T1-weighted fast fluid-attenuated inversion-recovery sequence (T1-FFLAIR) enables the visualization and quantification of fetal brain myelination in utero

OBJECTIVES

To investigate the advantage of T1-weighted fast fluid-attenuated inversion-recovery MRI sequence without (T1-FFLAIR) and with compressed sensing technology (T1-FFLAIR-CS), which shows improved T1-weighted contrast, over standard used T1-weighted fast field echo (T1-FFE) sequence for the assessment of fetal myelination.

MATERIALS AND METHODS

This retrospective single-center study included 115 consecutive fetal brain MRI examinations (63 axial and 76 coronal, mean gestational age (GA) 28.56 ± 5.23 weeks, range 19-39 weeks). Two raters, blinded to GA, qualitatively assessed a fetal myelin total score (MTS) on each T1-weighted sequence at five brain regions (medulla oblongata, pons, mesencephalon, thalamus, central region). One rater performed region-of-interest quantitative analysis (n = 61) at the same five brain regions. Pearson correlation analysis was applied for correlation of MTS and of the signal intensity ratios (relative to muscle) with GA on each T1-weighted sequence. Fetal MRI-based results were compared with myelination patterns of postmortem fetal human brains (n = 46; GA 18 to 42), processed by histological and immunohistochemical analysis.

RESULTS

MTS positively correlated with GA on all three sequences (all r between 0.802 and 0.908). The signal intensity ratios measured at the five brain regions correlated best with GA on T1-FFLAIR (r between 0.583 and 0.785). T1-FFLAIR demonstrated significantly better correlations with GA than T1-FFE for both qualitative and quantitative analysis (all p < 0.05). Furthermore, T1-FFLAIR enabled the best visualization of myelinated brain structures when compared to histology.

CONCLUSION

T1-FFLAIR outperforms the standard T1-FFE sequence in the visualization of fetal brain myelination, as demonstrated by qualitative and quantitative methods.

CLINICAL RELEVANCE STATEMENT

T1-weighted fast fluid-attenuated inversion-recovery sequence (T1-FFLAIR) provided best visualization and quantification of myelination in utero that, in addition to the relatively short acquisition time, makes feasible its routine application in fetal MRI for the assessment of brain myelination.

KEY POINTS

• So far, the assessment of fetal myelination in utero was limited due to the insufficient contrast. • T1-weighted fast fluid-attenuated inversion-recovery sequence allows a qualitative and quantitative assessment of fetal brain myelination. • T1-weighted fast fluid-attenuated inversion-recovery sequence outperforms the standard used T1-weighted sequence for visualization and quantification of myelination in utero.

Synthetic MR Imaging-Based WM Signal Suppression Identifies Neonatal Brainstem Pathways in Vivo

BACKGROUND AND PURPOSE

Multidynamic multiecho sequence-based imaging enables investigators to reconstruct multiple MR imaging contrasts on the basis of a single scan. This study investigated the feasibility of synthetic MRI-based WM signal suppression (syWMSS), a synthetic inversion recovery approach in which a short TI suppresses myelin-related signals, for the identification of early myelinating brainstem pathways.

MATERIALS AND METHODS

Thirty-one cases of neonatal MR imaging, which included multidynamic multiecho data and conventionally acquired T1- and T2-weighted sequences, were analyzed. The multidynamic multiecho postprocessing software SyMRI was used to generate syWMSS data (TR/TE/TI = 3000/5/410 ms). Two raters discriminated early myelinating brainstem pathways (decussation of the superior cerebellar peduncle, medial lemniscus, central tegmental tract, and medial longitudinal fascicle [the latter 3 assessed at the level of the pons]) on syWMSS data and reference standard contrasts.

RESULTS

On the basis of syWMSS data, the decussation of the superior cerebellar peduncle (31/31); left/right medial lemniscus (31/31; 30/31); left/right central tegmental tract (19/31; 20/31); and left/right medial longitudinal fascicle (30/31) were reliably identified by both raters. On the basis of T1-weighted contrasts, the decussation of the superior cerebellar peduncle (14/31); left/right medial lemniscus (22/31; 16/31); left/right central tegmental tract (1/31); and left/right medial longitudinal fascicle (9/31; 8/31) were reliably identified by both raters. On the basis of T2-weighted contrasts, the decussation of the superior cerebellar peduncle (28/31); left/right medial lemniscus (16/31; 12/31); left/right central tegmental tract (23/31; 18/31); and left/right medial longitudinal fascicle (15/31; 14/31) were reliably identified by both raters.

CONCLUSIONS

syWMSS data provide a feasible imaging technique with which to study early myelinating brainstem pathways. MR imaging approaches that use myelin signal suppression contribute to a more sensitive assessment of myelination patterns at early stages of cerebral development.

Influence of dilution on arterial-phase artifacts and signal intensity on gadoxetic acid-enhanced liver MRI

OBJECTIVES

To investigate the effect of saline-diluted gadoxetic acid, done for arterial-phase (AP) artifact reduction, on signal intensity (SI), and hence focal lesion conspicuity on MR imaging.

METHODS

We retrospectively examined 112 patients who each had at least two serial gadoxetic acid-enhanced liver MRIs performed at 1 ml/s, first with non-diluted (ND), then with 1:1 saline-diluted (D) contrast. Two blinded readers independently analyzed the artifacts and graded dynamic images using a 5-point scale. The absolute SI of liver parenchyma, focal liver lesions (if present), aorta, and portal vein at the level of the celiac trunk and the SI of the paraspinal muscle were measured in all phases. The signal-to-norm (SI_Norm) of the vascular structures, hepatic parenchyma and focal lesions, and the contrast-to-norm (C_Norm) of focal liver lesions were calculated.

RESULTS

AP artifacts were significantly reduced with dilution. Mean absolute contrast-enhanced liver SI was significantly higher on the D exams compared to the ND exams. Likewise, SI_Norm of liver parenchyma was significantly higher in all contrast-enhanced phases except transitional phase on the D exams. SI_Norm values in the AP for the aorta and in the PVP for portal vein were significantly higher on the diluted exams. The C_Norm was not significantly different between ND and D exams for lesions in any imaging phase. The interclass correlation coefficient was excellent (0.89).

CONCLUSION

Gadoxetic acid dilution injected at 1ml/s produces images with significantly fewer AP artifacts but no significant loss in SI_Norm or C_Norm compared to standard non-diluted images.

KEY POINTS

• Diluted gadoxetic acid at slow injection (1 ml/s) yielded images with higher SI_Norm of the liver parenchyma and preserved C_Norm for focal liver lesions. • Gadoxetic acid-enhanced MRI injected at 1 ml/s is associated with arterial-phase (AP) artifacts in 31% of exams, which may degrade image quality and limits focal liver lesion detection. • Saline dilution of gadoxetic acid 1:1 combined with a slow injection rate of 1 ml/s significantly reduced AP artifacts from 31 to 9% and non-diagnostic AP artifacts from 16 to 1%.

Different from the Beginning: WM Maturity of Female and Male Extremely Preterm Neonates-A Quantitative MRI Study

BACKGROUND AND PURPOSE

Former preterm born males are at higher risk for neurodevelopmental disabilities compared with female infants born at the same gestational age. This retrospective study investigated sex-related differences in the maturity of early myelinating brain regions in infants born <28 weeks' gestational age using diffusion tensor- and relaxometry-based MR imaging.

MATERIALS AND METHODS

Quantitative MR imaging sequence acquisitions were analyzed in a sample of 35 extremely preterm neonates imaged at term-equivalent ages. Quantitative MR imaging metrics (fractional anisotropy; ADC [10^-3mm²/s]; and T1-/T2-relaxation times [ms]) of the medulla oblongata, pontine tegmentum, midbrain, and the right/left posterior limbs of the internal capsule were determined on diffusion tensor- and multidynamic, multiecho sequence-based imaging data. ANCOVA and a paired t test were used to compare female and male infants and to detect hemispheric developmental asymmetries.

RESULTS

Seventeen female (mean gestational age at birth: 26 + 0 [SD, 1 + 4] weeks+days) and 18 male (mean gestational age at birth: 26 + 1 [SD, 1 + 3] weeks+days) infants were enrolled in this study. Significant differences were observed in the T2-relaxation time (P = .014) of the pontine tegmentum, T1-relaxation time (P = .011)/T2-relaxation time (P = .024) of the midbrain, and T1-relaxation time (P = .032) of the left posterior limb of the internal capsule. In both sexes, fractional anisotropy (P [♀] < .001/P [♂] < .001) and ADC (P [♀] = .017/P [♂] = .028) differed significantly between the right and left posterior limbs of the internal capsule.

CONCLUSIONS

The combined use of various quantitative MR imaging metrics detects sex-related and interhemispheric differences of WM maturity. The brainstem and the left posterior limb of the internal capsule of male preterm neonates are more immature compared with those of female infants at term-equivalent ages. Sex differences in WM maturation need further attention for the personalization of neonatal brain imaging.

Brainstem and cerebellar volumes at magnetic resonance imaging are smaller in fetuses with congenital heart disease

BACKGROUND

Congenital heart disease is associated with an increased risk of smaller brain volumes and structural brain damage, and impaired growth of supratentorial brain structures in utero has been linked to poor neurodevelopmental outcomes. However, little is known on brainstem and cerebellar volumes in fetuses with congenital heart disease. Moreover, it is not clear whether impaired infratentorial growth, if present, is associated with only certain types of fetal cardiac defects or with supratentorial brain growth, and whether altered biometry is already present before the third trimester.

OBJECTIVE

This study aimed to investigate brainstem and cerebellar volumes in fetuses with congenital heart disease and to compare them to infratentorial brain volumes in fetuses with normal hearts. Secondarily, the study aimed to identify associations between infratentorial brain biometry and the type of cardiac defects, supratentorial brain volumes, and gestational age.

STUDY DESIGN

In this retrospective case-control study, 141 magnetic resonance imaging studies of 135 fetuses with congenital heart disease and 141 magnetic resonance imaging studies of 125 controls with normal hearts at 20 to 37 gestational weeks (median, 25 weeks) were evaluated. All cases and controls had normal birthweight and no evidence of structural brain disease or genetic syndrome. Six types of congenital heart disease were included: tetralogy of Fallot (n=32); double-outlet right ventricle (n=22); transposition of the great arteries (n=27); aortic obstruction (n=24); hypoplastic left heart syndrome (n=22); and hypoplastic right heart syndrome (n=14). First, brainstem and cerebellar volumes of each fetus were segmented and compared between cases and controls. In addition, transverse cerebellar diameters, vermian areas, and supratentorial brain and cerebrospinal fluid volumes were quantified and differences assessed between cases and controls. Volumetric differences were further analyzed according to types of cardiac defects and supratentorial brain volumes. Finally, volume ratios were created for each brain structure ([volume in fetus with congenital heart disease/respective volume in control fetus] × 100) and correlated to gestational age.

RESULTS

Brainstem (cases, 2.1 cm³ vs controls, 2.4 cm³; P<.001) and cerebellar (cases, 3.2 cm³ vs controls, 3.4 cm³; P<.001) volumes were smaller in fetuses with congenital heart disease than in controls, whereas transverse cerebellar diameters (P=.681) and vermian areas (P=.947) did not differ between groups. Brainstem and cerebellar volumes differed between types of cardiac defects. Overall, the volume ratio of cases to controls was 80.8% for the brainstem, 90.5% for the cerebellum, and 90.1% for the supratentorial brain. Fetuses with tetralogy of Fallot and transposition of the great arteries were most severely affected by total brain volume reduction. Gestational age had no effect on volume ratios.

CONCLUSION

The volume of the infratentorial brain, which contains structures considered crucial to brain function, is significantly smaller in fetuses with congenital heart disease than in controls from midgestation onward. These findings suggest that impaired growth of both supra- and infratentorial brain structures in fetuses with congenital heart disease occurs in the second trimester. Further research is needed to elucidate associations between fetal brain volumes and neurodevelopmental outcomes in congenital heart disease.

Abnormal Extracardiac Development in Fetuses With Congenital Heart Disease

BACKGROUND

Knowledge about extracardiac anomalies (ECA) in fetal congenital heart disease (CHD) can improve our understanding of the developmental origins of various outcomes in these infants. The prevalence and spectrum of ECA, including structural brain anomalies (SBA), on magnetic resonance imaging (MRI) in fetuses with different types of CHD and at different gestational ages, is unknown.

OBJECTIVES

The purpose of this study was to evaluate ECA rates and types on MRI in fetuses with different types of CHD and across gestation.

METHODS

A total of 429 consecutive fetuses with CHD and MRI between 17 and 38 gestational weeks were evaluated. ECA and SBA rates were assessed for each type of CHD and classified by gestational age (<25 or ≥25 weeks) at MRI.

RESULTS

Of all 429 fetuses with CHD, 243 (56.6%) had ECA on MRI, and 109 (25.4%) had SBA. Among the 191 fetuses with normal genetic testing results, the ECA rate was 54.5% and the SBA rate 19.4%. Besides SBA, extrafetal (21.2%) and urogenital anomalies (10.7%) were the most prevalent ECA on MRI in all types of CHD. Predominant SBA were anomalies of hindbrain-midbrain (11.0% of all CHD), dorsal prosencephalon (10.0%) development, and abnormal cerebrospinal fluid spaces (10.5%). There was no difference in the prevalence or pattern of ECA between early (<25 weeks; 45.7%) and late (≥25 weeks; 54.3%) fetal MRI.

CONCLUSIONS

ECA and SBA rates on fetal MRI are high across all types of CHD studied, and ECA as well as SBA are already present from midgestation onward.

Mapping Human Fetal Brain Maturation In Vivo Using Quantitative MRI

BACKGROUND AND PURPOSE

On the basis of a single multidynamic multiecho sequence acquisition, SyMRI generates a variety of quantitative image data that can characterize tissue-specific properties. The aim of this retrospective study was to evaluate the feasibility of SyMRI for the qualitative and quantitative assessment of fetal brain maturation.

MATERIALS AND METHODS

In 52 fetuses, multidynamic multiecho sequence acquisitions were available. SyMRI was used to perform multidynamic multiecho-based postprocessing. Fetal brain maturity was scored qualitatively on the basis of SyMRI-generated MR imaging data. The results were compared with conventionally acquired T1-weighted/T2-weighted contrasts as a standard of reference. Myelin-related changes in T1-/T2-relaxation time/relaxation rate, proton density, and MR imaging signal intensity of the developing fetal brain stem were measured. A Pearson correlation analysis was used to detect correlations between the following: 1) the gestational age at MR imaging and the fetal brain maturity score, and 2) the gestational age at MR imaging and the quantitative measurements.

RESULTS

SyMRI provided images of sufficient quality in 12/52 (23.08%) (range, 23 + 6-34 + 0) fetal multidynamic multiecho sequence acquisitions. The fetal brain maturity score positively correlated with gestational age at MR imaging (SyMRI: r = 0.915, P < .001/standard of reference: r = 0.966, P < .001). Myelination-related changes in the T2 relaxation time/T2 relaxation rate of the medulla oblongata significantly correlated with gestational age at MR imaging (T2-relaxation time: r = -0.739, P = .006/T2-relaxation rate: r = 0.790, P = .002).

CONCLUSIONS

Fetal motion limits the applicability of multidynamic multiecho-based postprocessing. However, SyMRI-generated image data of sufficient quality enable the qualitative assessment of maturity-related changes of the fetal brain. In addition, quantitative T2 relaxation time/T2 relaxation rate mapping characterizes myelin-related changes of the brain stem prenatally. This approach, if successful, opens novel possibilities for the evaluation of structural and biochemical aspects of fetal brain maturation.

Diagnostic quality of 3Tesla postmortem magnetic resonance imaging in fetuses with and without congenital heart disease

BACKGROUND

Postmortem confirmation of prenatally diagnosed congenital heart disease after termination of pregnancy and evaluation of potential cardiac defects after spontaneous fetal or neonatal death are essential. Conventional autopsy rates are decreasing, and 1.5Tesla magnetic resonance imaging has demonstrated limited diagnostic accuracy for postmortem cardiovascular assessment.

OBJECTIVE

This study aimed to evaluate the feasibility and image quality of cardiac 3Tesla postmortem magnetic resonance imaging and to assess its diagnostic accuracy in detecting fetal heart defects compared with conventional autopsy. Secondarily, the study aimed to explore whether clinical factors affect the quality of 3Tesla postmortem magnetic resonance imaging.

STUDY DESIGN

A total of 222 consecutive fetuses between 12 and 41 weeks' gestation, who underwent 3Tesla postmortem magnetic resonance imaging and conventional autopsy after spontaneous death or termination of pregnancy for fetal malformations, were included. First, 3Tesla postmortem magnetic resonance imaging of each fetus was rated as diagnostic or nondiagnostic for fetal cardiac assessment by 2 independent raters. The image quality of individual cardiac structures was then further evaluated by visual grading analysis. Finally, the presence or absence of a congenital heart defect was assessed by 2 radiologists and compared with autopsy results.

RESULTS

Overall, 87.8% of 3Tesla postmortem magnetic resonance imaging examinations were rated as diagnostic for the fetal heart. Diagnostic imaging rates of individual cardiac structures at 3Tesla postmortem magnetic resonance imaging ranged from 85.1% (atrioventricular valves) to 94.6% (pericardium), with an interrater agreement of 0.82 (0.78-0.86). Diagnostic imaging of the fetal aortic arch and the systemic veins at 3Tesla postmortem magnetic resonance imaging was possible from 12+5 weeks' gestation onward in 90.1% and 92.3% of cases, respectively. A total of 55 fetuses (24.8%) had at least 1 cardiac anomaly according to autopsy, 164 (73.9%) had a normal heart, and in 3 fetuses (1.4%), autopsy was nondiagnostic for the heart. Considering all examinations rated as diagnostic, 3Tesla postmortem magnetic resonance imaging provided high diagnostic accuracy for the detection of fetal congenital heart defects with a sensitivity of 87.8%, a specificity of 97.9%, and concordance with autopsy of 95.3%. 3Tesla postmortem magnetic resonance imaging was less accurate in young fetuses (<20 weeks compared with ≥20 weeks; P<.001), in fetuses with low birthweight (≤100 g compared with >100 g; P<.001), in cases after spontaneous fetal death (compared with other modes of death; P=.012), in cases with increasing latency between death and 3Tesla postmortem magnetic resonance imaging (P<.001), and in cases in which there was a high degree of maceration (maceration score of 3 compared with a score from 0 to 2; P=.004).

CONCLUSION

Diagnostic 3Tesla postmortem magnetic resonance imaging assessment of the fetal heart is feasible in most fetuses from 12 weeks' gestation onward. In diagnostic images, sensitivity and, particularly, specificity in the detection of congenital heart disease are high compared with conventional autopsy. Owing to its high diagnostic accuracy, we suggest that 3Tesla postmortem magnetic resonance imaging may serve as a suitable imaging modality with which to direct a targeted conventional autopsy when pathology resources are limited or to provide a virtual autopsy when full autopsy is declined by the parents.

Comparison of the colon with T1 breath-hold vs T1 free-breathing-A retrospective fetal MRI study

OBJECTIVES

Fetal magnetic resonance imaging (MRI) plays an increasingly important role in the prenatal diagnosis of gastrointestinal abnormalities. During gestation, the bowel develops T1-weighted hyperintensity due to meconium formation. Currently used T1-weighted sequences are performed in maternal breath-hold (BH) technique, which may take up to 20 s. The free-breathing (FB) T1-weighted 3D radial VIBE (volumetric interpolated breath-hold examination) sequence requires no breath-hold, improving patient comfort. This study aimed to address how well the FB acquisition technique can visualize large bowel structures compared to the routinely performed breath-hold sequence.

METHODS

Forty-seven fetal MRI studies between 21 and 36 weeks of gestation without abdominal pathologies on prenatal MRI and ultrasound were included. All fetal scans were performed using a Philips Ingenia 1.5 T MRI. Coronal T1-weighted BH and FB sequences without fat suppression were compared. The following acquisition parameters were used (T1, FB): resolution 1.137 mm, 1.004 mm; matrix size 288 × 288, 448 × 448; FOV 328 mm, 450 mm; TR 81-132 ms, 3.47 ms; TE 4.6 ms, 1.47 ms. Due to the necessity of the breath-hold the duration of the sequence could not exceed 20 s (mean duration of the T1-weighted BH sequence 15.17 s, and mean duration of the FB sequence 26.42 s). In all examined fetuses the following structures were evaluated with respect to their visibility (0-not visible, 1-partially visible, 2-clearly visible): rectum, sigmoid, descending, transverse and ascending colon, cecum. Furthermore, motion artifacts were assessed (0-none, 1-intermediate, 2-severe motion artifacts), and the signal intensity (SI) ratio between maternal fat and fetal rectum SI was calculated.

RESULTS

No significant differences in the visibility of sigmoid and colon between BH and FB were detected, only the cecum could be seen slightly better (in 29.8 % of cases) using BH technique. Motion artifacts were similar between BH and FB. There was a non-significant SI difference (p = 0.68) in the rectum, with a higher SI in the BH sequence.

CONCLUSIONS

The FB acquisition technique compared to T1 using BH is equal regarding visibility of bowel structures and artifacts. Due to non-inferiority to the BH technique, the FB sequence is a good alternative in cases where BH cannot be performed. As the FB sequence further allows for thinner slices with a good signal, even small bowel loops may be visualized.

Prenatal assessment of cerebellar vermian lobulation: fetal MRI with 3-Tesla postmortem validation

OBJECTIVES

To optimize the imaging assessment of fetal hindbrain malformations, this observational magnetic resonance imaging (MRI) study aimed to assess whether fetal vermian lobulation can be quantified accurately and whether the relative growth of vermian lobules is uniform.

METHODS

This retrospective study included singleton fetuses which underwent T2-weighted MRI in vivo with a 1.5-Tesla (T) scanner or within 24 h postmortem with a 3-T scanner between January 2007 and November 2016 at the Medical University of Vienna. We included only those showing normal structural brain development on ultrasound and MRI and which had image quality appropriate for quantitative analysis, i.e. good image quality and a precise midsagittal slice. Fetal brains were segmented and, for all discernible vermian lobules, we determined the mean relative area contribution (MRAC, the proportion of the lobule relative to the total vermian area, in terms of number of voxels). Inter- and intrarater measurement variability of a representative selection (21 cases) was determined by intraclass correlation coefficient (ICC) for voxel-based differences. A linear regression model was used to assess the correlation between the relative size of each vermian lobule (i.e. MRAC) and gestational age.

RESULTS

A total of 78 fetuses scanned in vivo aged 18-32 gestational weeks and seven fetuses scanned postmortem aged 16-30 weeks had a precise midsagittal slice and image quality sufficient for quantitative analysis. After 22 weeks of gestation, seven of the nine known vermian lobules could be discriminated reliably. The MRAC showed a mean ± SD difference of only 2.89 ± 3.01% between in-vivo and postmortem measurements. The ICC of voxel-based interrater differences was mean ± SD, 0.91 ± 0.05 and the intrarater ICC was 0.95 ± 0.03. Growth of cerebellar lobules was non-uniform: the MRAC of culmen and DFT (declive + folium + tuber) increased with gestational age, whereas that of lingula, centralis, pyramis and nodulus decreased. The growth of the uvula showed no significant correlation with gestational age.

CONCLUSIONS

Fetal vermian lobulation can be assessed accurately and reliably after 22 weeks on precise midsagittal sequences with 1.5-T T2-weighted MRI. Fetal vermian lobules show non-uniform growth, with expansion of DFT and culmen at the expense of the other vermian lobules. Evaluation and elucidation of vermian lobulation in normal fetuses should enable better characterization of fetuses with hindbrain malformations. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.