Fetal hemodynamics and cardiac streaming assessed by 4D flow cardiovascular magnetic resonance in fetal sheep

Schrauben, Eric; Saini, Brahmdeep S.; Darby, Jack R. T.; Soo, Jia Yin; Lock, Mitchell C.; Stirrat, Elaine; Stortz, Greg; Sled, John G.; Morrison, Janna L.; Seed, Mike; Macgowan, Christopher K.

doi:10.1186/s12968-018-0512-5

Cited by 57 publications

(78 citation statements)

References 29 publications

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“…In common with the sheep fetus, the oxygen saturations of the blood in the late-gestation human left heart and ascending aorta (65%) are approximately 15% higher than in the right ventricle and pulmonary artery (50%). Human fetal MRI oximetry data therefore support the presence of the same streaming of oxygenated blood from the umbilical vein to the left heart via the ductus venosus and foramen ovale that we have demonstrated in fetal sheep using 4D flow MRI (a volumetric cine phase contrast MRI technique) [27]. The hemodynamics of the ductus venosus result in a remarkable mechanism whereby two columns of blood moving at different speeds and with different oxygen saturations coexist in the suprahepatic inferior vena cava.…”

Section: Normal Fetal Circulationsupporting

confidence: 77%

Understanding Fetal Hemodynamics Using Cardiovascular Magnetic Resonance Imaging

et al. 2020

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Human fetal circulatory physiology has been investigated extensively using grey-scale ultrasound, which provides excellent visualization of cardiac anatomy and function, while velocity profiles in the heart and vessels can be interrogated using Doppler. Measures of cerebral and placental vascular resistance, as well as indirect measures of intracardiac pressure obtained from the velocity waveform in the ductus venosus are routinely used to guide the management of fetal cardiovascular and placental disease. However, the characterization of some key elements of cardiovascular physiology such as vessel blood flow and the oxygen content of blood in the arteries and veins, as well as fetal oxygen delivery and consumption are not readily measured using ultrasound. To study these parameters, we have historically relied on data obtained using invasive measurements made in animal models, which are not equivalent to the human in every respect. Over recent years, a number of technical advances have been made that have allowed us to examine the human fetal circulatory system using cardiovascular magnetic resonance (CMR). The combination of vessel blood flow mea-

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Section: Normal Fetal Circulationsupporting

confidence: 77%

Understanding Fetal Hemodynamics Using Cardiovascular Magnetic Resonance Imaging

et al. 2020

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“…No cross-validation of available flow measurement techniques was performed in this study. However, our previous work in a smaller subset of normal fetal sheep in late gestation examined the cross-validation of 4D flow and 2D phase-contrast MRI in specific vessels (Schrauben et al 2019). This previous comparison comprised mainly cardiac vessels but also included the DV and UV.…”

Section: Discussionmentioning

confidence: 99%

“…Conservation of mass requires equal time-averaged flow entering and exiting a flow network. Fetal 4D flow internal consistency has previously been tested in large cardiac vessels with high blood speed (Macdonald et al 2018;Schrauben et al 2019), but has yet to be tested in smaller vessels with slower blood speed, such as those in the fetal liver. To test internal consistency, conservation of mass was assessed at the DV-IVC junction, following the equation:…”

Section: Statisticsmentioning

confidence: 99%

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Technique for comprehensive fetal hepatic blood flow assessment in sheep using 4D flow MRI

Schrauben

Darby

Saini³

et al. 2020

The Journal of Physiology

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Key points The comprehensive visualization and quantification of in vivo fetal hepatic haemodynamics, particularly the shunting of ductus venosus blood, has been elusive and is not yet fully understood. We introduce the combination of chronically instrumented fetal sheep and 4D flow MRI of the whole fetal liver, which allows retrospective blood flow measurement in all visible vessels as well as qualitative assessment. The applicability and usefulness of this technique is exhibited in normally grown fetal Merino sheep in mid‐ and late‐gestation with detailed dynamic distribution of hepatic blood flow presented. The feasibility of this approach in clinical pathology is demonstrated in two growth‐restricted fetuses at mid‐gestation. Further exemplification of blood flow quantification is performed over major hepatic vessels. Abstract Although the fetal vasculature has been demarcated and well understood for several decades, the corresponding haemodynamics permitting oxygen‐ and nutrient‐rich blood delivery to the fetal organs has been comparatively difficult to study. We married two well‐established methods: 4D flow MRI, a volumetric and dynamic blood‐flow measurement technique, and chronically instrumented sheep to broadly assess fetal hepatic circulation. We performed this technique in mid‐ and late‐gestation fetal Merino sheep under normoxemic conditions and major hepatic vasculature was segmented to quantify blood flow and related parameters. Dynamic blood flow was visualized, exhibiting an acceleration of umbilical vein blood through the ductus venosus as well as spiralling into the inferior vena cava where its stream remained separate from that of the hepatic veins and lower body. Ductus venosus changes from mid‐ to late‐gestation included larger diameter (mid: 5.8 ± 0.9 vs. late: 7.1 ± 1.1 mm; P = 0.003) and cross‐sectional area (mid: 27.1 ± 8.6 vs. late: 40.4 ± 11.8 mm2; P = 0.003), and lower velocity averaged over the cardiac cycle (mid: 15.7 ± 5.4 vs. late: 9.8 ± 7.0 cm s‐1; P = 0.020). This resulted in higher magnitude blood flow (indexed to umbilical vein input) at mid‐gestation in the ductus venosus (mid: 0.73 ± 0.21; late: 0.46 ± 0.21; P = 0.008). The visualization and quantification results support the further use of this technique to better understand regional blood flow changes during normal or abnormal fetal growth, as well as to observe acute haemodynamic responses to physiological challenges or drug interventions.

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“…Three-dimensional imaging permits visualisation of the intricate fetal vasculature and the complex connections and shunts within the developing heart. 4D flow imaging has been very recently demonstrated in the sheep fetus 16 , albeit with the use of anaesthetic to immobilise the mother and fetus, but until now only single-slice methods have been carried out in utero in the human fetus.…”

Section: Introductionmentioning

confidence: 99%

Fetal whole-heart 4D flow cine MRI using multiple non-coplanar balanced SSFP stacks

Roberts

Amerom

Uus

et al. 2019

Preprint

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Purpose:To develop an MRI framework for reconstruction of 4D velocity vector blood flow volumes for visualisation and quantification of circulation in the fetal heart and major vessels. Methods:A novel method of velocity-encoding using multiple non-coplanar stacks of bSSFP phase images was combined with a previous framework for reconstruction of motioncorrected 4D magnitude cine volumes to generate spatiotemporally-paired 4D flow cine volumes of the fetal circulatory system. The multiple stack velocity-encoding scheme was validated in a simulated flow phantom and compared with a gold-standard method for velocity-encoding in a physical flow phantom. The 4D flow cine framework was evaluated in seven fetal subjects. Reconstructed 4D flow volumes were evaluated by an expert fetal cardiologist and preliminary flow measurements were taken in various major vessels of the heart. Results:Phantom experiments showed that the multiple non-coplanar stack velocityencoding scheme was accurate. The 4D flow cine reconstruction framework was robust in fetal subjects and generated multi-dimensional velocity vector maps of blood flow through the cardiac cycle. Directionality of blood flow was consistent with expected fetal circulatory hemodynamics. Relative blood flow rates in the major vessels were in line with previous observations, although absolute values were underestimated by a factor of approximately two due to limitations of spatial and temporal resolution.Conclusion: 4D flow cine volumes can be reconstructed from multiple non-coplanar stacks of slices. The proposed framework was used to visualise and quantify flow through the whole fetal heart and great vessels, but is applicable to any imaging scenario where motion is a major challenge.

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Fetal hemodynamics and cardiac streaming assessed by 4D flow cardiovascular magnetic resonance in fetal sheep

Cited by 57 publications

References 29 publications

Understanding Fetal Hemodynamics Using Cardiovascular Magnetic Resonance Imaging

Understanding Fetal Hemodynamics Using Cardiovascular Magnetic Resonance Imaging

Technique for comprehensive fetal hepatic blood flow assessment in sheep using 4D flow MRI

Fetal whole-heart 4D flow cine MRI using multiple non-coplanar balanced SSFP stacks

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