Background Late-onset intrauterine growth restriction (IUGR) results from a failure of the placenta to supply adequate nutrients and oxygen to the rapidly growing late-gestation fetus. Limitations in ...current monitoring methods present the need for additional techniques for more accurate diagnosis of IUGR in utero. New magnetic resonance imaging (MRI) technology now provides a noninvasive technique for fetal hemodynamic assessment, which could provide additional information over conventional Doppler methods. Objective The objective of the study was to use new MRI techniques to measure hemodynamic parameters and brain growth in late-onset IUGR fetuses. Study Design This was a prospective observational case control study to compare the flow and T2 of blood in the major fetal vessels and brain imaging findings using MRI. Indexed fetal oxygen delivery and consumption were calculated. Middle cerebral artery and umbilical artery pulsatility indexes and cerebroplacental ratio were acquired using ultrasound. A score of ≥ 2 of the 4 following parameters defined IUGR: (1) birthweight the third centile or less or 20% or greater drop in the centile in estimated fetal weight; (2) lowest cerebroplacental ratio after 30 weeks less than the fifth centile; (3) ponderal index < 2.2; and (4) placental histology meets predefined criteria for placental underperfusion. Measurements were compared between the 2 groups (Student t test) and correlations between parameters were analyzed (Pearson’s correlation). MRI measurements were compared with Doppler parameters for identifying IUGR defined by postnatal criteria (birthweight, placental histology, ponderal index) using receiver-operating characteristic curves. Results We studied 14 IUGR and 26 non-IUGR fetuses at 35 weeks’ gestation. IUGR fetuses had lower umbilical vein ( P = .004) and pulmonary blood flow ( P = .01) and higher superior vena caval flow ( P < .0001) by MRI. IUGR fetuses had asymmetric growth but smaller brains than normal fetuses ( P < .0001). Newborns with IUGR also had smaller brains with otherwise essentially normal findings on MRI. Vessel T2s, oxygen delivery, oxygen consumption, middle cerebral artery pulsatility index, and cerebroplacental ratio were all significantly lower in IUGR fetuses, whereas there was no significant difference in umbilical artery pulsatility index. IUGR score correlated positively with superior vena caval flow and inversely with oxygen delivery, oxygen consumption, umbilical vein T2, and cerebroplacental ratio. Receiver-operating characteristic curves revealed equivalent performance of MRI and Doppler techniques in identifying IUGR that was defined based on postnatal parameters with superior vena caval flow area under the curve of 0.94 (95% confidence interval, 0.87–1.00) vs a cerebroplacental ratio area under the curve of 0.80 (95% confidence interval, 0.64–0.97). Conclusion MRI revealed the expected circulatory redistribution in response to hypoxia in IUGR fetuses. The reduced oxygen delivery in IUGR fetuses indicated impaired placental oxygen transport, whereas reduced oxygen consumption presumably reflected metabolic adaptation to diminished substrate delivery, resulting in slower fetal growth. Despite brain sparing, placental insufficiency limits fetal brain growth. Superior vena caval flow and umbilical vein T2 by MRI may be useful new markers of late-onset IUGR.
Abstract Objective To investigate preoperative cerebral hemodynamics in newborns with congenital heart disease. We hypothesized that cerebral blood flow and oxygen delivery would be decreased in ...newborns with congenital heart disease compared with controls. Methods Using a “feed-and-sleep” approach to performing neonatal magnetic resonance imaging, we measured cerebral blood flow by using a slice prescription perpendicular to the right and left internal carotid arteries and basilar artery at the level of the clivus. We calculated brain volume by segmenting a 3-dimensional steady-state free procession acquisition of the whole brain, allowing quantification of cerebral blood flow indexed to brain volume. Cerebral oxygen delivery was calculated as the product of cerebral blood flow and preductal systemic arterial oxygen content obtained via a combination of conventional pulse oximetry and laboratory analysis of venous blood samples for hemoglobin concentration. Results A complete set of measurements were obtained in 32 newborns with heart disease and 31 controls. There was no difference in gestational age between the heart disease and control groups. There was no difference in cerebral blood flow compared with controls (103.5 ± 34.0 vs 119.7 ± 40.4 mL/min), whereas cerebral oxygen delivery was significantly lower in the congenital heart disease subjects (1881 ± 625.7 vs 2712 ± 915.7 mLO2 /min). Ten newborns with congenital heart disease had diffuse excessive high signal intensity in their white matter and 2 had white matter injury whereas another 5 had both. Conclusions Newborns with unrepaired cyanotic congenital heart disease have decreased cerebral oxygen delivery due to arterial desaturation. If brain growth and development are adversely affected through oxygen conformance, our findings could have clinical implications in terms of timing of surgical repair.
Phase-contrast MRI with metric-optimized gating is a promising new technique for studying the distribution of the fetal circulation. However, mean and reference ranges for blood flow measurements ...made in the major fetal vessels using this technique are yet to be established.
We measured flow in the major vessels of the fetal circulation in 40 late-gestation normal human fetuses using phase-contrast MRI (mean gestational age, 37 SD=1.1 weeks). Flows were indexed to the fetal weight, which was estimated from the fetal volume calculated by MRI segmentation. The following mean flows (in mL/min per kilogram; ±2SD) were obtained: combined ventricular output, 465 (351, 579); main pulmonary artery, 261 (169, 353); ascending aorta, 191 (121, 261); superior vena cava, 137 (77, 197); ductus arteriosus, 187 (109, 265); descending aorta, 252 (160, 344); pulmonary blood flow, 77 (0, 160); umbilical vein, 134 (62, 206); and foramen ovale, 135 (37, 233). Expressed as percentages of the combined ventricular output, the mean flows±2 SD were as follows: main pulmonary artery, 56 (44, 68); ascending aorta, 41 (29, 53); superior vena cava, 29 (15, 43); ductus arteriosus, 41 (25, 57); descending aorta, 55 (35, 75); pulmonary blood flow, 16 (0, 34); umbilical vein, 29 (11, 47); and foramen ovale, 29 (7, 51). A strong inverse relationship between foramen ovale shunt and pulmonary blood flow was noted (r=-0.64; P<0.0001).
Although too small a sample size to provide normal ranges, these results are in keeping with those predicted in humans based on measurements made in fetal lambs using radioactive microspheres and provide preliminary reference ranges for the late-gestation human fetuses. The wide range we found in foramen ovale shunting suggests a degree of variability in the way blood is streamed through the fetal circulation.
Abstract Background Patients with single ventricle (SV) circulations are at risk for ventricular dysfunction. This study investigated whether there is evidence of increased myocardial fibrosis and ...myocardial dysfunction in children after the Fontan operation. Methods Consecutive children after the Fontan operation who underwent cardiac magnetic resonance (CMR) T1 relaxometry with a modified look-locker inversion recovery approach were included in this retrospective study. Native T1 times (T1) and extracellular volume fractions (ECV) in the free wall of the dominant ventricle (left, SLV; right, SRV) were compared with controls and correlated with hemodynamic and clinical parameters. Results Twenty-one SV patients (9.7 ± 4.6 years; 13 SLV; 8 SRV) and 24 healthy control children (13.9 ± 2.6 years, p = 0.002) were included. T1 and ECV were higher in SRV patients than in controls (1036 ± 46 ms vs 974 ± 27 ms, p < 0.001; 28 ± 4% vs 22 ± 3%, p = 0.002) and SLV patients (978 ± 39 ms, p = 0.002; 23 ± 5%, p = 0.012) while there was no difference between SLV patients and controls. Age at bidirectional cavopulmonary connection was correlated with T1 (R = 0.55, p = 0.015), while systolic blood pressure (R =-0.68, p < 0.001) and body weight (R =-0.54, p = 0.012) inversely correlated with ECV. T1 negatively correlated with radial and circumferential strain by CMR feature tracking. Conclusions Fontan patients with a SRV showed increased CMR markers of diffuse myocardial fibrosis, which were associated with decreased myocardial contractility. Whether their increased fibrosis burden is the greater risk for long-term complications in this population remains to be investigated.
We present the first phase contrast (PC) cardiovascular magnetic resonance (CMR) measurements of the distribution of blood flow in twelve late gestation human fetuses. These were obtained using a ...retrospective gating technique known as metric optimised gating (MOG).
A validation experiment was performed in five adult volunteers where conventional cardiac gating was compared with MOG. Linear regression and Bland Altman plots were used to compare MOG with the gold standard of conventional gating. Measurements using MOG were then made in twelve normal fetuses at a median gestational age of 37 weeks (range 30-39 weeks). Flow was measured in the major fetal vessels and indexed to the fetal weight.
There was good correlation between the conventional gated and MOG measurements in the adult validation experiment (R=0.96). Mean flows in ml/min/kg with standard deviations in the major fetal vessels were as follows: combined ventricular output (CVO) 540 ± 101, main pulmonary artery (MPA) 327 ± 68, ascending aorta (AAo) 198 ± 38, superior vena cava (SVC) 147 ± 46, ductus arteriosus (DA) 220 ± 39,pulmonary blood flow (PBF) 106 ± 59,descending aorta (DAo) 273 ± 85, umbilical vein (UV) 160 ± 62, foramen ovale (FO)107 ± 54. Results expressed as mean percentages of the CVO with standard deviations were as follows: MPA 60 ± 4, AAo37 ± 4, SVC 28 ± 7, DA 41 ± 8, PBF 19 ± 10, DAo50 ± 12, UV 30 ± 9, FO 21 ± 12.
This study demonstrates how PC CMR with MOG is a feasible technique for measuring the distribution of the normal human fetal circulation in late pregnancy. Our preliminary results are in keeping with findings from previous experimental work in fetal lambs.
To develop and evaluate a reconstruction framework for high resolution time-resolved CMR of the fetal heart in the presence of motion.
Data were acquired using a golden angle radial trajectory in ...seven fetal subjects and reconstructed as real-time images to detect fetal movement. Data acquired during through-plane motion were discarded whereas in-plane motion was corrected. A fetal cardiac gating signal was extracted to sort the corrected data by cardiac phase, allowing reconstruction of cine images. The quality of motion corrected images and the effect of data undersampling were quantified using separate expressions for spatial blur and image error.
Motion corrected reordered cine reconstructions (127 slices) showed improved image quality relative to both uncorrected cines and corresponding real-time images across a range of root-mean-squared (RMS) displacements (0.3-3.7 mm) and fetal heart rates (119-176 bpm). The relative spatial blur between cines with and without motion correction increased with in-plane RMS displacement leading to an effective decrease in the effective spatial resolution for images without motion correction. Image error between undersampled and reference images was less than 10% for reconstructions using 750 or more spokes, yielding a minimum acceptable scan time of approximately 4 s/slice during quiescent through plane motion.
By rejecting data corrupted by through-plane motion, and correcting data corrupted by in-plane translation, the proposed reconstruction framework accounts for common sources of motion artifact (gross fetal movement, maternal respiration, fetal cardiac contraction) to produce high quality images of the fetal heart.
To image multidimensional flow in fetuses using golden-angle radial phase contrast cardiovascular magnetic resonance (PC-CMR) with motion correction and retrospective gating.
A novel PC-CMR method ...was developed using an ungated golden-angle radial acquisition with continuously incremented velocity encoding. Healthy subjects (n = 5, 27 ± 3 years, males) and pregnant females (n = 5, 34 ± 2 weeks gestation) were imaged at 3 T using the proposed sequence. Real-time reconstructions were first performed for retrospective motion correction and cardiac gating (using metric optimized gating, MOG). CINE reconstructions of multidimensional flow were then performed using the corrected and gated data.
In adults, flows obtained using the proposed method agreed strongly with those obtained using a conventionally gated Cartesian acquisition. Across the five adults, bias and limits of agreement were - 1.0 cm/s and - 5.1, 3.2 cm/s for mean velocities and - 1.1 cm/s and - 6.5, 4.3 cm/s for peak velocities. Temporal correlation between corresponding waveforms was also high (R~ 0.98). Calculated timing errors between MOG and pulse-gating RR intervals were low (~ 20 ms). First insights into multidimensional fetal blood flows were achieved. Inter-subject consistency in fetal descending aortic flows (n = 3) was strong with an average velocity of 27.1 ± 0.4 cm/s, peak systolic velocity of 70.0 ± 1.8 cm/s and an intra-class correlation coefficient of 0.95 between the velocity waveforms. In one fetal case, high flow waveform reproducibility was demonstrated in the ascending aorta (R = 0.97) and main pulmonary artery (R = 0.99).
Multidimensional PC-CMR of fetal flow was developed and validated, incorporating retrospective motion compensation and cardiac gating. Using this method, the first quantification and visualization of multidimensional fetal blood flow was achieved using CMR.
Segmentation of the fetus from 2-dimensional (2D) magnetic resonance imaging (MRI) can aid radiologists with clinical decision making for disease diagnosis. Machine learning can facilitate this ...process of automatic segmentation, making diagnosis more accurate and user independent. We propose a deep learning (DL) framework for 2D fetal MRI segmentation using a Cross Attention Squeeze Excitation Network (CASE-Net) for research and clinical applications. CASE-Net is an end-to-end segmentation architecture with relevant modules that are evidence based. The goal of CASE-Net is to emphasize localization of contextual information that is relevant in biomedical segmentation, by combining attention mechanisms with squeeze-and-excitation (SE) blocks. This is a retrospective study with 34 patients. Our experiments have shown that our proposed CASE-Net achieved the highest segmentation Dice score of 87.36%, outperforming other competitive segmentation architectures.
In hypoplastic left heart syndrome (HLHS), the mechanisms leading to left heart hypoplasia and their associated fetal abnormalities are largely unknown. Current animal models have limited utility in ...resolving these questions as they either do not fully reproduce the cardiac phenotype, do not survive to term and/or have very low disease penetrance. Here, we report the development of a surgically induced mouse model of HLHS that overcomes these limitations. Briefly, we microinjected the fetal left atrium of embryonic day (E)14.5 mice with an embolizing agent under high-frequency ultrasound guidance, which partially blocks blood flow into the left heart and induces hypoplasia. At term (E18.5), all positively embolized mice exhibit retrograde aortic arch flow, non-apex-forming left ventricles and hypoplastic ascending aortas. We thus report the development of the first mouse model of isolated HLHS with a fully penetrant cardiac phenotype and survival to term. Our method allows for the interrogation of previously intractable questions, such as determining the mechanisms of cardiac hypoplasia and fetal abnormalities observed in HLHS, as well as testing of mechanism-based therapies, which are urgently lacking.
PDF
