Dynamic imaging of the fetal heart using metric optimized gating

Fetal Cardiac MRI Using Doppler US Gating: Emerging Technology and Clinical Implications

Fetal cardiac MRI using Doppler US gating is an emerging technique to support prenatal diagnosis of congenital heart disease and other cardiovascular abnormalities. Analogous to postnatal electrocardiographically gated cardiac MRI, this technique enables directly gated MRI of the fetal heart throughout the cardiac cycle, allowing for immediate data reconstruction and review of image quality. This review outlines the technical principles and challenges of cardiac MRI with Doppler US gating, such as loss of gating signal due to fetal movement. A practical workflow of patient preparation for the use of Doppler US-gated fetal cardiac MRI in clinical routine is provided. Currently applied MRI sequences (ie, cine or four-dimensional flow imaging), with special consideration of technical adaptations to the fetal heart, are summarized. The authors provide a literature review on the clinical benefits of Doppler US-gated fetal cardiac MRI for gaining additional diagnostic information on cardiovascular malformations and fetal hemodynamics. Finally, future perspectives of Doppler US-gated fetal cardiac MRI and further technical developments to reduce acquisition times and eliminate sources of artifacts are discussed. Keywords: MR Fetal, Ultrasound Doppler, Cardiac, Heart, Congenital, Obstetrics, Fetus Supplemental material is available for this article. © RSNA, 2024.

Deep learning denoising reconstruction for improved image quality in fetal cardiac cine MRI

Purpose

This study aims to evaluate deep learning (DL) denoising reconstructions for image quality improvement of Doppler ultrasound (DUS)-gated fetal cardiac MRI in congenital heart disease (CHD).

Methods

Twenty-five fetuses with CHD (mean gestational age: 35 ± 1 weeks) underwent fetal cardiac MRI at 3T. Cine imaging was acquired using a balanced steady-state free precession (bSSFP) sequence with Doppler ultrasound gating. Images were reconstructed using both compressed sensing (bSSFP CS) and a pre-trained convolutional neural network trained for DL denoising (bSSFP DL). Images were compared qualitatively based on a 5-point Likert scale (from 1 = non-diagnostic to 5 = excellent) and quantitatively by calculating the apparent signal-to-noise ratio (aSNR) and contrast-to-noise ratio (aCNR). Diagnostic confidence was assessed for the atria, ventricles, foramen ovale, valves, great vessels, aortic arch, and pulmonary veins.

Results

Fetal cardiac cine MRI was successful in 23 fetuses (92%), with two studies excluded due to extensive fetal motion. The image quality of bSSFP DL cine reconstructions was rated superior to standard bSSFP CS cine images in terms of contrast [3 (interquartile range: 2-4) vs. 5 (4-5), P < 0.001] and endocardial edge definition [3 (2-4) vs. 4 (4-5), P < 0.001], while the extent of artifacts was found to be comparable [4 (3-4.75) vs. 4 (3-4), P = 0.40]. bSSFP DL images had higher aSNR and aCNR compared with the bSSFP CS images (aSNR: 13.4 ± 6.9 vs. 8.3 ± 3.6, P < 0.001; aCNR: 26.6 ± 15.8 vs. 14.4 ± 6.8, P < 0.001). Diagnostic confidence of the bSSFP DL images was superior for the evaluation of cardiovascular structures (e.g., atria and ventricles: P = 0.003).

Conclusion

DL image denoising provides superior quality for DUS-gated fetal cardiac cine imaging of CHD compared to standard CS image reconstruction.

Integration of Prenatal Cardiovascular Magnetic Resonance Imaging in Congenital Heart Disease

Standard of care echocardiography can have limited diagnostic accuracy in certain cases of fetal congenital heart disease. Prenatal cardiovascular magnetic resonance (CMR) imaging has potential to provide additional anatomic imaging information, including excellent soft tissue images in multiple planes, improving prenatal diagnostics and in utero hemodynamic assessment. We conducted a literature review of fetal CMR, including its development and implementation into clinical practice, and compiled and analyzed the results. Our findings included the fact that technological and innovative approaches are required to overcome some of the challenges in fetal CMR, in part due to the dynamic nature of the fetal heart. A number of reconstruction algorithms and cardiac gating strategies have been developed over time to improve fetal CMR image quality, allowing unique investigations into fetal hemodynamics, oxygenation, and growth. Studies demonstrate that incorporating CMR in the prenatal arena influences postnatal clinical management. With further refinement and experience, fetal CMR in congenital heart disease continues to evolve and demonstrate ongoing potential as a complementary imaging modality to fetal echocardiography in the care of these patients.

Advanced imaging of fetal cardiac function

Over recent decades, a variety of advanced imaging techniques for assessing cardiovascular physiology and cardiac function in adults and children have been applied in the fetus. In many cases, technical development has been required to allow feasibility in the fetus, while an appreciation of the unique physiology of the fetal circulation is required for proper interpretation of the findings. This review will focus on recent advances in fetal echocardiography and cardiovascular magnetic resonance (CMR), providing examples of their application in research and clinical settings. We will also consider future directions for these technologies, including their ongoing technical development and potential clinical value.

Fetal Cardiac Cine MRI with Doppler US Gating in Complex Congenital Heart Disease

Purpose

To apply Doppler US (DUS)-gated fetal cardiac cine MRI in clinical routine and investigate diagnostic performance in complex congenital heart disease (CHD) compared with that of fetal echocardiography.

Materials and Methods

In this prospective study (May 2021 to March 2022), women with fetuses with CHD underwent fetal echocardiography and DUS-gated fetal cardiac MRI on the same day. For MRI, balanced steady-state free precession cine images were acquired in the axial and optional sagittal and/or coronal orientations. Overall image quality was assessed on a four-point Likert scale (from 1 = nondiagnostic to 4 = good image quality). The presence of abnormalities in 20 fetal cardiovascular features was independently assessed by using both modalities. The reference standard was postnatal examination results. Differences in sensitivities and specificities were determined by using a random-effects model.

Results

The study included 23 participants (mean age, 32 years ± 5 [SD]; mean gestational age, 36 weeks ± 1). Fetal cardiac MRI was completed in all participants. The median overall image quality of DUS-gated cine images was 3 (IQR, 2.5-4). In 21 of 23 participants (91%), underlying CHD was correctly assessed by using fetal cardiac MRI. In one case, the correct diagnosis was made by using MRI only (situs inversus and congenitally corrected transposition of the great arteries). Sensitivities (91.8% [95% CI: 85.7, 95.1] vs 93.6% [95% CI: 88.8, 96.2]; P = .53) and specificities (99.9% [95% CI: 99.2, 100] vs 99.9% [95% CI: 99.5, 100]; P > .99) for the detection of abnormal cardiovascular features were comparable between MRI and echocardiography, respectively.

Conclusion

Using DUS-gated fetal cine cardiac MRI resulted in performance comparable with that of using fetal echocardiography for diagnosing complex fetal CHD.Keywords: Pediatrics, MR-Fetal (Fetal MRI), Cardiac, Heart, Congenital, Fetal Imaging, Cardiac MRI, Prenatal, Congenital Heart DiseaseClinical trial registration no. NCT05066399 Supplemental material is available for this article. © RSNA, 2023See also the commentary by Biko and Fogel in this issue.

Fetal Brain Development in Congenital Heart Disease

Neurodevelopmental impairments are the most common extracardiac morbidities among patients with complex congenital heart disease (CHD) across the lifespan. Robust clinical research in this area has revealed several cardiac, medical, and social factors that can contribute to neurodevelopmental outcome in the context of CHD. Studies using brain magnetic resonance imaging (MRI) have been instrumental in identifying quantitative and qualitative difference in brain structure and maturation in this patient population. Full-term newborns with complex CHD are known to have abnormal microstructural and metabolic brain development with patterns similar to those seen in premature infants at approximately 34 to 36 weeks' gestation. With the advent of fetal brain MRI, these brain abnormalities are now documented as they begin in utero, as early as the third trimester. Importantly, disturbed brain development in utero is now known to be independently associated with neurodevelopmental outcome in early childhood, making the prenatal period an important timeframe for potential interventions. Advances in fetal brain MRI provide a robust imaging tool to use in future neuroprotective clinical trials. The causes of abnormal fetal brain development are multifactorial and include cardiovascular physiology, genetic abnormalities, placental impairment, and other environmental and social factors. This review provides an overview of current knowledge of brain development in the context of CHD, common prenatal imaging tools to evaluate the developing fetal brain in CHD, and known risk factors contributing to brain immaturity.

Fetal MRI of the heart and brain in congenital heart disease

Antenatal assessment of congenital heart disease and associated anomalies by ultrasound has improved perinatal care. Fetal cardiovascular MRI and fetal brain MRI are rapidly evolving for fetal diagnostic testing of congenital heart disease. We give an overview on the use of fetal cardiovascular MRI and fetal brain MRI in congenital heart disease, focusing on the current applications and diagnostic yield of structural and functional imaging during pregnancy. Fetal cardiovascular MRI in congenital heart disease is a promising supplementary imaging method to echocardiography for the diagnosis of antenatal congenital heart disease in weeks 30-40 of pregnancy. Concomitant fetal brain MRI is superior to brain ultrasound to show the complex relationship between fetal haemodynamics in congenital heart disease and brain development.

The Evolution and Developing Importance of Fetal Magnetic Resonance Imaging in the Diagnosis of Congenital Cardiac Anomalies: A Systematic Review

Magnetic Resonance Imaging (MRI) is a reliable method, with a complementary role to Ultrasound (US) Echocardiography, that can be used to fully comprehend and precisely diagnose congenital cardiac malformations. Besides the anatomical study of the fetal cardiovascular system, it allows us to study the function of the fetal heart, remaining, at the same time, a safe adjunct to the classic fetal echocardiography. MRI also allows for the investigation of cardiac and placental diseases by providing information about hematocrit, oxygen saturation, and blood flow in fetal vessels. It is crucial for fetal medicine specialists and pediatric cardiologists to closely follow the advances of fetal cardiac MRI in order to provide the best possible care. In this review, we summarize the advance in techniques and their practical utility to date.

Fetal Cardiovascular MRI - A Systemic Review of the Literature: Challenges, New Technical Developments, and Perspectives

BACKGROUND

Fetal magnetic resonance imaging (MRI) has become a valuable adjunct to ultrasound in the prenatal diagnosis of congenital pathologies of the central nervous system, thorax, and abdomen. Fetal cardiovascular magnetic resonance (CMR) was limited, mainly by the lack of cardiac gating, and has only recently evolved due to technical developments.

METHOD

A literature search was performed on PubMed, focusing on technical advancements to perform fetal CMR. In total, 20 publications on cardiac gating techniques in the human fetus were analyzed.

RESULTS

Fetal MRI is a safe imaging method with no developmental impairments found to be associated with in utero exposure to MRI. Fetal CMR is challenging due to general drawbacks (e. g., fetal motion) and specific limitations such as the difficulty to generate a cardiac gating signal to achieve high spatiotemporal resolution. Promising technical advancements include new methods for fetal cardiac gating, based on novel post-processing approaches and an external hardware device, as well as motion compensation and acceleration techniques.

CONCLUSION

Newly developed direct and indirect gating approaches were successfully applied to achieve high-quality morphologic and functional imaging as well as quantitative assessment of fetal hemodynamics in research settings. In cases when prenatal echocardiography is limited, e. g., by an unfavorable fetal position in utero, or when its results are inconclusive, fetal CMR could potentially serve as a valuable adjunct in the prenatal assessment of congenital cardiovascular malformations. However, sufficient data on the diagnostic performance and clinical benefit of new fetal CMR techniques is still lacking.

KEY POINTS

· New fetal cardiac gating methods allow high-quality fetal CMR.. · Motion compensation and acceleration techniques allow for improvement of image quality.. · Fetal CMR could potentially serve as an adjunct to fetal echocardiography in the future..

CITATION FORMAT

· Knapp J, Tavares de Sousa M, Schönnagel BP. Fetal Cardiovascular MRI - A Systemic Review of the Literature: Challenges, New Technical Developments, and Perspectives. Fortschr Röntgenstr 2022; 194: 841 - 851.

Structured analysis of the impact of fetal motion on phase-contrast MRI flow measurements with metric optimized gating

The impact of fetal motion on phase contrast magnetic resonance imaging (PC-MRI) with metric optimized gating (MOG) remains unknown, despite being a known limitation to prenatal MRI. This study aims to describe the effect of motion on fetal flow-measurements using PC-MRI with MOG and to generate a scoring-system that could be used to predict motion-corrupted datasets at the time of acquisition. Ten adult volunteers underwent PC-MRI with MOG using a motion-device to simulate reproducible in-plane motion encountered in fetuses. PC-MRI data were acquired on ten fetuses. All ungated images were rated on their quality from 0 (no motion) to 2 (severe motion). There was no significant difference in measured flows with in-plane motion during the first and last third of sequence acquisition. Movement in the middle section of acquisition produced a significant difference while all referring ungated images were rated with a score of 2. Intra-Class-Correlation (ICC) for flow-measurements in adult and fetal datasets was lower for datasets with scores of 2. For fetal applications, the use of a simple three-point scoring system reliably identifies motion-corrupted sequences from unprocessed data at the time of acquisition, with a high score corresponding to significant underestimation of flow values and increased interobserver variability.

Update on fetal cardiovascular magnetic resonance and utility in congenital heart disease

Background

Congenital heart disease (CHD) is the most common birth defect, affecting approximately eight per thousand newborns. Between one and two neonates per thousand have congenital cardiac lesions that require immediate post-natal treatment to stabilize the circulation, and the management of these patients in particular has been greatly enhanced by prenatal detection. The antenatal diagnosis of CHD has been made possible through the development of fetal echocardiography, which provides excellent visualization of cardiac anatomy and physiology and is widely available. However, late gestational fetal echocardiographic imaging can be hampered by suboptimal sonographic windows, particularly in the setting of oligohydramnios or adverse maternal body habitus.

Main body

Recent advances in fetal cardiovascular magnetic resonance (CMR) technology now provide a feasible alternative that could be helpful when echocardiography is inconclusive or limited. Fetal CMR has also been used to study fetal circulatory physiology in human fetuses with CHD, providing new insights into how these common anatomical abnormalities impact the distribution of blood flow and oxygen across the fetal circulation. In combination with conventional fetal and neonatal magnetic resonance imaging (MRI) techniques, fetal CMR can be used to explore the relationship between abnormal cardiovascular physiology and fetal development. Similarly, fetal CMR has been successfully applied in large animal models of the human fetal circulation, aiding in the evaluation of experimental interventions aimed at improving in utero development. With the advent of accelerated image acquisition techniques, post-processing approaches to correcting motion artifacts and commercial MRI compatible cardiotocography units for acquiring gated fetal cardiac imaging, an increasing number of CMR methods including angiography, ventricular volumetry, and the quantification of vessel blood flow and oxygen content are now possible.

Conclusion

Fetal CMR has reached an exciting stage whereby it may now be used to enhance the assessment of cardiac morphology and fetal hemodynamics in the setting of prenatal CHD.

Fetal dynamic magnetic resonance imaging using Doppler ultrasound gating for the assessment of the aortic isthmus: A feasibility study

INTRODUCTION

Cardiovascular magnetic resonance imaging (MRI) is established in cardiac evaluation in postnatal life, but its application to the fetus has been hampered by technical limitations. We aimed to investigate the feasibility of dynamic MRI of the fetal aortic isthmus using a magnetic resonance-compatible Doppler ultrasound device for cardiac gating.

MATERIAL AND METHODS

This prospective study included 19 fetuses at a median gestational age of 32.3 weeks (range 26-38 weeks). Imaging of the fetal aortic isthmus was assessed by (a) dynamic steady-state free precession MRI using a magnetic resonance-compatible Doppler ultrasound device for cardiac gating and (b) echocardiography. Diameters of the aortic isthmus were compared by two blinded observers. Magnetic resonance image quality was assessed independently by two observers using a four-point scale (1 = low quality, 4 = high quality). Furthermore, we performed four-dimensional flow MRI of the fetal aorta in three of these fetuses.

RESULTS

The Doppler ultrasound device for cardiac gating allowed successful dynamic MRI examinations of the aortic isthmus in 18/19 (95%) fetuses. Evaluation of the fetal aortic isthmus was possible by both MRI (15/18, 83%) and echocardiography (16/18, 89%) (P < .05). Diameters of the aortic isthmus were concordant for MRI (3.8 ± 0.9 mm) and echocardiography (4.0 ± 1.1 mm), with a variability of 10.8% (bias -2.3%, 95% limits of agreement -23.9% to 19.3%). Overall magnetic resonance image quality was good (score 4 in 67% and score 3 in 23%) with good inter-observer agreement (κ = 0.75; 95% CI 0.5-1). Fetal four-dimensional flow MRI allowed visualization of aortic flow dynamics.

CONCLUSIONS

Doppler ultrasound-gating allows dynamic MRI of the fetal aorta with the potential to serve as a complementary imaging tool in cases where echocardiography is inconclusive.

Feasibility of ventricular volumetry by cardiovascular MRI to assess cardiac function in the fetal sheep

KEY POINTS

The application of fetal cardiovascular magnetic resonance imaging (CMR) to assess fetal cardiovascular physiology and cardiac function through the quantification of ventricular volumes has previously been investigated, but the approach has not yet been fully validated. Ventricular output measurements calculated from heart rate and stroke volumes (SV) of the right and left ventricles measured by ventricular volumetry (VV) exhibited a high level of agreement with phase-contrast (PC) blood flow measurements in the main pulmonary artery and ascending aorta, respectively. Ejection fraction of the right ventricle, which is lower than that of the left ventricle in postnatal subjects, was similar to the left ventricular ejection fraction in the fetus; probably due to the different loading conditions present in the fetal circulation. This study provides evidence to support the reliability of VV in the sheep fetus, providing evidence for its use in animal models of human diseases affecting the fetal circulation.

ABSTRACT

The application of ventricular volumetry (VV) by cardiovascular magnetic resonance imaging (CMR) in the fetus remains challenging due to the small size of the fetal heart and high heart rate. The reliability of this technique in utero has not yet been established. The aim of this study was to assess the feasibility and reliability of VV in a fetal sheep model of human pregnancy. Right and left ventricular outputs by stroke volume (SV) measured using VV were compared with 2D phase-contrast (PC) CMR measurements of blood flow in the main pulmonary artery (MPA) and ascending aorta (AAo). At 124-140 days (d) gestation, singleton bearing Merino ewes underwent CMR under general anaesthesia using fetal femoral artery catheters, implanted at 109-117d, to trigger cine steady state free precession acquisitions of ventricular short-axis stacks. The short-axis cine stacks were segmented at end-systole and end-diastole, yielding right and left ventricular SV, ejection fraction, and cardiac outputs (SV × heart rate). PC cine acquisitions of MPA and AAo were analysed to measure blood flow, which served as comparators for the right and left cardiac outputs by VV. There was good correlation and agreement between VV and PC measures of ventricular outputs with no significant bias (r²  = 0.926; P < 0.0001; Bias = -4.7 ± 10.5 ml min^-1  kg^-1 ; 95% limits of agreement: -15.9 to 25.2 ml min^-1  kg^-1 ). This study validates fetal VV by CMR in a large animal model of human pregnancy and provides preliminary reference values of fetal sheep right and left ventricles in late gestation.

Advances in fetal echocardiography: myocardial deformation analysis, cardiac MRI and three-dimensional printing

PURPOSE OF REVIEW

Advances in ultrasound technology have led to new ways of evaluating cardiac function and structure, including myocardial deformation imaging (strain and strain rate), cardiac MRI and three-dimensional (3D) printing. As ultrasound technology has improved, it has become possible to use these modalities to evaluate the fetal heart. This article will review some of the more recent developments in applying these techniques to the evaluation of fetal cardiac structure and function.

RECENT FINDINGS

Myocardial deformation analyses have led to the establishment of normative values for strain and strain rate in the fetal heart and have also been used to evaluate fetal heart function in both fetal disease states and maternal disease states. Technological advances in MRI technology, 3D imaging and 3D printing have opened up new methods of evaluating fetal structural heart disease.

SUMMARY

A deeper understanding of the subtleties of myocardial dysfunction in various fetal and maternal disease states may elucidate the pathophysiology involved and lead to new treatment and/or counseling paradigms that may ultimately affect outcome. Similarly, the ability to image the fetal heart in new ways, including fetal MRI and 3D printing, could potentially change fetal counseling techniques and prenatal planning.

Understanding Fetal Hemodynamics Using Cardiovascular Magnetic Resonance Imaging

Human fetal circulatory physiology has been investigated extensively using grey-scale ultrasound, which provides excellent visualization of cardiac anatomy and function, while velocity profiles in the heart and vessels can be interrogated using Doppler. Measures of cerebral and placental vascular resistance, as well as indirect measures of intracardiac pressure obtained from the velocity waveform in the ductus venosus are routinely used to guide the management of fetal cardiovascular and placental disease. However, the characterization of some key elements of cardiovascular physiology such as vessel blood flow and the oxygen content of blood in the arteries and veins, as well as fetal oxygen delivery and consumption are not readily measured using ultrasound. To study these parameters, we have historically relied on data obtained using invasive measurements made in animal models, which are not equivalent to the human in every respect. Over recent years, a number of technical advances have been made that have allowed us to examine the human fetal circulatory system using cardiovascular magnetic resonance (CMR). The combination of vessel blood flow measurements made using cine phase contrast magnetic resonance imaging and vessel blood oxygen saturation and hematocrit measurements made using T1 and T2 mapping have enabled us to emulate those classic fetal sheep experiments defining the distribution of blood flow and oxygen transport across the fetal circulation in the human fetus. In addition, we have applied these techniques to study the relationship between abnormal fetal cardiovascular physiology and fetal development in the setting of congenital heart disease and placental insufficiency. CMR has become an important diagnostic tool in the assessment of cardiovascular physiology in the setting of postnatal cardiovascular disease, and is now being applied to the fetus to enhance our understanding of normal and abnormal fetal circulatory physiology and its impact on fetal well-being.

Fetal Cardiac MRI: A Review of Technical Advancements

Magnetic resonance imaging (MRI) is an appealing technology for fetal cardiovascular assessment. It can be used to visualize fetal cardiac and vascular anatomy, to quantify fetal blood flow, and to quantify fetal blood oxygen saturation and hematocrit. However, there are practical limitations to the use of conventional MRI for fetal cardiovascular assessment, including the small size and high heart rate of the human fetus, the lack of conventional cardiac gating methods to synchronize data acquisition, and the potential corruption of MRI data due to maternal respiration and unpredictable fetal movements. In this review, we discuss recent technical advances in accelerated imaging, image reconstruction, cardiac gating, and motion compensation that have enabled dynamic MRI of the fetal heart.

Current and future role of fetal cardiovascular MRI in the setting of fetal cardiac interventions

Over recent years, technical developments resulting in the feasibility of fetal cardiovascular magnetic resonance (CMR) have provided a new diagnostic tool for studying the human fetal heart and circulation. During the same period, we have witnessed the arrival of several minimally invasive fetal cardiac interventions (FCI) as a possible form of treatment in selected congenital heart diseases (CHDs). The role of fetal CMR in the planning and monitoring of FCI is not yet clear. Indeed, high-quality fetal CMR is not available or routinely offered at most centers caring for patients with prenatally detected CHD. However, in theory, fetal CMR could have much to offer in the setting of FCI by providing complementary anatomic and physiologic information relating to the specific intervention under consideration. Similarly, fetal CMR may be useful as an alternative imaging modality when ultrasound is hampered by technical limitations, for example, in the setting of oligohydramnios and in late gestation. In this review, we summarize current experience of the use of fetal CMR in the diagnosis and monitoring of fetuses with cardiopathies in the setting of a range of invasive in utero cardiac and vascular interventions and medical treatments and speculate about future directions for this versatile imaging medium.

Preliminary Experience Using Motion Compensated CINE Magnetic Resonance Imaging to Visualise Fetal Congenital Heart Disease

BACKGROUND

Recent advances in cardiovascular magnetic resonance (CMR) imaging have facilitated CINE imaging of the fetal heart. In this work, a preliminary investigation of the utility of multislice CINE CMR for assessing fetal congenital heart disease is performed and compared with echocardiography.

METHODS AND RESULTS

Multislice CINE CMR and echocardiography images were acquired in 25 pregnant women wherein the fetus had a suspected congenital heart defect based on routine obstetric ultrasound. Pathognomonic images were identified for each subject for qualitative comparison of CMR and echocardiography. Quantitative comparison of CMR and echocardiography was then performed by 2 reviewers using a binary scoring of 9 fetal cardiac anatomic features (identifiable/not-identifiable). Pathognomonic images demonstrated the ability of CMR to visualize a variety of congenital heart defects. Overall CMR was able to identify the majority of the 9 assessed fetal cardiac anatomic features (reviewer 1, 7.1±2.1; reviewer 2, 6.7±2.3). Although both reviewers identified more anatomic features with echocardiography (reviewer 1, 7.8±2.3; reviewer 2, 7.5±2.4; P=0.01), combining information from both modalities enabled identification of additional anatomic features across subjects (reviewer 1, 8.4±1.3; reviewer 2, 8.4±1.2). The primary limiting factor for CMR was inadequate coverage of the fetal cardiac anatomy or noncontiguous slices because of gross fetal movement.

CONCLUSIONS

CINE CMR enables visualization of fetal congenital heart disease. This work demonstrates the potential of CMR for diagnosing congenital heart disease in utero in conjunction with echocardiography during late gestation.

Free-breathing fetal cardiac MRI with doppler ultrasound gating, compressed sensing, and motion compensation

Background

Fetal cardiovascular MRI complements ultrasound to assess fetal cardiovascular pathophysiology.

Purpose

To develop a free‐breathing method for retrospective fetal cine MRI using Doppler ultrasound (DUS) cardiac gating and tiny golden angle radial sampling (tyGRASP) for accelerated acquisition capable of detecting fetal movements for motion compensation.

Study Type

Feasibility study.

Subjects

Nine volunteers (gestational week 34–40). Short‐axis and four‐chamber views were acquired during maternal free‐breathing and breath‐hold.

Field Strength/Sequence

1.5T cine balanced steady‐state free precession.

Assessment

A self‐gated reconstruction method was improved for clinical application by using 1) retrospective DUS gating, and 2) motion detection and rejection/correction algorithms for compensating for fetal motion. The free‐breathing reconstructions were qualitatively and quantitatively assessed, and DUS‐gating was compared with self‐gating in breath‐hold reconstructions. A scoring of 1–4 for overall image quality, cardiac, and extracardiac diagnostic quality was used.

Statistical Tests

Friedman's test was used to assess differences in qualitative scoring between observers. A Wilcoxon matched‐pairs signed rank test was used to assess differences between breath‐hold and free‐breathing acquisitions and between observers' quantitative measurements.

Results

In all cases, 111 free‐breathing and 145 breath‐hold acquisitions, the automatically calculated DUS‐based cardiac gating signal provided reconstructions of diagnostic quality (median score 4, range 1–4). Free‐breathing did not affect the DUS‐based cardiac gated retrospective radial reconstruction with respect to image or diagnostic quality (all P > 0.06). Motion detection with rejection/correction in k‐space produced high‐quality free‐breathing DUS‐based reconstructions [median 3, range (2–4)], whereas free‐breathing self‐gated methods failed in 80 out of 88 cases to produce a stable gating signal.

Data Conclusion

Free‐breathing fetal cine cardiac MRI based on DUS gating and tyGRASP with motion compensation yields diagnostic images. This simplifies acquisition for the pregnant woman and thus could help increase fetal cardiac MRI acceptance in the clinic.

Level of Evidence: 2

Technical Efficacy Stage: 1 J. Magn. Reson. Imaging 2020;51:260–272.

MR imaging of the fetal heart

In the last decade, technological advances have enabled the acquisition of high spatial and temporal resolution cardiac magnetic resonance imaging (MRI) in the fetus. Fetal cardiac MRI has emerged as an alternative to ultrasound, which may be helpful to confirm a diagnosis of congenital heart disease when ultrasound assessment is hampered, for example in late gestation or in the setting of oligohydramnios. MRI also provides unique physiologic information, including vessel blood flow, oxygen saturation and hematocrit, which may be helpful to investigate cardiac and placental diseases. In this review, we summarize some of the main techniques and significant advances in the field to date. Level of Evidence: 5 Technical Efficacy: Stage 5 J. Magn. Reson. Imaging 2020;51:1030-1044.

Fetal XCMR: a numerical phantom for fetal cardiovascular magnetic resonance imaging

BACKGROUND

Validating new techniques for fetal cardiovascular magnetic resonance (CMR) is challenging due to random fetal movement that precludes repeat measurements. Consequently, fetal CMR development has been largely performed using physical phantoms or postnatal volunteers. In this work, we present an open-source simulation designed to aid in the development and validation of new approaches for fetal CMR. Our approach, fetal extended Cardiac-Torso cardiovascular magnetic resonance imaging (Fetal XCMR), builds on established methods for simulating CMR acquisitions but is tailored toward the dynamic physiology of the fetal heart and body. We present comparisons between the Fetal XCMR phantom and data acquired in utero, resulting in image quality, anatomy, tissue signals and contrast.

METHODS

Existing extended Cardiac-Torso models are modified to create maternal and fetal anatomy, combined according to simulated motion, mapped to CMR contrast, and converted to CMR data. To provide a comparison between the proposed simulation and experimental fetal CMR images acquired in utero, images from a typical scan of a pregnant woman are included and simulated acquisitions were generated using matching CMR parameters, motion and noise levels. Three reconstruction (static, real-time, and CINE), and two motion estimation methods (translational motion, fetal heart rate) from data acquired in transverse, sagittal, coronal, and short-axis planes of the fetal heart were performed to compare to in utero acquisitions and demonstrate feasibility of the proposed simulation framework.

RESULTS

Overall, CMR contrast, morphologies, and relative proportions of the maternal and fetal anatomy are well represented by the Fetal XCMR images when comparing the simulation to static images acquired in utero. Additionally, visualization of maternal respiratory and fetal cardiac motion is comparable between Fetal XCMR and in utero real-time images. Finally, high quality CINE image reconstructions provide excellent delineation of fetal cardiac anatomy and temporal dynamics for both data types.

CONCLUSION

The fetal CMR phantom provides a new method for evaluating fetal CMR acquisition and reconstruction methods by simulating the underlying anatomy and physiology. As the field of fetal CMR continues to grow, new methods will become available and require careful validation. The fetal CMR phantom is therefore a powerful and convenient tool in the continued development of fetal cardiac imaging.

Dynamic fetal cardiac magnetic resonance imaging in four-chamber view using Doppler ultrasound gating in normal fetal heart and in congenital heart disease: comparison with fetal echocardiography

OBJECTIVES

To investigate the diagnostic performance of dynamic fetal cardiac magnetic resonance imaging (MRI), using a MR-compatible Doppler ultrasound (DUS) device for fetal cardiac gating, in differentiating fetuses with congenital heart disease from those with a normal heart, and to compare the technique with fetal echocardiography.

METHODS

This was a prospective study of eight fetuses with a normal heart and four with congenital heart disease (CHD), at a median of 34 (range, 28-36) weeks' gestation. Dynamic fetal cardiac MRI was performed using a DUS device for direct cardiac gating. The four-chamber view was evaluated according to qualitative findings. Measurements of the length of the left and right ventricles, diameter of the tricuspid and mitral valves, myocardial wall thickness, transverse cardiac diameter and left ventricular planimetry were performed. Fetal echocardiography and postnatal diagnoses were considered the reference standards.

RESULTS

Direct cardiac gating allowed continuous triggering of the fetal heart, showing high temporal and spatial resolution. Both fetal cardiac MRI and echocardiography in the four-chamber view detected pathological findings in three of the 12 fetuses. Qualitative evaluation revealed overall consistency between echocardiography and MRI. On both echocardiography and MRI, quantitative measurements revealed significant differences between fetuses with a normal heart and those with CHD with respect to the length of the right (P < 0.01 for both) and left (P < 0.01 for both) ventricles and transverse cardiac diameter (P < 0.05 and P < 0.01, respectively). Tricuspid valve diameter on cardiac MRI was found to be significantly different in healthy fetuses from in those with CHD (P < 0.05).

CONCLUSIONS

For the first time, this study has shown that dynamic fetal cardiac MRI in the four-chamber view, using external cardiac gating, allows evaluation of cardiac anatomy and diagnosis of congenital heart disease in agreement with fetal echocardiography. Dynamic fetal cardiac MRI may be useful as a second-line investigation if conditions for fetal echocardiography are unfavorable. Copyright © 2018 ISUOG. Published by John Wiley & Sons Ltd.

Fetal dynamic phase-contrast MR angiography using ultrasound gating and comparison with Doppler ultrasound measurements

OBJECTIVES

To investigate the feasibility of fetal phase-contrast (PC)-MR angiography of the descending aorta (AoD) using an MR-compatible Doppler ultrasound sensor (DUS) for fetal cardiac gating and to compare velocimetry with Doppler ultrasound measurements.

METHODS

In this prospective study, 2D PC-MR angiography was performed in 12 human fetuses (mean gestational age 32.8 weeks) using an MR-compatible DUS for gating of the fetal heart at 1.5 T. Peak flow velocities in the fetal AoD were compared with Doppler ultrasound measurements performed on the same day. Reproducibility of PC-MR measurements was tested by repeated PC-MR in five fetuses.

RESULTS

Dynamic PC-MR angiography in the AoD was successfully performed in all fetuses using the DUS, with an average fetal heart rate of 140 bpm (range 129-163). Time-velocity curves revealed typical arterial blood flow patterns. PC-MR mean flow velocity and mean flux were 21.2 cm/s (range 8.6-36.8) and 8.4 ml/s (range 3.2-14.6), respectively. A positive association between PC-MR mean flux and stroke volume with gestational age was obtained (r = 0.66, p = 0.02 and r = 0.63, p = 0.03). PC-MR and Doppler ultrasound peak velocities revealed a highly significant correlation (r = 0.8, p < 0.002). Peak velocities were lower for PC-MR with 69.1 cm/s (range 39-125) compared with 96.7 cm/s (range 60-142) for Doppler ultrasound (p < 0.001). Reproducibility of PC-MR was high (p > 0.05).

CONCLUSION

The MR-compatible DUS for fetal cardiac gating allows for PC-MR angiography in the fetal AoD. Comparison with Doppler ultrasound revealed a highly significant correlation of peak velocities with underestimation of PC-MR velocities. This new technique for direct fetal cardiac gating indicates the potential of PC-MR angiography for assessing fetal hemodynamics.

KEY POINTS

• The developed MR-compatible Doppler ultrasound sensor allows direct fetal cardiac gating and can be used for prenatal dynamic cardiovascular MRI. • The MR-compatible Doppler ultrasound sensor was successfully applied to perform intrauterine phase-contrast MR angiography of the fetal aorta, which revealed a highly significant correlation with Doppler ultrasound measurements. • As fetal flow hemodynamics is an important parameter in the diagnosis and management of fetal pathologies, fetal phase-contrast MR angiography may offer an alternative imaging method in addition to Doppler ultrasound and develop as a second line tool in the evaluation of fetal flow hemodynamics.

Dynamic fetal cardiovascular magnetic resonance imaging using Doppler ultrasound gating

BACKGROUND

Fetal cardiovascular magnetic resonance (CMR) imaging may provide a valuable adjunct to fetal echocardiography in the evaluation of congenital cardiovascular pathologies. However, dynamic fetal CMR is difficult due to the lack of direct in-utero cardiac gating. The aim of this study was to investigate the effectiveness of a newly developed Doppler ultrasound (DUS) device in humans for fetal CMR gating.

METHODS

Fifteen fetuses (gestational age 30-39 weeks) were examined using 1.5 T CMR scanners at three different imaging sites. A newly developed CMR-compatible DUS device was used to generate gating signals from fetal cardiac motion. Gated dynamic balanced steady-state free precession images were acquired in 4-chamber and short-axis cardiac views. Gating signals during data acquisition were analyzed with respect to trigger variability and sensitivity. Image quality was assessed by measuring endocardial blurring (EB) and by image evaluation using a 4-point scale. Left ventricular (LV) volumetry was performed using the single-plane ellipsoid model.

RESULTS

Gating signals from the fetal heart were detected with a variability of 26 ± 22 ms and a sensitivity of trigger detection of 96 ± 4%. EB was 2.9 ± 0.6 pixels (4-chamber) and 2.5 ± 0.1 pixels (short axis). Image quality scores were 3.6 ± 0.6 (overall), 3.4 ± 0.7 (mitral valve), 3.4 ± 0.7 (foramen ovale), 3.6 ± 0.7 (atrial septum), 3.7 ± 0.5 (papillary muscles), 3.8 ± 0.4 (differentiation myocardium/lumen), 3.7 ± 0.5 (differentiation myocardium/lung), and 3.9 ± 0.4 (systolic myocardial thickening). Inter-observer agreement for the scores was moderate to very good (kappa 0.57-0.84) for all structures. LV volumetry revealed mean values of 2.8 ± 1.2 ml (end-diastolic volume), 0.9 ± 0.4 ml (end systolic volume), 1.9 ± 0.8 ml (stroke volume), and 69.1 ± 8.4% (ejection fraction).

CONCLUSION

High-quality dynamic fetal CMR was successfully performed using a newly developed DUS device for direct fetal cardiac gating. This technique has the potential to improve the utility of fetal CMR in the evaluation of congenital pathologies.

Evaluation of a Portable Doppler Ultrasound Gating Device for Fetal Cardiac MR Imaging: Initial Results at 1.5T and 3T

Purpose:

Fetal cardiac MRI has the potential to play an important role in the assessment of fetal cardiac pathologies, but it is up to now not feasible due to a missing gating method. The purpose of this work was the evaluation of Doppler ultrasound (DUS) for external fetal cardiac gating with regard to compatibility, functionality, and reliability. Preliminary results were assessed performing fetal cardiac MRI.

Methods:

An MRI conditional DUS device was developed to obtain a gating signal from the fetal heart. The MRI compatibility was evaluated at 1.5T and 3T using B₁ field maps and gradient echo images. The quality and sensitivity of the DUS device to detect the fetal heart motion for cardiac gating were evaluated outside the MRI room in 15 fetuses. A dynamic fetal cardiac phantom was employed to evaluate distortions of the DUS device and gating signal due to electromagnetic interferences at 1.5T and 3T. In the first in vivo experience, dynamic fetal cardiac images were acquired in four-chamber view at 1.5T and 3T in two fetuses.

Results:

The maximum change in the B₁ field and signal intensity with and without the DUS device was <6.5% for 1.5T and 3T. The sensitivity of the DUS device to detect the fetal heartbeat was 99.1%. Validation of the DUS device using the fetal cardiac phantom revealed no electromagnetic interferences at 1.5T or 3T and a high correlation to the simulated heart frequencies. Fetal cardiac cine images were successfully applied and showed good image quality.

Conclusion:

An MR conditional DUS gating device was developed and evaluated revealing safety, compatibility, and reliability for different field strengths. In a preliminary experience, the DUS device was successfully applied for in vivo fetal cardiac imaging at 1.5T and 3T.

Fetal cardiac cine magnetic resonance imaging in utero

Fast magnetic resonance imaging (MRI) led to the emergence of 'cine MRI' techniques, which enable the visualization of the beating heart and the assessment of cardiac morphology and dynamics. However, established cine MRI methods are not suitable for fetal heart imaging in utero, where anatomical structures are considerably smaller and recording an electrocardiogram signal for synchronizing MRI data acquisition is difficult. Here we present a framework to overcome these challenges. We use methods for image acquisition and reconstruction that robustly produce images with sufficient spatial and temporal resolution to detect the heart contractions of the fetus, enabling a retrospective gating of the images and thus the generation of images of the beating heart. To underline the potential of our approach, we acquired in utero images in six pregnant patients and compared these with their echocardiograms. We found good agreement in terms of diameter and area measurements, and low inter- and intra- observer variability. These results establish MRI as a reliable modality for fetal cardiac imaging, with a substantial potential for prenatal evaluation of congenital heart defects.

Spatially Resolved MR-Compatible Doppler Ultrasound: Proof of Concept for Triggering of Diagnostic Quality Cardiovascular MRI for Function and Flow Quantification at 3T

OBJECTIVE

We demonstrate the use of a magnetic-resonance (MR)-compatible ultrasound (US) imaging probe using spatially resolved Doppler for diagnostic quality cardiovascular MR imaging (MRI) as an initial step toward hybrid US/MR fetal imaging.

METHODS

A newly developed technology for a dedicated MR-compatible phased array ultrasound-imaging probe acquired pulsed color Doppler carotid images, which were converted in near-real time to a trigger signal for cardiac cine and flow quantification MRI. Ultrasound and MR data acquired simultaneously were interference free. Conventional electrocardiogram (ECG) and the proposed spatially resolved Doppler triggering were compared in 10 healthy volunteers. A synthetic "false-triggered" image was retrospectively processed using metric optimized gating (MOG). Images were scored by expert readers, and sharpness, cardiac function and aortic flow were quantified. Four-dimensional (4-D) flow (two volunteers) showed feasibility of Doppler triggering over a long acquisition time.

RESULTS

Imaging modalities were compatible. US probe positioning was stable and comfortable. Image quality scores and quantified sharpness were statistically equal for Doppler- and ECG-triggering (p ). ECG-, Doppler-triggered, and MOG ejection fractions were equivalent (p ), with false-triggered values significantly lower (p < 0.0005). Aortic flow showed no difference between ECG- and Doppler-triggered and MOG (p > 0.05). 4-D flow quantification gave consistent results between ECG and Doppler triggering.

CONCLUSION

We report interference-free pulsed color Doppler ultrasound during MR data acquisition. Cardiovascular MRI of diagnostic quality was successfully obtained with pulsed color Doppler triggering.

SIGNIFICANCE

The hardware platform could further enable advanced free-breathing cardiac imaging. Doppler ultrasound triggering is applicable where ECG is compromised due to pathology or interference at higher magnetic fields, and where direct ECG is impossible, i.e., fetal imaging.

Feasibility of detecting myocardial infarction in the sheep fetus using late gadolinium enhancement CMR imaging

BACKGROUND

Late gadolinium enhancement (LGE) cardiovascular magnetic resonance (CMR) imaging has enabled the accurate assessment of myocardial infarction (MI). However, LGE CMR has not been performed successfully in the fetus, where it could be useful for animal studies of interventions to promote cardiac regeneration. We believe that LGE imaging could allow us to document the presence, extent and effect of MI in utero and would thereby expand our capacity for conducting fetal sheep MI research. We therefore aimed to investigate the feasibility of using LGE to detect MI in sheep fetuses.

METHODS

Six sheep fetuses underwent a thoracotomy and ligation of a left anterior descending (LAD) coronary artery branch; while two fetuses underwent a sham surgery. LGE CMR was performed in a subset of fetuses immediately after the surgery and three days later. Early gadolinium enhancement (EGE) CMR was also performed in a subset of fetuses on both days. Cine imaging of the heart was performed to measure ventricular function.

RESULTS

The imaging performed immediately after LAD ligation revealed no evidence of infarct on LGE (n=3). Two of four infarcted fetuses (50%) showed hypoenhancement at the infarct site on the EGE images. Three days after the ligation, LGE images revealed a clear, hyper-enhanced infarct zone in four of the five infarcted fetuses (80%). No hyper-enhanced infarct zone was seen on the one sham fetus that underwent LGE CMR. No hypoenhancement could be seen in the EGE images in either the sham (n=1) or the infarcted fetus (n=1). No regional wall motion abnormalities were apparent in two of the five infarcted fetuses.

CONCLUSION

LGE CMR detected the MI three days after LAD ligation, but not immediately after. Using available methods, EGE imaging was less useful for detecting deficits in perfusion. Our study provides evidence for the ability of a non-invasive tool to monitor the progression of cardiac repair and damage in fetuses with MI. However, further investigation into the optimal timing of LGE and EGE scans and improvement of the sequences should be pursued with the aim of expanding our capacity to monitor cardiac regeneration after MI in fetal sheep.

Magnetic resonance imaging of fetal persistent left superior vena cava

This study aimed to evaluate the diagnostic accuracy of fetal magnetic resonance imaging (MRI) for persistent left superior vena cava (LSVC). Prenatal echocardiography (echo) and/or ultrasound (US) and MRI data for 49 fetuses with persistent LSVC, confirmed via postnatal diagnoses between January 2010 and October 2015, were retrospectively reviewed. All prenatal MRI was performed at 1.5 T. Imaging sequences included steady-state free-precession (SSFP), single-shot turbo spin echo (SSTSE), and other sequences. All 49 cases of fetal persistent LSVC were correctly diagnosed via MRI, but only 34 cases (69.4%) were correctly diagnosed via an initial US and/or echo before MRI. Of the 15 cases that were not correctly diagnosed via US and/or echo, 8 had congenital heart diseases (CHDs) and 7 were without CHDs; however, they were associated with extracardiac abnormalities or maternal obesity. Thirty-five cases were associated with other cardiovascular abnormalities; 8, with extracardiac abnormalities; and 6, with no associated condition. In 44 (89.8%) cases, the innominate veins were absent; the remaining cases had innominate veins. In 14.3% of patients (7 cases), the persistent LSVC drained directly into the atrium. Fetal MRI can detect persistent LSVC and play an adjunctive role along with US in the evaluation of persistent LSVC.

Fetal cardiac cine imaging using highly accelerated dynamic MRI with retrospective motion correction and outlier rejection

PURPOSE

Development of a MRI acquisition and reconstruction strategy to depict fetal cardiac anatomy in the presence of maternal and fetal motion.

METHODS

The proposed strategy involves i) acquisition and reconstruction of highly accelerated dynamic MRI, followed by image-based ii) cardiac synchronization, iii) motion correction, iv) outlier rejection, and finally v) cardiac cine reconstruction. Postprocessing entirely was automated, aside from a user-defined region of interest delineating the fetal heart. The method was evaluated in 30 mid- to late gestational age singleton pregnancies scanned without maternal breath-hold.

RESULTS

The combination of complementary acquisition/reconstruction and correction/rejection steps in the pipeline served to improve the quality of the reconstructed 2D cine images, resulting in increased visibility of small, dynamic anatomical features. Artifact-free cine images successfully were produced in 36 of 39 acquired data sets; prolonged general fetal movements precluded processing of the remaining three data sets.

CONCLUSIONS

The proposed method shows promise as a motion-tolerant framework to enable further detail in MRI studies of the fetal heart and great vessels. Processing data in image-space allowed for spatial and temporal operations to be applied to the fetal heart in isolation, separate from extraneous changes elsewhere in the field of view. Magn Reson Med 79:327-338, 2018. © 2017 The Authors Magnetic Resonance in Medicine published by Wiley Periodicals, Inc. on behalf of International Society for Magnetic Resonance in Medicine. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Prospective cardiac motion self-gating

BACKGROUND

To develop a prospective cardiac motion self-gating method that provides robust and accurate cardiac triggers in real time.

METHODS

The proposed self-gating method consists of an "imaging mode" that acquires the k-space segments and a "self-gating mode" that captures the cardiac motion by repeatedly sampling the k-space centerline. A training based principal component analysis algorithm is utilized to process the self-gating data where the projection onto the first principal component was used as the self-gating signal. Retrospective studies using a sequence with self-gating mode only was performed on 8 healthy subjects to validate the accuracy and reliability of the self-gating triggers. Prospective studies using both ECG-gated and self-gated cardiac CINE sequences were conducted on 6 healthy subjects to compare the image quality.

RESULTS

Using the ECG as the reference, the proposed method was able to detect self-gating triggers within ±10 ms accuracy on all 8 subjects in the retrospective study. The prospectively self-gated CINE sequence successfully detected 100% of the cardiac triggers and provided excellent CINE image quality without using ECG signals.

CONCLUSIONS

The proposed cardiac self-gating method is a robust and accurate alternative to conventional ECG-based gating method for a number of cardiac MRI applications.

Motion compensated cine CMR of the fetal heart using radial undersampling and compressed sensing

BACKGROUND

To develop and evaluate a reconstruction framework for high resolution time-resolved CMR of the fetal heart in the presence of motion.

METHODS

Data were acquired using a golden angle radial trajectory in seven fetal subjects and reconstructed as real-time images to detect fetal movement. Data acquired during through-plane motion were discarded whereas in-plane motion was corrected. A fetal cardiac gating signal was extracted to sort the corrected data by cardiac phase, allowing reconstruction of cine images. The quality of motion corrected images and the effect of data undersampling were quantified using separate expressions for spatial blur and image error.

RESULTS

Motion corrected reordered cine reconstructions (127 slices) showed improved image quality relative to both uncorrected cines and corresponding real-time images across a range of root-mean-squared (RMS) displacements (0.3-3.7 mm) and fetal heart rates (119-176 bpm). The relative spatial blur between cines with and without motion correction increased with in-plane RMS displacement leading to an effective decrease in the effective spatial resolution for images without motion correction. Image error between undersampled and reference images was less than 10% for reconstructions using 750 or more spokes, yielding a minimum acceptable scan time of approximately 4 s/slice during quiescent through plane motion.

CONCLUSIONS

By rejecting data corrupted by through-plane motion, and correcting data corrupted by in-plane translation, the proposed reconstruction framework accounts for common sources of motion artifact (gross fetal movement, maternal respiration, fetal cardiac contraction) to produce high quality images of the fetal heart.

Self-gated fetal cardiac MRI with tiny golden angle iGRASP: A feasibility study

PURPOSE

To develop and assess a technique for self-gated fetal cardiac cine magnetic resonance imaging (MRI) using tiny golden angle radial sampling combined with iGRASP (iterative Golden-angle RAdial Sparse Parallel) for accelerated acquisition based on parallel imaging and compressed sensing.

MATERIALS AND METHODS

Fetal cardiac data were acquired from five volunteers in gestational week 29-37 at 1.5T using tiny golden angles for eddy currents reduction. The acquired multicoil radial projections were input to a principal component analysis-based compression stage. The cardiac self-gating (CSG) signal for cardiac gating was extracted from the acquired radial projections and the iGRASP reconstruction procedure was applied. In all acquisitions, a total of 4000 radial spokes were acquired within a breath-hold of less than 15 seconds using a balanced steady-state free precession pulse sequence. The images were qualitatively compared by two independent observers (on a scale of 1-4) to a single midventricular cine image from metric optimized gating (MOG) and real-time acquisitions.

RESULTS

For iGRASP and MOG images, good overall image quality (2.8 ± 0.4 and 2.6 ± 1.3, respectively, for observer 1; 3.6 ± 0.5 and 3.4 ± 0.9, respectively, for observer 2) and cardiac diagnostic quality (3.8 ± 0.4 and 3.4 ± 0.9, respectively, for observer 1; 3.6 ± 0.5 and 3.6 ± 0.9, respectively, for observer 2) were obtained, with visualized myocardial thickening over the cardiac cycle and well-defined myocardial borders to ventricular lumen and liver/lung tissue. For iGRASP, MOG, and real time, left ventricular lumen diameter (14.1 ± 2.2 mm, 14.2 ± 1.9 mm, 14.7 ± 1.1 mm, respectively) and wall thickness (2.7 ± 0.3 mm, 2.6 ± 0.3 mm, 3.0 ± 0.4, respectively) showed agreement and no statistically significant difference was found (all P > 0.05). Images with iGRASP tended to have higher overall image quality scores compared with MOG and particularly real-time images, albeit not statistically significant in this feasibility study (P > 0.99 and P = 0.12, respectively).

CONCLUSION

Fetal cardiac cine MRI can be performed with iGRASP using tiny golden angles and CSG. Comparison with other fetal cardiac cine MRI methods showed that the proposed method produces high-quality fetal cardiac reconstructions.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:207-217.

Cardiac image modelling: Breadth and depth in heart disease

With the advent of large-scale imaging studies and big health data, and the corresponding growth in analytics, machine learning and computational image analysis methods, there are now exciting opportunities for deepening our understanding of the mechanisms and characteristics of heart disease. Two emerging fields are computational analysis of cardiac remodelling (shape and motion changes due to disease) and computational analysis of physiology and mechanics to estimate biophysical properties from non-invasive imaging. Many large cohort studies now underway around the world have been specifically designed based on non-invasive imaging technologies in order to gain new information about the development of heart disease from asymptomatic to clinical manifestations. These give an unprecedented breadth to the quantification of population variation and disease development. Also, for the individual patient, it is now possible to determine biophysical properties of myocardial tissue in health and disease by interpreting detailed imaging data using computational modelling. For these population and patient-specific computational modelling methods to develop further, we need open benchmarks for algorithm comparison and validation, open sharing of data and algorithms, and demonstration of clinical efficacy in patient management and care. The combination of population and patient-specific modelling will give new insights into the mechanisms of cardiac disease, in particular the development of heart failure, congenital heart disease, myocardial infarction, contractile dysfunction and diastolic dysfunction.

Accelerated MRI of the fetal heart using compressed sensing and metric optimized gating

PURPOSE

To develop and validate a method for accelerated time-resolved imaging of the fetal heart using a combination of compressed sensing (CS) and metric optimized gating (MOG).

THEORY AND METHODS

Joint optimization of CS and MOG reconstructions was used to suppress competing artifact from random undersampling and ungated cardiac motion. Retrospectively and prospectively undersampled adult and fetal data were used to validate the proposed reconstruction algorithm qualitatively based on visual assessment, and quantitatively based on reconstruction error, blur, and MOG timing error.

RESULTS

Excellent agreement was observed between the fully sampled and retrospectively undersampled reconstructions, up to an undersampling factor of four. Visually, differences between ECG and MOG reconstructions of adult data were negligible. This was consistent with quantitative comparisons of reconstruction error (RMSE_ECG  = 0.07-0.13; RMSE_MOG  = 0.08-0.13), and image blur (B_ECG  = 1.03-1.20; B_MOG  = 1.03-1.20). The calculated MOG timing error (2-42 ms) was comparable to the acquired temporal resolution (∼60 ms). Quantitative evaluation of retrospectively undersampled (R = 2-8) fetal data (RMSE_MOG  = 0.06-0.12; B_MOG  = 1.04-1.27) was comparable to the adult volunteer results.

CONCLUSION

CS-MOG for dynamic imaging of the fetal heart was developed and validated. Using CS-MOG, images were obtained up to four times faster than conventional acquisitions. Magn Reson Med 77:2125-2135, 2017. © 2016 International Society for Magnetic Resonance in Medicine.

Diffusion MRI tractography of the developing human fetal heart

Objective

Human myocardium has a complex and anisotropic 3D fiber pattern. It remains unknown, however, when in fetal life this anisotropic pattern develops and whether the human heart is structurally fully mature at birth. We aimed here to use diffusion tensor MRI (DTI) tractography to characterize the evolution of fiber architecture in the developing human fetal heart.

Methods

Human fetal hearts (n = 5) between 10–19 weeks of gestation were studied. The heart from a 6-day old neonate and an adult human heart served as controls. The degree of myocardial anisotropy was measured by calculating the fractional anisotropy (FA) index. In addition, fiber tracts were created by numerically integrating the primary eigenvector field in the heart into coherent streamlines.

Results

At 10–14 weeks the fetal hearts were highly isotropic and few tracts could be resolved. Between 14–19 weeks the anisotropy seen in the adult heart began to develop. Coherent fiber tracts were well resolved by 19 weeks. The 19-week myocardium, however, remained weakly anisotropic with a low FA and no discernable sheet structure.

Conclusions

The human fetal heart remains highly isotropic until 14–19 weeks, at which time cardiomyocytes self-align into coherent tracts. This process lags 2–3 months behind the onset of cardiac contraction, which may be a prerequisite for cardiomyocyte maturation and alignment. No evidence of a connective tissue scaffold guiding this process could be identified by DTI. Maturation of the heart’s sheet structure occurs late in gestation and evolves further after birth.