Fetal magnetic resonance imaging

Fetal US and MRI in detection of craniospinal anomalies with postnatal correlation: single-center experience

Background/aim

To reveal the contribution of magnetic resonance imaging (MRI) to ultrasound (US) in prenatal diagnosis of fetal craniospinal anomalies by retrospectively comparing the prenatal and postnatal findings.

Materials and methods

After institutional review board approval, between January 2010 and May 2020, 301 pregnant women, which had a gestational age between 19–37 weeks (mean 26.5 ± 6.1 weeks), diagnosed with cranial and spinal anomalies on fetal US and later on imaged with MRI were evaluated, and in 179 of those cases prenatal imaging findings were compared with postnatal findings.

Results

A total of 191 fetal craniospinal anomalies were detected in 179 pregnant women. MRI and US diagnosis were completely correct in 145 (75.9%) and 112 (58.6%), respectively. Diagnostic performance of MRI was significantly higher than that of the US (p < 0.05). Both prenatal MRI and US findings were concordant with postnatal diagnosis in 53% of the cases. In 28.7% cases, prenatal MRI contributed to US by either changing the wrong US diagnosis (8.9%), demonstration of additional findings (14%), or confirming the suspicious US diagnosis (5.8%).

Conclusion

Due to its high resolution and multiplanar imaging capability, fetal MRI contributes significantly to US in the correct prenatal diagnosis of craniospinal anomalies. This contribution especially is significant in neural tube defects, cortical malformations, and ischemic-hemorrhagic lesions.

Diffusion-weighted imaging of placenta in intrauterine growth restriction with worsening Doppler US findings

PURPOSE

We aimed to compare the placental diffusion difference between intrauterine growth restriction (IUGR) patients with worsening Doppler ultrasonography (US) findings and control group with normal Doppler US findings by using diffusion-weighted imaging (DWI).

METHODS

We performed a prospective study to compare the placental diffusion difference in 63 patients (gestational week, 28-34 weeks), including 50 IUGR patients (mean gestational week, 30 weeks 3 days ±16.2 days) with worsening Doppler US findings and 13 patients with normal Doppler US findings (mean gestational week, 29 weeks 4 days ±12.3 days) by using DWI (b value, 0-1000 s/mm2). We classified IUGR patients into three groups according to the reference values of the umbilical artery pulsatility index (PI) chart. Placenta apparent diffusion coefficient (ADC) calculations were performed by freehand drawn regions-of-interest (ROIs) (min, 8.04 cm2; max, 200 cm2).

RESULTS

Placental ADC values in IUGR patients (mean, 1.624±0.181 ×10-³ mm²/s; range, 1.35-1.96 ×10-3 mm2/s) were significantly reduced compared with the control group (mean, 1.827±0.191 ×10-³ mm²/s; range, 1.35-2.84 ×10-3 mm2/s) (P = 0.001). For adjusted ROI area calculation, ADC values were significantly lower in groups 3, 2 and 1, respectively, compared with the control group (P < 0.05); and there was no significant difference between groups 1 and 2 (P > 0.05). Preeclampsia significantly reduced the placental diffusion compared with patients without preeclampsia (P = 0.003). Gestational aging did not significantly affect ADC values in control patients (r=0.08, P = 0.561). The sensitivity, specificity, negative and positive predictive values of ADC to detect IUGR were 72%, 84.6%, 44%, and 94.7% with a cutoff value of 1.727 ×10-3 mm2/s, respectively.

CONCLUSION

The diagnostic estimation of placental ADC values to predict the severity of IUGR is comparable to that of umbilical artery PI. Considering that at the very early onset of IUGR, placental diffusion diminishes, ADC as a marker for IUGR in lieu of umbilical artery PI has the potential to determine the threshold for decreased placental diffusion. Therefore, DWI should be added to routine fetal MRI to show diffusion changes in placenta.

Assessment of the Placenta in Intrauterine Growth Restriction by Diffusion-Weighted Imaging and Proton Magnetic Resonance Spectroscopy

Placental insufficiency is a major cause of intrauterine growth restriction (IUGR) and seriously affects fetal development. When placental insufficiency happened, the diffusion of water molecule was restricted and the metabolic balance was destroyed in the placenta. In this prospective study, we aimed to evaluate the diagnostic value of diffusion-weighted imaging (DWI) in combination with proton magnetic resonance spectroscopy (¹H MRS) for placental insufficiency in IUGR. The apparent diffusion coefficient (ADC) values were calculated using DWI, and the metabolism of N-acetylaspartate (NAA), choline, and lipid and their ratios in the placenta were calculated using ¹H MRS. Data were statistically analyzed by receiver operating characteristic (ROC) curves and logistic regression analysis. The NAA and choline peaks were decreased in IUGR placentas compared with normal placentas, while lipid peaks showed an opposite trend. The average ADC value and the NAA/lipid and choline/lipid ratios were lower in the IUGR group than in the normal group ( P < .01). Logistic regression with multiple parameters showed that combination of the ADC value and choline/lipid ratio was more favorable than either parameter alone in analyzing placental insufficiency of IUGR ( P < .05). The area under the ROC curve for the combination was 0.939, indicating reasonably good discrimination. We concluded that reduced ADC and NAA/lipid and choline/lipid ratios could serve as potential markers for placental insufficiency of IUGR. Furthermore, the combination of ADC value and choline/lipid ratio greatly improved the diagnostic value.

MRI and ultrasound fusion imaging for prenatal diagnosis

OBJECTIVE

A combination of magnetic resonance imaging (MRI) images with real time high-resolution ultrasound known as fusion imaging may improve prenatal examination. This study was undertaken to evaluate the feasibility of using fusion of MRI and ultrasound (US) in prenatal imaging.

STUDY DESIGN

This study was conducted in a tertiary referral center. All patients referred for prenatal MRI were offered to undergo fusion of MRI and US examination. All cases underwent 1.5 Tesla MRI protocol including at least 3 T2-weighted planes. The Digital Imaging and Communications in Medicine volume dataset was then loaded into the US system for manual registration of the live US image and fusion imaging examination.

RESULTS

Over the study period, 24 patients underwent fusion imaging at a median gestational age of 31 (range, 24-35) weeks. Data registration, matching and then volume navigation was feasible in all cases. Fusion imaging allowed superimposing MRI and US images therefore providing with real time imaging capabilities and high tissue contrast. It also allowed adding a real time Doppler signal on MRI images. Significant fetal movement required repeat-registration in 15 (60%) cases. The average duration of the overall additional scan with fusion imaging was 10 ± 5 minutes.

CONCLUSION

The combination of fetal real time MRI and US image fusion and navigation is feasible. Multimodality fusion imaging may enable easier and more extensive prenatal diagnosis.

Fetal MRI: is it really helpful?

OBJECTIVE

The aim of this study is to emphasize on the diagnostic effectiveness of fetal MRI that led to increased utilization in fetal medicine as well as its value in prognosis and decision making in the modern obstetric practice.

METHODS

One hundred five (n = 105) pregnant women were referred for a fetal MRI examination after a high detailed ultrasound examination revealed a fetal abnormality. Fetal MRI was performed using 1, 5 Tesla units, with T1, T2-weighted and diffusion-weighted images. The findings were analyzed in comparison to the previous ultrasound findings, according to the fetal organ affected and the value of the MRI for therapeutic decision making was addressed. A statistical analysis was performed.

RESULTS

The fetal MRI provides a more accurate diagnosis compared to ultrasound examination, and when the ultrasound detects fetal anomalies, the MRI can efficiently either confirm or reject the finding, proving its high value for prenatal diagnosis and perinatal and management. The sensitivity, specificity and positive predictive value of fetal MRI as a screening tool approaches 100%.

CONCLUSIONS

Despite the fact that ultrasound is the method of choice for fetal screening, MRI can add up significantly to the diagnosis and management of congenital abnormalities and the indications for MRI continue to increase as new sequences and shorter acquisition times evolve.

Magnetic resonance imaging of the placenta identifies placental vascular abnormalities independently of Doppler ultrasound

OBJECTIVE

To evaluate the relationship between placental vascular pathology detected by prenatal magnetic resonance imaging (MRI) and perinatal outcome.

METHODS

This was a retrospective, hospital-based, cross-sectional study in which all fetal MRI examinations of singleton pregnancies with vascular placental pathology (i.e. infarction with/without hemorrhage, subchorionic thrombi/hemorrhages, intervillous thrombi/hemorrhages, or retroplacental hematoma) in the period 2002-2007 were included. The extent of the pathology was expressed as a percentage of the total placental volume. Abnormalities of umbilical artery Doppler ultrasound examinations within 7 days between MRI and ultrasound examination were noted. Death in utero or postnatally was the primary outcome. Gestational age at MRI and at birth and the occurrence of intrauterine growth restriction (IUGR) were noted. Logistic regression analysis was performed to assess the impact of gestational age at MRI, extent of the vascular lesion and presence of pathological Doppler ultrasound measurements on the prediction of mortality.

RESULTS

Fifty-nine structurally normal singleton pregnancies with placental vascular abnormalities were included in the analysis. Mortality rate was 36%; among the survivors, 87% were born before 37 + 0 gestational weeks and 50% suffered from IUGR. In 55% of the pregnancies pathological umbilical artery Doppler findings were identified, of which 27% were non-survivors. Mortality was predicted by earlier gestational age at fetal MRI for placental pathology (P < 0.05) and increasing extent of the vascular lesion (P < 0.05), but not by the presence of pathological Doppler ultrasound data. Accuracy of the prediction was 82%, sensitivity was 67% and specificity 89%.

CONCLUSION

MRI-detected vascular placental pathologies may help to identify pregnancies at risk for adverse outcome and fetal death independently of umbilical artery Doppler status.

Diffusion-weighted MR imaging of the placenta in fetuses with placental insufficiency

PURPOSE

To evaluate diffusion-weighted magnetic resonance (MR) imaging of the human placenta in fetuses with and fetuses without intrauterine growth restriction (IUGR) who were suspected of having placental insufficiency.

MATERIALS AND METHODS

The study was approved by the local ethics committee, and written informed consent was obtained. The authors retrospectively evaluated 1.5-T fetal MR images from 102 singleton pregnancies (mean gestation ± standard deviation, 29 weeks ± 5; range, 21-41 weeks). Morphologic and diffusion-weighted MR imaging were performed. A region of interest analysis of the apparent diffusion coefficient (ADC) of the placenta was independently performed by two observers who were blinded to clinical data and outcome. Placental insufficiency was diagnosed if flattening of the growth curve was detected at obstetric ultrasonography (US), if the birth weight was in the 10th percentile or less, or if fetal weight estimated with US was below the 10th percentile. Abnormal findings at Doppler US of the umbilical artery and histopathologic examination of specimens from the placenta were recorded. The ADCs in fetuses with placental insufficiency were compared with those in fetuses of the same gestational age without placental insufficiency and tested for normal distribution. The t tests and Pearson correlation coefficients were used to compare these results at 5% levels of significance.

RESULTS

Thirty-three of the 102 pregnancies were ultimately categorized as having an insufficient placenta. MR imaging depicted morphologic changes (eg, infarction or bleeding) in 27 fetuses. Placental dysfunction was suspected in 33 fetuses at diffusion-weighted imaging (mean ADC, 146.4 sec/mm(2) ± 10.63 for fetuses with placental insufficiency vs 177.1 sec/mm(2) ± 18.90 for fetuses without placental insufficiency; P < .01, with one false-positive case). The use of diffusion-weighted imaging in addition to US increased sensitivity for the detection of placental insufficiency from 73% to 100%, increased accuracy from 91% to 99%, and preserved specificity at 99%.

CONCLUSION

Placental dysfunction associated with growth restriction is associated with restricted diffusion and reduced ADC. A decreased ADC used as an early marker of placental damage might be indicative of pregnancy complications such as IUGR.

SUPPLEMENTAL MATERIAL

http://radiology.rsna.org/lookup/suppl/doi:10.1148/radiol.10092283/-/DC1.

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.

Fetal and placental malignancies: prenatal diagnosis and management

Fetal and placental malignancies are rare complications during pregnancy, but when they occur they may present significant challenges for the perinatology team. Owing to their rarity, there is limited information on many of these entities, with much data derived from individual case reports or small case series. Prenatal diagnosis of these entities is rare and inconsistent, usually in the form of isolated case reports. In the majority of fetal tumors, prenatal features are those of a mass lesion, with or without other non-specific features of fetal compromise such as polyhydramnios, fetal hydrops or intrauterine death, the final diagnosis in most cases being based on postnatal pathological examination.Expectant management is almost always indicated antenatally, with serial ultrasound examinations performed to detect rapid enlargement, metastasis or secondary fetal complications, such as non-immune hydrops, which may require intervention. Delivery should be planned in a specialist center in conjunction with pediatric surgeons and oncologists to allow appropriate neonatal management. Placental malignancy is most commonly in the form of gestatational trophoblastic disease, which requires assessment and management in specialist centers.

Congenital malformations of the central nervous system: clinical approach

Central nervous system (CNS) malformations represent important factor of morbidity and mortality in children. The aim of the study was to determine the incidence, type and clinical features of CNS malformations in children who were admitted at the Neonatal and Child Neurology Department, Neonatal Intensive Care Unit and Paediatric Intensive Care Unit of Paediatric Clinic, University of Sarajevo Clinics Centre, from January 1st, 2002 to December 31st, 2006. There were total of 16520 admissions at the Paediatric Clinic over the studied period. CNS malformations, solitary or multiple, have been diagnosed in 100 patients (0,61%). The total number of various CNS malformations was 127. Lethal outcome was established in 9/100 cases (9%). The most frequent CNS malformations were neural tube defects 49/127 (38,6%). Hydrocephalus was seen in 34/127 (26,8%), microcephaly in 24/127 (18,9%), agenesis of corpus callosum in 10/127 (7,9%), Dandy Walker malformation in 6/127 (4,7%) and other CNS malformations in 4/127 (3,1%). In 20/100 of patients neural tube defect was associated with hydrocephalus (20%). CNS malformations were prenatally diagnosed in 13/100 of patients (13%). Primary prevention of CNS malformations can be improved in our country by better implementation of preconceptional folic acid therapy for all women of childbearing age. Secondary prevention by prenatal diagnosis requires advanced technical equipment and adequate education of physicians in the field of foetal ultrasonography. In our circumstances, prenatal diagnostics of CNS malformations is still not developed enough.

Management of congenital diaphragmatic hernia

PURPOSE OF REVIEW

To evaluate the impact of recent research on the management of congenital diaphragmatic hernia in the light of new theories on embryological development, earlier antenatal diagnosis, fetal and postnatal interventions together with advances in perinatal intensive care.

RECENT FINDINGS

The year 2007 provided in excess of 200 publications that address various aspects of congenital diaphragmatic hernia. The genetic basis and the causes of pulmonary hypoplasia at the molecular level are slowly being unravelled. Fetal MRI of lung volume, lung-head ratio, liver position and size of diaphragmatic defect have all been evaluated as early predictors of outcome and with a view to prenatal counselling. The impact of fetal interventions such as fetal endoluminal tracheal occlusion, the mode of delivery, the surgical techniques and agents for treating pulmonary hypertension were evaluated. The influence of associated anomalies and therapeutic interventions on the outcome and quality of life of survivors continue to be appraised.

SUMMARY

Deferred surgery after stabilization with gentle ventilation and reversal of pulmonary hypertension remain the cornerstones of management. Optimal presurgery and postsurgery ventilatory settings remain unproven. Continued improvement in neonatal intensive care raises the bar against which any intervention such as fetal endoluminal tracheal occlusion and extracorporeal membrane oxygenation will be judged.

MR fetography using heavily T2-weighted sequences: comparison of thin- and thick-slab acquisitions

PURPOSE

To evaluate the use of MR-fetography sequences in identifying the major fetal structures and to compare thick- and thin-slab acquisitions for their diagnostic value.

MATERIALS AND METHODS

Twenty-one consecutive, pregnant women with suspected fetal pathology underwent fetal magnetic resonance imaging (MRI) using a 1.5 T MRI unit. Heavily T2-weighted, single-shot fast spin-echo (SSFSE) sequences with a long echo train (MR-fetography) were acquired in a thick- and thin-slab modus. Thick- and thin-slab acquisitions were reviewed by two experienced radiologists with regard to the overall image quality and landmark anatomical structures (spinal canal, spinal cord, posterior fossa, cerebellum, brainstem, basal cisterns, stomach, urinary bladder and umbilical cord according to a three-scale grading system (good, moderate and poor). Visibility scores were calculated and compared between both sequences.

RESULTS

Overall image quality was graded good in 76.2%, moderate in 19.0% and poor in 4.8% for thick-slab images and good in 81%, moderate in 14.3% and poor in 4.8% for thin-slab images. The visibility scores of the thick/thin-slab images for evaluation of the main fetal structures were as follows: for the spinal canal 2.8+/-0.4/2.9+/-0.54 (p>0.05), spinal cord 2.4+/-0.75/2.7+/-0.66 (p>0.05), posterior fossa components (cerebellum, brainstem and basal cisterns) 2.4+/-0.68/2.8+/-0.54; 2.4+/-0.67/2.7+/-0.66; 2.5+/-0.51/2.7+/-0.56 (p<0.05), stomach 2.8+/-0.44/2.9+/-0.48 (p>0.05), urinary bladder 2.8+/-0.51/2.8+/-0.54 (p>0.05) and umbilical cord 2.9+/-0.30/2.6+/-0.60 (p<0.05).

CONCLUSION

Heavily T2-weighted MR-fetography renders a quick overview of fetal contours, fetal position, amount of amniotic fluid and integrity and presence of several major fluid containing structures. Thick- and thin-slab acquisitions render complementary information. Thick-slab images display the entire fetus in one projection while thin-slab images provide more detailed anatomical information. The short imaging time usually allows measuring both thick- and thin-slab images. MR-fetography is as a helpful addition to conventional fetal MRI. MR-fetography should not be viewed as a single, stand alone sequence but as a supporting fast MR sequence in a well-designed multisequence fetal MRI protocol. Future studies evaluating larger patient groups are mandatory.