

OBJECTIVE

To measure magnetic resonance parameters T1 and T2 of the fetal lungs and investigate the relationship of these parameters to changes in volume and gestation.

DESIGN

Prospective cross-sectional study.

SETTING

Large teaching hospital in Nottingham and the Magnetic Resonance Centre at the University of Nottingham.

POPULATION

Normal pregnancies from 20 weeks to term.

METHODS

T1, T2, and lung volume were measured in the fetus using echo-planar magnetic resonance imaging.

MAIN OUTCOME MEASURES

The relationship of T1 and T2 to gestational age and lung volume.

RESULTS

Linear regression demonstrated a significant relationship (P < 0.001) between gestational age and lung volume, T1 and T2. There was also a significant relationship between lung volume and T1 and T2 (P < 0-001).

CONCLUSIONS

Relaxation time measurements give additional information to lung volume estimation in the assessment of lung physiology in utero. We have demonstrated the progressive changes which take place in the fetal lungs between 20 weeks and term. The physiological changes which can be demonstrated with this non-invasive technique may have an important application in the demonstration of fetal lung maturity in a prospective non-invasive manner.

Assessment of fetal lung growth in utero with echo-planar MR imaging

PURPOSE

To measure changes in normal fetal lung volume with increasing gestation by using echo-planar magnetic resonance (MR) imaging.

MATERIALS AND METHODS

Fifty-six singleton fetuses were examined longitudinally with respect to lung volume by using echo-planar MR imaging between 19 weeks gestation and term.

RESULTS

Lung volume increased exponentially with gestation from 8 to 125 mL. Volume was related to gestation by using the equation, volume = 0.8375e0.1249g (R2 = 0.77), where g = gestation. Lung volume had a direct relationship to fetal volume with increasing gestation (R2 = 0.75). There was no significant relationship between amniotic fluid volume and lung volume (R2 = 0.11).

CONCLUSION

Variation in lung volumes can be assessed by using echo-planar MR imaging, regardless of variations in amniotic fluid volume. These measurements are less than those obtained from postmortem and neonatal studies but are similar to those obtained by using three-dimensional ultrasonography. Lung volume estimations obtained by using echo-planar imaging may have important clinical and research applications when noninvassive assessment of lung volume is required.

In vitro estimation of foetal liver volume using ultrasound, x-ray computed tomography and magnetic resonance imaging

Sixteen formalin-fixed foetal livers were scanned in vitro using a new system for estimating volume from a sequence of multiplanar 2D ultrasound images. Three different scan techniques were used (radial, parallel and slanted) and four volume estimation algorithms (ellipsoid, planimetry, tetrahedral and ray tracing). Actual liver volumes were measured by water displacement. Twelve of the sixteen livers also received x-ray computed tomography (CT) and magnetic resonance (MR) scans and the volumes were calculated using voxel counting and planimetry. The percentage accuracy (mean +/- SD) was 5.3 +/- 4.7%, -3.1 +/- 9.6% and -0.03 +/- 9.7% for ultrasound (radial scans, ray volumes), MR and CT (voxel counting) respectively. The new system may be useful for accurately estimating foetal liver volume in utero.