Congenital heart malformation is a common type of fetal congenital malformation, and its incidence accounts for 5‰ to 10‰ in live births and up to 30‰ in stillbirths [1]. Most of them are underdiagnosed or misdiagnosed for various reasons, and for complex congenital heart malformations, it is a great mental and economic burden to families and society.
Fetal cardiac ultrasonography is an effective tool and the only imaging method for screening fetal congenital heart malformations, and its main purpose is to detect complex and lethal cardiac malformations, which is an important part of fetal prenatal ultrasound screening and is widely used in clinical practice [2]. With the development of ultrasound technology, the detection rate of some malformations has been greatly improved. Feng Tianying, Department of Ultrasound Medicine, People’s Hospital of Inner Mongolia Autonomous Region
1. Development of the examination technology of echocardiography
In 1964, Wang Xinfang and Zhou Yongchang [2] were the first to propose the method of fetal heart ultrasonography and apply M-type ultrasound to observe the fetal heart. 1980, Kleinman et al [3] first applied diastolic ultrasound to detect fetal heart.
Gembrach et al [4] used 2DE to screen 579 fetuses and detected 59 cases of cardiac malformations including atrial septal defect, endocardial elastosis, and cardiac tumor, etc. Copel et al [5] used 2DE to screen 1022 fetuses and found 74 cases of cardiac malformations (sensitivity 92%, sensitivity 3.5). The sensitivity of 2DE screening was 92%, specificity was 99.7%, and the positive prevalence was 95.8%, which shows that the false positive rate and false negative rate still have a certain proportion.
2. New technology application of fetal echocardiography
Fetal echocardiography should include traditional 2DE, M-mode ultrasound and CDFI, but sometimes some complex congenital anomalies are difficult to be shown by conventional cross-section, and the accuracy of diagnosis will be improved by some new techniques.
2.1 Tissue Doppler imaging ( D T I ) technique
In 1992, M.D.I. et al [6] first proposed the tissue Doppler imaging (DTI) technique, which extracts low-frequency, high-amplitude Doppler frequency-shift signals directly from the myocardium, allowing direct observation of atrioventricular ring motion and simultaneous recording of the systolic and diastolic motion spectra.
Paladini et al [7] evaluated the velocity of fetal myocardial motion and its order difference by the DTI technique and concluded that the DTI technique could be used for fetal examination. Cao Li et al [8] recorded the maximum velocity of ventricular myocardial motion by DTI technique and found that the E/Ea ratio could be used as a quantitative index to evaluate the diastolic function of the fetal ventricle.
2.2 Tissue velocity imaging (T V I ) technique
TVI is a new technique established to acquire and analyze raw tissue velocity data on a scan line, which overcomes the limitations of M ultrasound and 2DE and allows comparison of velocity waveforms at the same time relative to any part of the heart over several cardiac cycles, allowing arbitrary sampling of the myocardium in tissue velocity imaging of the same fetus at different times, leading to a rapid diagnosis of fetal arrhythmias.The results of a study by Rein et al[9] showed that that it has a greater advantage in diagnosing various supraventricular and ventricular arrhythmias.
2.3 Harmonic imaging (H I ) technique
With the development of ultrasound technology, HI came into being. In a study by Kovalchin et al [10], the application of HI significantly improved the image quality and clarity of cardiac structures and increased the display rate of structures such as the fossa ovalis, the ductus arteriosus, and the aortic arch. Marjorie et al [11] demonstrated that HI significantly improved the visualization rate and contrast resolution of cardiac structures, especially in obese pregnant women.
2.4 Energy Doppler imaging (P D I )
PDI is a new technique of color Doppler, which is a third parameter extracted on the basis of CDFI, i.e., signal intensity, using the number of red blood cells per unit area in blood flow and the magnitude of signal amplitude for color-coded imaging, which is less affected by the detection angle and can improve the sensitivity of blood flow detection.
C h u a et al [12] concluded that PDI has a higher display rate than 2DE and CDFI in both control PDI and CDFI for septal and pulmonary vein examinations. Therefore, PDI has a very important role in assessing hemodynamics, but it also has disadvantages such as not being able to show the direction and flow velocity of blood flow.
2.5 Three-dimensional echocardiography (3DE)
3DE is a complement to 2DE. 3DE determines the temporal phase of the fetal cardiac cycle by Doppler gating, M-type gating or cardiac gating techniques, selecting a specific
Several sets of transverse and sagittal views of the region of interest are selected for 3D reconstruction and analysis. In contrast, real-time 3D echocardiography is an arbitrary sweep of the fetal heart with a 3D matrix volumetric probe that provides a more accurate estimation of fetal heart volume.
Meyer et al [13] respectively
Deng et al [14] demonstrated that real-time 3D imaging can show the three-dimensional morphology of cardiac structures in real time as well as dynamic changes, showing the adjacent location of each structure and lesion with This allows early diagnosis of fetal precocious heart disease.
2.6
Enhanced Energy Doppler Imaging (e-Flow)
The e-flow technique is a new type of blood flow imaging technique that uses advanced composite pulse emission technology to filter out noise interference, adopts broadband reception while adding motion artifact suppression to the self-coherent imaging, and improves blood flow resolution through high-speed acoustic beam parallel processing technology to truly reflect the perfusion of low-speed blood flow, effectively controls color spillover, improves temporal and spatial resolution, and makes blood and tissue free of blending. Liu Lin et al. Liu Lin et al [15] applied the e-Flow technique to observe four pulmonary veins in different sections of the fetus, and the display rate was 100%.
2.7 Time-space correlation imaging (STIC) technique
The time-space correlation imaging (STIC) technique acquires the basic data of the fetal heart from the cine playback of 3D images, obtaining a 3D profile consisting of a large number of consecutive 2D sections. The STIC technology has several imaging modes, including reconstruction mode, cross-sectional mode, tomographic ultrasound imaging (TUI mode), and volume analysis mode.
Each of these modes can be used in combination with color Doppler, energy Doppler, and e-FLOW techniques, and different imaging modes can be selected for analysis according to different study purposes. [16].
2.7.1 Reconstruction mode (Render mode)
Render mode is a three-dimensional reconstruction using two-dimensional images to display the cardiac structures in all directions, including: surface reconstruction mode, inversion reconstruction mode, and vitreous reconstruction mode. The inversion reconstruction mode in STIC technique was considered by Messing et al [18] as a simpler and more reproducible method for estimating fetal ventricular volumes using inversion reconstruction mode in combination with volume-assisted automatic measurement (VOCAL). This innovative approach [ 18.19] may add to the overall assessment of cardiac volumes and function and improve our understanding of cardiac structure and the assessment of prognosis and severity of cardiac lesions.
2.7.2 Section planes modality
Section planes mode includes multiplanar imaging mode, omniView mode, and niche mode. This mode does not require 3D reconstruction, but mainly acquires the coronal echo information that cannot be obtained by 2D ultrasound, and can clearly show the shape and structure of each section of the target area. By adjusting the 3D volume database, 72%-100% of the atria, ventricles, aorta and aortic connections were visualized in multiplanar mode, and the quality of the images could meet the needs of offline analysis of normal fetal heart anatomy. Most importantly, sagittal views of the ventricular septum can be obtained in this mode, which are not readily available with conventional 2D ultrasound.
2.7.3 X-ray tomographic ultrasound imaging mode (TUI mode)
TUI mode is an extended development of multiplanar imaging mode, in which parallel layered images in the volume can be viewed, including T UI standard imaging mode, V CAD
The heart mode, which automatically generates multiple views of the fetal heart for diagnostic purposes, was used by TU
RAN et al [ 22] used STIC-TUI technique and concluded the following: 1. fusion imaging combined with color Doppler, showed great advantages in early pregnancy screening for precordial disease, allowing to obtain more accurate anatomical structures in early pregnancy fetal heart images. 2. using this technique, the display rate of individual markers, starting from the identifiable four-chambered heart, ranged from 89. 7% to 99. 1% , with all structures fully displayed in 85% of patients All structures were shown in 85% of patients. Thus, it is believed that STIC-TUI examination of the fetal heart in early pregnancy can provide a good description.
2.7.4 Volume analysis mode
The volume analysis mode allows accurate quantification of fetal heart cavity volumes, independent of the irregularities of the measured structures, with high accuracy and reproducibility. The sonography based automated volume count (SonoAVC) is a method of measuring fetal heart volume.
Rizzo et al [25] showed high correlation and reliability of fetal ventricular volumes measured by virtual organ computer-assisted volumetric technique (Vocal technique) and SonoAVC, respectively.SonoAVC is a new method for estimating fetal heartbeat volume and is expected to become the first choice rapidly. In a study by Molina et al [26], right and left ventricular beat volumes per minute increased with gestational week, and the ratio of ventricular beat volumes varied significantly with gestational week.
2.8 Velocity vector imaging (VVI)
imaging (VVI) technique
VVI is a new technique to study myocardial structural mechanics and analyze local cardiac function. It is based on the principle of two-dimensional gray-scale imaging, using the spatial coherence of ultrasound pixels, speckle tracking and boundary tracking techniques to collect the amplitude and corresponding information of the original two-dimensional pixels, and use a real-time myocardial motion tracking algorithm to calculate and display the real activity direction, velocity, distance, and time of local myocardial tissue in a vector manner. distance, time, etc. A real-time myocardial motion tracking algorithm tracks the pixel points on each image frame and can obtain the velocity and direction of motion on a two-dimensional, high-frequency gray-scale image, quantifying the structural mechanics of myocardial tissue motion in multiple planes, independent of the angle between the ultrasound beam and the ventricular wall. The contribution of myocardium to the ejection fraction. Some foreign scholars using the VVI technique to evaluate fetal left ventricular torsional motion have concluded that the presence of myocardial bands in the fetal heart is closely related to the generation of cardiac torsional motion [27].
3. clinical value of fetal echocardiography The ultimate goal of fetal echocardiography is to inform and improve the prognosis in advance. It helps to plan perinatal treatment in advance, avoiding delays in neonatal diagnosis, avoiding possible exacerbation of hypoxia and acidosis leading to multiorgan failure and distant neurological damage, and improving immediate and long term survival. In an Italian multicenter study [28], 847 treated fetuses with congenital heart disease were analyzed, of which 29% terminated, 11% died intrauterine, and the remaining 602 newborns, only 45% survived more than 18 months after birth. Since prenatal knowledge of congenital heart disease makes termination of pregnancy one of the possible options, proper diagnosis of fetal cardiac anomalies and prenatal counseling are very important. Therefore, fetal echocardiography is now an effective method of prenatal screening for congenital heart disease in high-risk groups.
4 Problems and outlook
Echocardiography is a feasible, reliable, and noninvasive method for detecting fetal heart malformations, and its value is widely recognized by the medical community. However, the accuracy of fetal echocardiography is affected by many factors such as maternal body shape, fetal position, fetal movement, respiration and the experience of the examiner. With the rapid development of computer technology, the quality of gray-scale images can be improved by increasing the frame rate and pixels of the images, and the fetal blood flow can be better displayed, and the structure, volume and function of the fetal heart can be more accurately displayed in real time by combining with quantitative acoustic techniques. The application of various new technologies will significantly increase the detection rate of fetal congenital heart disease and provide valuable information for doctors and patients, which is important for early and proper management, eugenics, and improvement of population quality.