Three-dimensional (3D) and 4D color Doppler fetal echocardiography using spatio-temporal image correlation (STIC)

Transcription

1 Ultrasound Obstet Gynecol 2004; 23: Published online 6 May 2004 in Wiley InterScience ( DOI: /uog.1075 Three-dimensional (3D) and 4D color Doppler fetal echocardiography using spatio-temporal image correlation (STIC) R. CHUI, J. HOFFMANN and K. S. HELING Unit of Prenatal Diagnosis and Therapy, Charité University Hospital, Berlin Germany KEYWORDS: STIC 3D; 4D; color Doppler; congenital heart defects; fetal echocardiography; spatio-temporal image correlation; ABSTCT Objective Color Doppler echocardiography is used to visualize three transverse planes: the four-chamber, fivechamber, and three vessels and trachea views. Color Doppler spatio-temporal image correlation (STIC) is a new three-dimensional (3D) technique allowing the acquisition of a volume of data from the fetal heart that is displayed as a cineloop of a single cardiac cycle. The aim of the study was to examine the potential of color Doppler STIC to evaluate normal and abnormal fetal hearts. Methods This prospective study included 35 normal fetuses and 27 fetuses with congenital heart defects (CHD) examined between 18 and 35 weeks of gestation. Volume acquisition was achieved by initiating the image capture sequence from the transverse four-chamber view. Volumes were stored for later offline evaluation using a personal computer-based workstation in a multiplanar mode and as spatial volume rendering. Results Successful acquisition was possible in all 62 cases. The three planes could be demonstrated in 31/35 healthy fetuses and in 24/27 fetuses with CHD. Spatial volume rendering was attempted in 18 fetuses with CHD. In the four normal fetuses with inadequate visualization using color Doppler STIC, the region of interest was perpendicular to the ultrasound beam. In two fetuses with CHD inadequate visualization was related to an enlarged heart in late gestation, in which the entire cardiac volume could not be acquired. The third case was an 18-week fetus with complex CHD and transposed great vessels in which artifacts were related to confluent color signals as a result of low resolution in the reconstructed plane. Conclusions STIC in combination with color Doppler ultrasound is a promising new tool for multiplanar and 3D/4D rendering of the fetal heart. Limitations may be found later in gestation in fetuses with large hearts and early in gestation as a result of low discrimination of signals. In addition, insonation perpendicular to the structure of interest does not image color Doppler signals and should be avoided during acquisition. Copyright 2004 ISUOG. Published by John Wiley & Sons, Ltd. INTRODUCTION An extended fetal echocardiographic examination is achieved by acquiring and documenting sequential crosssectional planes 1 3. In a systematic segmental approach the venoatrial, atrioventricular and ventriculoarterial connections should be assessed to identify normal and abnormal cardiac anatomy 1. Several studies have demonstrated that the increased detection of heart anomalies may be achieved by a) understanding and implementing a systematic cardiac examination, b) visualizing the great vessels in addition to the plane of the four-chamber view, and c) using a checklist of identified planes to exclude cardiac malformations 4. Color Doppler ultrasound was introduced to fetal echocardiography in the late 1980s 5 and is used by many investigators during routine cardiac imaging to increase the accuracy and speed of the examination 6. In a recent review we presented three transverse planes for the routine color Doppler evaluation of the heart and demonstrated the numerous anomalies which could be identified in these planes 6. An examiner assessing a number of cross-sectional cardiac planes while the heart is beating is automatically mentally reconstructing the heart in the third (3D) and fourth (3D + time (4D)) dimensions. In the last decade 3D and 4D fetal Correspondence to: Prof. R. Chaoui, Department of Obstetrics and Gynecology, Charité Medical School, Humboldt University, Schumannstr. 20/21, D Berlin, Germany ( rabih.chaoui@charite.de) Accepted: 6 April 2004 Copyright 2004 ISUOG. Published by John Wiley & Sons, Ltd. ORIGINAL PAPER

2 536 Chaoui et al. echocardiography have been investigated using external workstations or static volume sweeps 7 14.Onlyafew studies have examined the combination of color with 3D cardiac acquisition, reporting low success rates and complicated gating techniques 15,16. The recent advent of the automated spatio-temporal image correlation (STIC TM ) technique provided the first 3D and 4D gray-scale images from the fetal heart 17,18. Recently, color Doppler and power Doppler have been combined with gray-scale STIC technology, making possible the assessment of hemodynamic changes throughout the cardiac cycle and in the different cardiac cavities. The purpose of this study was to evaluate the clinical potential of color Doppler STIC in normal fetuses and in those with heart malformations, aiming firstly to obtain offline the three defined planes from stored 4D volumes, and secondly to demonstrate new spatial views of the fetal heart in 3D/4D volume rendering. METHODS Basics of the spatio-temporal image correlation (STIC) technique, volume acquisition and display A short summary of the STIC principle is presented here; a more detailed description is given in a previous study by DeVore et al. 17. The integrated STIC software permits the acquisition of a cardiac volume dataset by analyzing and correlating numerous images from different heart cycles obtained during an automated sweep. The duration of the acquisition can be adjusted by the examiner (7.5, 10, 12.5 or 15 s). The acquisition angle sweep ranges from 15 to 40. The rendered volume includes a single hypothetical cardiac cycle, which is reconstructed from selected images of the acquisition plane (A-plane) during different phases of the heart cycle. The quality of the heart volume dataset depends on the frame rate of the two-dimensional (2D) image, the angle sweep and the acquisition time. The more images stored per acquisition period, the greater the number available for the reconstruction of a volume and the better the resolution. Color and power Doppler have a slower frame rate compared with gray scale during scanning, which leads unavoidably to a reduction in image quality using color STIC when compared with grayscale STIC. Once the volume is successfully obtained, it is displayed on the screen in a multiplanar image format, demonstrating one cardiac cycle beating in the three orthogonal planes (Figures 1 and 2). The A-plane is the acquisition plane and has the best image quality (upper left). The B (upper right) and C (lower left) planes are the orthogonal planes which have been reconstructed by the system. Therefore, the quality of the acquired volume can be estimated online by directly analyzing the B-plane. The examiner can repeat the acquisition if necessary, for example if fetal movements occurred during acquisition. The sweep angle can be widened if this was too narrow, and the mother can be asked to suspend breathing if maternal movements were recognized. The heart volume dataset can also be displayed as a single image of a 3D/4D surface or a transparent volume, in which gray-scale or color Doppler information or both can A-PNE B-PNE C-PNE Figure 1 Color Doppler spatio-temporal image correlation volume of a 26-week fetus displayed in the multiplanar mode. The A-plane is the acquisition plane, the B-plane is the orthogonal plane vertical to the A-plane and the C-plane is the orthogonal plane horizontal to the A-plane. The arrow shows the cineloop bar, which when activated allows visualization of heart contractions and color Doppler changes in the different planes (cf. Figure 3). In the right lower corner an orientation box can be displayed, demonstrating in this case that the A-plane is activated., left atrium;, left ventricle;, right atrium;, right ventricle.

3 Color Doppler STIC 537 Figure 2 One application of the multiplanar mode is demonstrated in this fetus with a ventricular septal defect (VSD) showing shunting from the left to the right ventricle (blue color crossing the septum). The arrows point to the dot present in all three planes which shows the intersection point of these planes. The examiner can place the dot in the region of interest in one plane (here in the A-plane) and see its position in both the other planes. In this case the dot has been placed on the VSD in plane A, which is then pinpointed in planes B and C., left ventricle;, right ventricle. a b c DA ISTH SVC Trachea Figure 3 One of the possible displays of the multiplanar view is offline re-examination. Taking the volume of Figure 1, the A-plane has been magnified and visualized alone. By scrolling through the volume the examiner can visualize any plane. Three planes are presented: the four-chamber view (a), the five-chamber view (b) and the three vessels and trachea view (c). By using the cineloop the examiner can choose within the volume the heart cycle phase of interest. Compare also with Figures 6 and 7., aorta; DA, ductus arteriosus; ISTH, aortic isthmus;, left atrium;, left ventricle;, right atrium;, right ventricle; SVC, superior vena cava;, pulmonary trunk.

4 538 Chaoui et al. be demonstrated (so called glass body mode), providing spatial relationships as for gray-scale STIC 17. Study population The study population included 62 fetuses, consisting of 35 fetuses with normal anatomy and 27 with a structural congenital heart defect (CHD). The normal population was recruited from pregnant women referred either for routine antenatal sonography or for targeted cardiac examination due to a positive family history of heart anomalies. All were singleton pregnancies between 20 weeks and term with structurally normal fetuses of appropriate size for gestational age, showing neither fetal arrhythmia nor other cardiac or extracardiac abnormalities. Patients gave oral consent to participate in the study, which was performed during a routine fetal echocardiography examination. The hospital ethics committee gave approval to perform the study and to store volumes for offline evaluation. The 27 fetuses with CHD were either detected in our unit or referred for a second opinion ultrasound examination because of a suspected CHD. They are grouped according to type of CHD in Table 1 and covered a range of gestational ages. Following traditional freehand 2D B-mode, color and pulsed Doppler examination of each fetus, STIC evaluation was performed. No clinical decisions were made as a result of the 3D findings. We divided the fetuses with CHD into three groups according to whether the abnormality was observed with color Doppler primarily in the four-chamber plane, in the planes of the great vessels, or in all planes. In addition, we evaluated the possibility of 3D/4D spatial surface volume rendering in selected fetuses with CHD. Examination technique Ultrasound examinations were performed using a Voluson 730 Expert system (GE Medical systems, Kretztechnik, Zipf, Austria) and the transabdominal probe (B- 4 8MHz) was used to acquire the STIC volumes. STIC software can be used either for gray-scale imaging or in combination with color and power Doppler. Our learning curve with color STIC was rapid due to previous experience with gray-scale STIC 20. Comprehensive 2D and color Doppler fetal echocardiography was performed with the 3D transducer. On completion of the examination a manual sweep was performed to determine whether all structures of interest were included in the acquired volume and the 3D STIC acquisition was activated. Volume datasets were acquired when fetuses were in a dorsoposterior position allowing either apical, right-sided or left-sided insonation of the heart. The manufacturer s settings for cardiac evaluation were used and slightly modified according to individual conditions, keeping the image frame rate as high as possible. The color box size was therefore selected to be as narrow as was needed for image acquisition. For the purposes of this study only transverse cardiac sweeps were Table 1 Details of fetuses with congenital heart defects (CHD) and the gestational age at examination divided according to whether the abnormality can be demonstrated by color Doppler in the four-chamber plane, in the five-chamber or three vessels and trachea view, or in all three planes Diagnosis Gestational age (weeks) Anomalies of the chambers VSD 33 VSD 22 VSD 24 AVSD 33 AVSD 23 Rhabdomyoma 22 Anomalies of the great vessels TOF 30 TOF, PA 29 TOF, APVS 24 D-TGA 26 D-TGA 28 CoA 30 D-AoA 28 R-AoA 26 DO 35 PS/PI 32 TAC 22 Combined anomalies HLHS 22 HLHS 20 HLHS 25 PA-IVS, TI 23 PA-IVS, severe TI 31 PA-IVS, VCAC 21 Ebstein, PA 27 SV-DO, R-AoA 22 SV-DO, R-iso 18 D-TGA + VSD 32 APVS, absent pulmonary valve syndrome; AVSD, atrioventricular septal defect; CoA, aortic coarctation; D-AoA, double aortic arch; DO, double outlet right ventricle; D-TGA, d-transposition of great arteries; HLHS, hypoplastic left heart syndrome; PA, pulmonary atresia; PA-IVS, pulmonary atresia with intact ventricular septum; PS/PI, pulmonary stenosis and insufficiency; R-AoA, right aortic arch; R-iso, right isomerism; SV, single ventricle; TAC, truncus arteriosus communis; TI, tricuspid insufficiency; TOF, tetralogy of Fallot; VCAC, ventriculocoronary arterial communications; VSD, ventricular septal defect. obtained to keep the examination as similar as possible to the proposed transverse 2D gray-scale and color Doppler planes 3,6. The acquisition angle of the volume box was selected between 15 and 35 according to the depth of the fetus in utero and to the size of the heart. Acquisition time ranged between 7.5 and 15 s, with 10-s acquisition times being most commonly used. In all cases with color STIC we attempted to maintain the image frame rate higher than 17 Hz to allow acquisition of a high number of images. Mechanical and thermal indices in color Doppler were kept as low as possible according to the A principle 21. After an adequate volume acquisition had been obtained, the volume data were stored on the hard disk of the computer. One to three STIC color

5 Color Doppler STIC 539 TI Figure 4 Spatio-temporal image correlation color volume of a fetus with hypoplastic right ventricle (pulmonary atresia with intact septum). The A-plane is magnified showing the four-chamber plane. By scrolling through the cineloop the only filling of the left ventricle during diastole can be demonstrated (a) as can the tricuspid insufficiency (TI) during systole (b)., left atrium;, left ventricle;, right atrium;, right ventricle. volumes were stored for each examination. The examinations were exported to a compact disk and transferred to a personal computer (PC) for later offline evaluation using specialized 3D software (4D View, GE Medical systems). Two examiners experienced in fetal echocardiography reviewed the color Doppler STIC volumes. RESULTS 3D and 4D volume acquisitions were technically possible in all cases. Since the examiner observes online the success of the acquisition, a second attempt can be made if necessary. The most common reason for performing a second volume acquisition was mainly a small sweep acquisition angle that did not include the great vessels; this occurred in 9/35 fetuses. We did not try to acquire volumes only with a strict apical view, since this does not reflect real examination conditions. In the multiplanar mode we were able to obtain in most fetuses, both those with normal and those with abnormal hearts, the necessary information in the corresponding planes. Figure 1 illustrates the multiplanar mode showing A, B and C-planes. Figure 2 demonstrates how the reference dot can be placed in one region of interest, simultaneously pinpointing this area in the two orthogonal planes. Figure 3 illustrates the three planes of interest in their corresponding phase during the heart cycle. Figure 4 demonstrates a hypoplastic right ventricle in which one plane (A-plane) is displayed during both systole and diastole (tricuspid regurgitation). Figures 5 and 6 show how from a stored volume the three planes with their typical color Doppler findings can be reviewed offline. This potential of the technique is demonstrated for two heart anomalies, hypoplastic left heart syndrome (Figure 5) and tetralogy of Fallot (Figure 6). In the group of normal fetuses 4/35 (11.5%) had an incomplete examination using color Doppler STIC, due mainly to perpendicular insonation in one of the three planes of interest. In one fetus the aorta did not show perfusion in a perpendicular right-sided heart insonation (Figure 7). In two other cases visualized from the left side the three vessels and trachea (3VT) view was seen on a real-time image but no flow was observed in the horizontal vessels. In the fourth case the four-chamber

6 540 Chaoui et al. A Trachea Aortic Isthm Figure 5 Spatio-temporal image correlation color volume of a 20-week fetus with hypoplastic left heart syndrome. Scrolling through the planes of the volume allows demonstration of the findings in the three planes (cf. Figure 3). The four-chamber view (a) shows the filling of the right ventricle during diastole and the empty hypoplastic left ventricle. The five-chamber view (b) shows the atretic hypoplastic aortic root with no antegrade flow in the ascending aorta (A). The three vessels and trachea view (c) shows the antegrade flow (blue) through the slightly dilated pulmonary trunk and the retrograde flow (red) in the hypoplastic aortic isthmus. Isthm, isthmus;, left atrium;, left ventricle;, right atrium;, right ventricle;, pulmonary trunk. view was insonated perpendicularly from the right side and did not show optimal filling of the chambers. In the 27 fetuses with heart abnormalities, inappropriate volumes were obtained in three cases (11%), one with a double outlet right ventricle seen at 35 weeks, in which rib shadows and a narrow volume sweep hindered visualization of the origin of one of the two vessels from the right ventricle. In another case with coarctation of the aorta at 36 weeks the continuity and perfusion of the aortic arch could not be observed in the acquired volume due to the fixed fetal position and rib shadowing. In the third fetus at 18 weeks a right isomerism and double outlet ventricle with anterior posterior transposed vessels was diagnosed. In the transverse plane only one vessel could be seen and in the reconstructed longitudinal plane the resolution was not sufficient to permit a reliable demonstration of the finding. A longitudinal acquisition was not achieved since this was not part of the study protocol. Volume rendering was attempted in several cases to obtain experience with this new technology. In eight selected cases we rendered the spatial 3D/4D volumes by demonstrating a cranial view of the heart and vessels in a glass body display (Figures 8 and 9). Figure 8 illustrates how within the volume the examiner can see simultaneously the chambers and the criss-crossing of the great vessels, while Figure 9 shows two examples of abnormalities: a transposition of the great arteries and a double aortic arch. In six cases the atrioventricular valves and the great vessels were visualized in an en-face view 14 (Figures 10 and 11) and in an additional four cases the interventricular septum was rendered, viewed from the right or left ventricle. DISCUSSION Spatio-temporal image correlation (STIC) feasibility and comparison with previous studies This study demonstrates the feasibility of using STIC technology in combination with color Doppler to provide 3D/4D imaging of fetal cardiac flow in normal fetuses and in fetuses with CHD. Previous systems used volume data acquisitions based either on a static volume sweep 12,22,23 or on attempts to gate the heart rate signal by means of spectral Doppler 15 or cardiotocography 16. Recent reports on gray-scale STIC demonstrated clearly the ease of use and the advantages of this new technique in providing 3D/4D information on the fetal heart in the second half of gestation Deng 24 suggested in an Opinion in this Journal that terminology should be used to describe accurately the system used when reporting 3D and 4D image acquisitions of the fetal heart. We believe that STIC could be defined as an online system with an indirect volume scan and post- 3D/4D-acquisition correlation. The color Doppler STIC

7 Color Doppler STIC 541 DA SVC Figure 6 Spatio-temporal image correlation (STIC) color volume of a 24-week fetus with tetralogy of Fallot. By scrolling through the STIC volume all three planes can be demonstrated (cf. Figure 3). The four-chamber plane (a) appears normal during diastole. The five-chamber plane (b) shows the overriding of the aorta receiving blood from both ventricles (arrows). The pulmonary trunk appears smaller than the aorta with antegrade flow (c)., aorta; DA, ductus arteriosus;, left atrium;, left ventricle;, right atrium;, right ventricle; SVC, superior vena cava;, pulmonary trunk. Figure 7 Limitation of color Doppler spatio-temporal image correlation (STIC) related to insonation angle. This STIC color volume was acquired from a right-sided four-chamber view and the aorta is lying horizontally. Due to the perpendicular insonation of the aortic valve, blood flow is not appropriately visualized (arrow)., aorta;, left ventricle;, right ventricle. approach is the first system to allow rapid, online image acquisition and display of information of spatial intracardiac flow. There are only a few reports of 3D/4D rendering of fetal cardiac blood flow. Experience with non-gated 3D static power Doppler has been reported by our group 12,22,23,25, which found it to have limitations as a result of the contracting heart hindering reliable rendering of the volume. In the last 2 years two studies have reported gated 3D/4D fetal echocardiography in combination with color Doppler 15,16. In the study by Deng et al. 15 two transducers were utilized, one for image acquisition and one for heart rate assessment by spectral Doppler. They were successful in triggering 8/15 attempts performed, obtaining six volumes with useful information, and complete information being obtained in only four cases. A similar observation was reported by Herberg et al. 16. According to our experience, STIC technology combined with color Doppler solved most of the problems confronted by other authors. If the examiner has experience with color Doppler settings on the 2D image, the learning curve will be very short. The main advantages of the system are the use of a single probe for the 2D and 3D examinations, with integrated software, and the short acquisition and display time, which occurs within 30 s instead of the min reported in the other studies 15,16. This may promote this system as a new tool that can be introduced into routine fetal cardiac screening, with its main advantage being the possibility of storing volumes of one cardiac cycle with color Doppler information. Our study showed that the multiplanar

8 542 Chaoui et al. A DA A Arch Figure 8 4D volume rendering with transparent gray-scale and surface color Doppler. The examiner looks at the heart volume from a cranial approach visualizing the great vessels and the chambers beneath (or behind in the image). By scrolling through the cineloop the different phases of the cardiac cycle can be visualized as the diastolic filling of the ventricles (a), the beginning of systole with blood flow streaming in the outflow tracts (b), and late systole with blood still recognizable in both great vessels. In this view the criss-crossing of the great vessels can be appreciated in a way not seen before in prenatal diagnosis (cf. transposition in Figure 9b). Due to the presetting of color persistence the volume in (b) shows simultaneously late diastole (red filling of chambers) and early systole (filling of the vessels). A, ascending aorta; A Arch, aortic arch;, aorta; DA, ductus arteriosus;, left atrium;, left ventricle;, right atrium;, right ventricle;, pulmonary trunk. DA L R Trachea Figure 9 The same view as demonstrated in Figure 8. (a) A normal finding with the regular criss-crossing of the aorta () and pulmonary trunk (). (b) A fetus with transposition of the great arteries with parallel course of both vessels; the two ventricles in late diastole can be seen (cf. Figure 8b). (c) A fetus with a double aortic arch; the three-dimensional rendering demonstrates the bifurcation (arrows) of the aortic arch in front of the trachea (line) into left (L) and right (R) arches. The ductus arteriosus (DA) connects to the left aortic arch. display in most (90%) cases (with either a normal or abnormal heart) permits a reliable offline demonstration of the findings, considering also hemodynamic changes that occurred during the cardiac cycle (Figures 1 6). In our opinion the information and data content in such a volume are far greater than can be obtained from a series of still images or video clips stored on a digital archiving system. Color Doppler STIC is the only tool available which permits the examiner to reliably recreate the color Doppler examination of the fetal heart offline and review the examination at a later time. Multiplanar mode display The three color Doppler planes we proposed recently 6 namely the four-chamber, the five-chamber- and the 3VT

9 Color Doppler STIC 543 MV TV Figure 10 4D surface rendering of the atrioventricular (AV) and semilunar valves during diastole systole in the en-face view of the AV valves. The view as shown by the green bar (a) is from the heart base towards the apex. In the rendered image (b) the en-face view of both mitral (MV) and tricuspid valve (TV) is demonstrated during diastolic flow (red) (cf. Figure 11b). Due to increased persistence of color Doppler, blood flow in early systole is seen simultaneously. Therefore the embedded aorta () can be recognized between both AV valves, and the pulmonary trunk () is in a normal position anterior to the aortic valve (cf. Figure 11b)., left atrium;, right atrium. Common AV-valve MV TV Figure 11 En-face view in two fetuses with a heart anomaly (cf. normal fetus in Figure 10). (a) A fetus with atrioventricular septal defect showing the common valve demonstrated by a single wide flow. (b) A fetus with complete transposition of the great arteries with side-by-side vessels, the aorta () being anterior and on the right side (d-transposition) of the pulmonary artery (). MV, mitral valve; TV, tricuspid valve.

10 544 Chaoui et al. views, can be reliably evaluated using color Doppler STIC volume datasets, with a 90% success rate. This approach was successful in 24/27 fetuses with cardiac anomalies and allowed a reviewer at a remote site to visualize the abnormality using at least one of the three planes. The advantages of such a volume dataset is that it can be displayed as a 2D cardiac cycle in a cineloop (Figure 4) 17. The loop may be demonstrated in slow motion or stopped at any time to be analyzed frame-by-frame, as shown in Figure 4 for diastole and systole. The visualization of color Doppler information can also be changed gradually by manually changing the color threshold button. Each of the scan planes can be moved and rotated during the synchronized cardiac loop and displayed as a single image (Figures 3 5) or as a combination of three orthogonal planes (Figures 1 and 2) 17. A reference dot that can be placed anywhere on the image by the examiner can assist in the visualization of the spatial orientation of the three orthogonal planes, as shown in Figure 2 for a ventricular septal defect demonstrated in the A-, B- and C-planes. This dot is used to facilitate orientation within the STIC volume 17,19. Such a STIC volume dataset can not only be used for a second opinion by a fetal cardiology expert 17 but it could also be used for teaching fetal echocardiography. Limitations of the technique The system we used also has some limitations and may produce artifacts as reported elsewhere 17. Besides artifacts typical for 3D volume acquisition such as fetal or maternal movements, there are limitations typical of STIC technology which occur with arrhythmias. Because of this fetuses with ectopic beats were excluded from the study as in other studies with heart rate gating. Other artifacts such as a non-magnified heart, a short acquisition time and a wide sweep angle were avoided by optimizing the image before activating the volume acquisition. Limitations specifically related to color STIC were the missing color Doppler signals when the vessel was perpendicular to the ultrasound beam (Figure 7). Because of the orientation of the heart, this artifact may be difficult to avoid in at least one of the three displayed orthogonal views. To avoid this problem the examiner should angle the transducer to obtain a cardiac plane with blood flow visualized in the structures of interest. Another method that can be used to address this problem is to acquire several volumes from different angles, which are then likely to include the information of interest. This aspect should be considered in future studies when volumes are sent via the Internet to obtain a second opinion from an expert in fetal cardiology. This disadvantage is inherent to color Doppler and is not found in gray-scale STIC, with which image acquisition can be achieved from any angle. Potential of spatial 3D/4D volume rendering This study focused mainly on the feasibility of acquiring a heart volume and on the reliability of multiplanar display of images in comparison with the standard color Doppler planes. An additional benefit of this new technique is 3D/4D surface and transparent volume rendering (Figures 9 and 10), allowing a spatial impression of the heart and great vessels. The 3D/4D rendering is obtained offline using the workstation by simply choosing the function rendering. The examiner should then place the render view direction bar (green line, Figure 10) so as to obtain a view of the volume of interest. In this study we tried rendering from three different views: from a cranial approach, from a basal approach looking enface to the atrioventricular (AV) valves and the great vessels, and from a septal approach looking at the interventricular septum from either the left or the right side. This preliminary experience shows that such 3D/4D rendering can be helpful in visualizing the relationship of the great vessels to each other (Figures 9 11), perfusion across the AV valves (Figures 10 and 11) and through a ventricular septal defect. Further studies are necessary to examine this new approach to fetal heart diagnosis. CONCLUSIONS In summary, we have shown in this study that the combination of STIC with color Doppler provides the examiner with a volume dataset that combines information regarding structure, blood flow dynamics and intracardiac flow. After adjusting the color Doppler presets the technique is easy to use and provides reliable volume datasets. These can be displayed in a multiplanar format permitting offline re-examination. We have demonstrated that planes proposed and used in color Doppler echocardiography can be obtained offline from a volume dataset using an external workstation. There is an additional possibility of using this technology to view 3D/4D surface and transparent volume rendered views, a new method with which to examine the fetal heart in a spatial dimension that requires further study. REFERENCES 1. Allan LD. Manual of fetal echocardiography. M Press Limited: London, Yagel S, Cohen SM, Achiron R. Examination of the fetal heart by five short-axis views: a proposed screening method for comprehensive cardiac evaluation. Ultrasound Obstet Gynecol 2001; 17: Chaoui R. The examination of the fetal heart using twodimensional echocardiography. In Fetal Cardiology, Yagel S, Silvermann N, Gembruch U (eds). Martin Dunitz: London, New York, 2003; Chaoui R. The four-chamber view: four reasons why it seems to fail in screening for cardiac abnormalities and suggestions to improve detection rate. Ultrasound Obstet Gynecol 2003; 22: Devore GR, Horenstein J, Siassi B, Platt LD. Fetal Echocardiography. 7. Doppler Color flow mapping a new technique for the diagnosis of congenital heart disease. Am J Obstet Gynecol 1987; 156: Chaoui R, McEwing R. Three cross-sectional planes for fetal color Doppler echocardiography. Ultrasound Obstet Gynecol 2003; 21:

11 Color Doppler STIC Deng J, Gardener JE, Rodeck CH, Lees WR. Fetal echocardiography in three and four dimensions. Ultrasound Med Biol 1996; 22: Nelson TR, Pretorius DH, Sklansky M, Hagen-Ansert S. Threedimensional echocardiographic evaluation of fetal heart anatomy and function: Acquisition, analysis, and display. J Ultrasound Med 1996; 15: Sklansky MS, Nelson TR, Pretorius DH. Usefulness of gated three-dimensional fetal echocardiography to reconstruct and display structures not visualized with two-dimensional imaging. Am J Cardiol 1997; 80: Sklansky MS, Nelson TR, Pretorius DH. Three-dimensional fetal echocardiography: Gated versus nongated techniques. J Ultrasound Med 1998; 17: Deng J, Ruff CF, Linney AD, Lees WR, Hanson MA, Rodeck CH. Simultaneous use of two ultrasound scanners for motion-gated three-dimensional fetal echocardiography. Ultrasound Med Biol 2000; 26: Chaoui R, Kalache KD. Three-dimensional power Doppler ultrasound of the fetal great vessels. Ultrasound Obstet Gynecol 2001; 17: Bega G, Kuhlman K, Lev-Toaff A, Kurtz A, Wapner R. Application of three-dimensional ultrasonography in the evaluation of the fetal heart. J Ultrasound Med 2001; 20: Meyer-Wittkopf M, Cooper S, Vaughan J, Sholler G. Threedimensional (3D) echocardiographic analysis of congenital heart disease in the fetus: comparison with cross-sectional (2D) fetal echocardiography. Ultrasound Obstet Gynecol 2001; 17: Deng J, Yates R, Sullivan ID, Mcdonald D, Linney AD, Lees WR, Anderson RH, Rodeck CH. Dynamic threedimensional color Doppler ultrasound of human fetal intracardiac flow. Ultrasound Obstet Gynecol 2002; 20: Herberg U, Goldberg H, Breuer J. Dynamic free-hand threedimensional fetal echocardiography gated by cardiotocography. Ultrasound Obstet Gynecol 2003; 22: Devore GR, Falkensammer P, Sklansky MS, Platt LD. Spatiotemporal image correlation (STIC): new technology for evaluation of the fetal heart. Ultrasound Obstet Gynecol 2003; 22: Vinals F, Poblete P, Giuliano A. Spatio-temporal image correlation (STIC): a new tool for the prenatal screening of congenital heart defects. Ultrasound Obstet Gynecol 2003; 22: Goncalves LF, Lee W, Espinoza J, Huang R, Chaiworapongsa T, Schoen ML, DeVore G, Romero R. Fourdimensional fetal echocardiography with spatio-temporal image correlation (STIC): a systematic study of standard cardiac views assessed by different observers. Ultrasound Obstet Gynecol 2003; 22(Suppl): 50[Abstract]. 20. Chaoui R, Kalache K, Heling KS. Potential of off-line 4D fetal echocardiography using new acquisition and rendering technique (STIC). Ultrasound Obstet Gynecol 2003; 22(Suppl): 50 [Abstract]. 21. Duck FA. Is it safe to use diagnostic ultrasound during the first trimester? Ultrasound Obstet Gynecol 1999; 13: Chaoui R, Kalache KD, Hartung J. Application of threedimensional power Doppler ultrasound in prenatal diagnosis. Ultrasound Obstet Gynecol 2001; 17: Chaoui R, Heling KS, Kalache KD, Schneider M. 3D-Power Doppler echocardiography: usefulness in spatial visualization of fetal cardiac vessels. Ultrasound Obstet Gynecol 2003; 22(Suppl): 45 [Abstract]. 24. Deng J. Terminology of three-dimensional and four-dimensional ultrasound imaging of the fetal heart and other moving body parts. Ultrasound Obstet Gynecol 2003; 22: Chaoui R, Schneider MBE, Kalache KD. Right aortic arch with vascular ring and aberrant left subclavian artery: prenatal diagnosis assisted by three-dimensional power Doppler ultrasound. Ultrasound Obstet Gynecol 2003; 22: