Magnetic resonance imaging of the fetus

Review of the Imaging Modalities in the Gynecological Neoplasms During Pregnancy

The aim of this review is to provide an update on the imaging triage, safety considerations, and cancer-imaging features of common and uncommon gynecological tumors during pregnancy. Clinical examination can be inconclusive, especially for the evaluation of intra-abdominal diseases since symptoms related to cancer such as fatigue, vomiting, or nausea overlap with common pregnancy-associated symptoms. Delayed pregnancy, advanced maternal age, and improvements in diagnostic imaging in developed countries have increased the incidence of cancer diagnosis in gravid populations. Non-invasive diagnostic imaging has a central role in the initial diagnosis and management of pregnancy tumors. Sonography is the first modality for the abdominal evaluation of gravid patients because it is widely available, low cost, and lacks adverse effects on the mother and fetus. MR imaging is considered the imaging modality of choice for diagnosis and staging of gynecologic cancer during pregnancy due to its larger imaging field of view, better reproducibility, and excellent soft tissue contrast. Moreover, whole-body diffusion-weighted imaging (DWI) has been proposed for the oncologic staging of pregnant patients; however, large prospective studies are needed to support its clinical implementation. Gynecological cancer diagnosed during pregnancy requires accurate diagnosis and staging to determine optimal treatment based on gestational age, and therefore multidisciplinary team collaboration is pivotal.

Safety of Magnetic Resonance Imaging in Pregnancy

Magnetic resonance imaging is being increasingly used to diagnose and follow up a variety of medical conditions in pregnancy, both for maternal and fetal indications. However, limited data regarding its safe use in pregnancy may be a source of anxiety and avoidance for both patients and their healthcare providers. In this review, we critically discuss the main safety concerns of Magnetic Resonance Imaging (MRI) in pregnancy including energy deposition, acoustic noise, and use of contrast agents, supported by data from animal and human studies. Use of maternal sedatives and concerns related to occupational exposure in pregnant personnel are also addressed. Exposure to gadolinium-based contrast agents and sedation for MRI during pregnancy should be avoided whenever feasible.

Fet-Net Algorithm for Automatic Detection of Fetal Orientation in Fetal MRI

Identifying fetal orientation is essential for determining the mode of delivery and for sequence planning in fetal magnetic resonance imaging (MRI). This manuscript describes a deep learning algorithm named Fet-Net, composed of convolutional neural networks (CNNs), which allows for the automatic detection of fetal orientation from a two-dimensional (2D) MRI slice. The architecture consists of four convolutional layers, which feed into a simple artificial neural network. Compared with eleven other prominent CNNs (different versions of ResNet, VGG, Xception, and Inception), Fet-Net has fewer architectural layers and parameters. From 144 3D MRI datasets indicative of vertex, breech, oblique and transverse fetal orientations, 6120 2D MRI slices were extracted to train, validate and test Fet-Net. Despite its simpler architecture, Fet-Net demonstrated an average accuracy and F1 score of 97.68% and a loss of 0.06828 on the 6120 2D MRI slices during a 5-fold cross-validation experiment. This architecture outperformed all eleven prominent architectures (p < 0.05). An ablation study proved each component's statistical significance and contribution to Fet-Net's performance. Fet-Net demonstrated robustness in classification accuracy even when noise was introduced to the images, outperforming eight of the 11 prominent architectures. Fet-Net's ability to automatically detect fetal orientation can profoundly decrease the time required for fetal MRI acquisition.

An ode to fetal, infant, and toddler neuroimaging: Chronicling early clinical to research applications with MRI, and an introduction to an academic society connecting the field

Fetal, infant, and toddler neuroimaging is commonly thought of as a development of modern times (last two decades). Yet, this field mobilized shortly after the discovery and implementation of MRI technology. Here, we provide a review of the parallel advancements in the fields of fetal, infant, and toddler neuroimaging, noting the shifts from clinical to research use, and the ongoing challenges in this fast-growing field. We chronicle the pioneering science of fetal, infant, and toddler neuroimaging, highlighting the early studies that set the stage for modern advances in imaging during this developmental period, and the large-scale multi-site efforts which ultimately led to the explosion of interest in the field today. Lastly, we consider the growing pains of the community and the need for an academic society that bridges expertise in developmental neuroscience, clinical science, as well as computational and biomedical engineering, to ensure special consideration of the vulnerable mother-offspring dyad (especially during pregnancy), data quality, and image processing tools that are created, rather than adapted, for the young brain.

Methods for Monitoring Risk of Hypoxic Damage in Fetal and Neonatal Brains: A Review

Fetal, perinatal, and neonatal asphyxia are vital health issues for the most vulnerable groups in human beings, including fetuses, newborns, and infants. Severe reduction in oxygen and blood supply to the fetal brain can cause hypoxic-ischemic encephalopathy (HIE), leading to long-term neurological disorders, including mental impairment and cerebral palsy. Such neurological disorders are major healthcare concerns. Therefore, there has been a continuous effort to develop clinically useful diagnostic tools for accurately and quantitatively measuring and monitoring blood and oxygen supply to the fetal and neonatal brain to avoid severe consequences of asphyxia HIE and neonatal encephalopathy. Major diagnostic technologies used for this purpose include fetal heart rate monitoring, fetus scalp blood sampling, ultrasound imaging, magnetic resonance imaging, X-ray computed tomography, and nuclear medicine. In addition, given the limitations and shortcomings of traditional diagnostic methods, emerging technologies such as near-infrared spectroscopy and photoacoustic imaging have also been introduced as stand-alone or complementary solutions to address this critical gap in fetal and neonatal care. This review provides a thorough overview of the traditional and emerging technologies for monitoring fetal and neonatal brain oxygenation status and describes their clinical utility, performance, advantages, and disadvantages.

Canadian Association of Radiologists Recommendations for the Safe Use of MRI During Pregnancy

The use of magnetic resonance imaging (MRI) during pregnancy is associated with concerns among patients and health professionals with regards to fetal safety. In this work, the Canadian Association of Radiologists (CAR) Working Group on MRI in Pregnancy presents recommendations for the use of MRI in pregnancy, derived from literature review as well as expert panel opinions and discussions. The working group, which consists of academic subspecialty radiologists and obstetrician-gynaecologists, aimed to provide updated, evidence-based recommendations addressing safety domains related to energy deposition, acoustic noise, and gadolinium-based contrast agent use based on magnetic field strength (1.5T and 3T) and trimester scanned, in addition to the effects of sedative use and occupational exposure.

Fetal Brain Biometry: Is there an Agreement among Ultrasound, MRI and the Measurements at Birth?

PURPOSE

Measurement of the fetal brain can be achieved by different modalities, we aimed to assess the agreement between these methods and the head circumference at birth.

METHODS

A retrospective study conducted between 2011-2018 at a tertiary referral medical center. Sonographic head circumference (HC), 2D MRI bi-parietal diameter (BPD) and occipito-frontal diameter (OFD), 3D MRI supra-tentorial volume (STV), and head circumference (HC) at birth were measured and converted into centiles according to gestational age. Spearman's rank correlation coefficient was used to assess the correlation between the modalities.

RESULTS

A total of 88 fetuses were included. Mean gestational age at the time of fetal US and brain MRI acquisition were 34.4 ± 2.8 and 34.6 ± 2.6 weeks, respectively. A correlation was found between prenatal sonographic HC and the 3D MRI STV centiles (Rs = 0.859, p < 0.001), the BPD in 2D MRI (Rs = 0.813, p < 0.001), and the OFD in 2D MRI (Rs = 0.840, p < 0.001). Sonographic HC, OFD on 2D MRI, and STV on 3D MRI were all found to be correlated with the HC at birth (Rs = 0.865, p < 0.001; Rs 0.816, p < 0.001; Rs = 0.825, p < 0.001, respectively).

CONCLUSIONS

There is a statistically significant agreement among the different prenatal clinically used modalities for measuring fetal brain and the head circumference at birth, however, this correlation is not perfect. Further study is needed to investigate the long-term prognosis of these fetuses.

A new approach to automatic fetal brain extraction from MRI using a variational level set method

BACKGROUND AND PURPOSE

Appropriate images extracted from the MRI of mothers' wombs can be of great help in the medical diagnosis of fetal abnormalities. As maternal tissue may appear in such images, affecting visualization of myelination of the fetal brain, it is not possible to use methods routinely used for extraction of adult brains for fetal brains. The aim of the present study was to use a variational level set approach to extract fetal brain from T2-weighted MR images of the womb.

METHODS

Coronal T2-weighted images were acquired using fast MRI protocols (to avoid artifacts). The database includes 105 MR images from eight subjects. After correcting the inhomogeneity of the images, the fetal eyes were located, and from that information, the location of the fetus brain was automatically determined. Then, the variational level set was used for fetus brain extraction. The results were analyzed by a clinical specialist (radiologist) and the similarity (Dice and Jaccard coefficients), sensitivity and specificity were calculated.

RESULTS AND CONCLUSIONS

The means of the statistical analysis for the Dice and Jaccard coefficients, sensitivity and specificity, were 99.56%, 96.89%, 95.71%, and 97.96%, respectively. Thus, extraction of fetal brain from MR images was confirmed, both statistically and visually through cross-validation.

Propaedeutic, Basis for Constitution, and Statute of the Bank of Human Embryonic and Fetal Cells

Article without abstract

Magnetic resonance imaging of the fetal brain at 3 Tesla: Preliminary experience from a single series

To report our preliminary experience with cerebral fetal magnetic resonance imaging (MRI) with a 3 Tesla (3T) scanner. We assessed feasibility, time of acquisition, and possibility to establish a diagnosis.Fifty-nine pregnant women had fetal MRI performed during the third trimester of pregnancy due to clinical or sonography concern of a central nervous system anomaly. No fetal or maternal sedation was used. The MRI protocol consisted of T2 turbo-spin-echo images in 3 planes of space. No T1-weighted images were performed. All images were analyzed by 2 pediatric neuroradiologists, who evaluated spatial resolution, artifacts, time of acquisition, and possibility to establish a diagnosis suspected by sonography.Examinations were performed safely for all patients. The images required longer time of acquisition (approximately 75 seconds for each plane in the space). The specific absorption rate was not exceeded in any fetus. Cerebral fetal MRI was normal in 22 cases. The spectrum of diagnostics included isolated ventriculomegaly, posterior fossa malformation, corpus callosum malformation, gyration anomalies, craniosynostosis, tuberous sclerosis, microcephaly, external hydrocephaly, midline arachnoid cyst, cerebral lesions, and persistent hyperplastic primitive vitreous.In our series, 3 T MRI of fetal brain was feasible and able to establish a diagnosis but required longer time of acquisition.

High resolution post-mortem MRI of non-fixed in situ foetal brain in the second trimester of gestation: Normal foetal brain development

PURPOSE

To describe normal foetal brain development with high resolution post-mortem MRI (PMMRI) of non-fixed foetal brains.

METHODS

We retrospectively collected PMMRIs of foetuses without intracranial abnormalities and chromosomal aberrations studied after a termination of pregnancy due to extracranial abnormalities or after a spontaneous intrauterine death. PMMRIs were performed on a 3-T scanner without any fixation and without removing the brain from the skull. All PMMRIs were evaluated in consensus by two neuroradiologists.

RESULTS

Our analysis included ten PMMRIs (median gestational age (GA): 21 weeks; range: 17-28 weeks). At 19 and 20 weeks of GA, the corticospinal tracts are recognisable in the medulla oblongata, becoming less visible from 21 weeks. Prior to 20 weeks the posterior limb of the internal capsule (PLIC) is more hypointense than surrounding deep grey nuclei; starting from 21 weeks the PLIC becomes isointense, and is hyperintense at 28 weeks. From 19-22 weeks, the cerebral hemispheres show transient layers: marginal zone, cortical plate, subplate, and intermediate, subventricular and germinal zones.

CONCLUSION

PMMRI of non-fixed in situ foetal brains preserves the natural tissue contrast and skull integrity. We assessed foetal brain development in a small cohort of foetuses, focusing on 19-22 weeks of gestation.

KEY POINTS

• Post-mortem magnetic resonance imaging (PMMRI) of non-fixed head is feasible. • PMMRI of unfixed in situ foetal brains preserves the natural tissue contrast. • PMMRI provide a good depiction of the normal foetal brain development. • PMMRI of unfixed in situ foetal brains preserves the skull integrity. • PMMRI pattern of foetal brain development at early gestational age is described.

Whole body MRI for systemic staging of breast cancer in pregnant women

When breast cancer is diagnosed during pregnancy, treatment should be as close; as possible to what is used in non-pregnant patients. This requires accurate local and systemic staging: ultrasound (US) is used for local staging and allows adequate evaluation of the liver and pelvis, but chest and bones cannot be explored and imaging techniques involving exposure to ionizing radiation would be needed. However, since imaging techniques involving ionizing radiation and the use of radionuclides should be limited, whole body magnetic resonance imaging (WB-MRI) without administration of contrast agent represents a very interesting alternative, but limited data is available. In this paper we describe the obstetrical and oncological outcome of 14 patients in whom breast cancer was diagnosed during the second or third trimester of pregnancy and that were staged using WB-MRI. Median age of the patient at diagnosis was 35 years (range 20-36), median gestational age at MRI was 30 weeks (range 13-32) and median age at delivery was 38 weeks (range 32-38). At birth, one new-born presented respiratory distress syndrome and one jaundice. We conclude that diffusion-weighted MRI is feasible accurate and safe for the mother and for the foetus. It may represent the staging technique of choice in pregnant women diagnosed with breast cancer after the first trimester of pregnancy.

MRI evaluation and safety in the developing brain

Magnetic resonance imaging (MRI) evaluation of the developing brain has dramatically increased over the last decade. Faster acquisitions and the development of advanced MRI sequences, such as magnetic resonance spectroscopy (MRS), diffusion tensor imaging (DTI), perfusion imaging, functional MR imaging (fMRI), and susceptibility-weighted imaging (SWI), as well as the use of higher magnetic field strengths has made MRI an invaluable tool for detailed evaluation of the developing brain. This article will provide an overview of the use and challenges associated with 1.5-T and 3-T static magnetic fields for evaluation of the developing brain. This review will also summarize the advantages, clinical challenges, and safety concerns specifically related to MRI in the fetus and newborn, including the implications of increased magnetic field strength, logistics related to transporting and monitoring of neonates during scanning, and sedation considerations, and a discussion of current technologies such as MRI conditional neonatal incubators and dedicated small-foot print neonatal intensive care unit (NICU) scanners.

Clinical Significance of Prenatal and Postnatal Heavily T2-Weighted Magnetic Resonance Images in Patients with Myelomeningocele

PURPOSE

To compare the utility and limitations of prenatal magnetic resonance (MR) imaging using half-Fourier acquisition single-shot turbo spin-echo (HASTE) with postnatal heavily T2-weighted imaging (hT2WI) for the evaluation of central nervous system abnormalities associated with myelomeningocele (MMC).

METHODS

Sixteen patients with MMC who had undergone pre- and postnatal MR imaging were included in this study. MR imaging, including HASTE, was undertaken in the 3rd trimester, and hT2WI was performed immediately after delivery. The precision with which each could distinguish MMC, hindbrain herniation and ventriculomegaly was compared retrospectively.

RESULTS

The skin defects and MMC sacs were clearly visible on prenatal HASTE images, although it was difficult to identify precisely the level of MMC compared with postnatal hT2WI, in which the detailed anatomical relationships of the spinal cord, neural placode and ventral nerve roots were evident in every case. Hindbrain herniation could be visualized on prenatal HASTE images, although its severity was difficult to evaluate because of the small size of the structures and neck flexion; again, the resolution was superior on postnatal hT2WI. For hydrocephalus, there were no significant differences in the diagnostic precision and ability to grade the severity between pre- and postnatal imaging.

CONCLUSION

Prenatal HASTE imaging permits the diagnosis and understanding of the gross anatomy of MMC and associated hindbrain herniation and ventriculomegaly, but postnatal hT2WI is superior for evaluating detailed anatomy.

The fundamentals of fetal MR imaging: Part 1

Congenital malformations detected in any fetal system using ultrasound may be further evaluated with magnetic resonance imaging (MRI) to improve counseling, to plan deliveries appropriately, and sometimes to enable fetal interventions. In this first half of a 2-part review, the history and safety factors regarding fetal MRI, as well as the practical aspects of image acquisition, are discussed. In addition, as central nervous system anomalies are most commonly and best evaluated using fetal MRI, challenging central nervous system anomalies, such as fetal ventriculomegaly, posterior anomalies, and neural tube defects, detected using prenatal ultrasound are also reviewed with a focus on the fundamental implications of these diagnoses.

Benefits and risks of MRI in pregnancy

Ultrasound remains the modality of choice in imaging the fetus due to its availability, safety, and low cost. With advances in technology, however, magnetic resonance imaging (MRI) has become an important adjuvant in the evaluation of the fetus. MRI is not limited by fetal lie, oligohydramnios, overlying bone, or obesity. MRI can image the fetus in any plane, providing a large field of view of the fetus and placenta with excellent soft tissue resolution of the brain, airway, lungs, and abdomen. Advanced techniques are being developed that provide volumetric data, spectroscopy, and functional images. MRI has its own set of challenges with a lack of consensus regarding its utility and safety. Artifact from the moving fetus and breathing mother limits the sequences available. While there is currently no evidence that fetal MRI produces harmful effects, long-term safety regarding radiofrequency fields and the loud acoustic environment continues to be studied. In this review, the benefits and potential risks of fetal MRI will be discussed.

Gynecologic malignancy in pregnancy

Gynecologic malignancy during pregnancy is a stressful problem. For the diagnosis and treatment of malignancy during pregnancy, a multidisciplinary approach is needed. Patients should be advised about the benefits and risk of treatment. When selecting a treatment for malignancy during pregnancy, the physiologic changes that occur with the pregnancy should be considered. Various diagnostic procedures that do not harm the fetus can be used. Laparoscopic surgery or laparotomy may be safely performed. The staging approach and treatment should be standard. Systemic chemotherapy during the first trimester should be delayed if possible. Radiation therapy should preferably start postpartum. Although delivery should be delayed preferably until after 35 weeks of gestation, termination of pregnancy may be considered when immediate treatment is required. Subsequent pregnancies do not increase the risk of malignancy recurrence.

Signal intensity changes of the fetal liver on MRI in-phase and out-of-phase sequence

OBJECTIVE

To study signal intensity (SI) of the fetal liver by MRI in-phase and out-of-phase over gestational age (GA).

METHODS

A total of 91 pregnant women from 19 to 38 gestational weeks were imaged using MRI. Liver-to-spleen SI ratios of the right and left fetal liver lobes on in-phase and out-of-phase were measured, calculated, and compared with each other. Curves of liver-to-spleen SI ratio of the right and left liver lobe were plotted by GA.

RESULTS

Liver-to-spleen SI ratio of the right lobe on in-phase was different from that of the left liver lobe (t = 3.95; p < 0.001). A statistically significant difference was also found for out-of-phase SI ratios (t = 3.69; p < 0.001). Curves of liver-to-spleen SI ratio of the fetal liver on in-phase and out-of-phase showed changes against GA.

CONCLUSION

Liver-to-spleen SI ratio is different between the right and left liver lobe, which probably results from the different blood supply. Curves of liver-to-spleen SI ratios between 19 to 38 gestational weeks reflect the changes of decreasing function of blood production by fetal liver. In-phase and out-of-phase may have clinical use in the early detection of disordered fetal growth and metabolism.

Prenatal magnetic resonance imaging (MRI) findings of a foregut duplication cyst of the tongue: value of real-time MRI evaluation of the fetal swallowing mechanism

Foregut duplication cysts of the oral cavity or lingual choristomas have a potential risk of airway obstruction. Two cases are reported that were initially detected by screening sonography. Further imaging with both static and real-time cine magnetic resonance imaging confirmed the lingual origin, relationship of the mass to fluid-filled spaces within the oral cavity, motion of the mass with the tongue during fetal swallowing, and airway patency. The additional information provided by magnetic resonance imaging aided in planning delivery and obviated the need for an ex utero intrapartum treatment procedure because airway patency was confirmed in both cases.

Digital atlas of fetal brain MRI

BACKGROUND

Fetal MRI can be performed in the second and third trimesters. During this time, the fetal brain undergoes profound structural changes. Interpretation of appropriate development might require comparison with normal age-based models. Consultation of a hard-copy atlas is limited by the inability to compare multiple ages simultaneously.

OBJECTIVE

To provide images of normal fetal brains from weeks 18 through 37 in a digital format that can be reviewed interactively. This will facilitate recognition of abnormal brain development.

MATERIALS AND METHODS

T2-W images for the atlas were obtained from fetal MR studies of normal brains scanned for other indications from 2005 to 2007. Images were oriented in standard axial, coronal and sagittal projections, with laterality established by situs. Gestational age was determined by last menstrual period, earliest US measurements and sonogram performed on the same day as the MR. The software program used for viewing the atlas, written in C#, permits linked scrolling and resizing the images. Simultaneous comparison of varying gestational ages is permissible.

RESULTS

Fetal brain images across gestational ages 18 to 37 weeks are provided as an interactive digital atlas and are available for free download from http://radiology.seattlechildrens.org/teaching/fetal_brain .

CONCLUSION

Improved interpretation of fetal brain abnormalities can be facilitated by the use of digital atlas cataloging of the normal changes throughout fetal development. Here we provide a description of the atlas and a discussion of normal fetal brain development.

MR imaging of the fetal brain

Fetal MRI is clinically performed to evaluate the brain in cases where an abnormality is detected by prenatal sonography. These most commonly include ventriculomegaly, abnormalities of the corpus callosum, and abnormalities of the posterior fossa. Fetal MRI is also increasingly performed to evaluate fetuses who have normal brain findings on prenatal sonogram but who are at increased risk for neurodevelopmental abnormalities, such as complicated monochorionic twin pregnancies. This paper will briefly discuss the common clinical conditions imaged by fetal MRI as well as recent advances in fetal MRI research.

MRI of the fetal central nervous system and body

MRI is being increasingly used to assess for fetal abnormalities. Although significant progress in the field of fetal MRI has occurred during the past 20 years, continued technical advances will likely contribute to significant growth of the field. Moreover, with continued hardware and software improvements, additional MRI sequences will likely become available. Prenatal MRI complements ultrasound because of larger field-of-view, superior soft tissue contrast, easier and more precise volumetric measurement, and greater accuracy in the demonstration of intracranial and spinal abnormalities. While ultrasound remains the primary modality for fetal imaging, these advantages of MRI make it a valuable adjunct to fetal surgery. Because fetal MRI involves many disciplines, the future of fetal MR will best be achieved through collaborative efforts.

Cancer presenting during pregnancy: radiological perspectives

Malignancy presenting during pregnancy is rare. When it does, there are important considerations and challenges for the radiologist. The physiological changes of pregnancy may mask signs and symptoms of malignancy leading to delayed presentation. Endocrine and physiological changes during pregnancy can interact with tumour biology to alter the behaviour and patterns of growth of certain tumours. The timing and choice of imaging technique pose potential risks to the foetus, but this must be weighed against the risks to both mother and foetus of inadequate investigation or misdiagnosis. This review outlines the general principles and approach to imaging the pregnant patient with suspected malignancy, following which there is a more detailed discussion of the effects of pregnancy on tumour biology and presentation of specific tumours. Imaging strategies are discussed for the different entities, and where possible, evidence-based imaging recommendations are made.

Fetal MRI of the central nervous system: clinical relevance

OBJECTIVE

Specific conditions of the mother sometimes reduce the quality of ultrasound. In these cases, fetal magnetic resonance imaging (MRI) can be performed after gestational week (GW) 18. Interpretation of subtle disorders or malformations becomes safe not before GW 23. Clinical development of children with central nervous system (CNS) disorders is not predictable with imaging alone. Statistical evidence and personal experience of the medical team are essential in counseling, but optimized imaging is helpful in being more precise. The value of fetal MRI (fMRI) is evaluated.

MATERIALS AND METHODS

Twenty-five pregnant women (30.5 +/- 4.5 years) were investigated by additional fMRI.

TECHNIQUE

Breath-hold technique with T2 half-Fourier acquisition single-shot turbo spin-echo and T1 FLASH-2D images in three dimensions with field of view of 350 x 400 mm. All cases have been correlated with postnatal MRI, ultrasound, and clinical follow-up.

RESULTS

In all fetuses, diagnostic MRI was performed 3-10 days after ultrasound between GW 22 and 34 (GW 26.1 +/- 3.6). Sedation was not necessary. In eight cases of suspicious ultrasound, fMRI confirmed ultrasound findings. In 13 cases, additional diagnoses or exclusions of suspected findings could be established. Complete revision of diagnosis was realized in four cases. Findings could be confirmed by postnatal MRI in 11 patients. The clinical course was not predictable in cases with ambivalent prognosis.

CONCLUSIONS

Prenatal diagnosis of CNS pathologies should result in parental counseling. Sufficient diagnostic information, statistical data, and experience of the involved professionals are essential. These results show that in detecting congenital CNS abnormalities fMRI is superior to ultrasound and should be considered in difficult cases.

Agenesis of the corpus callosum: an MR imaging analysis of associated abnormalities in the fetus

BACKGROUND AND PURPOSE

Anomalies associated with callosal agenesis (ACC) found postnatally have been well documented. However, to our knowledge, no detailed MR imaging analysis of associated anomalies has been reported in a large cohort of fetuses with ACC. This study will assess those anomalies and compare them with postnatal cohorts of ACC, to identify associated fetal brain abnormalities that may give insight into etiology and outcome.

MATERIALS AND METHODS

All cases of ACC diagnosed on fetal MR imaging during an 11-year period were retrospectively reviewed, including fetal MR imaging, postnatal MR imaging, and autopsy findings. Neurodevelopmental outcome was classified as poor in children with seizures and/or severe neurodevelopmental impairment or in cases of neonatal death.

RESULTS

Twenty-nine cases of ACC were identified. Median gestational age was 26.14 weeks (range, 19.71-36.43 weeks). Twenty-three fetuses had delayed sulcation and/or too-numerous cortical infoldings (abnormal morphology). Fifteen fetuses had cerebellar and/or brain stem abnormalities. Fetal MR imaging findings suggested a genetic syndrome in 5 fetuses and an acquired etiology or genetic/metabolic disorder in 2 fetuses. Findings were confirmed in 8 cases with postnatal MR imaging, except for delayed sulcation and small vermis, and in 4 cases with autopsy, except for periventricular nodular heterotopia and abnormalities in areas not examined by autopsy. Neurodevelopmental outcome was good in 7 and poor in 9 children. Abnormal sulcal morphology and/or infratentorial abnormalities were present in those with poor outcome and absent in those with good outcome.

CONCLUSIONS

ACC is infrequently isolated in fetuses. Abnormal sulcation is common and suggests more diffuse white matter dysgenesis in these fetuses.

The usefulness of fetal MRI for prenatal diagnosis

PURPOSE

Fast MRI has provided detailed and reproducible fetal anatomy. This study was performed to evaluate the usefulness of fetal MRI for prenatal diagnosis.

MATERIALS AND METHODS

Fifty-six fetuses with congenital abnormalities on ultrasonography were evaluated by fetal MRI from 2001 to 2004 in Severance Hospital. Final diagnosis was made by postnatal pathology, postnatal MRI, and other modalities (such as ultrasound, retrograde pyelogram). A 1.5-Tesla superconductive MR imaging unit was used to obtain half-Fourier acquisition single-shot turbo spin images.

RESULTS

Of the 56 fetuses, intracranial abnormalities were found in 26 fetuses, intraabdominal abnormalities in 17 fetuses, intrathoracic in 6 fetuses, head and neck in 5 fetuses, and other sites in 2 fetuses. There were six cases in which the diagnoses of fetal MRI and ultrasonography differed. In such cases, fetal MRI provided more exact diagnosis than ultrasonography (5 vs. 0). Three fetuses with intracranial abnormalities on ultrasonography were diagnosed as normal by fetal MRI and in postnatal diagnosis.

CONCLUSION

Although ultrasonography is known as a screening modality of choice in the evaluation of fetus because of the cost-effectiveness and safety, the sonographic findings are occasionally inconclusive or insufficient for choosing the proper management. Thus, in this study, we suggest that fetal MRI is more useful than ultrasonography for the evaluation of intracranial abnormalities in some instances. For prenatal counseling and postnatal treatment planning, fetal MRI can be informative when prenatal ultrasonography is inadequate and doubtful.

Twin-twin transfusion syndrome: cerebral ischemia is not the only fetal MR imaging finding

BACKGROUND

Twin-twin transfusion syndrome (TTTS) is a complication of monochorionic/diamniotic twin pregnancies. An imbalance of blood flow occurs through placental anastomoses, causing potentially significant morbidity and mortality in both twins. Although the sonographic findings of TTTS are well documented, we believe that MR imaging is a valuable adjunct.

OBJECTIVE

We describe the fetal MR imaging findings associated with TTTS.

MATERIALS AND METHODS

From 2003 to 2005, 37 consecutive MR imaging studies were performed on multiple-gestation pregnancies. Of the 37, 25 were consistent with TTTS, correlated and confirmed by sonographic criteria. MR fetal abnormalities were documented.

RESULTS

Cerebral ischemia, which could not be demonstrated by sonography, was delineated well by MR imaging. New findings noted on fetal MR imaging were enlargement of cerebral venous sinuses in both twins, dilatation of the renal collecting system in the recipient, lung lesions in the recipient and cerebral malformations in the donor.

CONCLUSION

MR imaging is an important adjunct in TTTS imaging. Its benefit over sonography is its clear definition of cerebral pathology, which is important for intervention and counseling. The new findings, particularly in the urinary tract and cerebral venous sinuses, also help support the diagnosis of TTTS and might reveal additional consequences of the altered hemodynamics that occur in TTTS.

Allantoic cyst: a prenatal clue to patent urachus

A patent urachus, which is typically diagnosed as leakage from the umbilicus postnatally, can present as an allantoic cyst in the umbilical cord antenatally. We report a case of a patent urachus with an allantoic cyst diagnosed via fetal MR imaging at 24 weeks' gestation. Early detection allowed for appropriate counseling and prompt corrective surgery after birth.

Quantitative MRI measurements of human fetal brain development in utero

Magnetic resonance imaging (MRI) allows for high resolution imaging of the central nervous system. We have tested the feasibility of using MRI in conjunction with quantitative image analysis to perform volumetric measurements of the brain in the developing human fetus in utero. The database comprises MR images of a total of 56 fetuses (gestational age 25-41 weeks) referred because of suspected abnormalities due to ultrasound findings, family history or maternal illness and scanned on a 1.5 T MR system using a single-shot fast spin echo (SSFSE) T2 sequence, slice thickness 3 mm, no gap. Four out of the 56 scans could not be used in the analysis due to poor image quality. Automatic segmentation (using NIH Image routines) was found to be unreliable in these fetal brains, so cerebral, cerebellar and ventricular regions were traced manually. Ventricular volumes did not vary with gestational age in normal fetuses (N=27, R=0.05, p=0.8) while cerebral parenchyma and cerebellum volumes increased significantly during the same period (R=0.67, p=0.0002 and R=0.51, p=0.0066 respectively). Two calculated parameters: percent ventricular asymmetry and volume ratio of ventricles to hemispheric parenchyma were found to be very sensitive to ventricular pathology; such that the mean value of the latter in normal fetuses was 4.4%+/-0.56 (mean+/-SEM, N=27) compared to 34.3%+/-17.6 (N=6, p<0.0001) in fetuses with ventriculomegaly. These results support the use of image analysis and MRI to produce normal growth curves as well as quantitative severity assessments of brain pathologies in the developing human fetus.

Fetal central nervous system MR imaging

MR imaging of the fetal brain is rapidly being embraced in clinical practice. Fetal MR imaging is proving to be a powerful modality with which to evaluate the fetal brain and is a valuable complement to prenatal ultrasound. Structural abnormalities, such as cerebral malformations and destructive lesions, can be sonographically occult on prenatal ultrasound yet detectable by fetal MR imaging. Moreover, fetal MR imaging offers the promise of contributing to our understanding of normal as well as abnormal brain development with continued advances in MR imaging techniques, such as diffusion-weighted and parallel imaging.

A new look at the fetus: Thick-slab T2-weighted sequences in fetal MRI

Although magnetic resonance imaging (MRI) of the fetus is considered an established adjunct to fetal ultrasound, stacks of images alone cannot provide an overall impression of the fetus. The present study evaluates the use of thick-slab T2-weighted MR images to obtain a three-dimensional impression of the fetus using MRI. A thick-slab T2-weighted sequence was added to the routine protocol in 100 fetal MRIs obtained for various indications (19th to 37th gestational weeks) on a 1.5 T magnet using a five-element phased-array surface coil. Slice thickness adapted to fetal size and uterine geometry varied between 25 and 50mm, as did the field of view (250-350 mm). Acquisition of one image took less than 1s. The pictorial essay shows that these images visualize fetal anatomy in a more comprehensive way than is possible with a series of 3-4mm thick slices. These thick-slab images facilitate the assessment of the whole fetus, fetal proportions, surface structures, and extremities. Fetal pathology may be captured in one image. Thick-slab T2-weighted images provide additional information that cannot be gathered from a series of images and are considered a valuable adjunct to conventional 2D MR images.

Fetal abdominal magnetic resonance imaging

This review deals with the in vivo magnetic resonance imaging (MRI) appearance of the human fetal abdomen. Imaging findings are correlated with current knowledge of human fetal anatomy and physiology, which are crucial to understand and interpret fetal abdominal MRI scans. As fetal MRI covers a period of more than 20 weeks, which is characterized not only by organ growth, but also by changes and maturation of organ function, a different MR appearance of the fetal abdomen results. This not only applies to the fetal intestines, but also to the fetal liver, spleen, and adrenal glands. Choosing the appropriate sequences, various aspects of age-related and organ-specific function can be visualized with fetal MRI, as these are mirrored by changes in signal intensities. Knowledge of normal development is essential to delineate normal from pathological findings in the respective developmental stages.

Obstetric MRI

Ultrasound is the imaging modality of choice for pregnant patients. However, MRI is increasingly utilized in patients in whom the sonographic diagnosis is unclear. These include maternal conditions unique to pregnancy such as ectopic pregnancy, placenta accreta, and uterine dehiscence. MRI is also being increasingly utilized in the assessment of abdominopelvic pain in pregnancy, in particular in assessment for appendicitis. Fetal MRI is performed to assess central nervous system (CNS) abnormalities and patients who are considering fetal surgery for conditions such as neural tube defects, congenital diaphragmatic hernia, and masses that obstruct the airway. In the future, functional MRI and fetal volumetry may provide additional information that can aid in our care of complicated pregnancies.

Cancer and pregnancy: Poena magna, not anymore

Cancer diagnosed during pregnancy constitutes a difficult clinical condition with a devastating impact on the patient's somatic and psychosocial health and possibly on foetal integrity. This circumstance also raises several moral, religious, social and familial dilemmas. In this review we critically present available evidence regarding the incidence, epidemiology and genetics of cancer in pregnant women, its presentation, diagnosis and staging as well as therapeutic management. Issues such as maternal/foetal prognosis, need for termination of pregnancy, risk of foetal health injury and necessity of psychosocial support are reviewed. Recent accumulating evidence suggests that, with appropriate management, poena magna should not be used to define neither cancer nor pregnancy.

Fetal MRI of Urine and Meconium by Gestational Age for the Diagnosis of Genitourinary and Gastrointestinal Abnormalities

OBJECTIVE

The purpose of our study was to assess the appearance of the colon and genitourinary tract in fetuses with respect to gestational age with T1- and T2-weighted MRI acquisitions and their applications to abnormalities in these systems.

MATERIALS AND METHODS

Retrospective review of the fetal MRI database was performed to select studies in which both T1- and T2-weighted acquisitions were obtained. The signal characteristics of fluid in the fetal colon and urine in the fetal bladder were evaluated, and gestational age and fetal MRI diagnosis were recorded. A Mantel-Haenszel chi-square analysis was performed to evaluate the relationship of gestational age to MRI signal intensity. In fetuses with suspected colonic and genitourinary abnormalities, an assessment was made about whether the T1-weighted findings added information to the T2-weighted findings.

RESULTS

Eighty fetal MRI studies were reviewed. Forty-three studies showed normal findings, and 37 depicted genitourinary or gastrointestinal abnormalities. The mean gestational age was 27 weeks 6 days. The MRI signal characteristics of urine and meconium became significantly more conspicuous with increasing gestational age (urine bright on T2, p < 0.001; urine dark on T1, p < 0.001; meconium bright on T1, p < 0.001; meconium dark on T2, p < 0.001). Of the 37 cases with suspected problems of the gastrointestinal or genitourinary systems, the T1-weighted images added additional information in 23 cases.

CONCLUSION

The appearance of urine and meconium on T1- and T2-weighted images is significantly more apparent with increasing gestational age. T1-weighted images identified meconium in the colon beyond 24 weeks' gestation and aided in the diagnosis of complex abnormalities.

Assessment of cortical maturation with prenatal MRI: part II: abnormalities of cortical maturation

The fetal cortical maturation is a long process with predefined steps. Abnormalities can occur at different stages of cortical maturation, resulting in various malformations. They can result from disturbance in cell proliferation, cell differentiation, cell migration and in organization of the cortex. Analysis of the different abnormalities of cortical maturation is given with illustrations of the principal malformations encountered in utero and accessible to MRI.

Role of fetal ultrasound and magnetic resonance imaging in the prenatal diagnosis of migration disorders

OBJECTIVES

To evaluate the contribution and limitations of fetal ultrasonography (US) and magnetic resonance imaging (MRI) for the diagnosis and management of migration disorders.

METHODS

Over a 5-year period, 14 fetuses with pathological migration disorders, without an infectious context, were taken care of in our centre. All underwent US; nine underwent MRI as well. Sonographic and MRI data were compared with neuropathological data.

RESULTS

The diagnosis of gyral disorders was obtained by US in 1/14 cases; other cerebral abnormalities were found suggesting neuronal disorder in the remainder. Cerebral MRI suggested gyral abnormality in eight of the nine cases.

CONCLUSIONS

US performance is increasing. MRI appears to be a promising method for the diagnosis of fetal migration disorders, giving better results than US. It may be recommended in cases of abnormal cerebral US findings or familial clinical history. However, interpretation of MRI can be tricky and the resulting diagnosis occurs late within the pregnancy.