Effect of fetal magnetic resonance imaging on fetal heart rate patterns

Computerized Analysis of Antepartum Cardiotocography: A Review

Cardiotocography measures the human fetal heart rate and uterine activity using ultrasound. While it has been a mainstay in antepartum care since the 1960s, cardiotocograms consist of complex signals that have proven difficult for clinicians to interpret accurately and as such clinical inference is often difficult and unreliable. Previous attempts at codifying approaches to analyzing the features within these signals have failed to demonstrate reliability or gain sufficient traction. Since the early 1990s, the Dawes-Redman system of automated computer analysis of cardiotocography signals has enabled robust analysis of cardiotocographic signal features, employing empirically-derived criteria for assessing fetal wellbeing in the antepartum. Over the past 30 years, the Dawes-Redman system has been iteratively updated, now incorporating analyses from over 100,000 pregnancies. In this review, we examine the history of cardiotocography, signal processing methodologies and feature identification, the development of the Dawes-Redman system, and its clinical applications.

Fetal Echoplanar Imaging: Promises and Challenges

Fetal magnetic resonance imaging (MRI) has been gaining increasing interest in both clinical radiology and research. Echoplanar imaging (EPI) offers a unique potential, as it can be used to acquire images very fast. It can be used to freeze motion, or to get multiple images with various contrast mechanisms that allow studying the microstructure and function of the fetal brain and body organs. In this article, we discuss the current clinical and research applications of fetal EPI. This includes T2*-weighted imaging to better identify blood products and vessels, using diffusion-weighted MRI to investigate connections of the developing brain and using functional MRI (fMRI) to identify the functional networks of the developing brain. EPI can also be used as an alternative structural sequence when banding or standing wave artifacts adversely affect the mainstream sequences used routinely in structural fetal MRI. We also discuss the challenges with EPI acquisitions, and potential solutions. As EPI acquisitions are inherently sensitive to susceptibility artifacts, geometric distortions limit the use of high-resolution EPI acquisitions. Also, interslice motion and transmit and receive field inhomogeneities may create significant artifacts in fetal EPI. We conclude by discussing promising research directions to overcome these challenges to improve the use of EPI in clinical and research applications.

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.

Functional Connectivity of the Human Brain in Utero

The brain is subject to dramatic developmental processes during the prenatal period. Nevertheless, information about the development of functional brain networks during gestation is scarce. Until recently it has not been possible to probe function in the living human fetal brain. Advances in functional MRI have changed the paradigm, making it possible to measure spontaneous activity in the fetal brain and to cross-correlate functional signals to attain information about neural connectional architecture across human gestation. We summarize the earliest MRI studies of fetal neural functional connectivity and highlight unique challenges and limitations inherent in the technique. In addition, we discuss future directions to unlock the potential of fetal brain functional MRI research.

Effects of Gestational Magnetic Resonance Imaging on Methylation Status of Leptin Promoter in the Placenta and Cord Blood

Over the past two decades, magnetic resonance imaging (MRI) has been widely used for diagnosis in gestational women. Though it has several advantages, animal and human studies on the safety of MRI for the fetus remain inconclusive. Epigenetic modifications, which are crucial for cellular functioning, are prone to being affected by environmental changes. Therefore, we hypothesized that MRI during gestation may cause epigenetic modification alterations. Here, we investigated DNA methylation patterns of leptin promoter in the placenta and cord blood of women exposed to MRI during gestation. Results showed that average methylation levels of leptin in the placenta and cord blood were not affected by MRI. We also found that the methylation levels in the placenta and cord blood were not affected by different magnetic fields (1.5T and 3.0T MRI). However, if pregnant women were exposed to MRI at 15 to 20 weeks of gestation, the methylation level of leptin in cord blood was visibly lower than that of pregnant women exposed to MRI after 20-weeks of gestation (P = 0.037). mRNA expression level of leptin in cord blood was also altered, though mRNA expression of leptin in the placenta was not significantly affected. Therefore, we concluded that gestational MRI may not have major effects on the methylation level of leptin in cord blood and the placenta except for MRI applied before 20 weeks of gestation.

Fetal magnetic resonance imaging: exposure times and functional outcomes at preschool age

BACKGROUND

Fetal magnetic resonance imaging (MRI) has been routinely used as a noninvasive diagnostic tool for more than a decade; however, there is a paucity of follow-up studies examining the effects of prenatal exposure to 1.5-T MRI on developmental outcome.

OBJECTIVE

The objective of this study was to assess the safety of 1.5-T fetal MRI by evaluating functional outcomes of preschool children who were exposed in utero.

MATERIALS AND METHODS

In the context of a prospective observational study, healthy pregnant women underwent a 1.5-T MRI study using single-shot fast spin echo (SSFSE) sequences during the second or third trimester of pregnancy. The study was approved by the institutional review board at our institution, and written informed consent was obtained from all study participants. MRI scanning times were recorded, and prenatal/postnatal clinical data were collected prospectively. Functional outcomes were assessed using the Vineland Adaptive Behavior Scale (VABS), a widely used, norm-referenced and psychometrically sound functional assessment.

RESULTS

We studied 72 healthy pregnant women, who underwent fetal MRI at a mean gestational age of 30.5 ± 3.1 weeks. The cohort of fetuses was composed of 43% females, and 18 fetuses were scanned during the second trimester. All fetuses were born at term with appropriate birth weights (3.54 ± 0.5 kg) for gestational age. Mean age at follow-up testing was 24.5 ± 6.7 months. All children had age-appropriate scores in the communication, daily living, socialization and motor skills subdomains of the VABS (z-scores, P > 0.05). Furthermore, all children passed their newborn otoacoustic emission test and had normal hearing at preschool age. MRI study duration and exposure time to radio frequency waves and SSFSE sequences were not associated with adverse functional outcomes or hearing impairment.

CONCLUSION

Prenatal exposure to 1.5-T MRI during the second or third trimester of pregnancy in a cohort of healthy fetuses is not associated with disturbances in functional outcomes or hearing impairment at preschool age.

The developing role of fetal magnetic resonance imaging in the diagnosis of congenital cardiac anomalies: A systematic review

Advances in the fetal magnetic resonance imaging (MRI) over the last few years have resulted in the exploring the use of fetal MRI to detect congenital cardiac anomalies. Early detection of congenital cardiac anomalies can help more appropriately manage the infant's delivery and neonatal management. MRI offers anatomical and functional studies and is a safe adjunct that can help more fully understand a fetus' cardiac anatomy. It is important for the obstetricians and pediatric cardiologists to be aware of the recent advancements in fetal MRI and it`s potential utility in diagnosing congenital cardiac anomalies.

Human birth observed in real-time open magnetic resonance imaging

OBJECTIVE

Knowledge about the mechanism of labor is based on assumptions and radiographic studies performed decades ago. The goal of this study was to describe the relationship between the fetus and the pelvis as the fetus travels through the birth canal, using an open magnetic resonance imaging (MRI) scanner.

STUDY DESIGN

The design of the study used a real-time MRI series during delivery of the fetal head.

RESULTS

Delivery occurred by progressive head extension. However, extension was a very late movement that was observed when the occiput was in close contact with the inferior margin of the symphysis pubis, occurring simultaneously with gliding downward of the fetal head.

CONCLUSION

This observational study shows, for the first time, that birth can be analyzed with real-time MRI. MRI technology allows assessment of maternal and fetal anatomy during labor and delivery.

The current state and future of fetal imaging

Fetal magnetic resonance imaging (MRI) may add important diagnostic information to prenatal sonography and has the power to confirm or change decisions at critical points in clinical care. Recent studies have shown MRI to be a critical clinical adjunct in the evaluation of the developing central nervous system (CNS), especially at early gestational ages, and MRI has been used in three significant ways: (1) for the quantification of brain growth and structural abnormalities using biometry, (2) for the qualitative evaluation of CNS microstructure, and (3) for the qualitative assessment of dynamic fetal movements in utero.

The emerging role of functional MRI for evaluating fetal brain activity

Although functional magnetic resonance imaging is a technique that is widely used in adult populations, its use within a fetal environment has been extremely limited. Problems associated with movement and technical scanning issues have limited its effectiveness in providing reliable and spatially accurate details of fetal brain activity. However, initial research has indicated that it is a viable tool for assessing functional maturation in the fetus, and recent advances in echo-planar imaging sequences on the abdomen at 3-T provide the potential for more reliable activation detection and higher resolution spatial information. If the technique can be further developed such that a similar reliability in activity patterns is observed as in conventional functional MRI, then fetal functional MRI could offer a useful contribution at a clinical level as well as at a research one in the assessment of brain development and maturation.

MR imaging methods for assessing fetal brain development

Fetal magnetic resonance imaging provides an ideal tool for investigating growth and development of the brain in vivo. Current imaging methods have been hampered by fetal motion but recent advances in image acquisition can produce high signal to noise, high resolution 3-dimensional datasets suitable for objective quantification by state of the art post acquisition computer programs. Continuing development of imaging techniques will allow a unique insight into the developing brain, more specifically process of cell migration, axonal pathway formation, and cortical maturation. Accurate quantification of these developmental processes in the normal fetus will allow us to identify subtle deviations from normal during the second and third trimester of pregnancy either in the compromised fetus or in infants born prematurely.

Fetal Magnetic Resonance Imaging as a Complement to Fetal Ultrasonography

Ultrasonography is the screening method of choice for the evaluation of the fetus. It is safe, inexpensive, and easily performed. However, it is operator dependent, and evaluation may be limited because of fetal position, maternal obesity, overlying bone, and/or oligohydramnios. Magnetic resonance imaging is an alternative modality that uses no ionizing radiation, has excellent tissue contrast and a large field of view, is not limited by obesity or overlying bone, and can image the fetus in multiple planes, no matter the fetal lie. Faster scanning techniques allow studies to be performed without sedation in the second and third trimester with minimal motion artifact.

A review of the current use of magnetic resonance imaging in pregnancy and safety implications for the fetus

This paper presents an overview of the application of and risks of exposure to Magnetic Resonance Imaging (MRI) in pregnancy. It reviews the risks to the fetus by considering the hazards in terms of the three main components of an MRI system. These are the static magnetic field, the time-varying magnetic gradient fields and the pulsed radio frequency fields. The hazards discussed are biological effects, miscarriage, heating effects and acoustic noise exposure. This paper also presents a survey of MRI sites within the United Kingdom to ascertain the extent of MRI usage in pregnancy. To validate the situation of MRI in pregnancy a survey was sent to 352 MR units throughout the United Kingdom. The questions were grouped to assess (a) maternal MRI diagnosis (b) fetal MRI and (c) work practices for pregnant MRI staff. The results showed that 91% of sites were imaging pregnant women in need of diagnosis in the second and third trimester. This paper highlights that MRI can add information for fetal central nervous system abnormalities identified by ultrasound screening, however within the UK direct fetal imaging was only performed in 8% of sites. This paper indicates the need for research to be undertaken for specific MRI clinical conditions. It also advises that risk assessment for pregnant staff working in MRI is performed, and that there is a clear need for further research into the effects of MRI in pregnancy as there is a need for clear authoritive advice.

Effect of electromagnetic field emitted by cellular phones on fetal heart rate patterns

The study was planned to determine the effects of electromagnetic fields produced by cellular phones on baseline fetal heart rate, acceleration and deceleration. Forty pregnant women undergoing non-stress test were admitted to the study. Non-stress test was obtained while the subjects were holding the CP on stand by mode and on dialing mode, each for 5 min. Similar recordings were taken while there were no phones around for 10 min. Electromagnetic fields produced by cellular phones do not cause any demonstrable affect in fetal heart rate, acceleration and deceleration.

Original report. Fetal cardiographic monitoring during 1.5-T MR imaging

OBJECTIVE

The aim of this report was to determine the feasibility of fetal cardiotocography during MR imaging and the safety of 1.5-T MR imaging on the basis of fetal heart activity and fetal movements.

CONCLUSION

Fetal cardiotocography is feasible during MR imaging using modified standard equipment. The use of 1.5-T MR imaging appears to be safe and to have no negative short-term effects on the heart rate or movement incidence of healthy third-trimester fetuses under our experimental conditions.

The fetal safety and clinical efficacy of gastrointestinal endoscopy during pregnancy

More than 12,000 pregnant patients in the United States per annum have conditions that are normally evaluated by EGD. More than 6000 pregnant patients in the United States per annum have conditions that are normally evaluated by sigmoidoscopy or colonoscopy. About one thousand more have symptomatic choledocholithiasis during pregnancy, which is a strong indication for endoscopic sphincterotomy in nonpregnant patients. Endoscopy during pregnancy raises the unique issue of fetal safety. Endoscopic medications comprise a significant component of fetal endoscopic risks. Safety of EGD during pregnancy has been examined in a case-controlled study of 83 patients, a mailed survey of 73 patients, and 28 case reports. Safety of sigmoidoscopy during pregnancy has been examined in a case-controlled study of 46 patients, a mailed survey of 13 patients, and 10 case reports. Safety of therapeutic ERCP during pregnancy has been analyzed in studies of 23, 10, 6, and 5 patients, and in 32 case reports. These studies suggested that EGD, sigmoidoscopy, and ERCP should be performed when strongly indicated: EGD for significant upper gastrointestinal bleeding, sigmoidoscopy for nonhemorrhoidal rectal bleeding, and ERCP for symptomatic choledocholithiasis when sphincterotomy is contemplated. PEG and colonoscopy are currently considered experimental during pregnancy because of insufficient data on fetal safety. Several cases of PEG and colonoscopy were successfully performed during pregnancy. Performance of endoscopy during pregnancy should increase with further technical refinements, and greater awareness of procedure safety.

In vivo diffusion measurements as an indication of fetal lung maturation using echo planar imaging at 0.5T

The aim of this study was twofold: First, to establish the normal range of fetal lung diffusion values measured during healthy pregnancy; and second, to determine whether fetal lung diffusion could be used as an indication of fetal lung maturity. The apparent diffusion coefficient (ADC), averaged over all 26 subjects with an average gestational age of 29 +/- 6 weeks (mean +/- sd), was found to be 2.0 +/- 0.6 x 10(-9) m(2)/sec (mean +/- sd), but a trend was found indicating that ADC increased with gestational age at the rate of 0.07 x 10(-9) m(2)/sec per week (P = 4 x 10(-5)). To determine the usefulness of this data in predicting lung maturity, a simple three-compartment model was proposed which was comprised of intra-lung amniotic fluid, intra-tissue water, and vascular blood. The relative proportions of each compartment were taken from the literature, and exchange between the compartments was assumed to be minimal. This model predicted the in vivo data reasonably well, and indicated that MR measurements of fetal lung diffusion are a marker for the degree of vascularization of the terminal tubules. Magn Reson Med 45:247-253, 2001.