Real-time 3-dimensional echocardiography in assessing atrial and ventricular septal defects: an echocardiographic-surgical correlative study

3D Echocardiography for Rheumatic Heart Disease Analysis: Ready for Prime Time

Rheumatic heart disease (RHD) remains to be a very important health issue worldwide, mainly in underdeveloped countries. It continues to be a leading cause of morbidity and mortality throughout developing countries. RHD is a delayed non-suppurative immunologically mediated inflammatory response to the throat infection caused by a hemolytic streptococcus from the A group (Streptococcus pyogenes). RHD keeps position 1 as the most common cardiovascular disease in young people aged <25 years considering all the continents. The disease can lead to valvular cardiac lesions as well as to carditis. Rheumatic fever valvular injuries lead most commonly to the fusion and thickening of the edges of the cusps and to the fusion, thickening, and shortening of the chordae and ultimately to calcification of the valves. Valvular commissures can also be deeply compromised, leading to severe stenosis. Atrial and ventricular remodeling is also common following rheumatic infection. Mixed valvular lesions are more common than isolated valvular disorders. Echocardiography is the most relevant imaging technique not only to provide diagnostic information but also to enable prognostic data. Further, it presents a very important role for the correction of complications after surgical repair of rheumatic heart valvulopathies. Three-dimensional (3D) echocardiography provides additional anatomical and morphofunctional information of utmost importance for patients presenting rheumatic valvopathies. Accordingly, three-dimensional echocardiography is ready for routine use in patients with RHD presenting with valvular abnormalities.

Real-time three-dimensional (3D) echocardiographic characterisation of an atrial septal defect in a horse

Atrial septal defects have been well reported in humans and dogs and the principles of intervention have been well established. In contrast, there is very little information published about these congenital anomalies in horses. True ASDs are regarded as rare and little is known about the clinical significance of these defects in horses. An 11‐year‐old Thoroughbred gelding with a history of poor performance was diagnosed with an atrial septal defect, measuring approximately 2 cm in diameter, on 2D transthoracic echocardiography. Real‐time three‐dimensional (3D) echocardiography was used to map the structure of the defect and was useful in fully characterising the ASD in this case.

Utility of cardiac MRI in determining percutaneous versus surgical post-infarction ventricular septal defect repair

AIM

Postmyocardial infarction ventricular septal defect (VSD) is a rare complication that can lead to rapid hemodynamic patient decompensation. The type of VSD repair relies on several factors including: size, location, timing and surgical expertise.

CASE

A 63-year-old man with a ST-elevation myocardial infarction underwent percutaneous coronary intervention of the right coronary artery. A holosystolic murmur was notable postcatheterization, and transthoracic echocardiogram confirmed a VSD. To characterize the VSD, a cardiac MRI demonstrated a large, serpiginous VSD and longitudinal septal tear. Given the anatomic complexity and stable hemodynamics, a surgical trans-left ventricular patch repair was performed.

CONCLUSION

We emphasize the importance of cardiac magnetic resonance as a decision-making tool, utilizing imaging to ascertain the anatomy combined with hemodynamics to determine optimal individualized therapy.

Role of HDLive in Imaging the Fetal Heart

HDLive is a rendering methodology that generates realistic images of the human fetus from sonographic data. The objective of this study is to demonstrate the utility of high-definition live in evaluating fetal heart especially in the first trimester (11-14-week) scan. The normal atrioventricular valve and its abnormalities along with septal defects can be vividly demonstrated with this technique, and eight cases with cardiac defects are illustrated. Its use in the first-trimester evaluation of heart would give a better perspective of the cardiac malformation, which provides the opportunity for counseling options early in pregnancy.

Three-dimensional Echocardiography in Congenital Heart Disease: An Expert Consensus Document from the European Association of Cardiovascular Imaging and the American Society of Echocardiography

Three-dimensional echocardiography (3DE) has become important in the management of patients with congenital heart disease (CHD), particularly with pre-surgical planning, guidance of catheter intervention, and functional assessment of the heart. 3DE is increasingly used in children because of good acoustic windows and the non-invasive nature of the technique. The aim of this paper is to provide a review of the optimal application of 3DE in CHD including technical considerations, image orientation, application to different lesions, procedural guidance, and functional assessment.

Three-Dimensional Echocardiographic En Face Views of Ventricular Septal Defects: Feasibility, Accuracy, Imaging Protocols and Reference Image Collection

BACKGROUND

Ventricular septal defect (VSD) is the most common congenital cardiac anomaly. Accurate assessment is critical for planning treatment. Recent advances in three-dimensional (3D) echocardiography have improved image quality and ease of use.

METHODS

The feasibility and accuracy of three specific 3D echocardiographic protocols to demonstrate en face views of VSDs were analyzed in a retrospective review of 100 consecutive patients. Sixty-four patients underwent transthoracic echocardiography and 36 transesophageal echocardiography. Types of VSDs included 34 muscular, 32 perimembranous, 18 malaligned, 11 inlet, four outlet, and one acquired. Ages ranged from 1 day to 77 years, and body weights from 3 to 92 kg. Three-dimensional echocardiographic full-volume mode with standard XYZ and adjustable plane cropping, 3D full-volume mode with iCrop, and narrow-sector live 3D protocols were compared for feasibility and accuracy to obtain a diagnostic-quality en face view of a VSD.

RESULTS

The success rate for obtaining a high-quality en face image for the three protocols was 100% for full-volume mode with iCrop, 97% for full-volume standard mode, and 94% for narrow-sector live 3D mode. The ability of both full-volume mode with iCrop and full-volume standard mode to demonstrate a VSD was slightly better than that of narrow-sector live 3D mode (P < .001 for both vs narrow-sector live 3D mode). In all patients, the type, size, and location of the VSD were demonstrated accurately by two or more of the protocols.

CONCLUSIONS

Three-dimensional echocardiography of VSDs is feasible and accurate in most patients using defined protocols. The protocols are described and illustrated in detail, and a reference 3D image collection is presented.

Accuracy of Transthoracic Echocardiography in Assessing Retro-aortic Rim prior to Device Closure of Atrial Septal Defects

OBJECTIVE

Deficient retro-aortic rim has been identified as a risk factor for device erosion following trans-catheter closure of atrial septal defects (ASDs). Transthoracic echocardiography (TTE) is the primary screening method for subjects for possible device closure of ASD, but its reliability in measuring retro-aortic rim size has not been assessed previously.

DESIGN

A single-institution cross-sectional analysis of children and adults referred for trans-catheter device closure of single ostium secundum ASD from January 1, 2005 to April 1, 2012 with reviewable TTE and trans-esophageal echocardiogram images was performed. Inter-rater reliability of measurements was tested in a 24% sample. Accuracy of TTE measurement of retro-aortic rim was assessed using a Bland-Altman plot with trans-esophageal echocardiogram measurement as the gold standard. Test characteristics of TTE detection of deficient retro-aortic rim were calculated. Risk factors for misclassification of deficient retro-aortic rim were assessed using receiver operator characteristic curves. Risk factors for measurement error were assessed through multivariate linear regression.

RESULTS

In total, 163 subjects of median age 5 years (range: 0.3-46 years) were included. Trans-thoracic echocardiography had 90% sensitivity, 84% specificity, 90% positive predictive value, and 83% negative predictive value to detect deficient retro-aortic rim. Bland-Altman plot demonstrated no fixed bias (P = .23), but errors in measurement increased on average as the aortic rim increased in size (P < .001). Prespecified patient level risk factors did not affect receiver operator characteristic curve area under the curve, nor were any patient-level risk factors independently associated with increased measurement error on TTE.

CONCLUSIONS

TTE is a sensitive and specific screening test for deficient retro-aortic rim across a range of patient ages and sizes.

3D transesophageal echocardiography is a decision-making tool for the management of cardiogenic shock following a large postinfarction ventricular defect

Postinfarction ventricular septal defect (PIVSD) is a devastating mechanical complication following acute myocardial infarction. The management of this pathology is quite challenging, especially in case of complicated cardiogenic shock. The difficulties lie in the timing and type of intervention. Debates exist with regard to immediate versus deferring repair, as well as open repair versus percutaneous closure. The anatomic characteristics and hemodynamic consequence of PIVSD are important elements determining which strategy to adopt, since large septal defect (>15 mm) cannot be appropriately treated by percutaneous occluder devices limiting by their available size, while compromised hemodynamics usually require emergent repair or mechanical support “bridging to surgery”. Herein, we report our experience of successful management of a case of cardiogenic shock complicating large PIVSD (38 mm) by delayed surgical repair bridged with Extracorporeal Membrane Oxygenation (ECMO) during 7 days. We emphasize the importance of 3-dimensional transesophageal echocardiography as a decision-making tool.

Comparative study between real time three dimensional echocardiogram and angiography in evaluation of patent ductus arteriosus, single center experience

In this study we compared the real time three dimensional echocardiogram data in evaluation of patent ductus arteriosus with the gold standard angiography.

METHODS

This study included 25 patients with PDA referred to Tanta University Hospital for elective cardiac catheterization. The patients comprised seven males and 18 females, with a mean age of 3.7 ± 0.36 years. The study duration was six months. All patients underwent full 2D echocardiogram as well as real time three-dimensional echocardiogram (RT3DE). Essential measurements included the pulmonary end of the duct, duct length, aortic end and aortic ampulla as well as the anatomical type of the PDA. Data obtained by RT3DE were compared against 2D echocardiogram and angiography.

RESULTS

There was no significant difference between 3D echocardiogram and angiography (P = 0.001) in the pulmonary end of the duct measurement. Neither were there any significant differences between the length of the duct or the aortic end measured by 3D echocardiogram and by angiography (P = 0.001 in both). While there was adequate agreement between both 2D and 3D echocardiogram and angiography in determining the anatomical type of the PDA, 3D echocardiogram determined type A and type E ductus more accurately than 2D echocardiogram. The feasibility of Q lab analysis of PDA was 96%, while the feasibility of gated color flow 3D acquisitions in determining anatomical types was 64%.

CONCLUSION

There was complete agreement on location, size, morphology and surrounding structure of PDA between 2D and 3D echocardiogram, and angiography. This result illustrates the need for the proper placement of the device in catheterization laboratories.

Shunt flow evaluation in congenital heart disease based on two-dimensional speckle tracking

High-frame-rate ultrasound speckle tracking was used for quantification of peak velocity in shunt flows resulting from septal defects in congenital heart disease. In a duplex acquisition scheme implemented on a research scanner, unfocused transmit beams and full parallel receive beamforming were used to achieve a frame rate of 107 frames/s for full field-of-view flow images with high accuracy, while also ensuring high-quality focused B-mode tissue imaging. The setup was evaluated in vivo for neonates with atrial and ventricular septal defects. The shunt position was automatically tracked in B-mode images and further used in blood speckle tracking to obtain calibrated shunt flow velocities throughout the cardiac cycle. Validation toward color flow imaging and pulsed wave Doppler with manual angle correction indicated that blood speckle tracking could provide accurate estimates of shunt flow velocities. The approach was less biased by clutter filtering compared with color flow imaging and was able to provide velocity estimates beyond the Nyquist range. Possible placements of sample volumes (and angle corrections) for conventional Doppler resulted in a peak shunt velocity variations of 0.49-0.56 m/s for the ventricular septal defect of patient 1 and 0.38-0.58 m/s for the atrial septal defect of patient 2. In comparison, the peak velocities found from speckle tracking were 0.77 and 0.33 m/s for patients 1 and 2, respectively. Results indicated that complex intraventricular flow velocity patterns could be quantified using high-frame-rate speckle tracking of both blood and tissue movement. This could potentially help increase diagnostic accuracy and decrease inter-observer variability when measuring peak velocity in shunt flows.

The development of echocardiography in China: the pioneering role of Xin-fang Wang

I cannot discuss the history of the development of echocardiography in China without describing the pioneering role of Xin-fang Wang (王新房) from Wuhan, China, who is the "father of modern echocardiography."(1) Although Inge Edler from Sweden(2-5) and Harvey Feigenbaum from the United States(6) were also oftentimes referred to as the fathers of echocardiography, both Edler(7) and Feigenbaum(8) recognized that the Chinese used cardiac ultrasonography in the very early years (Figure 1).

Three-dimensional echocardiography in congenital heart disease

Complex intracardiac anatomy and spatial relationships are inherent to congenital heart defects (CHDs). Recognition of the limitations of two-dimensional echocardiography has stimulated clinical interest in three-dimensional imaging. The current review examines contemporary studies in the following areas where three-dimensional echocardiography has provided additive value in CHD: (1) visualization of morphology, (2) quantitation of chamber sizes and ventricular function, and (3) image-guided interventions.

Current clinical applications of transthoracic three-dimensional echocardiography

The advent of three-dimensional echocardiography (3DE) has significantly improved the impact of non-invasive imaging on our understanding and management of cardiac diseases in clinical practice. Transthoracic 3DE enables an easier, more accurate and reproducible interpretation of the complex cardiac anatomy, overcoming the intrinsic limitations of conventional echocardiography. The availability of unprecedented views of cardiac structures from any perspective in the beating heart provides valuable clinical information and new levels of confidence in diagnosing heart disease. One major advantage of the third dimension is the improvement in the accuracy and reproducibility of chamber volume measurement by eliminating geometric assumptions and errors caused by foreshortened views. Another benefit of 3DE is the realistic en face views of heart valves, enabling a better appreciation of the severity and mechanisms of valve diseases in a unique, noninvasive manner. The purpose of this review is to provide readers with an update on the current clinical applications of transthoracic 3DE, emphasizing the incremental benefits of 3DE over conventional two-dimensional echocardiography.

Real-time three-dimensional transthoracic echocardiography in daily practice: initial experience

AIM OF THE WORK

To evaluate the feasibility and possible additional value of transthoracic real-time three-dimensional echocardiography (RT3D-TTE) for the assessment of cardiac structures as compared to 2D-TTE.

METHODS

320 patients (mean age 45 ± 8.4 years, 75% males) underwent 2D-TTE and RT3D-TTE using 3DQ-Q lab software for offline analysis. Volume quantification and functional assessment was performed in 90 patients for left ventricle and in 20 patients for right ventricle. Assessment of native (112 patients) and prosthetic (30 patients) valves morphology and functions was performed. RT3D-TTE was performed for evaluation of septal defects in 30 patients and intracardiac masses in 52 patients.

RESULTS

RT3D-TTE assessment of left ventricle was feasible and reproducible in 86% of patients while for right ventricle, it was (55%). RT3D-TTE could define the surface anatomy of mitral valve optimally (100%), while for aortic and tricuspid was (88% and 81% respectively). Valve area could be planimetered in 100% for the mitral and in 80% for the aortic. RT3D-TTE provided a comprehensive anatomical and functional evaluation of prosthetic valves. RT3D-TTE enface visualization of septal defects allowed optimal assessment of shape, size, area and number of defects and evaluated the outcome post device closure. RT3D-TTE allowed looking inside the intracardiac masses through multiple sectioning, valuable anatomical delineation and volume calculation.

CONCLUSION

Our initial experience showed that the use of RT3D-TTE in the assessment of cardiac patients is feasible and allowed detailed anatomical and functional assessment of many cardiac disorders.

Visualization of patent ductus arteriosus using real-time three-dimensional echocardiogram: Comparative study with 2D echocardiogram and angiography

PURPOSE

To determine the feasibility and accuracy of real time 3D echocardiography (RT3DE) in determining the dimensions and anatomical type of the patent ductus arteriosus (PDA).

METHODS

The study included 42 pediatric patients with a mean age of 3.6 years (ranging from 2 months to 14 years) who were referred for elective percutaneous PDA closure. All patients underwent full 2D echocardiogram as well as RT3DE with off line analysis using Q lab software within 6 h from their angiograms. The PDA was studied as regard the anatomical type, length of the duct as well as the ampulla and the pulmonary end of the PDA. Data obtained by RT3DE was compared against 2D echocardiogram and the gold standard angiography.

RESULTS

Offline analysis of the PDA was feasible in 97.6% of the cases while determination of the anatomical type using gated color flow 3D acquisitions was achieved in 78.5% of the cases. The pulmonary end of the duct was rather elliptical using 3D echocardiogram. There was significant difference between the pulmonary end measured by 3D echocardiogram and angiography (P < 0.001). There was no significant difference between either the length or the ampulla of the PDA measured by 3D echocardiogram and that measured by angiography (P value = 0.325 and 0.611, respectively). There was a good agreement between both 2D or 3D echocardiogram and angiography in determining the anatomical type of the PDA (K = 0.744 and 0.773, respectively). However 3D echocardiogram could more accurately determine type A and type E ductus compared to 2D echocardiogram.

CONCLUSION

3D echocardiogram was more accurate than 2D echocardiogram in determining the length and the ampulla of the PDA. The morphologic assessment of the PDA using gated 3D color flow was achieved in 78.5% of the patients. Nevertheless the use of 3D echocardiogram in assessment of small vascular structures like PDA in children with rapid heart rates is still of limited clinical value.

Non-Invasive Imaging for Congenital Heart Disease: Recent Innovations in Transthoracic Echocardiography

Transthoracic echocardiography (TTE) is an important tool for diagnosis and follow-up of patients with congenital heart disease (CHD). Appropriate use of TTE can reduce the need for more invasive and complex modalities, such as cardiac catheterization and cardiac magnetic resonance imaging. New echocardiographic techniques have emerged for the assessment of ventricular systolic and diastolic function: Tissue Doppler imaging, tissue tracking, strain and strain rate imaging, vector velocity imaging (VVI), myocardial performance index, myocardial acceleration during isovolumic contraction (IVA), the ratio of systolic to diastolic duration (S/D ratio), and other measurements of systolic right ventricular (RV) function like tricuspid annular plane systolic excursion (TAPSE). These modalities may become valuable indicators of ventricular performance, compliance and disease progression, with the caveat of preload-dependency of the variables measured. In addition, three-dimensional (3D) echocardiography for the assessment of cardiac anatomy, valvular function, device position, ventricular volumes and ejection fraction is integrated into routine clinical care. In this review, we discuss the potential use and limitations of these new echocardiographic techniques in patients with CHD. A particular focus is on the echocardiographic assessment of right ventricular (RV) function by means of tissue Doppler imaging, tissue tracking, and three-dimensional imaging, in conditions associated with increased right ventricular volume or pressure load.

Clinical value of stereoscopic three-dimensional echocardiography in assessment of atrial septal defects: feasibility and efficiency

Stereoscopic three-dimensional echocardiography(S-3DE) is a novel displaying technology based on real-time 3-dimensional echocardiography (RT-3DE). Our study was to evaluate the feasibility and efficiency of S-3DE in the diagnosis of atrial septal defect (ASD) and its use in the guidance for transcatheter ASD occlusion. Twelve patients with secundum ASD underwent RT-3DE examination and 9 of the 12 were subjected to transcatheter closure of ASD. Stereoscopic vision was generated with a high-performance volume renderer with red-green stereoscopic glasses. S-3DE was compared with standard RT-3D display for the assessment of the shape, size, and the surrounding tissues of ASD and for the guidance of ASD occlusion. The appearance rate of coronary sinus and the mean formation time of the IVC, SVC were compared. Our results showed that S-3DE could measure the diameter of ASD accurately and there was no significant difference in the measurements between S-3DE and standard 3D display (2.89+/-0.73 cm vs 2.85+/-0.72 cm, P>0.05; r=0.96, P<0.05). The appearance of coronary sinus for S-3DE was higher as compared with the standard 3D display (93.3% vs 100%). The mean time of the IVC, SVC for S-3DE monitor was slightly shorter than that of the standard 3D display (11.0+/-3.8 s vs 10.3+/-3.6 s, P>0.05). The mean completion time of interventional procedure was shortened with S-3DE display as compared with standard 3D display (17.3+/-3.1 min vs 23.0+/-3.9 min, P<0.05). Stereoscopic three-dimensional echocardiography could improve the visualization of three-dimensional echocardiography, facilitate the identification of the adjacent structures, decrease the time required for interventional manipulation. It may be a feasible, safe, and efficient tool for guiding transcatheter septal occlusion or the surgical interventions.

Direct en face imaging of secundum atrial septal defects by velocity-encoded cardiovascular magnetic resonance in patients evaluated for possible transcatheter closure

BACKGROUND

Atrial septal defect (ASD) flow can be measured indirectly by velocity-encoded cardiovascular magnetic resonance (veCMR) of the pulmonary artery and aorta. Imaging the secundum ASD en face could potentially enable direct flow measurement and provide valuable information about ASD size, shape, location, and proximity to other structures.

METHODS AND RESULTS

Forty-four patients referred for possible transcatheter ASD closure underwent a comprehensive standard evaluation, including transesophageal and/or intracardiac echocardiography and invasive oximetry. CMR was performed in parallel and included direct en face veCMR after an optimal double-oblique imaging plane was determined that accounted for ASD flow direction and cardiac-cycle interatrial septal motion. ASD flow measured by direct en face veCMR correlated better with invasive oximetry than indirect (pulmonary artery and aorta) veCMR (r=0.80 versus r=0.66). Additionally, 95% limits of agreement were narrower (+/-3.9 versus +/-5.1 L/min). En face veCMR determined that defects usually were eccentrically shaped (major/minor axis length >1.5) rather than circular, with 16% having extreme eccentricity (major/minor >2.0). Overall, ASD size by both veCMR and intracardiac echocardiography correlated with final device size; however, in small to medium defects (<3 cm(2)) and extremely eccentric defects, veCMR correlated better with final device size than did intracardiac echocardiography. Importantly, CMR identified additional information in 9 patients (20%) that altered clinical management. Specifically, en face veCMR detected additional defects (n=3), large ASD with insufficient rim tissue (n=2), and sinus venosus defect with anomalous pulmonary vein (n=1). Cine and/or morphological imaging detected interrupted inferior vena cava (n=2) and sinus of Valsalva aneurysm (n=1).

CONCLUSIONS

En face veCMR with an optimized imaging plane can determine ASD flow, size, and morphology. CMR provided information incremental to comprehensive standard evaluation that altered clinical management in 20% of patients.

Noninvasive imaging of the heart and coronary arteries

There are multiple imaging modalities currently available to noninvasively evaluate the heart and coronary arteries. Choosing the most appropriate modality depends on the pertinent clinical question and the underlying patient characteristics. This article provides an overview of the fields of echocardiography, myocardial perfusion imaging, cardiac computed tomography, and cardiac magnetic resonance imaging, with particular attention to specific clinical applications for cardiac surgery patients.

Evaluation of atrial septal defect using real-time three-dimensional echocardiography: comparison with surgical findings

The present study evaluated the application of three dimensional echocardigraphy (3DE) in the diagnosis of atrial septal defect (ASD) and the measurement of its size by 3DE and compared the size with surgical findings. Two-dimensional and real-time three dimensional echocardiography (RT3DE) was performed in 26 patients with atrial septal defect, and the echocardiographic data were compared with the surgical findings. Significant correlation was found between defect diameter by RT3DE and that measured during surgery (r=0.77, P<0.001). The defect area changed significantly during cardiac cycle. Percentage change in defect size during cardiac cycle ranged from 6%-70%. Our study showed that the size and morphology of atrial septal defect obtained with RT3DE correlate well with surgical findings. Therefore, RT3DE is a feasible and accurate non-invasive imaging tool for assessment of atrial septal size and dynamic changes.

Practical guide for three-dimensional transthoracic echocardiography using a fully sampled matrix array transducer

Real-time three-dimensional (3D) echocardiography is a major innovation in the history of cardiovascular ultrasound. Advances in computer and transducer technologies, especially the fully-sampled matrix array transducer, have permitted real-time 3D image acquisition and display. Several vendors provide 3D imaging but use different terminology for similar functions, creating confusion for consumers. This article provides a practical guide on how to acquire and analyze 3D images on-cart using currently available ultrasound systems (iE33, Philips Medical System, Andover, MA; Vivid7, GE Healthcare, Wauwatosa, WI) in daily clinical practice.

Clinical application of three-dimensional echocardiography: past, present and future

Significant advances in three-dimensional echocardiography have made this modality a powerful diagnostic tool in the cardiology clinic. It can provide accurate and reliable measurements of chamber size and function, including the quantification of left ventricular mechanical dyssynchrony to guide patient selection for cardiac resynchron-isation therapy. Furthermore, three-dimensional echocardiography offers novel views and comprehensive anatomic definition of valvular and congenital abnormalities, improving diagnosis and preoperative planning. In addition, it is extremely useful in monitoring the effectiveness of surgical or percutaneous transcatheter interventions. As its efficacy for more and more clinical applications is demonstrated, it is clear that three-dimensional echocardiography has become part of the routine clinical diagnostic armamentarium. In this article, we describe the development of three-dimensional echocardiography over the last decades, review the scientific evidence for its current clinical use and discuss potential future applications. (Neth Heart J 2009;17:18-24.).

Real-time three-dimensional echocardiography: an update

Real-time three-dimensional echocardiography (RT3DE) is the only on-line 3D method based on real-time volumetric scanning, as compared with other 3D imaging techniques such as computed tomography and magnetic resonance imaging, which are based on post-acquisition reconstruction and not on volumetric scanning. In recent years, several studies have revealed possible advantages of 3DE in daily clinical practice. The aim of this manuscript is to give a brief review of the development of the clinical applications of RT3DE.