Magnetic resonance imaging of the fetus

Stroke in pregnancy

Stroke in pregnancy and the puerperium is a rare but serious cause of maternal and fetal mortality. Pregnancy-associated maternal changes should remain additional considerations in the evaluation and treatment of the pregnant patient who has stroke and not preclude a comprehensive stroke evaluation. Instead, the approach to the pregnant patient who has stroke should include the evaluation of general causes of stroke in the young, with the additional consideration of the rare pregnancy-specific causes. Understanding the potential maternal and fetal risks of diagnostic testing and treatment is crucial to appropriate decision making when caring for the pregnant patient who has stroke.

Fetal Anomalies: Comparison of MR Imaging and US for Diagnosis

PURPOSE

To compare prenatal ultrasonography (US) and magnetic resonance (MR) imaging for the diagnosis of fetal anomalies.

MATERIALS AND METHODS

Images of 27 fetuses (28 diagnostic cases) with anomalies diagnosed at US were evaluated; in these fetuses, prenatal MR imaging was performed within 15 days of US. Prenatal US and MR imaging findings were compared with postnatal diagnoses. Postnatal evaluation included US, MR imaging, autopsy, surgery, voiding cystourethrography, computed tomography, angiography, and physical examination.

RESULTS

In seven diagnostic cases, US and MR imaging findings were in complete agreement with postnatal diagnoses. MR imaging correctly provided additional information to the US-determined diagnosis in another seven and correctly changed the US diagnosis in three. The MR imaging-determined diagnosis was incorrect and the US diagnosis was correct in four cases. In seven cases, the diagnoses at both US and MR imaging were incorrect when correlated with the postnatal outcome. MR imaging was most valuable in the assessment of anomalies of the central nervous system.

CONCLUSION

MR imaging may have a place as an adjunct to US in evaluation of fetal anomalies, particularly those involving the central nervous system.

Fetal Brain MRI: Segmentation and Biometric Analysis of the Posterior Fossa

This paper presents a novel approach to fetal magnetic resonance image segmentation and biometric analysis of the posterior fossa's midline structures. We developed a semi-automatic segmentation method (based on a region growing technique) and tested the algorithm on images of 104 normal fetuses. Using the segmented regions of interest (posterior fossa, vermis, and brainstem), we computed four relative area ratios. Statistical and clinical analysis of our results showed that the relative development of these structures appears to be independent of pregnancy term. In an additional study of 23 pathological cases, one of the four measurements was always significantly different from the corresponding value observed in normal cases.

Fetal brain injury

Improvements in MRI techniques widen the indications for fetal brain imaging and fetal brain injury represents the third indication of fetal brain magnetic resonance imaging (MRI) after the evaluation of suspected central nervous system (CNS) malformations and ventricular dilatation. Optimal MR imaging technique is necessary in order to collect as much data as possible about the fetal brain. Diffusion images can be used routinely in addition to the standard protocol of fetal brain MRI that consists of T1 and T2 weighted images of the fetal brain. Monovoxel proton magnetic resonance spectroscopy can also be performed in utero, but this technique is still more part of research protocol than of routine clinical protocol. Fetal brain injury includes hypoxia-ischemia, congenital infections (especially toxoplasmosis and cytomegalovirus infections), brain damage due to malformation such as vascular brain malformation and heart malformation, pregnancies at risk of fetal brain damage, and even inherited metabolic diseases, especially mitochondrial diseases. MRI findings in fetal brain injury consist of acute or chronic lesions that can be seen alone or in combination. Acute response of the fetal brain is less commonly seen than the chronic response compared to the brain response encountered in the postnatal period.

The value of fast MR imaging as an adjunct to ultrasound in prenatal diagnosis

The aim of this study was to evaluate the role of MR imaging of the fetus to improve sonographic prenatal diagnosis of congenital anomalies. In 40 fetuses (not consecutive cases) with an abnormality diagnosed with ultrasound, additional MR imaging was performed. The basic sequence was a T2-weighted single-shot half Fourier (HASTE) technique. Head, neck, spinal, thoracic, urogenital, and abdominal fetal pathologies were found. This retrospective, observational study compared MR imaging findings with ultrasonographic findings regarding detection, topography, and etiology of the pathology. The MR findings were evaluated as superior, equal to, or inferior compared with US, in consent with the referring gynecologists. The role of these findings in relation to pregnancy management was studied and compared with postnatal follow-up in 30 of 40 babies. Fetal MRI technique was successful in 36 of 39 examinations and provided additional information in 21 of 40 fetuses (one twin pregnancy with two members to evaluate). More precise anatomy and location of fetal pathology (20 of 40 cases) and additional etiologic information (8 of 40 cases) were substantial advantages in cerebrospinal abnormalities [ventriculomegaly, encephalocele, vein of Galen malformation, callosal malformations, meningo(myelo)cele], in retroperitoneal abnormalities (lymphangioma, renal agenesis, multicystic renal dysplasia), and in neck/thoracic pathology [cervical cystic teratoma, congenital hernia diaphragmatica, congenital cystic adenomatoid lung malformation (CCAM)]. This improved parental counseling and pregnancy management in 15 pregnancies. In 3 cases, prenatal MRI findings did not correlate with prenatal ultrasonographic findings or neonatal diagnosis. The MRI provided a more detailed description and insight into fetal anatomy, pathology, and etiology in the vast majority of these selected cases. This improved prenatal parental counseling and postnatal therapeutic planning.

Three-dimensional volume rendering of fetal MR images for the diagnosis of congenital cystic adenomatoid malformation

RATIONALE AND OBJECTIVES

Great expertise is necessary to mentally compile a series of individual two-dimensional image sections into a three-dimensional (3D) composite view that can aid in differential diagnosis. The purpose of this study was to test 3D volume-rendering techniques for differentiating congenital cystic adenomatoid malformation from congenital diaphragmatic hernia.

MATERIALS AND METHODS

The authors acquired T2-weighted magnetic resonance (MR) images of a 27-week fetus in the sagittal plane and then applied the 3D volume-rendering method to the MR image data sets to obtain a composite 3D image.

RESULTS

It was unclear on the MR images whether the intestines were situated above or below the diaphragm. The composite image showed that the intestines were not herniated into the chest, and this facilitated a diagnosis of congenital cystic adenomatoid malformation rather than congenital diaphragmatic hernia.

CONCLUSION

The 3D volume-rendering techniques aided in the assessment of fetal organ structure and could be applied also to preoperative simulation and planning of fetal surgery.

Imaging of congenital cystic lung lesions

Congenital cystic lung lesions are a rare but clinically significant group of anomalies, including congenital cystic adenomatoid malformation (CCAM), pulmonary sequestration, congenital lobar emphysema (CLE) and bronchogenic cysts. These conditions can all present on imaging studies as air or fluid filled cysts. Widespread use of antenatal ultrasound has led to increased detection of infants with congenital thoracic abnormalities in utero, resulting in a better understanding of the natural history of many of these lesions and also allowing provision to be made for delivery and postnatal management. More recently antenatal magnetic resonance (MR) imaging has provided further information on the nature of many of these lesions and helped to differentiate them from extrathoracic abnormalities such as congenital diaphragmatic hernia (CDH), which is important in parental counselling. Many children with congenital cystic lung lesions will present with symptoms resulting in the need for prompt diagnosis and treatment and imaging has an essential role in the management of these children. Some congenital lung lesions are treated surgically, whilst others are managed conservatively.

Gemelidade imperfeita: avaliação pelos métodos de imagem

Os gêmeos acoplados são raros e constituem um desafio para os radiologistas e cirurgiões pediátricos. O estudo pré-natal é essencial para a definição da fusão anatômica e de outras anormalidades associadas, visando o adequado planejamento cirúrgico e a avaliação do prognóstico fetal. Os autores apresentam os achados clínicos e de imagem de um caso de gêmeos toracópagos, unidos pela porção anterior do tórax e compartilhando o coração e o fígado, diagnosticados ao estudo ultra-sonográfico e submetidos ao estudo por ressonância magnética fetal intra-útero para confirmação dos achados e detecção de outras anormalidades.

Advances in postnatal neuroimaging: relevance to pathogenesis and treatment of brain injury

The human brain is susceptible to a wide variety of insults. The permanent residua of these abnormalities are represented in dysfunction of one or more areas of neurodevelopment. A full understanding of normal brain development, mechanisms of brain injury, and consequences for subsequent brain development is required to determine which infants are at risk for neurodevelopmental handicap, and to monitor the effects of new treatments and management regimens designed to prevent these disabilities. Advanced magnetic resonance techniques, such as quantitative morphometric magnetic resonance techniques, diffusion-weighted magnetic resonance techniques, and magnetic resonance spectroscopy applied to the study of early human brain development have given us a better understanding of the pathophysiologic mechanisms of brain injury and its effects on subsequent brain development. Magnetic resonance imaging has provided an invaluable tool for the study of the fetal and newborn brain in vivo.

Ultrafast MRI of the fetus

During the last decade there has been increasing interest in MRI for the evaluation of ultrasound-detected fetal abnormalities. Motion artefacts previously precluded detailed imaging, but this is now possible using single-shot rapid acquisition sequences. These ultrafast techniques with subsecond images capture 'snap-shot' views of the fetus. By virtue of the infinitely long relaxation time (TR) these images are heavily T2-weighted so that fluid around and within the fetus delineates the anatomy. Currently, fetal MRI has shown to be most beneficial in the investigation of cerebral abnormalities suspected from sonography, and in the detection of subtle associated anomalies. It clearly has a role in the evaluation of complex somatic abnormalities, and is helpful in the evaluation of fetuses prior to surgery. We present a pictorial review of our experience with single-shot fast spin-echo (SSFSE) imaging, demonstrating normal anatomy of the fetal brain and body. In addition we present cerebral and somatic abnormalities to illustrate cases where we have found fetal MRI to be a useful adjunct to sonography.

Correlation of prenatal MRI and autopsy findings in the diagnosis of vein of galen arteriovenous malformation

SUMMARY

We report the case of an arteriovenous malformation (AVM) of the vein of Galen diagnosed in utero at the 34th week of gestation by ultrasound and MRI. Following interdisciplinary advice, the family decided to terminate the pregnancy. This was carried out in the 36th week of gestation. Mascroscopic study of the fetus confirmed the in utero diagnosis: considerable dilatation of the cerebral arteries, the Galen vein and the anteroinferior sinuses. Based on the correlation of pre and post natal examinations, this study highlights the accuracy of in utero MRI, coupled with ultrasound scanning in the diagnosis of an AVM of the Galen vein. It provides specific information on the degree of cerebral impairment. MRI in utero helps in decision-making for pregnancy termination.

Diffusion tensor imaging of the developing mouse brain

It is shown that diffusion tensor MR imaging (DTI) can discretely delineate the microstructure of white matter and gray matter in embryonic and early postnatal mouse brains based on the existence and orientation of ordered structures. This order was found not only in white matter but also in the cortical plate and the periventricular zone, which are precursors of the cerebral cortex. This DTI-based information could be used to accomplish the automated spatial definition of the cortical plate and various axonal tracts. The DTI studies also revealed a characteristic evolution of diffusion anisotropy in the cortex of the developing brain. This ability to detect changes in the organization of the brain during development will greatly enhance morphological studies of transgenic and knockout models of cortical dysfunction. Magn Reson Med 46:18-23, 2001.

Ultrafast magnetic resonance imaging of central nervous system abnormalities in utero in the second and third trimester of pregnancy: comparison with ultrasound

OBJECTIVE

To assess the ability of ultrafast magnetic resonance imaging to visualise abnormalities in the central nervous system of third trimester fetuses in utero and to compare the results with the current 'reference standard' of ultrasound and postnatal imaging or post-mortem data.

DESIGN

A prospective, observational study comparing the diagnostic accuracy of two imaging methods: antenatal ultrasound and antenatal magnetic resonance with each other and postnatal or post mortem data.

POPULATION

Twenty-one pregnant women of 19-36 weeks of gestation whose fetus were thought to have a central nervous system abnormality on the basis of antenatal ultrasound. The women had either not been offered or had refused a termination and were willing to have a magnetic resonance scan.

METHODS

A 1.5T magnetic resonance scanner used a single shot fast spin echo sequence, in three image planes. The results were compared with the ultrasound results obtained by an experienced investigator independently. A series of 21 patients, with a range of pathologies of central nervous system, were imaged. Postnatal ultrasound and/or magnetic resonance imaging, or post-mortem data were used for additional confirmation of the pathology in all cases.

RESULTS

The magnetic resonance report was different to the ultrasound in 10/21 (47.6%), magnetic resonance provided information additional to the ultrasound in 5/21 (23.8%), ultrasound and magnetic resonance results agreed in 6/21 cases (28.6%).

CONCLUSION

Magnetic resonance in the third trimester provides a useful adjuvant to ultrasound imaging of the fetus when assessing abnormalities of the central nervous system after 19 weeks of gestation particularly if the abnormality involves the posterior fossa.

The role of magnetic resonance imaging in prenatal diagnosis of fetal anomalies

Magnetic resonance imaging (MR) has become a useful adjuvant in evaluating fetal structural anomalies when ultrasound (US) is equivocal. It has a significant promise in confirming a US suspected abnormality and providing new information that was previously not available. The first studies on prenatal MR were hindered by fetal motion and long acquisition times. This degraded imaging and, therefore, maternal or fetal sedation was needed. Since fast and ultrafast MR with scan times of <1 s have become available, the amount of motion artifacts is decreased and sedation is no longer needed.MR has proved to be especially beneficial in detecting CNS anomalies. Agenesis of the corpus callosum, migration abnormalities and abnormalities of the posterior fossa are better seen on MR. Masses in the fetal neck and thorax can be identified on MR, as some abdominal anomalies. However, the fetal skeletal is difficult to visualize with MR. In the future, it is most likely that real time MR will become clinically available which would improve MR imaging even more.

Magnetic resonance techniques in the evaluation of the fetal and neonatal brain

Magnetic resonance imaging (MRI) has contributed dramatically to our understanding of the newborn with neurologic problems. Recently developed magnetic resonance techniques, such as fetal MRI and MR spectroscopy, offer additional insight into normal and pathologic processes affecting the fetal and neonatal CNS. This article examines developmental abnormalities as reflected in neuroimaging studies and discusses some of the newer MR modalities and their capabilities.

Prenatal diagnosis of esophageal atresia using sonography and magnetic resonance imaging

BACKGROUND

The diagnosis of esophageal atresia may be suspected on prenatal ultrasound scan in fetuses with a small or absent stomach or unexplained polyhydramnios. However, these findings are thought to have a low positive predictive value and clinical decisions affecting timing or site of delivery may be made erroneously. The authors evaluated the accuracy of fetal sonography followed by magnetic resonance imaging (MRI) for the diagnosis of this lesion.

METHODS

Fetuses considered to be at risk for esophageal atresia based on detailed obstetric sonography underwent fetal MRI using a single-shot rapid-acquisition technique, and the T(2)-weighted images were evaluated prospectively. Scans were considered to be positive if the proximal esophagus was dilated, and the distal esophagus was not seen and negative if the esophagus was visualized throughout its length.

RESULTS

Ten fetuses underwent MRI scanning. All had a small or absent stomach bubble with unexplained polyhydramnios. Four scans were considered to be negative for esophageal atresia; all 4 were found to have a normal esophagus after delivery. Six scans were considered to be positive; 5 had esophageal atresia (2 with tracheoesophageal fistula and 3 without), and one had a neurologic syndrome with a normal esophagus.

CONCLUSIONS

Magnetic resonance imaging appears to be accurate for establishing or ruling out a prenatal diagnosis of esophageal atresia, and should be considered in fetuses who are at high risk based on ultrasound findings.

Magnetic resonance techniques in the evaluation of the perinatal brain: recent advances and future directions

Magnetic resonance (MR) techniques are attractive for use in the developing brain because of their resolving power and their relative noninvasiveness. Their ability to provide detailed structural as well as metabolic and functional information without the use of ionizing radiation is unique. Conventional MR Imaging has widely proven its potential for identifying normal and pathologic brain morphology. Functional MR imaging such as diffusion-weighted imaging (DWI) and perfusion and blood-oxygenation-dependent BOLD imaging are newer imaging methods providing insights into brain physiology. This review will focus on the application of different MR techniques including the conventional structural MR imaging techniques and the more advanced MR techniques, such as the quantitative morphometric MR methods, the diffusion weighted MR techniques, the functional MR techniques and MR spectroscopy in the study of the fetal and newborn brain.

Fast MRI in obstetric diagnoses

This article describes the fast MRI of fetal abnormalities and placental anomalies in evaluation of the usefulness of fast MRI in obstetric diagnoses. Fast MRI provides excellent resolution for imaging fetal and maternal anatomies without the need for sedation. Fast MRI is therefore useful to clarify diagnoses suggested by equivocal ultrasonographic findings and to obtain additional information for prenatal counseling and management.

Role of magnetic resonance imaging in fetal surgery

Prenatal magnetic resonance imaging (MRI) has several advantages over obstetric ultrasound, including a larger field of view, superior soft-tissue contrast, more precise volumetric measurements, and greater accuracy in the demonstration of intracranial abnormalities. Prenatal MRI has been shown to positively and incrementally influence management in a substantial proportion of patients being considered for fetal intervention. Despite these findings, precise indications for prenatal MRI in the setting of fetal surgery are not yet established, because both prenatal MRI and fetal surgery are relatively new techniques that remain in evolution. Conditions in which prenatal MRI appears to contribute to fetal surgical planning and postoperative evaluation are described in this review. These conditions include congenital diaphragmatic hernia, cystic adenomatoid malformation, sacrococcygeal teratoma, complicated twin pregnancies, upper airway obstruction, and myelomeningocele.

MRI of conjoined twins illustrating advances in fetal imaging

Complex congenital fetal abnormalities are optimally evaluated with both ultrasound and magnetic resonance imaging. With the advent of ultrafast imaging sequences, fetal imaging has significantly improved. We present two cases of conjoined thoracoomphalopagus twins to discuss this unusual anomaly and to illustrate the recent advances in magnetic resonance imaging of the fetus.

Ultrafast MR imaging of the normal posterior fossa in fetuses

OBJECTIVE

The purpose of our study was to determine if a standard imaging protocol using ultrafast MR sequences could adequately reveal normal posterior fossa anatomy in fetuses and, if so, to document a template on MR imaging for normal posterior fossa development.

MATERIALS AND METHODS

A retrospective review found 66 MR imaging studies of 63 fetuses, 16-39 weeks' gestation age (mean, 25 weeks' gestation), who were referred between June 1996 and May 1999 for evaluation of non-central nervous system anomalies revealed on prenatal sonography. All fetuses had normal brains and spines on prenatal sonography. The standard MR imaging protocol included axial, sagittal, and coronal half-Fourier acquisition single-shot turbo spin echo (HASTE); sagittal and coronal two-dimensional fast low-angle shot (FLASH); and axial turbo T1-weighted FLASH images through the fetal brain. Structures that we analyzed were the fourth ventricle, the cisterna magna, the vermis, the cerebellar hemispheres, and the brainstem. Using the HASTE sequences, we documented gestational age-specific signal intensity changes in the cerebellar hemispheres and the brainstem.

RESULTS

The posterior fossa anatomy was sufficiently well defined to exclude abnormalities of the fourth ventricle and cerebellar vermis in all cases. Because of high T2-weighting, good contrast enhancement, and good signal-to-noise ratios, HASTE images provided the best anatomic definition of the posterior fossa.

CONCLUSION

Normal posterior fossa anatomy can be adequately shown on ultrafast MR images, which can be helpful when prenatal sonography is equivocal.

MRI of the spine and spinal cord: imaging techniques, normal anatomy, artifacts, and pitfalls

BACKGROUND

Magnetic resonance imaging (MRI) is widely used to evaluate the spine and spinal cord.

OBJECTIVE

In this article, MRI of the spine is discussed in terms of normal anatomy, standard and advanced imaging techniques, general indications, limitations, and potential for the future.

DISCUSSION

Although MRI does not provide the high bony detail possible with computed tomography, the appropriate combination of the sequences takes advantage of the different tissue characteristics to discriminate the various bony-and soft-tissue structures of the spine.

CONCLUSION

MRI enables the imaging specialist to evaluate a large anatomic region in multiple planes and can better examine the spinal cord.

Developmental neuroimaging of children using magnetic resonance techniques

Cognitive and motor development in children remain fascinating processes that are uniquely human. Progress has been made in recent years in elucidating the prenatal process of human brain development. In addition, much information exists regarding the behavioral aspects of postnatal human development. However, little is known about the relationship between anatomic postnatal central nervous system development and the accretion of functional milestones observed in children from the neonatal period through adolescence. Recently, powerful qualitative and quantitative magnetic resonance techniques have been developed that will permit detailed inquiry into the connection between the developing brain and the developing mind. In this review, first, the steps of prenatal and postnatal brain development are reviewed briefly. Subsequently, recent magnetic resonance imaging data related to human brain development during the fetal, neonatal, and later childhood periods are presented. Finally, functional magnetic resonance imaging (fMRI) is discussed. Specific examples of its usefulness are provided. Magnetic resonance imaging techniques such as quantitative MRI, volumetric MRI, diffusion tensor imaging, and functional magnetic resonance imaging (fMRI) when combined with neurologic and neuropsychologic evaluation, will provide new insights into the cognitive development of children. MRDD Research Reviews 6:68-80, 2000.

In vivo studies of brain development by magnetic resonance techniques

Understanding of the morphological development of the human brain has largely come from neuropathological studies obtained postmortem. Magnetic resonance (MR) techniques have recently allowed the provision of detailed structural, metabolic, and functional information in vivo on the human brain. These techniques have been utilized in studies from premature infants to adults and have provided invaluable data on the sequence of normal human brain development. This article will focus on MR techniques including conventional structural MR imaging techniques, quantitative morphometric MR techniques, diffusion weighted MR techniques, and MR spectroscopy. In order to understand the potential applications and limitations of MR techniques, relevant physical and biological principles for each of the MR techniques are first reviewed. This is followed by a review of the understanding of the sequence of normal brain development utilizing these techniques. MRDD Research Reviews 6:59-67, 2000.

Effect of fetal magnetic resonance imaging on fetal heart rate patterns

OBJECTIVE

Our aim was to record the fetal heart rate before and during magnetic resonance imaging to observe the effects of the magnetic resonance imaging process on fetal heart rate parameters during imaging.

STUDY DESIGN

Fetal heart rate recordings were obtained in 10 pregnant volunteers at the time of magnetic resonance imaging. All the pregnant women were at term (37-41 weeks) with singleton fetuses in the cephalic presentation. The scanning was performed on a 0.5-T purpose-built superconductive magnet by use of echo-planar imaging. The fetal heart recordings were obtained with a modified Sonicaid Meridian 800 (Oxford) Doppler ultrasound monitor. Recordings of the fetal heart were made for a period of at least 15 minutes outside the magnet and then for at least 15 minutes inside the magnet.

RESULTS

There were no significant changes in any fetal heart rate parameters before and during the magnetic resonance imaging, as determined by the Wilcoxon matched-pairs signed-ranks test (P >.3).

CONCLUSION

This is the first report of fetal heart rate recording during magnetic resonance imaging of the fetus. Magnetic resonance imaging does not produce demonstrable effects on fetal heart rate patterns.

Complex fetal disorders: effect of MR imaging on management--preliminary clinical experience

PURPOSE

To determine the effect of magnetic resonance (MR) imaging findings on management of complex fetal disorders.

MATERIALS AND METHODS

MR imaging of the fetus was performed in 25 consecutive pregnant patients referred because of possible complex fetal disorders suspected on the basis of ultrasonographic (US) findings. Spoiled gradient-echo and single-shot rapid acquisition with relaxation enhancement MR imaging were performed in multiple planes anatomic to the fetus during maternal breath holding.

RESULTS

In the fetuses in 24 of 25 women, MR studies were technically satisfactory. MR imaging directly influenced fetal care in four (17%) of 24 cases by demonstrating congenital high airway obstruction syndrome, congenital hemochromatosis, unilateral cerebellar deficiency in association with congenital diaphragmatic hernia, and severe facial disfigurement due to a giant anterior neck mass. In eight (33%) cases, MR imaging provided supplementary findings, but did not affect fetal care. In 12 (50%) cases, MR imaging results confirmed US findings.

CONCLUSION

In cases of complex fetal disorders, MR imaging results can be used to supplement or confirm US findings and may directly affect management.

The diagnostic role of "in utero" magnetic resonance imaging

OBJECTIVE

To assess the diagnostic potential of Magnetic Resonance Imaging (MRI) in the management of ultrasonically diagnosed congenital anomalies.

PATIENTS AND METHODS

Ninety-two patients were included into the study after the ultrasonic diagnosis of an abnormality. Sixty-three of these patients were affected by an abnormality of the central nervous system (CNS) and 29 by abnormalities in other apparatuses. The GRE technique was used to obtain T1 and T2 star-weighted images.

RESULTS AND DISCUSSION

Satisfactory imaging was obtained in all but one case. In order to define the "reliability" of MRI for a given condition, a diagnostic score was designed and separately given by the obstetrician and the radiologist involved in the case. MRI scored less than ultrasonography for abnormalities of the fetal contour and for large and complex distortion of the CNS as holoprosencephaly. For subtle midbrain anomalies, as well as for neuronal migration disorders, MRI definitely was superior to sonography. For other anomalies, as for example congenital diaphragmatic hernia, MRI was better than conventional techniques in assessing prognosis and outcome, but less reliable in assessing associated anomalies. MRI seems to be a valuable adjunct to us for prenatal diagnosis of only selected fetal anomalies and requires precise guidelines in a multidisciplinary approach to prenatal pathology.

Normal anatomy of the fetus at MR imaging

Owing to recent advances in magnetic resonance (MR) imaging, the role of obstetric MR imaging has increased in cases in which the results of ultrasonography are equivocal. Fast MR imaging sequences, such as T2-weighted fast spin-echo (SE), half-Fourier single-shot fast SE, 0.5-signal-acquired single-shot fast SE, and echo-planar imaging, have virtually eliminated the need for fetal premedication, with a concomitant improvement in image resolution and diminished blurring. Artifacts related to maternal respiratory motion and fetal motion no longer limit the anatomic detail that can be demonstrated with MR imaging. With such advances in obstetric MR imaging, knowledge of normal fetal anatomy at MR imaging is essential to detect disease in utero. MR imaging can demonstrate fetal anatomy in detail, especially the brain, thorax, abdomen, pelvis, and vasculature. Major developmental structures of the fetus, particularly the cranial nervous system, naso- and oropharynx, lungs, and major abdominal viscera, can be adequately evaluated with targeted fast MR imaging as early as the beginning of the second trimester. However, MR imaging of the heart remains limited. Fetal MR imaging during the first trimester remains controversial secondary to biosafety issues and is limited due to diminutive fetal size.