Abstract
Objectives
Manual and intelligent navigation (i.e. fetal intelligent navigation echocardiography or FINE) by the operator are two methods to obtain standard fetal cardiac views from spatiotemporal image correlation (STIC) volumes. The objective was to compare the performance between manual and intelligent navigation (FINE) of the fetal heart by non-expert sonologists.
Methods
In this prospective observational study, ten sonologists underwent formal training on both navigational methods. Subsequently, they were tested on their ability to obtain nine cardiac views from five STIC volumes of normal fetal hearts (19–28 gestational weeks) using such methods. The following parameters were determined for both methods: (1) success rate of obtaining nine cardiac views; (2) mean time to obtain nine cardiac views per sonologist; and (3) maximum number of cardiac views successfully obtained for each STIC volume.
Results
All fetal cardiac images obtained from 100 STIC volumes (50 for each navigational method) were reviewed by an expert in fetal echocardiography. Compared to manual navigation, FINE was associated with a significantly: (1) higher success rate of obtaining eight (excluding the abdomen view) appropriate cardiac views (92–100% vs. 56–88%; all p<0.05); (2) shorter mean time (minute:seconds) to obtain nine cardiac views (2:11 ± 0:37 vs. 15:49 ± 7:44; p<0.0001); and (3) higher success rate of obtaining all nine cardiac views for a given STIC volume (86 vs. 14%; p<0.001).
Conclusions
When performed by non-expert sonologists, intelligent navigation (FINE) had a superior performance compared to manual navigation of the normal fetal heart. Specifically, FINE obtained appropriate fetal cardiac views in 92–100% of cases.
Introduction
A comprehensive fetal cardiac examination should be performed in all pregnancies [1], [2], [3], since more than half of infants with congenital heart disease (CHD) are born to women without prior known risk factors [4]. Yet, adequate real-time sonographic examination of the fetal heart is a challenge, requiring operator skill and expertise [5], [6], [7], [8]. In addition, difficulty in imaging can be attributed to the complex anatomy of the fetal heart, its motion, and small size. As a result, such examinations often do not include all the standard recommended cardiac views [9], [10], [11], [12], [13].
Four-dimensional (4D) sonography with spatiotemporal image correlation (STIC) has been shown to facilitate examination of both the normal [14], [15], [16], [17], [18], [19], [20], [21], [22] and abnormal fetal heart [14, 23], [24], [25], [26], [27], [28], [29], [30], [31], [32], [33]. STIC technology allows acquisition of a fetal cardiac volume dataset, and displays a cine loop of a complete single cardiac cycle in motion [34], [35], [36], [37], [38]. Since such technology allows the review of any fetal cardiac plane at any time during the cardiac cycle, this could be helpful in cardiac examinations.
Indeed, manual navigation of STIC volumes has been shown to be an effective method to examine the normal fetal heart [38], [39], [40], [41], [42], [43], [44], [45]. Manual navigation is the conventional method to analyze a cardiac volume dataset [46, 47], using controls that interrogate three orthogonal planes in the multiplanar display. As a result, the standard fetal cardiac views required for prenatal diagnosis are generated. Yet, such navigational method requires a comprehensive understanding of fetal cardiac anatomy, is highly operator dependent, and can be difficult to perform [47, 48].
Intelligent navigation is a different and novel method to interrogate a volume dataset (e.g. STIC), whereby identification and selection of key anatomical landmarks allow the system to: (1) generate a geometric model of the organ of interest (e.g. fetal heart); and (2) automatically navigate, find, extract, and display specific diagnostic planes [47]. When intelligent navigation technology is applied to STIC volume datasets, Fetal Intelligent Navigation Echocardiography (FINE) is the end result, in which there is automatic generation and display of nine standard fetal echocardiography views required to diagnose most cardiac defects [46], [47], [48], [49], [50], [51], [52]. Importantly, manual manipulation or standardization of STIC volume datasets and cardiac planes is not required for such method. Therefore, FINE considerably simplifies the fetal cardiac examination, and operator dependency is decreased [48]. As of this writing, FINE technology has been integrated into six ultrasound platforms thus far (e.g. HERA W10; Samsung Healthcare, Seoul, Korea), and is commercially known as 5D Heart.
The advantage of intelligent (vs. manual) navigation in volumetric sonography is the short time required for both the retrieval and display of diagnostic planes [47]. Yet, to be clinically useful and relevant, a given navigational method should be successful in obtaining fetal cardiac views that are also appropriate. This is especially the case for sonologists who have limited experience in examining the fetal heart. Therefore, we conducted this study to directly compare the performance between manual and intelligent navigation (FINE) of the fetal heart by non-expert sonologists.
Materials and methods
Study participants
This was a prospective observational study in which study participants were examined at the Detroit Medical Center/Wayne State University and the Perinatology Research Branch of the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD), National Institutes of Health (NIH), and Department of Health and Human Services. All women had been enrolled in research protocols approved by the Institutional Review Board of NICHD, NIH, and by the Human Investigation Committee of Wayne State University. All participants provided written informed consent for the use of sonographic images for research purposes.
Spatiotemporal image correlation volume datasets
Using STIC technology (Voluson E8 Expert, GE Healthcare, Milwaukee, WI, USA), 4D sonographic volume datasets of the normal fetal heart (19–28 weeks of gestation) containing grayscale information were acquired from a four-chamber view using hybrid mechanical and curved array transducers (2–5 or 4–8 MHz) by transverse sweeps through the fetal chest. All fetuses were in a vertex presentation at the time of STIC volume acquisition. The acquisition time ranged from 10 to 12.5 s (depending on fetal motion), and the acquisition angle ranged from 25 to 35° (depending on gestational age).
Eight de-identified STIC volume datasets (three for training; five for testing) from different fetuses were used for analysis by manual and intelligent navigation (FINE) if they met the following criteria: (1) fetal spine located between the 5- and 7-o’clock positions (reducing the possibility of shadowing from the spine or ribs); (2) upper fetal mediastinum and stomach included and visible in the STIC volume; (3) adequate image quality, such that fetal anatomy could be visualized; and (4) absence of excessive motion artifacts that could distort anatomical structures.
Overall study design
Ten non-expert sonologists participated in the study, all of whom had limited experience in performing obstetric sonography, and without formal training in fetal echocardiography. None of the sonologists acquired the STIC volumes analyzed in this study.
First, all sonologists underwent formal training, and then immediate testing using intelligent navigation (FINE). After an interval of seven or more days (depending upon sonologist availability), a second training session on manual navigation took place, followed immediately by testing using this method. Such sequence in methods (i.e. intelligent navigation followed by manual navigation) was chosen to provide a theoretical advantage to manual navigation, since sonologists could “learn” about normal fetal cardiac views and anatomy from the FINE method [48]. The sequence of STIC volumes was randomized for each method, and for each sonologist using a randomization program (www.random.org). Training sessions on each method were undertaken on the same set of three STIC volumes of different fetuses with normal hearts (19–28 weeks of gestation).
For the testing sessions, sonologists were tested on their ability to obtain nine fetal cardiac views using intelligent and manual navigation applied to the same set of five STIC volumes of different fetuses with normal hearts (19–28 weeks of gestation). The standard fetal cardiac views were: (1) four chamber; (2) five chamber; (3) left ventricular outflow tract; (4) short-axis view of great vessels/right ventricular outflow tract; (5) three vessels and trachea (3VT); (6) abdomen/stomach; (7) ductal arch; (8) aortic arch; and (9) superior and inferior vena cava. Such cardiac views are those required to diagnose most cardiac defects [53, 54]. To assist sonologists throughout both the training and testing sessions, a reference sheet created by the authors was provided, which featured normal characteristics of each fetal cardiac view.
After each testing session using intelligent or manual navigation was completed, all cardiac images were saved as video clips for later review by an expert in fetal echocardiography, who determined whether each cardiac view was appropriate or not. Each sonologist had been assigned a randomly generated number (www.random.org) to prevent recognition of the sonologist’s identity by the expert reviewer. Moreover, such reviewer did not participate in any of the sonologist training and testing sessions for both navigational methods.
Finally, at study completion, all sonologists completed a survey based on their experience with intelligent and manual navigation. Responses to survey statements were evaluated using a 5-point Likert scale, and related free text responses were also recorded. Moreover, sonologists were additionally asked to provide overall comments about each navigational method.
Training and testing on intelligent navigation (FINE)
Each of the ten sonologists individually underwent training (didactic and practical) on the FINE method in a 2 h session. First, they viewed four didactic videos from the YouTube channel created by the developers of FINE (Fetal Intelligent Navigation Echocardiography PRB - YouTube): (1) Video #3: What is Fetal Intelligent Navigation Echocardiography (FINE)?; (2) Video #9: What is Anatomic Box ® ?; (3) Video #10: How to Mark Using Anatomic Box ® ; and (4) Video #13: Fetal Cardiac Views. Sonologists also reviewed a separate slide presentation developed by the authors on the nine cardiac views. Next, practical training on the FINE method was performed using three STIC volumes of different fetuses with normal hearts, which also included a session on how to technically use the software system (5D Heart/FINE, version 2015.09.30; Samsung Healthcare, Seoul, Korea).
Immediately following the training session, sonologists were then tested on their ability to obtain nine fetal cardiac views using the FINE method applied to five STIC volumes of different fetuses with normal hearts. Volumes were imported by a separate assistant into the software system installed in a laptop computer. Sonologists were allowed to adjust image settings (e.g. brightness) according to individual preference, prior to commencement of testing. Recording of timing began when the sonologist started marking seven anatomical structures of the fetal heart using the Anatomic Box® tool [46]. Once the marking process is completed, FINE automatically displays nine fetal cardiac views (known as diagnostic planes) simultaneously in a single template [46, 47]. For the purposes of this study only, the display was changed such that the sonologist could assess only a single cardiac diagnostic plane at a time.
For any cardiac diagnostic plane, the sonologist also had the option of activating the Virtual Intelligent Sonographer Assistance (VIS-Assistance®) video clip for such plane [46, 47, 51]. If activated, such time duration was included in the total time taken to obtain the cardiac view. VIS-Assistance® allows operator-independent (i.e. automatic) sonographic navigation and exploration of surrounding structures in a given cardiac diagnostic plane, essentially functioning as a “virtual” sonographer [46], [47], [48]. As a result, this tool can improve the success of obtaining fetal cardiac views. Recording of timing ended when sonologists vocalized that they had obtained the fetal cardiac view of interest. All fetal cardiac images were saved as video clips for later expert review (Figure 1 and Supplementary Video 1). Each sonologist was permitted 1 h to evaluate each STIC volume, so that the total testing session duration was 5 h.
Left ventricular outflow tract view successfully obtained by a non-expert sonologist when intelligent navigation technology has been applied to a spatiotemporal image correlation (STIC) volume dataset of the normal fetal heart (also see Supplementary Video 1).
Training and testing on manual navigation
After an interval of seven or more days (depending upon sonologist availability), each sonologist individually underwent training (didactic and practical) on manual navigation in a 2-h session. This included education about the following subjects [34, 35]: (1) multiplanar display format of STIC volume datasets (which allows correlation between image planes that are perpendicular to the main acquisition plane); (2) transverse, sagittal, and coronal planes; (3) “reference dot” tool (used to manually navigate through a STIC volume dataset and localize the same anatomic structure in three orthogonal planes); (4) rotation of planes on the X, Y, and Z axes; and (5) parallel shift movements. The multiplanar display format of STIC volumes allows multiple planes of the fetal heart in motion to be visualized and examined simultaneously [23, 34]. Moreover, each plane can be moved and rotated, while maintaining synchronization within the cardiac cycle [34].
Sonologists again reviewed the same slide presentation (part of the training session on FINE) developed by the authors on the nine cardiac views. Practical training on manual navigation was performed using the same three STIC volumes of normal fetal hearts (previously used for FINE training), which also included a session on how to technically use the software system (4D View; GE Healthcare, Zipf, Austria).
Immediately following the training session, sonologists were then tested on their ability to obtain nine fetal cardiac views using manual navigation applied to the same five STIC volumes (used in FINE testing) of different fetuses with normal hearts. Volumes were imported by a separate assistant into the software system installed in a laptop computer, and the Auto Cine speed was set to 50%. Sonologists were allowed to adjust image settings (e.g. gray chroma map) according to preference, prior to commencement of testing. Recording of timing began upon manual navigation of the STIC volume dataset, and ended when sonologists vocalized they had obtained the fetal cardiac view of interest. All fetal cardiac images were saved as video clips for later expert review (Figure 2 and Supplementary Video 2). Each sonologist was permitted 1 h to evaluate each STIC volume using manual navigation, so that the total testing session duration was 5 h.
Short-axis view of great vessels/right ventricular outflow tract view successfully obtained by a non-expert sonologist when manual navigation technology has been applied to a spatiotemporal image correlation (STIC) volume dataset of the normal fetal heart (also see Supplementary Video 2). Notice the “reference dot” tool (located in the cross-section of the aorta) which is used to manually navigate through the STIC volume.
Outcome measures
After all sonologists completed the intelligent and manual navigation testing sessions, an expert in fetal echocardiography reviewed each fetal cardiac view (as a video clip) and determined the appropriateness of such views. The following outcome measures were determined for both navigational methods: (1) success rate of obtaining nine cardiac views; (2) mean time to obtain nine cardiac views per sonologist; (3) mean time to obtain nine cardiac views per STIC volume dataset; and (4) maximum number of cardiac views successfully obtained for each STIC volume dataset, as well as the success rate of obtaining four specific cardiac views (four chamber; left ventricular outflow tract; short-axis view of great vessels/right ventricular outflow tract; and abdomen/stomach) for each STIC volume dataset.
Insofar as the survey administered to all sonologists about their experience with intelligent and manual navigation, responses to survey statements were evaluated using a 5-point Likert scale (1-strongly disagree; 2-disagree; 3-undecided; 4-agree; 5-strongly agree), and related free text responses were also recorded. The survey statements were: (1) “The interface and ‘knobology’ of the method were easy to use”; (2) “The images obtained are appropriate for fetal cardiac examination”; and (3) “Overall, this was an easy method”. We defined “knobology” as the manipulation of buttons and system controls to carry out the navigational method. Finally, sonologists were asked to additionally provide overall comments about each navigational method.
Statistical analysis
Fisher’s exact test was used to assess the difference in success rates of obtaining each fetal cardiac view between intelligent and manual navigation methods, based on 50 observations (10 sonologists × 5 STIC volumes). A linear mixed effects model was used to compare the difference in mean time to obtain fetal cardiac views between intelligent and manual navigation, in which the STIC volumes and the method were considered as fixed effects, while sonologists were allowed to have a random effect on the time response variable. Models were fit using the lme4 package in the R statistical language and environment. The difference in the success rates of obtaining all 9 or 8–9 cardiac views between the two methods were also evaluated via Fisher’s exact test. For all statistical analyses, p<0.05 was considered statistically significant. Likert scale results from the survey were displayed as diverging stacked bar charts for each navigational method.
Results
A total of 100 STIC volume datasets were evaluated by sonologists using intelligent and manual navigation (50 for each method) in the testing sessions. The median gestational age at the time of STIC volume acquisition for such cases was 25 (interquartile range, 21.5–28) weeks. The interval between the testing sessions of each navigational method ranged from 7 – 19 days.
Success rates of obtaining fetal cardiac views
Using intelligent navigation (FINE), all ten sonologists submitted nine cardiac views for every STIC volume dataset to the expert reviewer. In contrast, when the same STIC volumes were analyzed by manual navigation, two sonologists were not able to successfully obtain all nine cardiac views for submission. Specifically, one sonologist was unable to obtain the aortic arch view from a STIC volume in the allotted time. A different sonologist could not obtain the 3VT from a STIC volume, and the short-axis view of great vessels/right ventricular outflow tract from a different STIC volume in the allotted time.
The success rates of obtaining nine fetal cardiac views by intelligent and manual navigation are depicted in Table 1. Except for the abdomen view, the success rates of obtaining eight appropriate fetal cardiac views were significantly higher for intelligent navigation (92–100%) compared to manual navigation (56–88%) (all p<0.05). The abdomen view was obtained successfully in 100% of STIC volumes, regardless of the navigational method used.
Success rate of obtaining nine fetal cardiac views by intelligent vs. manual navigation (n=50 STIC volumes).
| Fetal cardiac view | Intelligent navigation (FINE) n (%) | Manual navigation n (%) | p-Valuea |
|---|---|---|---|
| 3VT | 46 (92) | 32 (64) | 0.001 |
| Four chamber | 50 (100) | 44 (88) | 0.027 |
| Five chamber | 50 (100) | 37 (74) | <0.0001 |
| LVOT | 50 (100) | 41 (82) | 0.003 |
| Short-axis view of great vessels/RVOT | 48 (96) | 40 (80) | 0.028 |
| Abdomen | 50 (100) | 50 (100) | NS |
| Ductal arch | 50 (100) | 41 (82) | 0.003 |
| Aortic arch | 48 (96) | 28 (56) | <0.0001 |
| Venae cavae | 50 (100) | 44 (88) | 0.027 |
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ap<0.05 defines statistical significance. 3VT, three vessels and trachea view; FINE, fetal intelligent navigation echocardiography; LVOT, left ventricular outflow tract; NS, not significant; RVOT, right ventricular outflow tract; STIC, spatiotemporal image correlation.
The most difficult fetal cardiac views to obtain by manual navigation were the 3VT (Figure 3 and Supplementary Video 3), and aortic arch views (Figure 4 and Supplementary Video 4), which were obtained in only 64% (32/50) and 56% (28/50) of cases, respectively. However, when using FINE, the same views were successfully obtained in 92% (46/50) and 96% (48/50) of cases, respectively (Table 1, Figures 3 and 4, Supplementary Videos 3 and 4). It is also noteworthy that manual navigation successfully obtained the four-chamber view in only 88% (44/50) of cases, while the same view was obtained using intelligent navigation in 100% (50/50) of cases.
Attempts to obtain the three vessels and trachea view (3VT) by the same non-expert sonologist after both manual and intelligent navigation technology have been applied to the same spatiotemporal image correlation (STIC) volume dataset of the normal fetal heart (also see Supplementary Video 3). As depicted in the left image, the 3VT could not be obtained using manual navigation. However, by using fetal intelligent navigation echocardiography (FINE), the 3VT has been successfully generated (right image).
Attempts to obtain the aortic arch view by the same non-expert sonologist after both manual and intelligent navigation technology have been applied to the same spatiotemporal image correlation (STIC) volume dataset of the normal fetal heart (also see Supplementary Video 4). As depicted in the left image, instead of the aortic arch, only a portion of the ductal arch could actually be obtained using manual navigation. However, by using fetal intelligent navigation echocardiography (FINE), the aortic arch was successfully generated (right image).
Time to obtain fetal cardiac views per sonologist
Each of the ten sonologists took a significantly shorter mean time to obtain the nine fetal cardiac views using intelligent (vs. manual) navigation (all p<0.05) (Table 2). Insofar as the mean time (minute:seconds) ± SD for all sonologists collectively to obtain nine fetal cardiac views using intelligent vs. manual navigation, this was 2:11 ± 0:37 vs. 15:49 ± 7:44 (p<0.0001), respectively (or 131.5 ± 37 vs. 949.3 ± 464 s).
Mean time to obtain nine fetal cardiac views using intelligent vs. manual navigation per sonologist.
| Non-expert sonologist | Intelligent navigation (FINE) | Manual navigation | p-Valuea | ||
|---|---|---|---|---|---|
| Time, s | SD | Time, s | SD | ||
| 1 | 160.9 | 25.9 | 702.4 | 278.2 | 0.001 |
| 2 | 90.1 | 25.5 | 830.8 | 377.5 | 0.003 |
| 3 | 98.8 | 24.7 | 447.6 | 144.3 | 0.001 |
| 4 | 101.5 | 6.9 | 898.1 | 295.2 | <0.0001 |
| 5 | 108.8 | 27.7 | 1247.7 | 1331.5 | 0.012 |
| 6 | 111.4 | 19.7 | 371.5 | 193.7 | 0.012 |
| 7 | 175.4 | 36 | 1823.7 | 1631.6 | 0.015 |
| 8 | 199.6 | 69 | 1565.2 | 584.1 | <0.0001 |
| 9 | 124.6 | 18.1 | 833.6 | 489.7 | 0.004 |
| 10 | 143.6 | 25.7 | 772.4 | 217.5 | 0.001 |
| Total | 131.5 (or 2 min, 11 s) | 37 | 949.3 (or 15 min, 49 s) | 464 | <0.0001 |
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ap<0.05 defines statistical significance. FINE, fetal intelligent navigation echocardiography; SD, standard deviation.
It is noteworthy that the range of mean individual times to obtain nine fetal cardiac views using intelligent navigation was narrow, ranging from 90.1 to 199.6 s (i.e. 1 min, 30 s to 3 min, 20 s), regardless of the sonologist. However, for manual navigation, the range of mean individual times varied widely, from 371.5 to 1823.7 s (i.e. 6 min, 11 s to 30 min, 24 s), depending upon the sonologist (Table 2).
Time to obtain fetal cardiac views per STIC volume dataset
Regardless of the STIC volume dataset analyzed, intelligent navigation (FINE) was significantly faster than manual navigation to obtain nine fetal cardiac views (all p<0.0001) (Table 3).
Mean time to obtain nine fetal cardiac views using intelligent vs. manual navigation per STIC volume dataset.
STIC volume |
Intelligent navigation (FINE) | Manual navigation | p-Valuea | ||
|---|---|---|---|---|---|
| Time, s | SD | Time, s | SD | ||
| 1 | 151.1 | 68.8 | 1285.4 | 928.7 | <0.0001 |
| 2 | 106.5 | 24.3 | 1186.4 | 967.9 | <0.0001 |
| 3 | 133.4 | 34.1 | 1012.4 | 940.8 | <0.0001 |
| 4 | 122.5 | 39 | 743 | 545.9 | <0.0001 |
| 5 | 143.9 | 43.8 | 519.3 | 251.8 | <0.0001 |
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ap<0.05 defines statistical significance. FINE, fetal intelligent navigation echocardiography; SD, standard deviation; STIC, spatiotemporal image correlation.
Maximum number of cardiac views successfully obtained through intelligent vs. manual navigation for each STIC volume dataset
For a given STIC volume that was analyzed by intelligent or manual navigation, the number of fetal cardiac views (from a maximum of nine) that were successfully obtained is depicted in Table 4. Intelligent navigation (FINE) obtained all nine fetal cardiac views 86% (43/50) of the time, while for manual navigation such value was only 14% (7/50) (p<0.001). Similarly, for a given STIC volume, intelligent navigation obtained eight to nine fetal cardiac views 98% (49/50) of the time, while for manual navigation such value was only 42% (21/50) (p<0.001).
Number of fetal cardiac views successfully obtained through intelligent vs. manual navigation for each STIC volume dataset (n=50).
| Number of fetal cardiac views successfully obtained for each STIC volume dataset (n=9 maximum) | Intelligent navigation (FINE) (n=50) |
Manual navigation (n=50) | ||
|---|---|---|---|---|
| n | % | n | % | |
| 4 | 0 | 0 | 2 | 4 |
| 5 | 0 | 0 | 4 | 8 |
| 6 | 0 | 0 | 6 | 12 |
| 7 | 1 | 12 | 17 | 34 |
| 8 | 6 | 12a | 14 | 28a |
| All 9 cardiac views obtained | 43 | 86a,b | 7 | 14a,b |
| TOTAL | 50 | 100 | 50 | 100 |
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FINE, fetal intelligent navigation echocardiography; STIC, spatiotemporal image correlation. ap<0.001; intelligent vs. manual navigation (eight to nine fetal cardiac views). bp<0.001; intelligent vs. manual navigation (all nine fetal cardiac views).
We also analyzed the success rate of obtaining four specific cardiac views (four-chamber, left ventricular outflow tract; short-axis view of great vessels/right ventricular outflow tract; abdomen/stomach) for each STIC volume dataset (n=50). Using intelligent navigation, the success rate was 96% (48/50), while for manual navigation such value was only 62% (31/50) (p<0.00004).
Survey on sonologist experience and overall comments about both navigational methods
Sonologists’ responses to survey statements about the navigational methods were evaluated using a 5-point Likert scale (Figure 5). Specific free text responses to such statements are also displayed in Table 5.
Responses by non-expert sonologists to survey statements about manual and intelligent navigation (or FINE) methods were evaluated using a 5-point Likert scale (1-strongly disagree; 2-disagree; 3-undecided; 4-agree; 5-strongly agree). The three survey statements are depicted on the left side of the image. Please see text for descriptive detail about the survey responses. FINE, fetal intelligent navigation echocardiography.
Sonologists’ free text responses to survey statements about intelligent and manual navigational methods.
| Survey statement | Examples of free text responses by sonologists |
|---|---|
|
|
|
|
|
|
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FINE, fetal intelligent navigation echocardiography.
When asked to evaluate the first statement (“The interface and ‘knobology’ were easy to use”), 70% of sonologists strongly agreed with such statement for intelligent navigation, while for manual navigation, it was only 30%. Moreover, for the latter method, an additional 30% disagreed that its interface and “knobology” were easy to use (Figure 5). Sonologists commented that intelligent navigation (FINE) was “very straightforward, with easy-to-use software, self-explanatory”. In contrast, for manual navigation the following response was made: “the fine control to adjust angles is not present; conceptualizing and integrating manipulation of images is much harder … ” (Table 5).
For the second statement (“The images obtained are appropriate for fetal cardiac examination”), 90 and 50% of sonologists strongly agreed/agreed with this statement for intelligent and manual navigation, respectively. Moreover, for the latter method, an additional 40% were undecided, and 10% disagreed with this statement (Figure 5). Sonologists remarked that for intelligent navigation, “All views are quickly obtained for adequate and diagnostic purposes”. Yet, images obtained through manual navigation are appropriate for fetal cardiac examination “… if manipulation is done correctly” and noted that such modality “… is operator dependent and relies on skills of the operator” (Table 5).
Insofar as the third statement (“Overall, this was an easy method”), 100 and 30% of sonologists strongly agreed/agreed with this statement for intelligent and manual navigation, respectively (Figure 5). Furthermore, an additional 30% were undecided, and 40% disagreed/strongly disagreed with this statement for manual navigation. Sonologists commented that intelligent navigation was “Straightforward and intuitive after a few practice views. Overall, an easy-to-use interface with easy trouble shooting.” For manual navigation, however, they noted that it was “not intuitive” and was “difficult to anticipate how pictures will change based on X, Y, Z manipulation” (Table 5).
Sonologists were also asked to provide overall comments about each navigational method after study completion (Table 6). In summary, comments on the FINE method pertained to its ease, speed, and automatic generation of cardiac planes. Sonologists also noted that the reference fetal cardiac images (automatically depicted during the marking process using Anatomic Box®) were very helpful, especially for non-experts in fetal cardiac imaging.
Overall comments provided by sonologists about intelligent and manual navigational methods.
| Navigational method | Overall comments by sonologists on navigational methods |
|---|---|
| Intelligent navigation (FINE) |
|
| Manual navigation |
|
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FINE, fetal intelligent navigation echocardiography; STIC, spatiotemporal image correlation.
Insofar as manual navigation, sonologists commented on the amount of STIC volume manipulation required, as well as the requirements of “a lot of mental reconstruction”, and “a high knowledge of anatomy to manipulate the volume appropriately”. They also remarked that during the navigational process, “… it is easy to get disoriented”, and they weren’t “always thinking through the rotations logically …” However, the sonologists did note that manual navigation would be clinically useful with more training and experience (Table 6).
Discussion
Principal findings of the study
Sonologists were tested on their ability to obtain nine cardiac views from STIC volumes of normal fetal hearts using intelligent (FINE) and manual navigation. Compared to manual navigation, FINE was associated with a significantly: (1) higher success rate of obtaining eight (excluding the abdomen view) appropriate fetal cardiac views (92–100% vs. 56–88%; all p<0.05); (2) shorter mean (±SD) time to obtain nine cardiac views per sonologist [131.5 ± 37 s (or 2 min, 11 s) vs. 949.3 ± 464 s (or 15 min, 49 s); p<0.0001]; (3) shorter mean time to obtain nine cardiac views per STIC volume dataset (all p<0.0001); (4) higher success rate of obtaining all nine cardiac views for a given STIC volume (86 vs. 14%; p<0.001); and (5) higher success rate of obtaining four specific cardiac views for a given STIC volume (96 vs. 62%; p<0.00004).
It is noteworthy that this study was designed so that sonologists underwent training/testing on intelligent navigation prior to manual navigation, to provide a theoretical advantage to the latter method. Yet despite this strategy, intelligent navigation (FINE) had a superior performance compared to manual navigation of the normal fetal heart when performed by non-expert sonologists.
Why this study was conducted
Adequate real-time sonographic examination of the fetal heart is challenging, due to its complex anatomy, motion, and small size. Moreover, this requires considerable operator skill and expertise [5], [6], [7], [8, 41], which can take many years to master. Therefore, sonologists with limited experience may have difficulty in obtaining the appropriate fetal cardiac views required for prenatal diagnosis.
One possible solution is to implement 4D sonography with STIC, since an unlimited number of cardiac planes may be extracted from the volume dataset and displayed in any orientation. Indeed, manual navigation of STIC volumes is an effective modality to examine the normal fetal heart [38], [39], [40, 42], [43], [44], [45], even in non-expert hands [41]. The FINE method, in which intelligent navigation technology is applied to STIC volume datasets, has also been shown to improve assessment of the normal fetal heart [46, 47], and is considered a cardiac screening and diagnostic tool in the clinical setting [48, 51]. Moreover, FINE aids cardiac evaluations performed by those less experienced in fetal echocardiography [55, 56].
Therefore, we conducted the study herein to directly compare the performance between intelligent and manual navigation of the fetal heart by non-expert sonologists. Such participants were chosen deliberately, since this is the group most likely to benefit from a modality that facilitates the successful generation of fetal cardiac views.
Performance in obtaining fetal cardiac views
In non-expert hands, FINE successfully obtained appropriate fetal cardiac views in 92–100% of cases. This is consistent with prior studies reporting that nine standard fetal echocardiography views were automatically generated by FINE in 96–100% of normal cases [46, 48], [49], [50], even when performed by physicians without any experience in fetal echocardiography [55]. The findings herein are encouraging, since they suggest that novice sonologists with limited experience in performing obstetric ultrasound (and without formal training in fetal echocardiography), can successfully obtain nine fetal cardiac views in at least 92% of cases. For both navigational methods, the abdomen view was obtained successfully in 100% of cases. This was not surprising, since this is a straightforward transverse plane to obtain.
Using manual navigation, the most difficult fetal cardiac views to generate were the 3VT and aortic arch, which were obtained in only 64 and 56% of cases, respectively. However, when using FINE, the same views were successfully obtained in 92% (3VT) and 96% (aortic arch) of cases. This is clinically relevant, since professional organizations increasingly recommend inclusion of the 3VT view in routine fetal cardiac screening to improve the prenatal detection of CHD (e.g. major conotruncal anomalies) [54, 57]. Obtaining the aortic arch view via manual navigation in only half the cases is suboptimal, since prenatal detection of coarctation of the aorta has been shown to improve perinatal survival and reduce morbidity [58]. It is noteworthy and was surprising to us that the four-chamber view was obtained in only 88% of cases using manual navigation, since this is the cardiac plane most easily obtained in the fetus [60], and is reported to be obtained successfully in 95% of routine sonographic examinations [59]. Moreover, the four-chamber view is an essential component of both fetal cardiac screening examinations and fetal echocardiography studies.
The lower success rate(s) of obtaining appropriate fetal cardiac views (56–88%) using manual navigation is most likely attributable due to the high operator dependency of this method [46], [47], [48], [49], [50]. In contrast, FINE is characterized by reduced operator dependency [46], [47], [48, 50, 56, 61, 62], since manual manipulation or standardization of the STIC volume dataset and cardiac planes is not required.
Intelligent navigation is faster than manual navigation in obtaining cardiac views
We have previously reported that for manual navigation, the duration of time to obtain cardiac views is unpredictable and may be long, while for intelligent navigation, it is both predictable and short [47]. The current study now provides empirical evidence supporting such characteristic features of both methods. Regardless of which sonologist was tested, the mean time to obtain nine fetal cardiac views was significantly shorter for FINE, as compared to manual navigation (Table 2). This is clinically relevant and important, since generating standard fetal cardiac views from STIC volume datasets in several minutes can potentially improve the efficiency and workflow for providers [46, 55, 56]. Other studies have confirmed the rapidity with which FINE is performed (204 ± 40 s) [63], even by novice physicians (mean examination time 82.80 ± 30.23 s) [55].
The duration of time to obtain fetal cardiac views by manual navigation of STIC volumes is unpredictable and varies amongst operators, since it is highly dependent on one’s inherent aptitude and skills, amongst other factors. For example, understanding the X, Y, and Z dimensions is not necessarily intuitive [34], as described by the free text responses and overall sonologists’ comments in the current study (Tables 5 and 6). Therefore, while one sonologist may learn and perform manual navigation quite easily, for others the opposite may be the case. This is confirmed by our results, in which the range of mean individual times to obtain all fetal cardiac views using manual navigation varied widely, from 371.5 to 1823.7 s (i.e. 6 min, 11 s to 30 min, 24 s), depending upon the sonologist (Table 2). In contrast, the range of mean individual times to obtain the same fetal cardiac views using the FINE method was narrow. Taken together, the wide variability in the time required to complete a cardiac examination could make manual navigation potentially inefficient for some practitioners in the clinical setting.
We also found that regardless of the STIC volume dataset analyzed, intelligent navigation was still significantly faster than manual navigation in obtaining all nine fetal cardiac views. This suggests that FINE is consistently faster not only across different sonologists, but also across various fetal cases.
Intelligent navigation successfully obtains more cardiac views than manual navigation
An essential clinical question is that for a given STIC volume, what is the maximum number of fetal cardiac views (and which views) can be obtained using the two navigational methods? Such information is pertinent, because if the answer is only two views (e.g. venae cavae and abdomen), then the method would be utterly inadequate to examine the fetal heart. This study showed that for a given STIC volume, FINE and manual navigation by non-expert sonologists obtained all nine fetal cardiac views 86 and 14% of the time, and eight to nine fetal cardiac views 98 and 42% of the time, respectively. Based on such results, implementing a method (i.e. manual navigation) that yields essential cardiac views from a given STIC volume only 14–42% of the time is substandard. In contrast, even in novice hands, the success rate of obtaining all nine fetal cardiac views from a given STIC volume using intelligent navigation is 86%, and this can be accomplished within several minutes. Therefore, this provides an opportunity for clinical practitioners to successfully interrogate the fetal heart, while still maintaining workflow efficiency.
We found the success rate of obtaining four specific cardiac views (four-chamber, left ventricular outflow tract, short-axis view of great vessels/right ventricular outflow tract, abdomen) for a given STIC volume dataset to be 96% for FINE, and 62% for manual navigation. The latter is concerning, since professional organizations clearly recommend that cardiac screening examinations should include both the four-chamber and outflow tract views based on scientific evidence [54, 64], [65], [66].
Clinical implications of the study
All non-expert sonologists participating in this study received standardized training (didactic and practical) for both navigational methods in just a 2 h session per method. All had limited experience in performing obstetric ultrasound, and none had formal training in fetal echocardiography. Yet, despite such circumstances, the sonologists could successfully perform a brief, but comprehensive cardiac examination using intelligent navigation. Similarly, Gembicki et al. described how FINE was successful in generating cardiac views (96.7%; 261/270), by a novice physician after undergoing just a 1-h theoretical training session in fetal echocardiography and FINE [55]. Moreover, the same authors reported that FINE was an easily learned method [55]. Analysis of sonologists’ free text responses to survey statements and overall comments about intelligent navigation from the study herein strongly support this view. Reviews also favored the consistency and speed of the method, as well as the automatic generation of cardiac planes. On the other hand, impressions about manual navigation as a modality for fetal cardiac examination centered around the overall difficulty of the method, need for mental conceptualization and reconstruction (as well as comprehension of X, Y, Z rotations and their resulting effects), and the high degree of STIC volume manipulation required. Taken together, such perceptions have clinical implications, and should therefore be considered by providers when performing volumetric sonography. Specifically, once appropriate and high-quality STIC volumes have been acquired [34], intelligent navigation could be implemented as the preferred method to generate fetal cardiac views, especially in non-expert hands.
Study limitations
The STIC volumes evaluated in the current study were not acquired by any of the participating sonologists. It is possible that if they had been, the study results would differ since one can directly influence the environment under which volume acquisition occurs, as well as be familiar with the anatomy of a given fetus.
Since manual navigation is a highly operator dependent modality, longer and more intense training of the study sonologists, as well as experience with more STIC volume datasets could have possibly yielded improved results. Indeed, the presence of a learning curve for the manipulation and analysis of STIC volumes has been suggested [40, 67]. Yet, we anticipate that even after further training and experience, manual navigation would still remain a highly operator dependent modality, with FINE continuing to produce superior performance results. It is worth reiterating that after just a 2-h training session, FINE proved to be a highly successful method.
Finally, the manual navigation approach used to analyze STIC volume datasets was left to the discretion of each individual sonologist. It is possible that study results for this method would have improved if STIC volumes were examined using a systematic approach or algorithm [18, 22, 38, 42], [43], [44, 68, 69]. Yet, the objective of the current study was not to test specific published algorithms. Moreover, with the exception of one approach [44], none of the other published algorithms provide steps to obtain all nine fetal cardiac views, but rather just a subset of cardiac views.
Conclusions
Adequate real-time sonographic examination of the fetal heart is challenging, and requires considerable operator skill and expertise to perform. Therefore, sonologists with limited experience may have difficulty in obtaining the appropriate fetal cardiac views required to diagnose most congenital heart disease. Manual and intelligent navigation (FINE) are two methods to obtain standard fetal cardiac views from STIC volume datasets. This study presents for the first time a direct comparison of such methods when performed by non-expert sonologists.
FINE had a superior performance compared to manual navigation of the normal fetal heart. Specifically, appropriate fetal cardiac views were successfully obtained in 92–100% of cases, and this occurred within a time duration of several minutes. Taken together, these findings suggest that non-expert sonologists could benefit from implementing this modality when examining the fetal heart. Moreover, intelligent navigation was perceived by all sonologists to be an easy method to perform, generating images that are appropriate for fetal cardiac examination.
Award Identifier / Grant number: HHSN275201300006C
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Research funding: This research was supported, in part, by the Perinatology Research Branch, Division of Obstetrics and Maternal-Fetal Medicine, Division of Intramural Research, Eunice Kennedy Shriver National Institute of Child Health and Human Development, National Institutes of Health, U.S. Department of Health and Human Services (NICHD/NIH/DHHS); and, in part, with Federal funds from NICHD/NIH/DHHS under Contract No. HHSN275201300006C.
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Author contributions: All authors have accepted responsibility for the entire content of this manuscript and approved its submission. Dr. Romero has contributed to this work as part of his official duties as an employee of the United States Federal Government.
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Competing interests: An application for a patent (“Apparatus and Method for Fetal Intelligent Navigation Echocardiography”) has been filed with the U.S. Patent and Trademark Office, and the patent is pending. Dr. Lami Yeo and Dr. Roberto Romero are coinventors, along with Mr. Gustavo Abella and Mr. Ricardo Gayoso. The rights of Drs. Yeo and Romero have been assigned to Wayne State University and the National Institute of Child Health and Human Development/National Institutes of Health (NICHD/ NIH), respectively.
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Informed consent: Informed consent was obtained from all individuals included in this study.
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Ethical approval: Research involving human subjects complied with all relevant national regulations and institutional policies; is in accordance with the tenets of the Helsinki Declaration (as revised in 2013); and has been approved by the Institutional Review Board of NICHD, NIH, and by the Human Investigation Committee of Wayne State University.
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Supplementary Material
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