Fetal Anomalies: Comparison of MR Imaging and US for Diagnosis

MRI findings in fetuses with an abdominal wall defect: gastroschisis, omphalocele, and cloacal exstrophy

Congenital abdominal wall defects include several entities such as gastroschisis, omphalocele, and cloacal exstrophy. It is important for perinatal management and parental counseling to understand the magnetic resonance (MR) imaging features essential for correctly diagnosing the clinical condition and predicting the prognosis of fetal patients. The purpose of this pictorial review is to demonstrate the MR imaging features of fetal cases with an abdominal wall defect and the pitfalls of image findings.

MRI: is there a role in obstetrics?

Magnetic resonance imaging has a complementary role in obstetrical imaging to ultrasound (US). Although US has advantages as an initial imaging technique, there are significant numbers of patients who cannot be adequately evaluated for a variety of reasons including calvarial calcification, oligoanhydramnios, or simply obesity. MR can provide additional information that cannot be obtained by US and is invaluable in central nervous system anomaly evaluation, airway management, and planning for postnatal intervention. Newer techniques established in the postnatal population such as spectroscopy, diffusion-weighted imaging, and functional imaging have future applications in the fetus.

Motion-compensation techniques in neonatal and fetal MR imaging

SUMMARY

Fetal and neonatal MR imaging is increasingly used as a complementary diagnostic tool to sonography. MR imaging is an ideal technique for imaging fetuses and neonates because of the absence of ionizing radiation, the superior contrast of soft tissues compared with sonography, the availability of different contrast options, and the increased FOV. Motion in the normally mobile fetus and the unsettled, sleeping, or sedated neonate during a long acquisition will decrease image quality in the form of motion artifacts, hamper image interpretation, and often necessitate a repeat MR imaging to establish a diagnosis. This article reviews current techniques of motion compensation in fetal and neonatal MR imaging, including the following: 1) motion-prevention strategies (such as adequate patient preparation, patient coaching, and sedation, when required), 2) motion-artifacts minimization methods (such as fast imaging protocols, data undersampling, and motion-resistant sequences), and 3) motion-detection/correction schemes (such as navigators and self-navigated sequences, external motion-tracking devices, and postprocessing approaches) and their application in fetal and neonatal brain MR imaging. Additionally some background on the repertoire of motion of the fetal and neonatal patient and the resulting artifacts will be presented, as well as insights into future developments and emerging techniques of motion compensation.

Magnetic resonance imaging in the normal fetal heart and in congenital heart disease

OBJECTIVE

To evaluate prospectively the feasibility of magnetic resonance imaging (MRI) for assessment of the fetal heart for congenital heart disease (CHD).

METHODS

This was a cross-sectional study, including 66 fetuses with a normal heart and 40 with CHD. The fetal heart was examined on MRI using axial steady-state free precession (SSFP) sequences. Regression analysis was used to investigate the effect on the ability to visualize cardiac anatomy of gestational age at examination, maternal body mass index, presence of fetal cardiac abnormality, fetal movements, fetal lie and twinning. The sensitivity and specificity of detecting cardiac defects were calculated.

RESULTS

The four-chamber view was visualized in 98.1% of fetuses. The sensitivity of detecting a cardiac defect on the four-chamber view was 88% and the specificity 96%. The ability to visualize the left and right outflow tracts was only influenced by the presence of fetal movements: for the left outflow tract 94.4 vs. 50.0% visualization and for the right outflow tract 92.6 vs. 53.8% visualization without and with fetal movements, respectively. The sensitivity of detecting a cardiac defect of the left outflow tract was 63% and the specificity 100%, while sensitivity and specificity were 59 and 97%, respectively, for the right outflow tract.

CONCLUSIONS

Despite the use of SSFP sequences, MRI in the fetal heart remains of limited value. It can only be used as a second-line approach for abnormalities of the four-chamber view suspected at prenatal ultrasound.

Abnormalities of the upper extremities on fetal magnetic resonance imaging

OBJECTIVE

In view of the increasing use of fetal magnetic resonance imaging (MRI) as an adjunct to prenatal ultrasonography, we sought to demonstrate the visualization of upper extremity abnormalities and associated defects on MRI, with regard to fetal outcomes and compared with ultrasound imaging.

METHODS

This retrospective study included 29 fetuses with upper extremity abnormalities visualized with fetal MRI following suspicious ultrasound findings and confirmed by postnatal assessment or autopsy. On a 1.5-Tesla unit, dedicated sequences were applied to image the extremities. Central nervous system (CNS) and extra-CNS anomalies were assessed to define extremity abnormalities as isolated or as complex, with associated defects. Fetal outcome was identified from medical records. MRI and ultrasound findings, when available, were compared.

RESULTS

Isolated upper extremity abnormalities were found in three (10.3%) fetuses. In 26 (89.7%) fetuses complex abnormalities, including postural extremity disorders (21/26) and structural extremity abnormalities (15/26), were demonstrated. Associated defects involved: face (15/26); musculoskeletal system (14/26); thorax and cardio/pulmonary system (12/26); lower extremities (12/26); brain and skull (10/26); and abdomen (8/26). Of the 29 cases, 18 (62.1%) pregnancies were delivered and 11 (37.9%) were terminated. MRI and US findings were compared in 27/29 cases: the diagnosis was concordant in 14 (51.9%) of these cases, and additional findings were made on MRI in 13/27 (48.1%) cases.

CONCLUSIONS

Visualization of upper extremity abnormalities on fetal MRI enables differentiation between isolated defects and complex ones, which may be related to poor fetal prognosis. MRI generally confirms the ultrasound diagnosis, and may provide additional findings in certain cases.

High-resolution in utero 3D MR imaging of inner ear microstructures in fetal sheep

BACKGROUND AND PURPOSE

Developmental inner ear abnormalities can occur due to embryopathies as well as in the context of syndromal diseases like the CHARGE association. In severe cases, an early and definite in utero diagnosis is important for decision-making; here, fetal MR imaging can be a helpful tool. We present results of performing high-resolution MR imaging of the inner ear structures of fetal sheep in vivo.

METHODS AND MATERIALS

Six ewes carrying singleton fetuses (mean gestational age, 120 days) were examined under general anesthesia at 1.5T. A 3D true FISP sequence with isotropic voxel size (0.7 mm) was applied; acquisition time was 2:35 minutes. For a standard of reference, 1 stillborn lamb of equivalent gestation age was examined. Image analysis was performed in consensus by 2 radiologists regarding the depiction of anatomic landmarks on a 5-point scale. Motion artifacts were quantified on a 3-point scale.

RESULTS

The turns and modiolus of the cochlea as well as the origins of all 3 semicircular canals of the vestibular system of both sides could be reliably identified in every animal. Motion artifacts due to maternal breathing excursions or movements of the fetus were minimal. In case of breech presentation, the ventilation of the ewe had to be paused during the image acquisition to achieve acceptable results.

CONCLUSIONS

High-resolution intrauterine MR imaging of the inner ear microstructures in an animal model is feasible. However, the acquisition time of the sequence applied is still too long to perform such measurement in a clinical setting.

Obstetrical sonography in obese women: a review

Obstetric sonographic imaging in pregnant women is adversely affected by obesity with a negative impact on the detection rate of congenital anomalies. This review aims to analyze relevant data regarding this issue and to discuss clinical and technical problems associated with sonographic examination of obese pregnant women.

Ultrasound vs MRI in Diagnosis of Fetal and Maternal Complications

Ultrasound is the screening modality of choice for the fetal imaging. However, there are circumstances in which an alternative imaging technique is needed for additional information regarding fetal anatomy and pathology as well as different maternal conditions.

Magnetic resonance imaging (MRI) is being increasingly used as correlative imaging modality in pregnancy because it uses no ionizing radiation, provides excellent soft-tissue contrast, and has multiple planes for reconstruction and large field of view, allowing better depiction of anatomy in fetuses with large or complex anomalies.

In this review, we attempted to identify strengths and weaknesses of each modality both from the literature and our own working experience, and to propose to some practical recommendations on when to use which imaging modality.

Both ultrasonography and MRI are operator-dependant and neither technique obviates the need for thorough knowledge of normal and abnormal anatomy. In early pregnancy, and where repeated assessment is needed, ultrasound has the obvious advantage. In circumstances where ultrasound examination is difficult, as in the obese patient or severe oligohydramnion, better images might be obtained by MRI examination. MRI might also identify early fetal ischemic lesions after an insult, such as maternal trauma or death of a monochorionic co-twin. From the published literature, it would appear that MRI may provide additional diagnostic information to that given by ultrasound in 25 to 55% of cases, which in turn may have influence on parental counseling and/or management of affected pregnancies. Individual circumstances and expertise influence the accuracy of both modalities. Ultrasound and MRI should be performed to the highest possible standard, and the final diagnosis should be made in a multidisciplinary setting.

Ultrafast MRI of the fetus: an increasingly important tool in prenatal diagnosis of congenital anomalies

OBJECTIVE

To demonstrate the additional utility of ultrafast magnetic resonance imaging (MRI) of the fetus in the evaluation of sonographically detected or equivocal fetal congenital anomalies.

MATERIAL AND METHODS

Twenty five pregnant women with ultrasound detected fetal congenital anomalies underwent ultrafast fetal MRI.

RESULTS

MRI findings altered the diagnosis of two cases of giant arachnoid cyst and sizable interhemispheric cyst associated with agenesis of the corpus callosum. MRI added additional findings of occult spinal diastematomyelia in two out of four cases of Chiari/meningocele malformation. MRI revealed impaired sulcation and unilateral cleft palate in suspected case of Walker-Warburg syndrome. In the remaining 18 cases MRI confirmed the diagnosis of Meckel-Gruber syndrome in three cases, hydronephrosis in six cases, cerebral ventriculomegaly in five cases, isolated omphalocele in three cases and findings suggestive of aneuploidy in the last case.

CONCLUSION

Ultrasound is the screening method of choice for evaluation of the fetus. Ultrafast MRI is a complementary adjunctive modality with excellent tissue contrast that can image the fetus in multiple planes and add information in sonographically detected or equivocal congenital anomalies that may be significant to establish definitive accurate diagnosis and hence adequate management and counseling.

Additive manufacturing models of fetuses built from three-dimensional ultrasound, magnetic resonance imaging and computed tomography scan data

OBJECTIVE

To generate physical fetal models using images obtained by three-dimensional ultrasonography (3DUS), magnetic resonance imaging (MRI) and computed tomography (CT) to guide additive manufacturing technology.

METHODS

Images from 33 fetuses, including three sets of twins, were used. Fifteen fetuses were normal and evaluated only by 3DUS. Eighteen cases had abnormalities such as conjoined twins, tumors, aneuploidy, skeletal abnormalities, central nervous system abnormalities and facial or thoracic defects. Scans were performed using high-resolution 3DUS. In cases of abnormalities, MRI and CT were performed on the same day as 3DUS. The images obtained with 3DUS, CT or MRI were exported to a workstation in DICOM format. A single observer performed slice-by-slice manual segmentation using a digital high-definition screen. Software that converts medical images into numerical models was used to construct virtual 3D models, which were physically realized using additive manufacturing technologies.

RESULTS

Physical models based on 3DUS, MRI and CT images either separately or combined were successfully generated. They were remarkably similar to the postnatal appearance of the aborted fetus or newborn baby, especially in cases with pathology.

CONCLUSION

The use of 3DUS, MRI and CT may improve our understanding of fetal anatomical characteristics, and these technologies can be used for educational purposes and as a method for parents to visualize their unborn baby. The images can be segmented and applied separately or combined to construct 3D virtual and physical models.

Avaliação de linfangiomas cervicais fetais por ressonância magnética e correlação com achados ultrassonográficos

OBJETIVO: Avaliar três casos de linfangioma cervical por ressonância magnética e correlacionar com os achados da ultrassonografia. MATERIAIS E MÉTODOS: Três pacientes com idade gestacional entre 24 e 35 semanas, com suspeita de higromas císticos cervicais fetais na ultrassonografia obstétrica de rotina, foram submetidas a ressonância magnética e, posteriormente, a nova ultrassonografia para correlação dos achados. Em ambos os métodos de imagem foram avaliadas as dimensões, a localização, o conteúdo e a extensão das lesões. RESULTADOS: Tanto a ultrassonografia quanto a ressonância magnética avaliaram de modo semelhante a localização, o tamanho e o conteúdo dos tumores. As três lesões localizavam-se na região cervical posterior e lateral. Quanto ao conteúdo, duas eram predominantemente císticas com finos septos em seu interior e uma era heterogênea. A extensão e invasão das estruturas adjacentes foram mais bem caracterizadas na ressonância magnética do que na ultrassonografia, demonstrando de forma adequada o acometimento do pavilhão auditivo do feto em um caso e do mediastino superior em outro. CONCLUSÃO: A ressonância magnética fetal pode ser um complemento útil da ultrassonografia em fetos portadores de linfangiomas, avaliando de forma mais precisa a extensão e invasão de estruturas vizinhas, permitindo melhor planejamento cirúrgico pós-natal.

[Significance of magnetic resonance studies in prenatal diagnosis of malformations of the fetal central nervous system]

MRI investigation, as an imaging technique, has been gaining more and more importance in prenatal diagnostics. It has become essential due to its advantages in diagnosing the malformations of the central nervous system. Similarly to ultrasonography, its reliability is greatly dependent on the knowledge of the person performing the investigation. In addition to the knowledge of the exact anatomy of central nervous system, the researcher should have a multidisciplinary approach. In the case of malformations where repeated investigations are needed to provide a diagnosis in early pregnancy (e.g. neural tube defects), ultrasonography is more effective than MRI. In case of intrauterine infections and malformations of the posterior fossa, however, the two imaging techniques are excellent supplements to each other. MRI also plays an important role in making the prognosis for fetal ventriculomegaly, as well as in the short term diagnosis of ischaemias affecting the fetal nervous system. Difficulties in evaluating ultrasonographic images (owing to maternal obesity, oligohydramnion) render MRI an important technique in making the final diagnosis. Currently, the drawbacks of MRI include reduced accessibility, poor cost-effectiveness and shortage of skilled experts in this technique.

Fetal central nervous system malformations on MR images

Sonography is the method of choice for prenatal malformation screening but it does not always provide sufficient information for correct diagnosis or adequate abnormality evaluation. Fetal magnetic resonance imaging (MRI) is considered as a valuable second line imaging tool for confirmation, completion and correction of sonographic findings. Fetal MRI has proven its value in the evaluation of central nervous system pathologies, especially of midline and posterior fossa malformations. The role of MRI is not only to confirm or exclude possible lesions but also to define their full extent, aiding in their characterization, and to demonstrate associated abnormalities. The authors describe the most common anomalies of CNS revealed by fetal MRI in a chronological way related to the age of pregnancy, with a review of own MR images and with reference to the literature and own experience.

Fetal MRI of the central nervous system: clinical relevance

OBJECTIVE

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

MATERIALS AND METHODS

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

TECHNIQUE

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

RESULTS

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

CONCLUSIONS

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

H, Daltro PA, Rodrigues L, Amim B, Guerra F, Domingues RC, Gasparetto EL. Correlação entre os achados ultra-sonográficos e de ressonância magnética no teratoma sacrococcígeo fetal

OBJETIVO: Correlacionar os achados ultra-sonográficos e de ressonância magnética no teratoma sacrococcígeo fetal. MATERIAIS E MÉTODOS: Três pacientes com idade gestacional entre 30 e 35 semanas, com diagnóstico ultra-sonográfico suspeito de teratoma sacrococcígeo fetal, foram submetidas a ressonância magnética e, posteriormente, a ultra-sonografia para correlação dos achados. Tanto na ressonância magnética quanto na ultra-sonografia foram avaliadas as dimensões, a localização, a extensão e os conteúdos dos tumores. RESULTADOS: A ultra-sonografia e a ressonância magnética obtiveram resultados semelhantes em relação à localização, ao tamanho e ao conteúdo dos tumores. Todas as lesões localizavam-se na região sacrococcígea, com dimensões médias de 6,0 cm x 9,0 cm. Quanto ao conteúdo dos tumores, um dos casos era completamente cístico e dois eram sólidos e císticos. A extensão exata das lesões foi mais bem avaliada pela ressonância magnética do que pela ultra-sonografia, mostrando de forma adequada o acometimento pélvico nos três casos. CONCLUSÃO: A ressonância magnética fetal é capaz de complementar os achados ultra-sonográficos do teratoma sacrococcígeo fetal, uma vez que determina com melhor precisão o conteúdo e a extensão do tumor, auxiliando na conduta terapêutica e aumentando as chances de cura desses fetos.

Correlation between ultrasound and autopsy findings after 2nd trimester terminations of pregnancy

OBJECTIVE

To compare ultrasound (US) and fetal autopsy findings in 2(nd) trimester termination of pregnancy because of structural fetal anomalies.

METHODS

A total of 112 terminations of pregnancy (TOP) between 1999-2003 were reviewed retrospectively. The cases originated from a secondary and a tertiary Fetal Medicine unit in the south Stockholm area, using a common specialized perinatal pathology service. Karyotype was not known at the time of US examination. The findings were compared and classified into four groups according to the degree of agreement between US and autopsy.

RESULTS

In 45% of cases there was total agreement between US and autopsy. In 40%, autopsy confirmed all US findings but provided additional information of clinical importance. Partial or total lack of agreement was noted in 11% and 4% of the cases, respectively. Areas of discrepancy involved mainly CNS- and cardiovascular abnormalities and, to a lesser extent, renal anomalies, abdominal wall defects and hydrops/hygroma. Regarding CNS abnormalities the overall rate of agreement was 62%; it was highest in acrania/anencephaly (92%) and lowest in hydrocephaly (39%).

CONCLUSION

We find an overall high degree of agreement between US and autopsy findings. Autopsy often provided additional information of clinical value and it should always follow US examination and TOP. Fixation of CNS is crucial for optimal results. Specific limitations of autopsy, i.e., detection of CNS abnormalities, may be reduced by complementary imaging techniques, such as MRI. The ability of US to detect cardiac anomalies is enhanced with the close contact to specialized fetal cardiology.

Foetal brain imaging: ultrasound or MRI. A comparison between magnetic resonance imaging and a dedicated multidisciplinary neurosonographic opinion

OBJECTIVES

(i) To compare original foetal brain ultrasound findings with a multidisciplinary expert opinion; (ii) to compare the multidisciplinary expert ultrasound opinion with foetal magnetic resonance imaging (MRI) findings and (iii) to determine in which circumstances foetal MRI gives additional information, and in how many cases management is changed by having information from MRI.

STUDY DESIGN

Ultrasound scans of 51 consecutive foetuses where foetal brain MR had been performed were retrospectively reviewed by a panel consisting of maternal-foetal-medicine (MFM) consultants, a geneticist, neonatologists and MFM subspecialty trainees. The original ultrasound opinion was compared with the multidisciplinary opinion, which was then compared with MRI findings. In the cases where MRI gave additional information, an assessment was made as to whether this changed management.

RESULTS

The multidisciplinary ultrasound opinion differed from the original opinion in 9 of 51 (17%) cases. In 19 patients (37%), the MRI gave additional information to the original ultrasound, in 7 (13%) cases, management, and in 7 (13%) cases, counselling was altered by additional information gained from MRI. The multidisciplinary ultrasound and MRI diagnoses were similar in 36 cases (71%).

CONCLUSION

Multidisciplinary review of an apparently abnormal foetal brain ultrasound can provide additional diagnostic information. When compared with this level of ultrasound expertise, MRI gave additional information in 29% of cases, but only resulted in change in management in about 13%.

H, Daltro PA, Antunes E, Fazecas T, Rodrigues L, Guerra F, Marchiori E, Gasparetto EL, Domingues RC. O valor da ultra-sonografia e da ressonância magnética fetal na avaliação das hérnias diafragmáticas

OBJETIVO: Demonstrar a significância dos achados da ressonância magnética e da ultra-sonografia na caracterização pré-natal e avaliação do prognóstico de pacientes com hérnia diafragmática congênita. MATERIAIS E MÉTODOS: Catorze gestantes (idade gestacional média de 28,7 semanas) examinadas com ultra-sonografia e apresentando fetos com suspeita de hérnia diafragmática congênita foram avaliadas por meio da ressonância magnética. Os exames foram realizados em aparelho de 1,5 tesla usando seqüências-padrão. Dois radiologistas avaliaram as imagens e estabeleceram os achados por consenso. RESULTADOS: Doze fetos tinham hérnia diafragmática à esquerda e dois, à direita. O fígado fetal foi localizado no interior do tórax de cinco fetos pela ultra-sonografia (três com hérnia diafragmática esquerda e dois com hérnia diafragmática direita) e de oito pela ressonância magnética (seis com hérnia diafragmática esquerda e dois com hérnia diafragmática direita). Herniação do estômago e alças de intestino delgado foi observada em todos os fetos com hérnia diafragmática esquerda (n = 12), tanto pela ultra-sonografia quanto pela ressonância magnética. Oito fetos sobreviveram após cirurgia (sete com hérnia diafragmática esquerda e um com hérnia diafragmática direita). CONCLUSÃO: A ultra-sonografia e a ressonância magnética são métodos de imagens complementares na avaliação das hérnias diafragmáticas congênitas. A ressonância magnética pode auxiliar a ultra-sonografia na avaliação da posição do fígado, o qual representa importante fator prognóstico.

Comparison of magnetic resonance urography with ultrasound studies in detection of fetal urogenital anomalies

PURPOSE

Prenatal ultrasonography detects the vast majority of urogenital anomalies, but in some cases the diagnosis remains in doubt. We assessed the potential of magnetic resonance urography (MRU) in the evaluation of different urogenital anomalies in fetuses when ultrasound study was equivocal.

PATIENTS AND METHODS

We retrospectively reviewed the medical records of 46 fetuses in whom the presence of urogenital anomalies was suspected at ultrasound studies, but remained inconclusive. Fetal MRU was performed within the same week as ultrasound studies. All patients underwent MRU, comprising overview, fast, thick-slab, heavily T2-weighted sequences, followed by focused, high-resolution T2-weighted sequences obtained in sagittal, axial and coronal planes. T1-weighted sequences were obtained in selected cases for assessment of the gastrointestinal tract. All MRU results were compared with ultrasound findings. Sensitivity of each imaging modality was estimated based on definite diagnoses made after birth or abortion.

RESULTS

The mean (range) gestational age was 27 (18-36)weeks. The final diagnosis was ureteropelvic junction obstruction in 12, ureteral dilation (due to vesicoureteral junction obstruction) in five, ureterocele in five, posterior urethral valve in 16, multicystic dysplastic kidney in six, mesenteric cyst in one and abdominoscrotal hydrocele in one. Overall diagnostic sensitivity of fetal MRU was 96% compared to sonography with 58% sensitivity (p<0.05). Fetal MRU studies provided additional information to sonography in 17 (37%) cases, and were especially more sensitive in evaluation of ureteral anatomy.

CONCLUSIONS

Fetal MRU can accurately diagnose a wide variety of urinary tract disorders and must be regarded as a valuable complementary tool to ultrasound in the assessment of the urinary system, particularly in cases of inconclusive ultrasound findings. The present study had a selection bias, as only fetuses with possible anomalies proposed by sonography were referred for MRU; however, this is the population that probably benefits most from MRU studies.

Fetal Magnetic Resonance Imaging as a Complement to Fetal Ultrasonography

Ultrasonography is the screening method of choice for the evaluation of the fetus. It is safe, inexpensive, and easily performed. However, it is operator dependent, and evaluation may be limited because of fetal position, maternal obesity, overlying bone, and/or oligohydramnios. Magnetic resonance imaging is an alternative modality that uses no ionizing radiation, has excellent tissue contrast and a large field of view, is not limited by obesity or overlying bone, and can image the fetus in multiple planes, no matter the fetal lie. Faster scanning techniques allow studies to be performed without sedation in the second and third trimester with minimal motion artifact.

Water imaging (hydrography) in the fetus: the value of a heavily T2-weighted sequence

BACKGROUND

Since the development of fast imaging sequences, MR has proved to be a helpful tool in the evaluation of fetal pathology. Because of the high water content of fetal tissues and pathology, hydrography imaging (MR fetography) can provide additional diagnostic information.

OBJECTIVE

To demonstrate the benefit of MR fetography in fetal imaging.

MATERIALS AND METHODS

From 2004 to 2005, 126 fetal MR examinations were performed for evaluation of an abnormality depicted on an antenatal sonogram. Single-shot fast spin-echo MR imaging and MR fetography were performed through the area of fetal pathology. The two studies were retrospectively compared.

RESULTS

The primary diagnosis was not changed with the addition of MR fetography. New findings, particularly in the kidneys and spine, were identified in 9% of the patients. When fetal pathology was of high water content (80% patients), the MR fetography imaging increased diagnostic confidence. In 11% of the patients, those with cardiovascular or low water pathology, the MR fetography was not beneficial.

CONCLUSION

The mainstay of fetal imaging is currently the HASTE and SSFSE sequences. However, MR fetography is an excellent adjunct that highlights fetal pathology by reinforcing the diagnosis, identifying additional findings, and providing high-contrast high-resolution images that are helpful when counseling clinicians and patients.

[MRI of esophagus. N staging and more...]

Esophageal disease is common. Fluoroscopy with or without fast cine-sequences is able to depict swallowing dynamics precisely and therefore is used in cases with swallowing disturbance, achalasia or diverticula etc. It is performed in addition to primary endoscopy. There is no evidence based indication for MRI in these settings as it is not to rule out post-surgical fistula and incompetence. Endoscopy and endosonography are gold standard for the depiction as well as staging of esophageal tumors hence differentiation of the esophageal wall layers and detection of suspicious lymph nodes is possible. And from both, biopsies may be taken. New techniques as OCT (optical coherence tomography) can demonstrate in situ carcinoma and therefore helps to decide for limited treatments as mucosectomy. For today multimodular treatment strategies in esophageal carcinoma the T-stage will lead to the treatment decision whereas the nodal-stage will give information about the prognosis. As a matter of fact endoscopy is unable to pass a stenosis esophageal tumor in up to 50% of the cases and will therefore not be able to give precise information on both T- and N-stage resulting in a good indication for MRI. Fetal MRI of the chest is a new topic in which MRI seems to be superior to ultrasonography.

Two-dimensional fast imaging employing steady-state acquisition (FIESTA) cine acquisition of fetal non–central nervous system abnormalities

PURPOSE

To evaluate the value of two-dimensional fast imaging employing steady-state acquisition (2D FIESTA) cine MR with parallel imaging techniques in the diagnosis of fetal non-central nervous system (CNS) anomalies.

MATERIALS AND METHODS

A total of 28 pregnant women were referred for further MR evaluation on fetuses after abnormal sonographic results. A total of 33 fetal MR examinations were performed by a 1.5 T MR scanner with eight-channel phase-arrayed body coils. Single-shot fast spin-echo (SSFSE(R), GE) of three orthogonal planes and 2D FIESTA for cine fetal MR of three sagittal planes (midsagittal and 10 mm off midline on left and right) were routinely acquired. Additional planes on target organs with variable imaging frames were added if indicated.

RESULTS

Nine of the 33 examinations (9/33; 27.3%) had motion artifacts obscuring the detail in SSFSE imaging; 2D FIESTA imaging provided motion-artifact-free imaging in all of them. Cine 2D FIESTA imaging provided additional information on the visceral peristalsis. The information helped in differentiating dilated gastrointestinal (GI) tract from other intraabdominal cystic lesions and in confirming the nature and level of GI tract obstruction.

CONCLUSION

With sub-half-second temporal resolution of the 2D FIESTA sequences, fetal movement is no longer problematic. In addition to the anatomical information also provided by conventional SSFSE sequences, 2D FIESTA demonstrates information on motility and peristalsis of hollow organs and helps the diagnosis of fetal visceral anomalies.

Fetal MR Imaging

Ultrasonography is the primary prenatal screening modality used in the evaluation of the fetus and the maternal pelvis. However, fetal MR imaging plays a complementary role to prenatal ultrasound in the evaluation of the fetus with suspected abnormalities. MR imaging's role includes confirming or excluding possible lesions, defining their full extent, aiding in their characterization, and demonstrating other associated abnormalities. As newer techniques such as diffusion imaging, MR spectroscopy, and functional studies are used more widely, it is hoped that additional information will be made available by this modality to physicians evaluating and taking care of fetuses.

Fetal Sheep Development on Ultrasound and Magnetic Resonance Imaging: A Standard for the in utero Assessment of Models of Congenital Abnormalities

OBJECTIVE

To establish normative data for the size, conspicuity, and imaging characteristics of normal developing fetal sheep organs on ultrasound (US) and magnetic resonance (MR) imaging.

METHODS

US and MR images of ten normal pregnant sheep, at 40, 65, 90, 115, and 140 gestational days (term = 145 days), were scored for organ conspicuity and imaging characteristics. Imaging biometry was correlated with specimens. Gestational age-based growth parameters were modeled using regression.

RESULTS

Imaging biometry showed excellent correlation with specimens. Kidney, bladder, stomach, lung, liver, and spine were seen well from 65 days to term by US. More organs were consistently visible from 90 days to term by MR than by US. Most organ imaging characteristics tended not to change throughout gestation.

CONCLUSION

Normal fetal sheep biometry, organ conspicuity, and imaging characteristics are established for US and MR and have potential use for the in utero assessment of sheep models of congenital abnormalities.

Liver, meconium, haemorrhage: the value of T1-weighted images in fetal MRI

BACKGROUND

Ultrafast T2-weighted (T2-W) MRI sequences are currently considered a routine technique for fetal MR imaging. Limited experience exists with fetal T1-weighted (T1-W) imaging techniques.

OBJECTIVE

To determine MRI patterns of some fetal abdominal or haemorrhagic disorders with particular respect to the diagnostic value of T1-W images.

MATERIALS AND METHODS

In addition to standard T2-W single-shot sequences, T1-W single-shot and/or multislice sequences were employed in 25 MR examinations performed in 23 fetuses between 20 and 36 weeks of gestation for more detailed assessment of liver, meconium-filled digestive tract, haemorrhage, or further characterization of a fetal abdominal mass. Diagnostic value and presence of motion artefacts on T1-W images was recorded in each case.

RESULTS

T1-W images enabled superior delineation of fetal liver and large intestine. They provided additional diagnostic information in 9 (39%) of 23 fetuses. One false-positive and one false-negative MRI diagnosis of malrotation anomaly were encountered. Use of single-shot T1-W sequences reduced the occurrence of motion artefacts in 64%.

CONCLUSION

Our results suggest that the specific signal properties of methaemoglobin, meconium and liver are sufficiently important for T1-W sequences to become a routine part of fetal MRI protocols when dealing with digestive tract anomalies, diaphragmatic and abdominal wall defects, intraabdominal masses, and fetal haemorrhage.

[Fetal magnetic resonance imaging. Diagnostics in cases of congenital cystadenomatoid malformation of the lung (CCAM)]

Despite advancing therapeutic strategies, congenital cystadenomatoid malformation of the fetal lung is still a potentially life-threatening anomaly. Antenatally, the development of hydrops as well as the natural history of the malformation is of particular therapeutic and prognostic importance. Postnatally, respiratory distress due to pulmonary hypoplasia counts as a crucial limiting factor. Owing to its feasibility and practicability, as well as a high sensitivity, antenatal ultrasound is still the screening method of choice for the detection of fetal thoracic malformations. However, particularly in cases of indistinguishable sonographic findings, fetal MRI is the modality of choice for proving the diagnosis and preliminary appraisal of intensive care therapy and extracorporal membrane oxygenation postnatally. Furthermore, fetal MRI often facilitates assessment and planning of intrauterine surgical procedures. These two features frequently require a close transfer to an expert neonatal centre.

Fetal Lung Volume Measurements: Determination with MR Imaging—Effect of Various Factors

PURPOSE

To retrospectively determine the effect of gestational age (GA), imaging plane, section thickness, and inter- and intraobserver variability on fetal lung volume (FLV) measurements obtained with magnetic resonance (MR) imaging in a cohort of fetuses without thoracic abnormalities.

MATERIALS AND METHODS

Institutional review board approval was obtained. Informed consent for this retrospective cohort study was waived, and the conduct of this study was HIPAA compliant. FLV was measured in 30 fetuses (GA, 17-36 weeks) referred for MR imaging for indications other than pulmonary abnormalities. Measurements were made on single-shot fast spin-echo images by tracing free-form regions of interest on individual consecutive sections in the transverse, sagittal, and coronal planes. Measurements were performed twice by two observers independently. Correlations between FLV and GA, imaging plane, and section thickness were assessed, as were intra- and interobserver variability. Time to perform FLV was assessed in a subset of fetuses.

RESULTS

Total FLV ranged from 2 to 110 mL. Mixed-effects regression model showed significant quadratic trend in FLV with increasing GA, with comparable strength of correlation (r = 0.89-0.91) in the three imaging planes of measurement. Intraobserver agreement was good in all three planes (r = 0.65-0.83) and was highest in the transverse plane. Interobserver agreement was good in all three planes (r = 0.68-0.76). FLV showed no significant dependence on section thickness (P = .23) or imaging plane (P = .82). Mean time to obtain FLV measurements ranged from 48 seconds at GA of 21 weeks to 77 seconds at GA of 29-30 weeks.

CONCLUSION

GA-based FLV measurements obtained with MR images are independent of section thickness and imaging plane and can be performed with good inter- and intraobserver agreement in less than 2 minutes.

Three-dimensional magnetic resonance imaging after ultrasonography for assessment of fetal gastroschisis

A 24-year-old woman (Gravida I, Para I) at estimated 32 weeks of pregnancy was referred to our department for evaluation of a suspected fetal gastroschisis. Ultrasound scan revealed multiple loops of dilated bowel outside the fetal abdomen and absence of membrane surrounding the herniated loops of the intestines. Three-dimensional (3D) magnetic resonance imaging was performed to obtain more information on the bowel both outside and inside the abdomen. Images were constructed with T1-weighted fat-suppressed 3D fast low-angle shot sequences using a maximum intensity projection algorithm. The 3D images made possible the realization of fetal bowel conditions with greater definition and accuracy.