Three-dimensional ultrasonography of normal fetal heart: comparison with two-dimensional imaging

4D fetal echocardiography-An update

With the introduction of the electronic 4-dimensional and spatial-temporal image Correlation (e-STIC), it is now possible to obtain large volume datasets of the fetal heart that are virtually free of artifact. This allows the examiner to use a number of imaging modalities when recording the volumes that include two-dimensional real time, power and color Doppler, and B-flow images. Once the volumes are obtained, manipulation of the volume dataset allows the examiner to recreate views of the fetal heart that enable examination of cardiac anatomy. The value of this technology is that a volume of the fetal heart can be obtained, irrespective of the position of the fetus in utero, and manipulated to render images for interpretation and diagnosis. This article presents a summary of the various imaging techniques and provides clinical examples of its application used for prenatal diagnosis of congenital heart defects and abnormal cardiac function.

Renal volumes measured by 3-dimensional sonography in healthy fetuses from 20 to 40 weeks

OBJECTIVES

The purpose of this study was to establish reference values for fetal kidney volumes as a function of gestational age, estimated by 3-dimensional sonography using the Virtual Organ Computer-Aided Analysis (VOCAL) technique (GE Healthcare, Kretztechnik, Zipf, Austria).

METHODS

Volumes of right and left kidneys were assessed in 213 healthy fetuses by 3-dimensional sonography using the VOCAL technique. Inclusion criteria were healthy women with singleton pregnancies, unremarkable comprehensive fetal sonographic findings, well-known gestational age established by first-trimester sonography, and gestational ages between 20 and 40 weeks. Exclusion criteria were patients lost to follow-up and birth weight abnormalities. Each patient was scanned once during pregnancy. Regression analysis was used to calculate unified formulas.

RESULTS

The mathematical models calculated in the study were as follows: expected right kidney volume = exp[-1.01 + (0.12 × gestational age)]; and expected left kidney volume = exp[-0.90 + (0.12 × gestational age)]. No significant intraobserver or inter-observer variability was observed for the determined volumes.

CONCLUSIONS

Reference values for right and left fetal kidney volumes throughout gestation using the rotational technique (VOCAL) are described. The use of this technique might aid in further definition of gestational age kidney volume standards to help in defining variations from the norm.

Usefulness of fetal three-dimensional ultrasonography for detecting of congenital heart defects and associated syndromes

Congenital heart defects (CHDs) occur in 1% of live-born infants and frequently are associated with extracardiac malformations. This study aimed to assess the feasibility and accuracy of three-dimensional ultrasonography (3DUS) in fetuses with CHD and to investigate whether 3DUS can add information about the heart and general fetal morphology that shows other congenital malformations or suggests syndromes. For 30 fetuses affected by CHD, 3DUS was performed using a Sonos 7500 ultrasound machine with a cardiac 3D transducer. In 44% of the exams, 3DUS was completely diagnostic for the CHD, providing additional information in 28% of the exams. Furthermore, 3DUS showed 82% of associated malformations, providing the complete diagnosis in 57% of the cases and helping with recognition of syndromes in others. The diagnostic accuracy of 3DUS was superior, with a higher number of acquisitions per exam. Performance was better in fetuses younger than 24 weeks for general morphologic details and in fetuses older than 24 weeks for the heart morphology.

Contemporary clinical applications of spatio-temporal image correlation in prenatal diagnosis

PURPOSE OF REVIEW

Four-dimensional fetal echocardiography has the potential to reduce the operator dependency of two-dimensional ultrasonography and increase the detection rate of congenital heart defects (CHDs). This review is intended to summarize recent evidence of the important role that four-dimensional ultrasonography with spatio-temporal image correlation (STIC) may play in the prenatal diagnosis of CHDs.

RECENT FINDINGS

Four-dimensional ultrasonography with STIC may provide the opportunity for telemedicine in the prenatal diagnosis of CHDs because four-dimensional volume datasets can be remotely acquired and accurately interpreted by different centers. Four-dimensional ultrasonography with STIC is an accurate and reproducible technique for the prenatal diagnosis of CHDs. Different four-dimensional rendering techniques can provide important insight into the spatial relationships of normal and abnormal fetal vascular structures.

SUMMARY

Four-dimensional fetal echocardiography with STIC may facilitate the examination of the fetal heart and could potentially increase the detection rate of CHDs.

Added value of three-/four-dimensional ultrasound in offline analysis and diagnosis of congenital heart disease

OBJECTIVE

Many published studies have shown that application of three-dimensional (3D) and real-time 3D (4D) ultrasound modalities can improve certain aspects of fetal echocardiography, but have left open the question of whether these modalities improved the accuracy of prenatal detection of anatomical fetal cardiovascular malformations. We aimed to determine whether 3D/4D ultrasound improved diagnostic ability in cases of congenital heart disease (CHD).

METHODS

Women who attended for early- or midtrimester targeted organ scans had complete fetal echocardiography according to our five-planes protocol, as well as examination of the ductus venosus and longitudinal aortic arch planes, performed with 2D ultrasound combined with 2D color Doppler, spatiotemporal image correlation (STIC), STIC with color Doppler, and STIC with B-flow. Ultrasound data of cases of CHD were stored in a dedicated archive. Stored cases were anonymized and the list order was randomized. Stored 2D ultrasound cineloops and 4D ultrasound volumes were reviewed separately according to a standardized table of 23 specified structures on five required planes of visualization: the upper abdomen, four-chamber view, five-chamber view, pulmonary artery bifurcation view, and three vessels and trachea plane. Separate diagnoses were recorded and finally compared. Diagnoses were confirmed by pathological examination or neonatal echocardiography.

RESULTS

During the study period, 13 101 examinations were performed; 181 diagnoses of CHD were made. In 12 of these, 3D/4D ultrasound added to the accuracy of our diagnosis: one right aortic arch with anomalous branching; one transposition of the great arteries with pulmonary atresia diagnosed with tomographic ultrasound imaging (TUI); one segmental interrupted aortic arch diagnosed with TUI; one right ventricle aneurysm diagnosed with B-flow; two agenesis of ductus venosus to the coronary sinus diagnosed by multiplanar reconstruction (MPR) and B-flow; two total anomalous pulmonary venous connection diagnosed with MPR; and four ventricular septal defect (VSD) diagnosed with the aid of virtual planes. There were 12 missed diagnoses and no false-positive results.

CONCLUSIONS

3D/4D ultrasound modalities may have advantages in some aspects of fetal cardiovascular evaluation, however, overall 3D/4D ultrasound modalities had added value in only about 6% of cases of fetal anatomical cardiovascular anomalies.

Collaborative study on 4-dimensional echocardiography for the diagnosis of fetal heart defects: the COFEHD study

OBJECTIVE

Congenital anomalies are the leading cause of infant mortality in the United States, and congenital heart defects (CHDs) are the most common type of birth defects. Recently, 4-dimensional ultrasonography (4DUS) with spatiotemporal image correlation (STIC) has been introduced for fetal echocardiography. Accumulating evidence indicates that 4DUS with STIC may facilitate the examination of the fetal heart. Our objectives were to determine the accuracy of 4DUS for the diagnosis of CHDs and the agreement among centers.

METHODS

This study included 7 centers with expertise in 4D fetal echocardiography. Fetuses with and without confirmed heart defects were scanned between 18 and 26 weeks, and their volume data sets were uploaded onto a centralized file transfer protocol server. Intercenter agreement was determined using a κ statistic for multiple raters.

RESULTS

Ninety volume data sets were randomly selected for blinded analysis. Overall, the median (range) sensitivity, specificity, positive and negative predictive values, and false-positive and -negative rates for the identification of fetuses with CHDs were 93% (77%-100%), 96% (84%-100%), 96% (83%-100%), 93% (79%-100%), 4.8% (2.7%-25%), and 6.8% (5%-22%), respectively. The most frequent CHDs were conotruncal anomalies (36%). There was excellent intercenter agreement (κ = 0.97).

CONCLUSIONS

(1) Four-dimensional volume data sets can be remotely acquired and accurately interpreted by different centers. (2) Among centers with technical expertise, 4DUS is an accurate and reliable method for fetal echocardiography.

Four-dimensional echocardiography with B-flow imaging and spatiotemporal image correlation in the assessment of congenital heart defects

OBJECTIVE

The objective of the present study was to evaluate the role of four-dimensional ultrasound with B-flow imaging and spatiotemporal image correlation (STIC) in the detection of congenital heart defects.

METHODS

Automated longitudinal and transverse sweeping of the fetal chest was utilized to obtain the volume datasets of the heart. Among the fetuses recruited in the study, 20 were normal and 13 were fetuses with congenital heart anomalies. Reconstructed images of abnormal hearts were compared with those of normal fetuses.

RESULTS

Of the 20 normal fetuses, all extracardiac vessels such as aorta, pulmonary artery, ductus artery, inferior vena cava, and ductus venosus could be detected on reconstructed images of 16 fetuses. In five normal cases, a four-dimensional image was recorded to allow simultaneous visualization of all four pulmonary veins. In the 13 fetuses with cardiac anomalies, four-dimensional sonography with B-flow imaging and STIC detected the 'digital casts' of the outflow tracts, great arteries, and veins draining into the heart. These results demonstrate spatial relationship among these structures which provide important anatomical information.

CONCLUSIONS

The use of four-dimensional ultrasound examination with B-flow imaging and STIC is a very useful technique in identifying anatomical features of different congenital cardiac anomalies.

Four-dimensional fetal echocardiography with spatiotemporal image correlation (STIC): A systematic study of standard cardiac views assessed by different observers

OBJECTIVE

To test the agreement between observers and reproducibility of a technique to display standard cardiac views of the left and right ventricular outflow tracts from four-dimensional volume datasets acquired with Spatiotemporal Image Correlation (STIC).

METHODS

A technique was developed to obtain dynamic multiplanar images of the left ventricular outflow tract (LVOT) and right ventricular outflow tract (RVOT) from volume datasets acquired with STIC. Volume datasets were acquired from fetuses with normal cardiac anatomy. Twenty volume datasets of satisfactory quality were pre-selected by one investigator. The data was randomly assigned for a blinded review by two independent observers with previous experience in fetal echocardiography. Only one volume dataset was used for each fetus. After a training session, the observers obtained standardized cardiac views of the LVOT and RVOT, which were scored on a scale of 1 to 5, based on diagnostic value and image quality (1=unacceptable, 2=marginal, 3=acceptable, 4=good, and 5=excellent). Median scores and interquartile range, as well as inter- and intraobserver agreement were calculated for each view.

RESULTS

The mean menstrual age at the time of volume acquisition was 25.5+/-4.5 weeks. Median scores (interquartile range) for LVOT images, obtained by the first and second observers, were 3.5 (2.25-5.00) and 4 (3.00-5.00), respectively. The median scores (interquartile range) for RVOT images obtained by the first and second observers were 3 (3.00-5.00) and 3 (2.00-4.00), respectively. The interobserver intraclass correlation coefficient for the LVOT was 0.693 (95% CI 0.380-0.822), and 0.696 (95% CI 0.382-0.866) for the RVOT. For the intraobserver agreement analysis, observer 1 gave higher scores to the LVOT the second time the volumes were analyzed [LVOT: 3.50 (2.25-5.00) vs. 5.00 (4.00-5.00, p=0.008)].

CONCLUSION

STIC can be reproducibly used to evaluate fetal cardiac outflow tracts by independent examiners. Slightly better image quality rating scores during the intraobserver variability trial suggests the presence of a learning curve for the manipulation and analysis of volume data obtained by STIC.

Three- and 4-dimensional ultrasonography in the prenatal evaluation of fetal anomalies associated with trisomy 18

OBJECTIVE

The purpose of this study was to assess the usefulness of 3- and 4-dimensional ultrasonography (3D/4DUS) for the description of anomalies associated with trisomy 18 and to determine whether 3D/4DUS adds diagnostic information over what is provided by conventional 2-dimensional ultrasonography (2DUS) alone.

METHODS

Twenty-six fetuses subsequently proven to have trisomy 18 underwent prenatal ultrasonographic evaluations by both 2DUS and 3D/4DUS. Volume data sets were acquired by the same sonographers after the conventional 2DUS examinations and were explored with 4-dimensional imaging software by another independent examiner blinded to the indications of 2DUS. The findings detected by 2DUS and 3D/4DUS were compared with those acquired at autopsy. The sensitivity of each modality for detecting anomalies was calculated and compared by the McNemar test.

RESULTS

Excluding polyhydramnios, there were 131 anomalies confirmed postnatally in 26 fetuses with trisomy 18. There was a statistically significant difference in the sensitivity for detecting anomalies between 3D/4DUS and 2DUS (93.89% versus 73.28%; McNemar value = 23.31; P < .05), especially in anomalies of the face/neck (96.15% versus 65.38%; McNemar value = 6.13; P < .05) and extremities (96.3% versus 48.15%; McNemar value = 11.07; P < .05). Three- and 4-dimensional ultrasonography provided additional diagnostic information for 83.97% of the anomalies related to trisomy 18 and influenced the obstetric management of 4 fetuses.

CONCLUSIONS

Three- and 4-dimensional ultrasonography offered diagnostic advantages for many anomalies associated with trisomy 18, especially for anomalies of the extremities and face. This modality could be a powerful adjunct to 2DUS in the prenatal anatomic evaluation of fetuses with trisomy 18.

A review of findings in fetal cardiac section drawings, part 1: The 4-chamber view

OBJECTIVES

The goal of this presentation is to review some of the common and rare fetal heart abnormalities and to provide an easy approach to these findings with schematic drawings.

METHODS

Over the past 10 years, we collected cases in which the common views of the heart were abnormal and the differential diagnoses that existed for each. The presentation shows the normal sonographic sections and then variations of these sections and the associated anomalies. We used illustrative drawings to present these findings, enabling us to point out the main sonographic features of abnormalities of the heart.

RESULTS

The work reviews 17 fetal heart abnormalities in schematic drawings.

CONCLUSIONS

This short review highlights several of the anomalies that can be recognized on the common sonographic views. The drawings tend to simplify the findings but serve as a basis for those doing fetal echocardiography when they encounter an unusual finding.

The role of the sagittal view of the ductal arch in identification of fetuses with conotruncal anomalies using 4-dimensional ultrasonography

OBJECTIVE

Conotruncal anomalies represent one fifth of all congenital heart defects (CHDs) detected in the fetus. However, the spatial relationship of the great vessels is incorrectly defined in about 20% of these cases. The sagittal view of the ductal arch is considered a standard ultrasonographic view in fetal echocardiography and can be easily visualized using 4-dimensional (4D) ultrasonography. This study was designed to determine the role of this ultrasonographic plane for the prenatal diagnosis of conotruncal anomalies.

METHODS

We reviewed 4D volume data sets, acquired with the spatiotemporal image correlation technique, from fetuses with and without confirmed conotruncal anomalies. The visualization rate of the sagittal view of the ductal arch was compared among groups using standardized multiplanar views.

RESULTS

This study included 183 volume data sets from fetuses in the following groups: (1) normal echocardiographic findings (n = 130); (2) conotruncal anomalies (n = 18); and (3) other CHDs (n = 35). Volumes of poor image quality were excluded from analysis (8.2% [15/183]). The visualization rate of the sagittal view of the ductal arch was significantly lower in fetuses with conotruncal anomalies (5.6% [1/18]) than that in fetuses without abnormalities (93.1% [108/116]) and that in fetuses with other CHDs (79.4% [27/34]; P < .01). Absence of visualization of the sagittal view of the ductal arch was associated with a likelihood ratio of 9.44 (95% confidence interval, 5.8-15.5) to have conotruncal anomalies.

CONCLUSIONS

The sagittal view of the ductal arch may play an important role in the screening and prenatal diagnosis of conotruncal anomalies in 4D ultrasonography.

Comparison of two- and three-dimensional ultrasonography in the evaluation of fetal heart: image quality and time spent in the exam

OBJECTIVES

To compare fetal heart evaluation done through two-dimensional (2DUS) and three-dimensional ultrasonography (3DUS) as to optimal plane imaging, image quality, and time needed to perform the examination.

METHODS

Prospective study involving 12 normal pregnant women, with gestational ages ranging from 22 to 26 weeks, scanned with a VOLUSON 730 with a convex 4.0-7.0 MHz transducer, in both two- and three-dimensional modes. In each case, three basic view planes were obtained: four-chambers view, right, and left ventricular outflow tracts. Each view was subjectively evaluated by three different examiners as to image quality, and graded from 0 (minimum) to 4 (maximum) cross-marks (+). The sum of all grades obtained for each case was used to classify the quality of the exam as unsatisfactory (0 to 1+), poor (2 to 4+), regular (5 to 7+), and good (8 to 12+). The time taken to obtain the views was recorded for each case, starting with the acquisition of the first view on the 2D exam and with the identification and opening of the volume blocks on the three-dimensional software.

RESULTS

The number of three-dimensional blocks with good, regular, poor, and unsatisfactory grades were, respectively, 6, 15, 9, and 10. The average in cross-marks of the cases graded good in each group without the worst result for each plane was 8. 2DUS was superior to 3DUS regarding the quality of the images obtained by the three pattern view planes and the average time to obtain high quality view planes was longer for 3DUS when compared to 2DUS. 2DUS offered better quality images and in less time than 3DUS.

CONCLUSIONS

Three-dimensional ultrasound is an advancement in fetal heart evaluation; however two-dimensional ultrasound remains the best screening method in diagnosing cardiac malformations, due to the good quality of its images and the lesser time needed to perform the exam.

3D and 4D ultrasound in fetal cardiac scanning: a new look at the fetal heart

Over the last decade we have been witness to a burgeoning literature on three-dimensional (3D) and four-dimensional (4D) ultrasound-based studies of the fetal cardiovascular system. Recent advances in the technology of 3D/4D ultrasound systems allow almost real-time 3D/4D fetal heart scans. It appears that 3D/4D ultrasound in fetal echocardiography may make a significant contribution to interdisciplinary management team consultation, health delivery systems, parental counseling, and professional training. Our aim is to review the state of the art in 3D/4D fetal echocardiography through the literature and index cases of normal and anomalous fetal hearts.

Three-Dimensional Echocardiography

Over the past 3 decades, echocardiography has become a major diagnostic tool in the arsenal of clinical cardiology for real-time imaging of cardiac dynamics. More and more, cardiologists' decisions are based on images created from ultrasound wave reflections. From the time ultrasound imaging technology provided the first insight into the human heart, our diagnostic capabilities have increased exponentially as a result of our growing knowledge and developing technology. One of the most significant developments of the last decades was the introduction of 3-dimensional (3D) imaging and its evolution from slow and labor-intense off-line reconstruction to real-time volumetric imaging. While continuing its meteoric rise instigated by constant technological refinements and continuing increase in computing power, this tool is guaranteed to be integrated in routine clinical practice. The major proven advantage of this technique is the improvement in the accuracy of the echocardiographic evaluation of cardiac chamber volumes, which is achieved by eliminating the need for geometric modeling and the errors caused by foreshortened views. Another benefit of 3D imaging is the realistic and unique comprehensive views of cardiac valves and congenital abnormalities. In addition, 3D imaging is extremely useful in the intraoperative and postoperative settings because it allows immediate feedback on the effectiveness of surgical interventions. In this article, we review the published reports that have provided the scientific basis for the clinical use of 3D ultrasound imaging of the heart and discuss its potential future applications.

A novel algorithm for comprehensive fetal echocardiography using 4-dimensional ultrasonography and tomographic imaging

OBJECTIVE

Tomographic ultrasound imaging (TUI) is a new display modality that allows simultaneous visualization of up to 8 parallel anatomic planes. This study was designed to determine the role of a novel algorithm combining spatiotemporal image correlation and TUI to visualize standard fetal echocardiographic planes.

METHODS

Volume data sets from fetuses with and without congenital heart defects (CHDs) were examined with a novel algorithm that allows simultaneous visualization of the 3-vessel and trachea view, the 4-chamber view, and outflow tracts. Visualization rates for these planes as well as the ductal arch and 5-chamber view were calculated.

RESULTS

(1) Two hundred twenty-seven volume data sets from fetuses without (n = 138) and with (n = 14) CHDs were reviewed; (2) among fetuses without CHDs, the 4-chamber view, 5-chamber view, ductal arch, 3-vessel and trachea view, left outflow tract, and short axis of the aorta were visualized in 99% (193/195), 96.9% (189/195), 98.5% (192/195), 88.2% (172/195), 93.3% (182/195), and 87.2% (170/195) of the volume data sets, respectively; (3) these views were visualized in 85% (17/20), 80% (16/20), 65% (13/20), 55% (11/20), 55% (11/20), and 70% (14/20) of the volume data sets, respectively, from fetuses with CHDs; and (4) simultaneous visualization of the short axis of the aorta, 3-vessel and trachea view, left outflow tract, and 4-chamber view was obtained in 78% (152/195) of the volume data sets from fetuses without CHDs and in 40% (8/20) of those with CHDs.

CONCLUSIONS

The 3-vessel and trachea view, the 4-chamber view, and both outflow tracts can be simultaneously visualized using a novel algorithm combining spatiotemporal image correlation and TUI.

Four-dimensional ultrasonography of the fetal heart using a novel Tomographic Ultrasound Imaging display

OBJECTIVE

The objective of this study was to investigate the feasibility of examining the fetal heart with Tomographic Ultrasound Imaging (TUI) using four-dimensional (4D) volume datasets acquired with spatiotemporal image correlation (STIC).

MATERIAL AND METHODS

One hundred and ninety-five fetuses underwent 4D ultrasonography (US) of the fetal heart with STIC. Volume datasets were acquired with B-mode (n=195) and color Doppler imaging (CDI) (n=168), and were reviewed offline using TUI, a new display modality that automatically slices 3D/4D volume datasets, providing simultaneous visualization of up to eight parallel planes in a single screen. Visualization rates for standard transverse planes used to examine the fetal heart were calculated and compared for volumes acquired with B-mode or CDI. Diagnoses by TUI were compared to postnatal diagnoses.

RESULTS

(1) The four- and five-chamber views and the three-vessel and trachea view were visualized in 97.4% (190/195), 88.2% (172/195), and 79.5% (142/195), respectively, of the volume datasets acquired with B-mode; (2) these views were visualized in 98.2% (165/168), 97.0% (163/168), and 83.6% (145/168), respectively, of the volume datasets acquired with CDI; (3) CDI contributed additional diagnostic information to 12.5% (21/168), 14.2% (24/168) and 10.1% (17/168) of the four- and five-chamber and the three-vessel and trachea views; (4) cardiac anomalies other than isolated ventricular septal defects were identified by TUI in 16 of 195 fetuses (8.2%) and, among these, CDI provided additional diagnostic information in 5 (31.3%); (5) the sensitivity, specificity, positive- and negative-predictive values of TUI to diagnose congenital heart disease in cases where both B-mode and CDI volume datasets were acquired prenatally were 92.9%, 98.8%, 92.9% and 98.8%, respectively.

CONCLUSION

Standard transverse planes commonly used to examine the fetal heart can be automatically displayed with TUI in the majority of fetuses undergoing 4D US with STIC. Due to the retrospective nature of this study, the results should be interpreted with caution and independently confirmed before this methodology is introduced into clinical practice.

Three- and 4-dimensional ultrasound in obstetric practice: does it help?

OBJECTIVE

The purpose of this article was to review the published literature on 3-dimensional ultrasound (3DUS) and 4-dimensional ultrasound (4DUS) in obstetrics and determine whether 3DUS adds diagnostic information to what is currently provided by 2-dimensional ultrasound (2DUS) and, if so, in what areas.

METHODS

A PubMed search was conducted for articles reporting on the use of 3DUS or 4DUS in obstetrics. Seven-hundred six articles were identified, and among those, 525 were actually related to the subject of this review. Articles describing technical developments, clinical studies, reviews, editorials, and studies on fetal behavior or maternal-fetal bonding were reviewed.

RESULTS

Three-dimensional ultrasound provides additional diagnostic information for the diagnosis of facial anomalies, especially facial clefts. There is also evidence that 3DUS provides additional diagnostic information in neural tube defects and skeletal malformations. Large studies comparing 2DUS and 3DUS for the diagnosis of congenital anomalies have not provided conclusive results. Preliminary evidence suggests that sonographic tomography may decrease the examination time of the obstetric ultrasound examination, with minimal impact on the visualization rates of anatomic structures.

CONCLUSIONS

Three-dimensional ultrasound provides additional diagnostic information for the diagnosis of facial anomalies, evaluation of neural tube defects, and skeletal malformations. Additional research is needed to determine the clinical role of 3DUS and 4DUS for the diagnosis of congenital heart disease and central nervous system anomalies. Future studies should determine whether the information contained in the volume data set, by itself, is sufficient to evaluate fetal biometric measurements and diagnose congenital anomalies.

Three- and 4-dimensional ultrasound in obstetrics and gynecology: proceedings of the American Institute of Ultrasound in Medicine Consensus Conference

The American Institute of Ultrasound in Medicine convened a panel of physicians and scientists with interest and expertise in 3-dimensional (3D) ultrasound in obstetrics and gynecology to discuss the current diagnostic benefits and technical limitations in obstetrics and gynecology and consider the utility and role of this type of imaging in clinical practice now and in the future. This conference was held in Orlando, Florida, June 16 and 17, 2005. Discussions considered state-of-the-art applications of 3D ultrasound, specific clinical situations in which it has been found to be helpful, the role of 3D volume acquisition for improving diagnostic efficiency and patient throughput, and recommendations for future investigations related to the utility of volume sonography in obstetrics and gynecology.

Three-dimensional and four-dimensional fetal echocardiography: a new frontier

PURPOSE OF REVIEW

One of the difficulties of conventional two-dimensional cardiac imaging is the inability to examine fetal cardiac anatomy from multiple angle planes. Three-dimensional and four-dimensional ultrasound allows the fetal examiner to more accurately accomplish this task. Currently, multiple disciplines may be involved in the examination of the fetal heart (pediatric cardiologists, obstetricians, maternal-fetal medicine specialists, and radiologists). The three-dimensional and four-dimensional imaging equipment used by these specialty physicians varies greatly. The purpose of this communication is to review techniques using three-dimensional and four-dimensional imaging that the pediatric cardiologist may not be exposed to in the clinical environment, however, in consulting with colleagues needs to have an understanding of these imaging modalities.

RECENT FINDINGS

The reconstruction of cardiac structures using this technology allows the examiner to view cardiac anatomy in a manner that was limited by previous two-dimensional imaging. Volume datasets are obtained in the three-dimensional static mode (no cardiac motion) or using four-dimensional - the three-dimensional heart is observed contracting during one or multiple cardiac cycles. Therefore, the fourth dimension is time. Using either three-dimensional or four-dimensional technology datasets are acquired, followed by image reconstruction. The image reconstruction enables the examiner to evaluate a two-dimensional image using multiple views, evaluate intracardiac anatomy at different depth planes, and recreate casts of blood flow of the chambers and great vessels.

SUMMARY

This new technology has enhanced the ability of the examiner to identify normal and complex fetal heart anatomy during the early second to the late third trimesters of pregnancy.

Three- and four-dimensional freehand fetal echocardiography: a feasibility study using a hand-held Doppler probe for cardiac gating

OBJECTIVE

To evaluate the clinical feasibility of the signal from a hand-held Doppler probe as a real-time tracking signal for dynamic three-dimensional (3D) (so-called four-dimensional (4D)) fetal echocardiography in a random patient cohort.

METHODS

Seventy fetuses, with and without congenital heart disease, at various gestational ages (mean, 25 weeks; range, 18-38 weeks) were investigated using freehand 3D echocardiography. Time gating was achieved concurrently by obtaining a Doppler signal of the fetal heart without further signal averaging. In 10 fetuses, Doppler gating was compared to cardiotocogram (CTG)-gated 3D echo using signal averaging. Gray-scale and color Doppler dynamic 3D displays and multiplanar views were assessed according to their ability to accurately depict cardiac gating and cardiac morphology.

RESULTS

In 68/70 fetuses, valid Doppler-based trigger signals were obtained. Correct cardiac gating was achieved in 231/275 (84%) 4D datasets. Doppler tracing of the fetal heart allowed beat-to-beat triggering without the necessity for signal averaging. Doppler gating detected rapid changes in the fetal heart rate more reliably than CTG gating, but was more sensitive to acoustic interference between the gating and echo-transducer when color-coded Doppler imaging was used. Image quality was highly dependent on random motion and the acoustic window. A total of 171/231 (74%) correctly gated datasets successfully demonstrated clinically useful 4D images of the fetal heart. The reconstruction of 3D and multiplanar views provided additional views not obtainable by two-dimensional imaging.

CONCLUSION

These results show that a hand-held Doppler probe can be used as a reliable online gating source for 4D fetal echocardiography.

Validation of volume and mass assessments for human fetal heart imaging by 4-dimensional spatiotemporal image correlation echocardiography: in vitro balloon model experiments

OBJECTIVE

This study was designed to validate a slow-sweep real-time 4-dimensional (4D) spatiotemporal image correlation method for producing quantitatively accurate dynamic fetal heart images using an in vitro pulsatile balloon model and apparatus.

METHODS

To model fetal heart chambers, asymmetric double-walled finger stalls (tips of surgical latex gloves) were used and attached to a laboratory-designed circuit that allowed calibrated changes in the inner balloon volume as well as an intermediate gel mass interposed between the 2 layers. The water-submerged model was attached to a small-volume pulsatile pump to produce phasic changes in volume within the inner balloon at a fixed rate. A sonography system with 4D spatiotemporal image correlation (STIC) capabilities was used for 3-dimensional (3D) and 4D data acquisition. Volume data were analyzed by customized radial summation techniques with 4D data analysis software and compared with known volumes and masses.

RESULTS

Fifty-six individual volumes ranging from 2.5 to 10 mL were analyzed. Volume and mass measurements with 4D STIC were highly correlated (R2 > 0.90). The mean percentage error was better (<6%) for volumes exceeding 4 mL and was as low as 0.3% for 6-mL estimations. Measurements in the diastolic phase were the most accurate, followed by mass estimations equivalent to chamber walls. There was a wider range of percentage error in the lowest volumes tested (2.5 mL), which might have arisen from difficulties in spatial resolution or distortions from within the model apparatus itself. Resolution limitations of 4D technology in combination with extremely small volume targets may explain higher error rates at these small volumes.

CONCLUSIONS

Four-dimensional STIC is an acceptably accurate method for volume and mass estimations in the ranges comparable with mid- and late-gestation fetal hearts. It is particularly accurate for diastolic estimations, for chamber wall mass measurements, and at volumes of greater than 2.5 mL. This study validates use of 4D STIC technology to overcome the limitations of nongated 3D technology for phasic and quantitative assessments in fetal echocardiography.

Fetal ventricular mass determination on three-dimensional echocardiography: studies in normal fetuses and validation experiments

BACKGROUND

Estimation of ventricular volume and mass is important for baseline and serial evaluation of fetuses with normal or abnormal hearts. Direct measurement of chamber wall volumes and mass can be made without geometric assumptions by 3D fetal echocardiography. Our goals were to determine the feasibility of using fast nongated 3D echocardiography for fetal volumetric and mass assessments, to validate the accuracy of the ultrasound system and the measurement technique, and if satisfactory, to develop normal values for fetal ventricular mass during the second and third trimesters.

METHODS AND RESULTS

This was a prospective outpatient study of 90 consecutive normal pregnancies during routine obstetric services at Oregon Health & Science University (Portland). Optimized 3D volumes of the fetal thorax and cardiac chambers were rapidly acquired and later analyzed for right and left ventricular mass by radial summation technique from manual epicardial and endocardial traces. Experiments to validate the ultrasound system and measurement technique were performed with modified small balloon models and in vivo and ex vivo small animal experiments. Our study established the feasibility of fetal ventricular mass measurements with 3D ultrasound technology and developed normal values for right and left ventricular mass from 15 weeks' gestation to term.

CONCLUSIONS

Nongated fast 3D fetal echocardiography is an acceptable modality for determination of cardiac chamber wall volume and mass with good accuracy and acceptable interobserver variability. The method should be especially valuable as an objective serial measurement in clinical fetal studies with structurally or functionally abnormal hearts.

Application of free-hand three-dimensional echocardiography in the evaluation of fetal cardiac ejection fraction: a preliminary study

OBJECTIVE

To investigate the feasibility of using free-hand three-dimensional (3D) echocardiography to evaluate fetal cardiac function.

METHODS

3D cardiac data were collected during screening examinations for 37 normal fetuses with gestational ages of between 16 and 26 weeks. Processing of the 3D volumes included separation of the end-diastolic and end-systolic slices, segmentation of right and left ventricles, measurement of end-diastolic and end-systolic volumes, and calculation of the ejection fraction (EF) for each ventricle. In 21 fetuses at 21-24 weeks, right and left ventricle volumes and EF were compared.

RESULTS

Twenty-five cases were appropriate for final statistical analysis. The volume of the ventricles increased with gestational age and estimated fetal weight. There was no significant trend in the difference between the volumes and EF of the right and left ventricles in the 21-24-week subgroup. The mean right and left ventricular EF were 54 +/- 11.2% and 57.5 +/- 14.6%, respectively. The mean combined EF of ventricles during gestation was 55.1 +/- 10.7% and seemed to remain constant during the gestational ages studied.

CONCLUSIONS

3D echocardiography can provide estimates of ventricular volume and function and may in future be used for evaluation of fetuses with congenital heart disease and cardiac dysfunction.

Real-time 3-dimensional fetal echocardiography with an instantaneous volume-rendered display: early description and pictorial essay

OBJECTIVE

Random fetal motion, rapid fetal heart rates, and cumbersome processing algorithms have limited reconstructive approaches to 3-dimensional fetal cardiac imaging. Given the recent development of real-time, instantaneous volume-rendered sonographic displays of volume data, we sought to apply this technology to fetal cardiac imaging.

METHODS

We obtained 1 to 6 volume data sets on each of 30 fetal hearts referred for formal fetal echocardiography. Each volume data set was acquired over 2 to 8 seconds and stored on the system's hard drive. Rendered images were subsequently processed to optimize translucency, smoothing, and orientation and cropped to reveal "surgeon's eye views" of clinically relevant anatomic structures. Qualitative comparison was made with conventional fetal echocardiography for each subject.

RESULTS

Volume-rendered displays identified all major abnormalities but failed to identify small ventricular septal defects in 2 patients. Important planes and views not visualized during the actual scans were generated with minimal processing of rendered image displays. Volume-rendered displays tended to have slightly inferior image quality compared with conventional 2-dimensional images.

CONCLUSIONS

Real-time 3-dimensional echocardiography with instantaneous volume-rendered displays of the fetal heart represents a new approach to fetal cardiac imaging with tremendous clinical potential.

New fetal cardiac imaging techniques

Rapid advances in graphics computing and micro-engineering have offered new techniques for prenatal cardiac imaging. Some of them can be non-invasively applied to both clinical and laboratory settings, including dynamic three-dimensional echocardiography, myocardial Doppler imaging, harmonic ultrasound imaging, and B-flow sonography. With clinical constraints, a few others have been mainly used in laboratories, such as endoscopic ultrasound, magnetic resonance imaging and biomicroscopy. Appropriate use and co-use of these new tools will not only provide unique information for better clinical assessment of fetal cardiac disease but also offer new ways to improved understanding of cardiovascular development and pathogenesis.

Dynamic free-hand three-dimensional fetal echocardiography gated by cardiotocography

OBJECTIVE

To evaluate the clinical feasibility of conventional cardiotocography (CTG) as a cardiac cycle triggering signal for three-dimensional (3D) fetal echocardiography.

METHOD

Free-hand 3D echocardiography was performed on a total of 25 fetuses with and without congenital heart disease at various gestational ages (mean, 29 weeks; range, 19-35 weeks). Simultaneously, online CTG was used for time gating. Gray-scale and color Doppler dynamic 3D displays, as well as multiplanar views, were assessed for their ability to depict the cardiac morphology and correct cardiac gating.

RESULTS

Valid CTG-based trigger signals could be obtained in 24 of the 25 fetuses. Correct cardiac gating was achieved in 101 of the 111 (91%) 3D datasets. Color Doppler imaging of blood flow in four dimensions was possible in 34 of 36 (94%) datasets. Reconstructed 3D and multiplanar views provided additional views not available in two-dimensional (2D) imaging. Acoustic interference between the CTG transducer and echotransducer could be reduced by the use of a high-frequency echotransducer, second-harmonic frequency imaging and appropriate positioning of the two transducers. Imaging quality was highly dependent on the quality of 2D images and random motion artifacts.

CONCLUSIONS

CTG can be used as an online gating source for dynamic 3D fetal echocardiography.

New dimensions and directions in fetal cardiology

PURPOSE OF REVIEW

The purpose of this review is to describe several of the most relevant and exciting recent advances in the field of fetal cardiology.

RECENT FINDINGS

First, the prenatal detection of congenital heart disease has improved, and continues to improve, with the increasingly widespread incorporation of the four-chamber view and outflow tracts into the routine screening fetal ultrasound evaluation. Second, increasingly sophisticated computer processing systems and improvements in imaging technology have enabled the development of automated three-dimensional ultrasound imaging systems that promise to revolutionize both the prenatal detection and diagnosis of congenital heart disease. Conventional two-dimensional imaging approaches may soon become obsolete. Third, there has been an increasing ability to intervene successfully prenatally not only for fetal arrhythmias and heart failure, but also for some forms of structural heart disease. In some cases of left or right ventricular outflow tract obstruction, early intervention during the second trimester may prevent the development of ventricular hypoplasia. Finally, several recent studies suggest that prenatal diagnosis may improve neonatal outcome for fetuses with congenital heart disease. The growing ability to intervene prenatally has the potential to improve neonatal outcome still further.

SUMMARY

These critical and exciting developments in fetal cardiology promise to increase fetal echocardiography's clinical impact dramatically during the years to come.

Spatio-temporal image correlation (STIC): new technology for evaluation of the fetal heart

Spatio-temporal image correlation (STIC) is a new approach for clinical assessment of the fetal heart. It offers an easy to use technique to acquire data from the fetal heart and to aid in visualization with both two-dimensional and three-dimensional (3D) cine sequences. The acquisition is performed in two steps: first, images are acquired by a single, automatic volume sweep. Second, the system analyzes the image data according to their spatial and temporal domain and processes an online dynamic 3D image sequence that is displayed in a multiplanar reformatted cross-sectional display and/or a surface rendered display. The examiner can navigate within the heart, re-slice, and produce all of the standard image planes necessary for a comprehensive diagnosis. The advantages of STIC for use in evaluation of the fetal heart are as follows: the technique delivers a temporal resolution which corresponds to a B-mode frame rate of approximately 80 frames/s; it provides the examiner with an unlimited number of images for review; it allows for correlation between image planes that are perpendicular to the main image acquisition plane; it may shorten the evaluation time when complex heart defects are suspected; it enables the reconstruction of a 3D rendered image that contains depth and volume which may provide additional information that is not available from the thin multiplanar image slices (e.g. for pulmonary veins, septal thickness); it lends itself to storage and review of volume data by the examiner or by experts at a remote site; it provides the examiner with the ability to review all images in a looped cine sequence.

Spatio-temporal image correlation (STIC): a new tool for the prenatal screening of congenital heart defects

OBJECTIVE

To assess the feasibility and capability of STIC acquisition, performed by a general obstetrician performing antenatal ultrasound, to visualize fetal cardiac structures in women undergoing routine obstetric ultrasound examination, in order to obtain information to confirm normality of the fetal heart during intrauterine life.

METHODS

This was a prospective study of one hundred fetuses with echocardiographically confirmed normal hearts and no extracardiac anomalies with gestational ages ranging between 18 and 37 weeks. A general obstetrician was invited to acquire the STIC volumes. The four-chamber view was obtained as a starting point. A standard 7.5-s acquisition time and 30 degrees angle of acquisition were used and the resulting STIC was stored for later offline analysis by a fetal echocardiologist. For each patient, the stored STIC data were first evaluated by sweeping from the initial acquisition plane, in the caudal direction and then cranially, zooming, slowing or stopping the cardiac motion to visualize views and structures. If a structure or view was rated as inadequate or not identifiable, a multiplanar three-dimensional (3D) examination of the STIC volume was taken in order to try to visualize it adequately. The rates obtained using just the STIC sweeps were compared independently, and then the 3D multiplanar study was added.

RESULTS

STIC acquisition was possible in all cases. The mean time required for STIC acquisition was 7.5 min. A complete cardiac examination according to the set criteria was achieved in 94.2% (95% confidence interval (CI), 90-99) of cases. We obtained a 94.2% success rate of visualizing different structures and views of the fetal heart using the STIC sweep alone (95% CI, 90-99) and 96.2% adding 3D multiplanar examination (95% CI, 92-100).

CONCLUSION

STIC acquisition of the fetal heart is feasible with high success rates in visualization of the principal connections. The STIC data acquired by a general obstetrician can subsequently be used by a fetal echocardiologist for prenatal confirmation of normal cardiac structure or exclusion of major cardiac malformations.

Real-time three-dimensional fetal echocardiography--optimal imaging windows

A total of 15 fetuses were scanned using 2-D array volumetric ultrasound (US). Acquired cardiac data were converted for rendering dynamic 3-D surface views and reformatting cross-sectional views. The image usefulness was compared between the data obtained from subcostal/subxiphoid and other imaging windows; the former are usually free of acoustic shadowing. Of 60 data sets recorded, 12 (20%) were acquired through subcostal windows in 6 (40%) patients. Subcostal windows were unavailable from the remaining patients due to unfavourable fetal positions. Of the 12 sets, 6 (50%) provided the dynamic 3-D and/or cross-sectional views of either the entire fetal heart or a great portion of it for sufficient assessments of its major structures and their spatial relationships. Of 48 data sets from other windows, only 9 (19%) provided such 3-D and/or cross-sectional views; the lower rate being due to acoustic shadowing. Real-time 3-D US is a convenient method for volumetric data acquisition. Through subcostal windows, useful information about the spatial relationships between major cardiac structures can be acquired. However, to offer detailed information, considerable improvement in imaging quality is needed.

Diagnosis of cardiac defects: where we've been, where we are and where we're going

There has been tremendous development in the field of prenatal diagnosis of cardiac disease in the last 30 years. Early work centered on the technical aspects of providing an accurate assessment of cardiac structure and function. Techniques of fetal cardiac screening have been developed and utilized throughout the world. More recently, investigators have begun to explore the ramifications of fetal cardiac diagnosis by assessing measures of outcome. In this article, the field of fetal echocardiography, as a screening tool for identifying congenital heart disease, and its impact on disease outcome is reviewed.

Imaging comparison of basic cardiac views between two- and three-dimensional ultrasound in normal fetuses in anterior spine positions

OBJECTIVE

When the fetal spine is in anterior position, it shadows the fetal heart, resulting in the difficult visualization using two-dimensional (2D) ultrasound. The purpose of this study was to compare the basic cardiac views of normal fetuses between 2D and 3D ultrasound to demonstrate whether 3D ultrasound improved the visualization of these views in fetuses in anterior spine positions. In addition, inter- and intra-observation reliabilities of basic cardiac views using 3D ultrasound were evaluated for their clinical applicability.

METHODS

Using a multiplanar technique, integrated 3D ultrasound was used to display the four-chamber view, aortic outflow tract and pulmonary outflow tract in fetuses in anterior spine positions for 23 uncomplicated singleton pregnant women. The imaging visualizations of these views for the 23 fetuses in 3D ultrasound were compared with those in 2D ultrasound using the McNemar test. We also evaluated the inter- and intra-observation differences of each basic cardiac view in 3D ultrasound using the kappa statistic and McNemar test, respectively.

RESULTS

Only in the pulmonary outflow tract, 3D ultrasound had significantly better visualization than the 2D ultrasound in the fetuses in anterior spine positions (p < 0.05). There was good inter-observation reliability and no intra-observation differences for the technique were observed.

CONCLUSIONS

Among the basic cardiac views in fetuses in anterior spine positions, 3D ultrasound improved the visualization of pulmonary outflow and provided reliable alternate technique for clinical use.

Detailed three-dimensional fetal echocardiography facilitated by an Internet link

OBJECTIVES

To assess whether a complete virtual cardiological examination can be achieved in stored three-dimensional volumes of the fetal heart, transmitted to a tertiary fetal cardiology center via the Internet.

METHODS

Thirty sequential normal singleton pregnancies were included in the study. Four cardiac volumes were acquired using a three-dimensional ultrasound system. The volumes were sent via the Internet to a tertiary fetal cardiology center, where a detailed fetal cardiac examination was attempted using the three-dimensional volumetric dataset.

RESULTS

The median gestational age was 24 (range, 22-28) weeks. A complete heart examination was accomplished in 23 of 30 cases (76.7%; 95% confidence interval, 58-90%). The four-chamber view and the cardiac situs were seen in all cases. The right ventricular outflow tract was seen in 29 (96.7%) cases and the left ventricular outflow tract in 25 (83.3%) cases. The long-axis view of the aortic arch, superior vena cava, inferior vena cava and pulmonary veins were visualized in more than 80% of cases. The mean time of volume acquisition was 9.5 (standard deviation, 2.3) min and the mean examination time by the fetal cardiologist was 17 (standard deviation, 4.8) min.

CONCLUSIONS

These preliminary results demonstrate that a three-dimensional virtual examination of the fetal heart is possible. There are limitations such as the lack of flow and functional information but complete ascertainment of the main cardiac connections was possible in the majority of cases. The use of an Internet link has major implications, particularly for situations in which the scanning center is geographically remote from the tertiary referral center.

Three-dimensional (3D) echocardiographic analysis of congenital heart disease in the fetus: comparison with cross-sectional (2D) fetal echocardiography

OBJECTIVE

We attempted to assess the ability of Doppler-gated three-dimensional (3D) fetal echocardiography to reconstruct and display specific cardiac structures in fetuses with cardiac anomalies and to determine whether any advantage is offered by 3D sonographic cardiac examination over conventional fetal echocardiography.

DESIGN

After 2D fetal echocardiographic examination, 3D cardiac data were collected prospectively in 22 fetuses with various congenital heart defects. Their ages ranged from 19 to 35 weeks' gestation. Basic echocardiographic key views of the venoatrial, atrioventricular and ventriculoarterial connections were derived from volume data sets and selected for 3D reconstruction and analysis. Comparisons were made with 2D echocardiographic imaging of the fetal hearts and the diagnostic image quality of visualized structural details was evaluated.

RESULTS

The underlying cardiac malformation was well or satisfactorily visualized in 20 fetuses using 2D imaging. Gated 3D volume data sets enabled diagnostically acceptable visualization of all affected cardiac structures in 7 of 22 fetuses. High-quality 3D reconstruction of the site and spatial orientation of ventricular septal defects was obtained in 9 of 13 patients. Two-dimensional imaging remained the principal diagnostic modality in all cases with additional structural detail being obtained by 3D imaging in only two fetuses.

CONCLUSIONS

Three-dimensional imaging of fetal heart disease is feasible for a wide range of lesions, and may provide additional information of clinical value in a small number of cases when compared with 2D imaging.

Comparison of septal defects in 2D and 3D echocardiography using active contour models

Three-dimensional ultrasound is emerging as a viable resource for the imaging of internal organs. Quantitative studies correlating ultrasonic volume measurements with MRI data continue to validate this modality as a more efficient alternative for 3D imaging studies. However, the processing required to form 3D images from a set of 2D images may result in a loss of spatial resolution and may give rise to artifacts. This paper examines a method of automatic feature extraction and data quantification in 3D data sets as compared with original 2D data. This work will implement an active contour algorithm to automatically extract the endocardial borders of septal defects in echocardiographic images, and compare the size of the defects in the original 2D images and the 3D data sets.

New modalities for imaging the fetal heart

Improvement in the prenatal diagnosis of congenital heart disease requires familiarity with advances ultrasound equipment and features and any new imaging methods that can effectively provide cardiac information from the fetus. This article discusses imaging the fetal heart with transvaginal ultrasound, Doppler ultrasound, intrauterine sonography, three-dimensional ultrasound (3DUS) and magnetic resonance imaging.

Use of free-hand three-dimensional ultrasound software in the study of the fetal heart

OBJECTIVE

To propose a new approach to the study of the fetal heart using free-hand three-dimensional (3D) ultrasound software.

METHODS

We studied a total of 28 fetuses, of which 26 were normal and two were known to have heart pathology. In all of them a B-mode scan was performed. After obtaining a four-chamber view, and keeping the transducer in the same position, the free-hand 3D-View software was activated. A sequence of frames was stored. Additional information was recorded looking from the four-chamber view towards the outflow tract, and also adding color Doppler.

RESULTS

We obtained a multiplanar display of one B-mode and two perpendicular M-modes in all cases studied. In this multiplanar mode, Y and X axes represent distance and Z axis represents time. We were able to obtain M-modes and a variation of color-M-mode in any desired position. Moving the information along the Z axis, a frame sequence of the B-mode was obtained. Using this approach we observed one case of fetal supraventricular extrasystoles and other having an interventricular septum defect.

CONCLUSIONS

This modality gives a new perspective of fetal heart scanning using the free-hand 3D-View software, in which there is benefit from many of the advantages of the 3D software, although the power of this procedure must be improved.

Three-dimensional ultrasound in the evaluation of fetal anomalies

OBJECTIVES

To determine the additional information and clinical impact provided by three-dimensional ultrasound (3D US) imaging of fetal anomalies compared to conventional 2-dimensional ultrasound (2D US).

MATERIALS AND METHODS

Sixty-three patients with 103 anomalies were scanned prospectively with both 2D and 3D US. Each anomaly was reviewed by one or more fetal imaging specialists to determine whether the 3D US data were advantageous, equivalent, or disadvantageous when compared with 2D US images. Clinical impact and pathologic or clinical outcome were determined in all cases.

RESULTS

The 3D US images provided additional information in 53 anomalies (51%), were equivalent to 2D US images in 46 anomalies (45%), and were disadvantageous in four anomalies (4%). The 3D US was most helpful in evaluating fetuses with facial anomalies, hand and foot abnormalities and axial spine and neural tube defects. Planar images derived from 3D US volume data sets generally were more helpful for diagnostic purposes, whereas rendered 3D US images were more useful as a point of reference and were better appreciated by patients in understanding fetal abnormalities. Additional information provided by 3D US images impacted clinical management in 5% of patients. The 3D US images were disadvantageous in two fetuses with multiple anomalies and two with cardiac anomalies.

CONCLUSION

The 3D US offered diagnostic advantages in about one-half of the selected cases studied and had effect on patient management in 5% of cases. This modality can be a powerful adjunctive tool to 2D US in providing a more comprehensible, 3D US impression of congenital anomalies. Thus, 3D US is currently most helpful as a targeted study complementing 2D US.

Sources and impact of artifacts on clinical three-dimensional ultrasound imaging

The purpose of this paper is to investigate, identify and discuss artifacts and their sources arising in three-dimensional ultrasound (3D US) in clinical practice in order to increase the awareness of clinicians and sonographers with respect to common 3D US artifacts and to use this increased awareness to avoid or reduce the occurrence of misdiagnosis in 3D US studies. Patient 3D US data were acquired using several different scanners and reviewed interactively on the scanner and graphics workstations. Artifacts were catalogued according to artifact origin. Two-dimensional ultrasound (2D US) artifacts were classified whether they were of a B-mode or color/power Doppler origin and their presentation in the original scan planes and the resulting volume re-sliced planes and rendered images was identified. Artifacts unique to 3D US were observed, noted and catalogued on the basis of whether they arose during acquisition, rendering or volume editing operations. Acoustic artifacts identified included drop-out, shadowing, etc. whose presentation depended on the relationship between slice and imaging plane orientation. Color/power Doppler artifacts were related to gain, aliasing, and flash which could add apparent structure or confusion to the volume images. Rendered images also demonstrated artifacts due to shadowing and motion of adjacent structures, cardiac motion or pulsatility of the cardiac septum or vessel walls. Editing artifacts potentially removed important structures. Three-dimensional ultrasound is prone to the same types of artifacts encountered in 2D US imaging plus others unique to volume acquisition and visualization. The consequences of these diagnostically significant artifacts include mimicking of abnormal development, masses, or missing structures thus requiring careful study before reaching a diagnosis.

Three-dimensional fetal ultrasound

Three-dimensional (3D) imaging by ultrasound was proposed in the 1950s. Since the end of the 1980s, 3D ultrasound has become a major field of research in obstetrics and gynaecology. The technique of acquiring 3D data involves making a set of consecutive 2D ultrasound slices by moving the transducer and continuously storing the images. These ultrasound data must be converted into a regular cubic representation before presentation in different 3D visualization modes. The creation of new ultrasound sections from the 3D block and also the surface shading of a structure of interest promise improvement in the diagnosis of congenital anomalies and dysmorphology. In addition, the possibility of volume calculation by 3D ultrasound has to be considered as a clear innovation. At present, almost all of the diagnoses illustrated by 3D ultrasound can be made by 2D ultrasound, and this will continue to be so in the foreseeable future.

Simultaneous use of two ultrasound scanners for motion-gated three-dimensional fetal echocardiography

The aim of this study was to determine whether or not simultaneous use of an additional Doppler transducer could provide sufficient cardiovascular motion information without significantly interfering with three-dimensional (3-D) cardiac structural data acquisition by a primary two-dimensional (2-D) transducer. To determine sources of interference, paired transducers were activated alternatively and simultaneously in and out of a water bath, with and without electrical insulating and electromagnetic shielding. To determine factors affecting interference, pairs were tested on a phantom with different separating distances and angles between paired ultrasound (US) beams and under different 2-D depths and Doppler scales. Results show that the dominant source of interference is acoustic cross talk. The severity was mainly affected by transducer pairing and by separating distances and angles, and the pattern by display settings. With optimised settings, sufficient structural and motion data were obtained simultaneously in 9 of 12 fetal hearts, and detailed 3-D views could be reconstructed free of motion artefacts, confirming the feasibility of using the method for motion-gated 3-D fetal cardiac imaging. New scanner design strategy was then proposed.

Fetal renal volume assessment by three-dimensional ultrasonography

OBJECTIVE

This study was undertaken to measure fetal renal volume by means of three-dimensional ultrasonography and to use those data to establish the accurate constant and formula for fetal renal volume assessment with two-dimensional ultrasonography.

STUDY DESIGN

Singleton fetuses between 15 and 40 weeks' gestation were included. The volumes of both fetal kidneys were measured with three-dimensional ultrasonography. Three fetal renal diameters (largest anteroposterior, transverse, and longitudinal diameters) were measured, and the constant of the fetal renal volume formula was calculated. Linear regression curves were made for each kidney from the fetal renal volume, the three diameters, and the constant.

RESULTS

A total of 112 fetuses were included. The following fetal renal volume formula was established: Fetal renal volume = Constant (R) x Largest anteroposterior diameter (x) x Largest transverse diameter (y) x Largest longitudinal diameter (z). The volumes, the three diameters, and the constants appeared different between the right and left kidneys but not statistically significantly so.

CONCLUSION

Three-dimensional ultrasonography is useful in assessing fetal renal volume. The fetal renal volume formula makes possible accurate measurements of fetal renal volume by two-dimensional ultrasonography.