Techniques,terminology, and indications for MRI in pregnancy

Fetal MRI is now a well-established imaging modality for the diagnostic evaluation of fetuses with congenital anomalies. In this article, the authors provide a brief overview of the physical principles involved in fetal MRI imaging, the sequences that are used in clinical practice today, current indications, and limitations. A review of current evidence supports the following indications for fetal MRI: suspected central nervous system anomalies, neck and oropharyngeal masses, diaphragmatic hernia, abdominal masses or bowel pathology not fully characterized by ultrasonography, and suspected fetal infection. Other indications should be decided on a case-by-case basis with close collaboration between the departments of maternal–fetal medicine and radiology. More research is needed to determine the role of fetal MRI in functional neuroimaging at higher magnetic field strengths (3 T).     

Fetal magnetic resonance imaging.

Fast magnetic resonance imaging (MRI) has revolutionized our ability to image the fetus. Using fast scanning techniques, individual images are obtained in 300-400 ms, allowing for imaging of the fetus without sedation. MRI is most useful for evaluation of the anomalous fetal central nervous system, for further characterization of complex anomalies not fully elucidated by ultrasound and for evaluation of patients desiring fetal surgery. This review describes the history of fetal MRI, discusses current applications and mentions developments on the horizon.     

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.     

Fast-scan magnetic resonance imaging of fetal anomalies.

OBJECTIVE--To identify those congenital fetal anomalies, previously identified by ultrasound scanning, in which fast-scan magnetic resonance imaging (F-SMRI) would give additional information for the perinatal management of the infants. DESIGN--Observational clinical study. SETTING--Hospital Department of Obstetrics and Gynaecology/Resonance Research Centre. SUBJECTS--Seven women carrying eight fetuses in whom congenital abnormalities had been identified using ultrasound scans. The duration of the pregnancies was 28 to 39 weeks gestation. INTERVENTIONS--Fast-scan magnetic resonance imaging at between 28 and 39 weeks gestation. MAIN OUTCOME MEASURES--Identification of fetal abnormalities. RESULTS AND CONCLUSIONS--F-SMRI was of limited value in the diagnosis of further assessment of fetuses with abnormalities of accumulation of tissue fluid. Renal anomalies were poorly identified unless associated with cystic formation of the kidney. Further study is required in the imaging of fetal central nervous system anomalies. Until echoplanar imaging is more widely available, MRI does not contribute to the diagnosis of cardiac anomalies. F-SMRI appears to be most useful in the diagnosis and management of soft tissue gastro intestinal abnormalities.     

Magnetic resonance imaging and ultrasound in the assessment of the fetal central nervous system

Ultrasound is the screening modality of choice for evaluation of the fetal central nervous system (CNS). However, in cases of difficult diagnosis further fetal investigation is desirable. Due to ultrafast magnetic resonance imaging (MRI) techniques artifacts from fetal motions are minimized. MRI involves no exposure to radiation and hence appears to be safe. Due to the better soft tissue contrast, additional investigation by MRI may extend the sonographic diagnosis of fetal CNS-anomalies. Ultrasound and MRI are complementary imaging methods in the evaluation of the fetal CNS. The most important indications for ultrasound are screening for CNS anomalies and serial assessment of the dynamic of the disorder. The most important indications for fetal MRI are the "second opinion" and investigation by fetal MRI instead of postpartum MRI (especially in cases of planned postpartum intervention). In this article the indications and limitations of ultrasound and magnetic resonance imaging in the evaluation of the fetal CNS are discussed.     

Fetal magnetic resonance imaging and neurosonography in congenital neurological anomalies: supplementary diagnostic and postnatal prognostic value

Abstract

Objective: To compare the diagnostic conclusions between fetal neurosonography and MRI in the cases of congenital neurological abnormalities, and with postnatal clinical and imaging evaluation, when available.

Methods: A retrospective study of 28 patients who underwent a fetal MRI study for suspected congenital neurological anomalies. The diagnoses obtained by neurosonography and MRI were collected and compared. Both of them were compared with the final diagnosis when available by necropsy or postnatal evaluation. Postnatal imaging tests were performed only when clinically indicated.

Results: The indications for the fetal MRI examination were: fetal ventriculomegaly, posterior fossa anomalies, suspected midline defects, small-for-gestational-age cephalic biometry and confirmed congenital CMV infection. There was a good degree of agreement beyond chance between both techniques (kappa test?=?0.76).

Conclusions: Both imaging modalities give a high-diagnostic performance with a good degree of agreement between them, when made by specialized staff. Fetal MRI is a valuable complementary tool to detailed neurosonography which allows an evaluation of the normal brain maturation from the second trimester. It also offers a higher diagnostic performance for some congenital abnormalities such as cortical development or acquired lesions.     

Magnetic resonance imaging of anomalous fetuses

Magnetic resonance imaging (MRI) has been used sparingly in obstetrics. The reasons for this relate mainly to cost, availability, difficulty obtaining clear images because of fetal movement, and the convenience and utility of ultrasound. However, MRI use is expanding and has the potential to play an important role in selected problem pregnancies. We studied the pregnancies of five women whose fetuses showed anomalies by ultrasound. These included cases of a large body wall defect, a diaphragmatic hernia, hydrocephalus, Meckel-Gruber syndrome, and iniencephaly with a diaphragmatic hernia (the iniencephaly sequence). Three of these examinations followed fetal neuromuscular blockade, and two were associated with oligohydramnios without fetal paralysis. Paralysis provided superior images. The fetal central nervous system, subcutaneous tissue, and liver imaged particularly well. This study illustrates that MRI can enhance and even clarify certain information provided by ultrasound.     

Fetal MR imaging in urogenital system anomalies

Fetal magnetic resonance imaging (MRI) is an important adjunct to ultrasound in evaluation of fetal urogenital system. While, ultrasound remains the primary modality, MRI helps in more complicated cases or where ultrasound is limited due to technical factors such as poor acoustic window. The goal of this article is to review the common fetal urogenital anomalies and their imaging manifestations on ultrasound and MRI, and discuss how MRI adds diagnostic value.     

Three-dimensional color power imaging of the fetal hepatic circulation

OBJECTIVE: The purpose of this study was to describe the use of three-dimensional power Doppler ultrasonography to identify vascular congenital anomalies of fetal portosystemic and umbilical venous systems. STUDY DESIGN: In a prospective study, the hepatic and umbilical venous systems were examined in 390 fetuses with two-dimensional ultrasonography, color, and spectral Doppler imaging. Fetuses suspected to have anomalies of the portal system and ductus venosus were additionally examined with three-dimensional power Doppler ultrasonography. RESULTS: Vascular anomalies were identified in 8 fetuses (absent ductus venosus, n=4; direct connection between the umbilical vein and the right atrium, n=2; and direct connection between the umbilical vein and the inferior vena cava, n=2) out of the 310 in which the venous system could be adequately imaged (prevalence=2.6%). Three-dimensional power Doppler imaging showed the course of the umbilical vein, its relationship to the portosystemic circulation, and whether a ductus venosus was present. CONCLUSION: Three-dimensional power Doppler ultrasonography can be used to image normal fetal hepatic and portal circulation, as well as identify anomalies of the fetal portosystemic and umbilical venous systems.     

MR imaging of the fetal musculoskeletal system

Magnetic resonance imaging (MRI) appears to be increasingly used, in addition to standard ultrasonography for the diagnosis of abnormalities in utero. Previous studies have recently drawn attention to the technical refinement of MRI to visualize the fetal bones and muscles. Beyond commonly used T2-weighted MRI, echoplanar, thick-slab T2-weighted and dynamic sequences, and three-dimensional MRI techniques, are about to provide new imaging insights into the normal and the pathological musculoskeletal system of the fetus. This review emphasizes the potential significance of MRI in the visualization of the fetal musculoskeletal system.     

Osteogenesis imperfecta type II: fetal magnetic resonance imaging findings

We describe the prenatal magnetic resonance imaging (MRI) findings in a 25-week-old fetus with proven osteogenesis imperfecta type II. Fetal MRI findings are correlated with prenatal ultrasonography, conventional x-ray fetography and postpartal findings. Fetal MRI proves to be superior to conventional fetography in the evaluation of the skeletal findings. The high soft tissue resolution, the large field of view and the multiplanar imaging make it possible to study the non-ossified fetal skeleton in detail. Compared to prenatal ultrasonography, fetal MRI gives important additional information about the expected lung functionality by estimating fetal lung volume and signal intensity and rules out possible additional abnormalities of major fetal organs. These parameters may serve as valuable, additional prognostic markers in the prenatal diagnostic work-up.     

Fetal and early postnatal magnetic resonance imaging--is there a difference?

AIM: To evaluate whether fetal magnetic resonance imaging (MRI) could replace early postnatal MRI in fetuses with central nervous system (CNS) anomalies. METHODS: Thirteen pregnancies presenting with fetal CNS anomalies were investigated using MRI. Indications included ventriculomegaly combined with additional CNS anomaly (n=5), isolated ventriculomegaly (n=2), arachnoid cyst (n=2), holoprosencephaly (n=1), complex malformation syndrome (n=1), Dandy walker malformation (n=1) and midline cyst (n=1). Early postnatal MRI followed within the first six weeks of life. RESULTS: Investigation with early postnatal MRI confirmed the fetal MRI diagnosis in all cases. Investigation with postnatal MRI presented additional information in two cases. However, there was no change in patient care. CONCLUSIONS: Fetal MRI should replace early postnatal MRI in infants with CNS anomalies.     

Hydrographic magnetic resonance imaging of the fetal eye

Previous work has shown that fetal hydrographic magnetic resonance imaging (MRI) provided additional information complementary to T2-weighted single-shot fast spin echo (ssFSE) images. The objective of this study was to determine if hydrographic MRI provides better conspicuity of fetal eye structures compared with ssFSE MRI. ssFSE and hydrographic images were retrospectively examined in 82 consecutive fetal studies with normal central nervous system without sensitivity encoding. Relative signal intensity values on ssFSE and hydrographic MRI were obtained for vitreous and sclera. Ratios of the signal intensity of vitreous to the signal intensity of sclera were calculated to determine conspicuity. Similar measurements were obtained in a smaller separate data set (n = 41) using hydrographic imaging with sensitivity encoding techniques. The hydrographic images significantly demonstrated greater conspicuity (ratio of vitreous to sclera) than ssFSE images. This was consistent for both sensitivity encoding and no-sensitivity encoding groups. The difference in conspicuity was on average approximately two times greater in the hydrographic images compared with ssFSE images. Hydrographic MRI of the fetal eye provides on average two times greater conspicuity of fetal eye structures than ssFSE imaging. This enhancement is not affected by gestational age or the use of sensitivity encoding parallel imaging techniques.     

磁共振检查在妊娠期的应用

妊娠期磁共振(magnetic resonance,MR)检查可以作为超声的有益补充,已广泛应用于非产科、产科母体及胎儿疾病。妊娠期MR检查相对安全,在孕妇或胎儿的获益高于潜在风险时,可以进行MR平扫检查。妊娠期含钆对比剂的使用会增加胎死宫内和新生儿死亡等不良事件的发生风险,因此不推荐妊娠期常规使用含钆对比剂。MR检查的指征和扫描方案在妊娠期可根据需要进行一定调整。MR检查软组织分辨率高、没有电离辐射,在妊娠期可以替代部分辐射性检查用于妊娠合并肿瘤患者。妊娠期母体合并急腹症、瘢痕妊娠和胎盘植入等,以及胎儿疾病,MR检查均可以作为超声的补充,有助于诊断和妊娠期管理。     

Fetal MRI of a severe Dandy-Walker malformation with an enlarged posterior fossa cyst causing severe hydrocephalus

We present a case of severe Dandy-Walker malformation with enlarged posterior fossa cyst extruding through the incisura of the tentorium and causing severe hydrocephalus. A posterior fossa malformation was suspected by ultrasonography and was further evaluated by fetal magnetic resonance imaging (MRI). Fetal MRI demonstrated that there were no associated anomalies and the decision was made to continue with labor instead of terminating the pregnancy. The precise diagnosis and absence of associated anomalies revealed by MRI aided in parent counseling and obstetrical management.     

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.     

Comparison of magnetic resonance imaging and ultrasonography in the prenatal diagnosis of congenital thoracic abnormalities

OBJECTIVES: To evaluate prenatal MRI in the diagnosis of fetal thoracic abnormalities and to determine whether MRI provides useful information in addition to that of ultrasonography (US). METHODS: Ultrafast MR scanning was performed in 7 pregnant women in whom US was suspicious of fetal congenital anomalies of the thorax [3 cases of congenital diaphragmatic hernia (CDH), 3 cases of chylothorax and 1 case of congenital cystic adenomatoid malformation (CCAM) type III]. The presence, position, size and characteristics of the congenital lesions were determined and compared with postnatal diagnoses. RESULTS: The MRI diagnoses were 3 cases of CDH, 2 of chylothorax and one each of esophageal atresia and CCAM type III. The results of MRI were in agreement with those of US in 6 cases and in disagreement in 1 case of esophageal atresia. Final diagnoses were confirmed at surgery or autopsy in all fetuses. Combined use of MR and US imaging enabled a correct diagnosis in 5 cases and led to an error in the diagnosis of 1 fetus with bronchial stenosis, which had been diagnosed as CCAM type III by US and MRI. MRI led to a correct diagnosis in 1 fetus with esophageal atresia, in whom US had been equivocal in the prenatal diagnosis. CONCLUSION: MRI helped further characterize the fetal thoracic lesions and confirmed or changed the prenatal diagnosis based on US. MRI seems to be powerful in the prenatal diagnosis of thoracic lesions that are atypical or complicated by multiple abnormalities.     

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.     

Assessment of fetal behavior and general movements by four-dimensional sonography

The aim of this paper was to review the clinical applications of four-dimensional ultrasonography in the assessment of fetal behavior. With the use of a computerized database, articles on three-dimensional ultrasonography were reviewed. Several applications of dynamic three-dimensional ultrasonography have been reported, including imaging of fetal movements, facial expression and fetal hand movements. The importance of the assessment of fetal behavior by four-dimensional sonography is stressed. Four-dimensional sonography seems to be a useful imaging tool for clinical problem solving in perinatology, especially in observing the development of the central nervous system in utero.     

Prenatal ultrasound and magnetic resonance imaging in fetal varicella syndrome: correlation with pathology findings

OBJECTIVES: To assess the diagnostic value of prenatal magnetic resonance imaging (MRI) in addition to prenatal ultrasound in a case of fetal varicella syndrome. METHODS: Comparison of prenatal ultrasound and MRI features obtained at 26 and 32 weeks, respectively, with neonatal imaging (ultrasound, MRI and CT) and macroscopic and microscopic pathology findings in a fatal case of varicella embryopathy. RESULTS: Prenatal ultrasound correlated fairly well with neonatal imaging and pathology findings. Most lesions of thoracic, abdominal and retroperitoneal viscera, limb involvement and even dermatologic features were apparent on ultrasonography. Involvement of the CNS, including cerebellar hypoplasia, was not apparent on ultrasound examination, but was clearly demonstrated by prenatal MRI. CONCLUSION: If maternal seroconversion for the varicella-zoster virus is suspected, combining prenatal ultrasound and magnetic resonance imaging may document the extent of tissue damage in fetal varicella syndrome to a larger extent than has been reported until now and therefore contribute to due counselling following maternal varicella exposure.