Magnetic resonance imaging versus ultrasonography in fetal pathology

Fetal MRI: what's new? A short review

Fetal magnetic resonance imaging (fetal MRI) is usually performed as a second-level examination following routine ultrasound examination, generally exploiting morphological and diffusion MRI sequences. The objective of this review is to describe the novelties and new applications of fetal MRI, focusing on three main aspects: the new sequences with their applications, the transition from 1.5-T to 3-T magnetic field, and the new applications of artificial intelligence software. This review was carried out by consulting the MEDLINE references (PubMed) and including only peer-reviewed articles written in English. Among the most important novelties in fetal MRI, we find the intravoxel incoherent motion model which allow to discriminate the diffusion from the perfusion component in fetal and placenta tissues. The transition from 1.5-T to 3-T magnetic field allowed for higher quality images, thanks to the higher signal-to-noise ratio with a trade-off of more frequent artifacts. The application of motion-correction software makes it possible to overcome movement artifacts by obtaining higher quality images and to generate three-dimensional images useful in preoperative planning.Relevance statementThis review shows the latest developments offered by fetal MRI focusing on new sequences, transition from 1.5-T to 3-T magnetic field and the emerging role of AI software that are paving the way for new diagnostic strategies.Key points• Fetal magnetic resonance imaging (MRI) is a second-line imaging after ultrasound.• Diffusion-weighted imaging and intravoxel incoherent motion sequences provide quantitative biomarkers on fetal microstructure and perfusion.• 3-T MRI improves the detection of cerebral malformations.• 3-T MRI is useful for both body and nervous system indications.• Automatic MRI motion tracking overcomes fetal movement artifacts and improve fetal imaging.

Association of gestational age with MRI-based biometrics of brain development in fetuses

Background

Reported date of last menstrual period and ultrasonography measurements are the most commonly used methods for determining gestational age in antenatal life. However, the mother cannot always determine the last menstrual period with certainty, and ultrasonography measurements are accurate only in the first trimester. We aimed to assess the ability of various biometric measurements on magnetic resonance imaging (MRI) in determining the accurate gestational age of an individual fetus in the second half of gestation.

Methods

We used MRI to scan a total of 637 fetuses ranging in age from 22 to 40 gestational weeks. We evaluated 9 standard fetal 2D biometric parameters, and regression models were fitted to assess normal fetal brain development. A stepwise linear regression model was constructed to predict gestational age, and measurement accuracy was determined in a held-out, unseen test sample (n = 49).

Results

A second-order polynomial regression model was found to be the best descriptor of biometric measures including brain bi-parietal diameter, head circumference, and fronto-occipital diameter in relation to normal fetal growth. Normal fetuses showed divergent growth patterns for the cerebrum and cerebellum, where the cerebrum undergoes rapid growth in the second trimester, while the cerebellum undergoes rapid growth in the third trimester. Moreover, a linear model based on biometrics of brain bi-parietal diameter, length of the corpus callosum, vermis area, transverse cerebellar diameter, and cerebellar area accurately predicted gestational age in the second and third trimesters (cross-validation R² = 0.822, p < 0.001).

Conclusions

These results support the use of MRI biometry charts to improve MRI evaluation of fetal growth and suggest that MRI biometry measurements offer a potential estimation model of fetal gestational age in the second half of gestation, which is vital to any assessment of pregnancy, fetal development, and neonatal care.

Fetal tongue posture associated with micrognathia: An ultrasound marker of cleft secondary palate?

Cleft lip and cleft palate (CP) are the most common facial malformations. Two-dimensional (2D) ultrasound (US) is the first-line examination in the prenatal diagnosis of CP. Three-dimensional, four-dimensional US and MRI provide a better detection of facial clefts. We present two fetuses with micrognathia and suspected secondary CP on 2D US: fetal tongue appeared in an unusual position (low tip and high dorsum position) and showed uncoordinated movements. MRI did not confirm the US suspicion, but at birth the two fetuses were affected by Pierre Robin sequence.

Magnetic Resonance Imaging in Pregnancy with Intrauterine Growth Restriction: A Pilot Study

Objective

Intrauterine growth restriction (IUGR) is a major cause of late stillbirth, though not all compromised babies remain small or are considered growth restricted as pregnancy progresses. Fetal Magnetic Resonance Imaging (f-MRI) represents a second-line tool to study pregnancies with IUGR fetuses. The aim of our study was to evaluate the usefulness of f-MRI on predicting fetal growth and the offspring's perinatal respiratory outcome.

Design

All f-MRI performed between 2014 and 2016 in Siena were analysed. Pregnancies with IUGR (Study group (SG)) were recruited together with a control population (Control group (CG)), coupled for gestational age (GA) at the time of f-MRI (mean GA 31 wks). Neonatal information was collected. The f-MRI protocol consisted of T2w images. Six regions of interest (ROI) were placed as follows: 2 on the lung, 2 on the liver, and 2 on the amniotic fluid. The signal intensities (SI) of each ROI were measured. The SI lung to liver ratio (SI lung/liver) and SI lung to amniotic fluid ratio (SI lung/amniotic fluid) were obtained for each fetus. Each ratio was compared between SG and CG. Therefore, SG was divided into two subgroups: adequate and small for gestational age (AGA and SGA) newborns. All measurements were related to offspring's perinatal respiratory outcome.

Results

SI lung/liver was linearly related with GA at the time of f-MRI and with EFW. SI lung/amniotic fluid was significantly higher in SG than in CG (p = 0,014). In contrast, among SG, lower values of SI lung/amniotic fluid were found in the SGA compared to AGA (p = 0,036). The days of oxygen supply were higher in the SGA subgroup than in the AGA subgroup (p = 0,028).

Conclusions

SI lung/liver increases with fetal lung maturation and appears to be useful to estimate intrauterine fetal growth. SI lung/amniotic fluid seems to be a reliable predictive index to distinguish the IUGR fetuses that can recover their growth from those that were born SGA. f-MRI represents a promising frontier to predict IUGR fetus outcome, thus contributing to ameliorate the perinatal management.

Prenatal diagnosis of congenital head, face, and neck malformations-Is complementary fetal MRI of value?

OBJECTIVES

The aim of this study was to evaluate the role of fetal magnetic resonance imaging (MRI) as a complement to ultrasound (US) in the prenatal diagnosis of craniofacial anomalies.

METHODS

A historical cohort study including all pregnant women who were referred for fetal MRI because of antenatal diagnosis of craniofacial anomalies on screening US. Prenatal diagnostic US, MRI, and postnatal diagnosis were compared for consistencies and discrepancies.

RESULTS

Forty-five pregnant women with 73 suspected fetal craniofacial anomalies diagnosed by US underwent MRI. In 40 out of 73 anomalies (54.8%), US and MRI findings were in complete agreement with postnatal diagnoses. MRI correctly ruled out the diagnosis of 24 anomalies suspected on US and diagnosed four additional pathologies that were not demonstrated by US. Out of the 85 anomalies (suspected by imaging or confirmed postnatally), confident diagnosis could be made by MRI in 68 anomalies (80%), not diagnosed in 10 (11.8%), and over-diagnosed in seven (8.2%). By US, confident diagnosis could be made in 44 anomalies (51.8%), not diagnosed in 11 (12.9%), and over-diagnosed in 30 (35.3%).

CONCLUSION

MRI is valuable in the antenatal evaluation of fetal craniofacial anomalies and may be useful as an adjunct to US in the prenatal work-up of craniofacial anomalies.

MR Imaging of Fetal Musculoskeletal Disorders

This article outlines the main findings in prenatal musculoskeletal disorders. Three main technologies are generally used to obtain images within the uterus during pregnancy: ultrasound (US), MR imaging, and computed tomography (CT). Currently, the primary imaging method used for fetal assessment during pregnancy is US because it is patient friendly, useful, cost-effective, and (considered) safe. MR imaging is generally performed when US yields equivocal results because it offers additional information about fetal abnormalities and conditions in situations in which US is unable to provide high-quality images.

Fetal Cardiac Functional Assessment by Fetal Heart Magnetic Resonance Imaging

OBJECTIVE

We attempted to evaluate fetal cardiac activity of congenital heart disease (CHD) and normal heart fetuses by magnetic resonance imaging (MRI).

METHODS

We evaluated the fetal cardiac functional assessment and the blood flow of descending aorta at 34 weeks' gestation or more by MRI and compared the results with ultrasonography findings. We measured 6 normal heart fetuses and 14 CHD fetuses.

RESULTS

The ejection fraction (EF) and descending aorta blood flow in the CHD group were 76.4% ± 11.9%, 687.5 ± 303.8 mL/min by ultrasonography and 48.3% ± 7.1%, 711.4 ± 273.1 mL/min by MRI; those in the normal group were 66.9% ± 12.2%, 898.1 ± 245.9 mL/min by ultrasonography and 51.3% ± 4.2%, 911.9 ± 223.1 mL/min by MRI.

CONCLUSIONS

There was no significant difference in descending aorta blood flow measurements between ultrasonography and MRI, but the EF showed a significant between-group difference. In the normal group, the variation of EF and blood flow measured by MRI was significantly smaller compared with those of ultrasonography.

The role of a novel magnetic resonance imaging sequence in the evaluation of the fetal skeleton: a pilot study

Objective

We aimed to study the role of magnetic resonance imaging (MRI), including a novel MRI sequence-the modified volumetric interpolated breath-hold examination (VIBE)-in the characterization of the fetal skeleton. This novel sequence was useful for reconstructing three-dimensional images of the skeleton.

Materials and Methods

We enrolled 22 pregnant women whose fetuses had shown congenital abnormalities on ultrasound examinations. The women underwent prenatal fetal MRI in a 1.5-T scanner with a T2-weighted modified VIBE sequence. Three-dimensional reconstructions of the fetal skeleton were performed manually on the instrument itself or via an interactive pen-tablet workstation.

Results

Three-dimensional reconstructions of the fetal skeleton were performed after the acquisition of modified VIBE MRI sequences, and it was possible to characterize the fetal skeleton in all MRI examinations.

Conclusion

A detailed evaluation of the three-dimensional reconstructions of fetal skeleton performed after acquisition of a modified VIBE MRI sequence allowed a full characterization of the skeleton. However, improvements to the proposed sequence should be addressed in future studies.

Different information by MRI compare to ultrasound in fetal intracranial space occupying lesions

PURPOSE

The purpose of this study was to evaluate the value of prenatal magnetic resonance imaging (MRI) in characterizing fetal intracranial space occupying lesions in comparison to prenatal ultrasound.

METHODS

This retrospective study included 50 fetuses (mean age 26 years, mean gestational weeks 31 + 1 GW) with intracranial space occupying lesions, suspected by prenatal screening ultrasound. T2-weighted, T1-weighted, SSFP, and diffusion-weighted sequences of the fetal brain were obtained on a 1.5 T unit. Pathology (n = 5), postmortem MRI (n = 3), or postnatal US (n = 42) was available as standard of reference.

RESULTS

The fetal MRI provided correct diagnosis in 49 cases (98%), while 35 (70%) by ultrasound, and MRI failed in 1 case (2%), while ultrasound failed in 15 cases (30%). Fetal MR and ultrasound were concordant in 35 of 50 cases (70%), completely discordant in 4 (8%), and partially discordant in 11 (22%) cases.

CONCLUSIONS

MRI could provide detailed information about the minor lesions, such as focal hemorrhage and periventricular nodules. Meanwhile, it could provide whole view of the lesion in order to delineate the surrounding anatomical structure. But there are still some limitations of its soft-tissue resolution in a case with teratoma; more effort is needed to improve the sequences.

Dandy-Walker Malformation: is the 'tail sign' the key sign?

OBJECTIVE

The study aims to demonstrate the value of the 'tail sign' in the assessment of Dandy-Walker malformation.

METHODS

A total of 31 fetal magnetic resonance imaging (MRI), performed before 24 weeks of gestation after second-line ultrasound examination between May 2013 and September 2014, were examined retrospectively. All MRI examinations were performed using a 1.5 Tesla magnet without maternal sedation.

RESULTS

Magnetic resonance imaging diagnosed 15/31 cases of Dandy-Walker malformation, 6/31 of vermian partial caudal agenesis, 2/31 of vermian hypoplasia, 4/31 of vermian malrotation, 2/31 of Walker-Warburg syndrome, 1/31 of Blake pouch cyst and 1/31 of rhombencephalosynapsis. All data were compared with fetopsy results, fetal MRI after the 30th week or postnatal MRI; the follow-up depended on the maternal decision to terminate or continue pregnancy. In our review study, we found the presence of the 'tail sign'; this sign was visible only in Dandy-Walker malformation and Walker-Warburg syndrome.

CONCLUSION

The 'tail sign' could be helpful in the difficult differential diagnosis between Dandy-Walker, vermian malrotation, vermian hypoplasia and vermian partial agenesis.

Role of magnetic resonance imaging in the prenatal diagnosis of gastrointestinal fetal anomalies

PURPOSE

This study was done to evaluate the role of fetal magnetic resonance imaging (MRI) in the study of gastrointestinal malformations in comparison to prenatal ultrasound (US).

MATERIALS AND METHODS

A prospective (2010-2012) study of 38 fetal MRI scans was performed on 38 fetuses between 24 and 38 weeks of gestation. All the fetuses had a US diagnosis of gastrointestinal anomalies. T2-weighted HASTE, T1-weighted fast gradient echo, TrueFISP and diffusion-weighted images of the fetal abdomen were obtained on a 1.5-Tesla magnet. All fetal MRI diagnoses were compared with postnatal US findings, autopsy or surgical reports.

RESULTS

Fetal MRI was able to confirm the sonographic findings in nine of 38 fetuses (23.7%), to provide additional information in 23 of 38 fetuses (60.6%), to exclude the US diagnosis in five cases (5.2%) and to change it in two cases (5.2%). It was not able to characterize a case of gastric duplication and a case of abdominal cystic lymphangioma (5.2%).

CONCLUSIONS

Fetal MRI can be used as a complementary imaging modality to US in prenatal evaluation of gastrointestinal anomalies and can be considered a valuable tool not only for confirming or excluding but also for providing additional information to fetal ultrasonographic findings.

The Reliability of Fetal MRI in the Assessment of Brain Malformations

Objectives: To assess the inter- and intraobserver reliability of different fetal MRI measurements in cases of fetal brain malformations and to examine the concordance between ultrasonography (US) and MRI findings. Methods: Fetal brain MRIs and US findings of 56 pregnant women were retrieved from the institutional database. Standardized fetal brain MRI measurements were performed by 4 observers, and the inter- and intraobserver reliability was determined. Additionally, US and MRI findings were retrospectively compared. Results: The interobserver intraclass correlation coefficient (ICC) was above 0.9 for the cerebellum and posterior horn of the lateral ventricle. The measurements regarding the third ventricle (0.50), the fourth ventricle (0.58), and the corpus callosum (0.63) showed poor reliability. Overall, the intraobserver reliability was greater than the interobserver reliability. US and MRI findings were discordant in 29% of the cases with MRI rendering an extended diagnosis in 18%, a change of diagnosis in 3.6%, and excluding pathological findings suspected on US in 7.1%. Conclusions: Fetal MRI is a valuable complement to US in the investigation of fetal brain malformations. The reliability of most parameters was high, except for the measurements of the third and fourth ventricles and the corpus callosum.

Magnetic resonance imaging of fetal heart: anatomical and pathological findings

Congenital heart disease is one of the most frequent prenatal malformation representing an incidence of 5/1000 live births; moreover, it represents the first cause of death in the first year of life. There is a wide range of severity in congenital heart malformations from lesions which require no treatment such as small ventricular septal defects, to lesions which can only be treated with palliative surgery such as hypoplastic left heart syndrome. A good prenatal examination acquires great importance in order to formulate an early diagnosis and improve pregnancy management. Nowadays, echocardiography still represents the gold standard examination for fetal heart disease. However, especially when preliminary ultrasound is inconclusive, fetal MRI is considered as a third-level imaging modality. Preliminary experiences have demonstrated the validity of this reporting a diagnostic accuracy of 79%. Our article aims to outline feasibility of fetal MRI in the anatomic evaluation, the common indication to fetal MRI, its role in the characterization of congenital heart defects, and at last its main limitations.

Prenatal diagnosis of bladder exstrophy by fetal MRI

PURPOSE

To review our experience with prenatal diagnosis of bladder exstrophy by fetal magnetic resonance imaging (MRI). Bladder exstrophy can be diagnosed by ultrasonography (US) evaluation of the fetus based on absence of bladder filling, low-set umbilicus, small genitalia and lower abdominal mass, although in some instances more accurate anatomical information is desired.

MATERIAL AND METHODS

We studied three patients at mean gestational age of 27.3 weeks. The fetal MRI exam was performed on axial, sagittal, coronal planes and echo gradient in the best plan for acquisition of fetus. Images were analyzed by a group of three radiologists with experience in fetal MRI.

RESULTS

The MRI defined a lower abdominal mass prolapsing below the umbilical vessels, having the ureters ending on it in an anterior position. A cloacal malformation or a cloacal exstrophy could be excluded, as well as other accompanying spinal abnormalities. The renal system and oligohydramnios could be well documented.

CONCLUSIONS

The MRI showed a detailed scenario of the abnormality with advantages over the US evaluation in regard to excluding cloacal anomalies. MRI allowed accurate sexual differentiation and may be indicated after suspected bladder exstrophy on US evaluation.

Quantification of the subcutaneous fat layer with MRI in fetuses of healthy mothers with no underlying metabolic disease vs. fetuses of diabetic and obese mothers

OBJECTIVE

To assess the age-dependent fetal subcutaneous fat layer (SCFL) of non-diabetic, normal-weight mothers and fetuses of mothers with gestational diabetes (GDM) and normal body weight or obesity.

METHODS

In a prospective study, we evaluated 115 MRI examinations of fetuses with no history of (maternal) metabolic disease [gestational week (GW) 29 to 39/40] and 50 examinations of mothers with GDM and normal body weight or obesity. The SCFL was measured at predetermined anatomical landmarks. Measurements were correlated with the maternal body mass index (BMI) and glycated hemoglobin A1c (HbA1c)-values in diabetic mothers.

RESULTS

In fetuses of non-diabetic, normal-weight mothers, measurements showed high consistency within the respective GW and ranged from 2 mm at GW 29 at all measured points, up to 4.5 mm at the trunk and 6.0 mm at the extremities at GW 39/40. In 47/50 fetuses of mothers with GDM, the SCFL was within the range of fetuses of mothers with no metabolic disease. In three patients with GDM and BMI<30, the SCFL-thickness was decreased. No fetuses showed an increased SCFL-thickness.

CONCLUSION

The SCFL of normally developed fetuses is easily detectable from GW 29 on T1-weighted images (T1-W), and increases with gestational age. The presented data provide physiological benchmarks to evaluate developmental status and may help in the prenatal diagnosis of abnormal growth and macrosomia. In pregnant women with well-controlled GDM, an increase of the SCFL is not expected.

Magnetic resonance imaging of the fetus

Fetal magnetic resonance imaging (MRI) has become established as part of clinical practice in many centres worldwide especially when visualization of the central nervous system pathology is required. In this review we summarize the recent literature and provide an overview of fetal development and the commonly encountered fetal pathologies visualized with MRI and illustrated with numerous MR images. We aim to convey the role of fetal MRI in clinical practice and its value as an additional investigation alongside ultrasound yet emphasize the need for caution when interpreting fetal MR images especially where experience is limited.

Magnetic resonance imaging versus ultrasonography for the in utero evaluation of central nervous system anomalies

OBJECT

The use of fetal MR imaging for the in utero evaluation of pathological conditions of the CNS is widely accepted as an adjunct to fetal ultrasonography studies. Magnetic resonance imaging is thought to characterize CNS anomalies better, and to provide a more exact diagnosis and accurate prognosis. The purpose of this study was to determine the role of and indications for fetal MR imaging in evaluating fetuses with different CNS abnormalities that were seen initially on prenatal sonograms.

METHODS

Over a 3-year period, fetuses with prior sonographic evidence of CNS abnormalities who consequently received prenatal MR imaging at Columbus Nationwide Children's Hospital within 2 weeks of the fetal ultrasonography study were included in this study. For each patient, radiological reports from both studies were reviewed, analyzed, and compared with the findings at postnatal imaging or physical examination. Results of the 2 modalities were then compared in terms of diagnostic accuracy.

RESULTS

Twenty-six fetuses were included in this study on the basis of an in utero sonogram showing a CNS anomaly. Their gestational age ranged from 17 to 35 weeks, with a mean of 25 weeks at the time of fetal ultrasonography. Hydrocephalus was identified in 16 fetuses, 6 had evidence of a spinal dysraphic defect, 2 had holoprosencephaly, 1 had an encephalocele, and 1 had multiple body abnormalities requiring detailed CNS evaluation. Twenty-five of the fetuses were correctly evaluated as having abnormal CNS findings on both fetal ultrasonography and fetal MR imaging. Fetal ultrasonography provided a correct prenatal diagnosis in 20 cases, whereas fetal MR imaging was correct in 22 cases. There were 9 cumulative false-positive results for fetal ultrasonography and 7 for fetal MR imaging, whereas for false-negative results there were a total of 34 and 19, respectively.

CONCLUSIONS

Fetal MR imaging is more sensitive in detecting fetal CNS abnormalities, but its ability to provide a correct prenatal diagnosis is only marginally superior to fetal ultrasonography. Moreover, fetal MR imaging is not exempt from misdiagnosis, and still shows a significantly high rate of false-negative results. Particularly for spinal dysraphic defects, fetal MR imaging does not seem to add important diagnostic or prognostic details when compared with fetal ultrasonography.

Magnetic resonance imaging of the fetal brain

PURPOSE OF REVIEW

Fetal magnetic resonance imaging (MRI) is a relatively new clinical application but is becoming increasingly used in fetal medicine in combination with the established technique of antenatal ultrasound. A review of the literature to date provides information for clinicians to help assess which patients they should be referring for fetal MRI and what additional information to ultrasound they can obtain.

RECENT FINDINGS

This review covers recent articles on practical aspects of imaging, MR findings in common disorders and comparisons with ultrasound. It includes information on current applications for fetal MRI, new sequence acquisitions and postprocessing techniques. Fetal motion is the single most important barrier to improving image data.

SUMMARY

Fetal MR has become an established tool for assessing the fetal brain. It provides complementary information to ultrasound. However, further optimization of this technique is still required to ensure it is exploited to the full in fetal medicine.

Fetal MRI of the cardiovascular system: role of steady-state free precession sequences for the evaluation of normal and pathological appearances

PURPOSE

This study aimed to evaluate the feasibility of fetal magnetic resonance imaging (MRI) with steady-state free precession (SSFP) sequences to visualise the normal and pathological appearances of the cardiovascular system.

MATERIALS AND METHODS

This is a prospective observational study of 83 pregnant women who underwent fetal cardiac MRI: 43 patients (cases) had echocardiographic suspicion of congenital heart disease; 40 patients (controls) did not. Fetal cardiac MRI consisted of a static phase with multiplanar SSFP sequences and a dynamic phase with real-time SSFP sequences. Two radiologists evaluated the diagnostic quality of the SSFP images in both the controls and cases, the MRI morphological and functional features in the controls and the MRI signs of congenital heart disease in the cases.

RESULTS

In both groups, SSFP sequences produced goodquality MR images and good visualisation of morphological features. Functional data appeared to be unavailable due to the current small temporal resolution and the technical impossibility of fetal cardiac triggering. MRI detected direct signs of congenital heart disease in 21 fetuses, indirect signs in six and both signs in 15.

CONCLUSIONS

SSFP sequences are effective in demonstrating the morphological features of the cardiovascular system, whereas dynamic SSFP cine-MRI sequences may provide adjunctive albeit suboptimal functional information.