Quantifiable study of magnetic resonance super resolution reconstruction in Placenta Accreta Spectrum using Image Quality Metrics

Magnetic Resonance Images are increasingly being used for detection and diagnosis of Placental Complications1 . Here we apply this technology to reconstruction of placenta accreta spectrum. Super-Resolution Reconstruction (SRR) allows for a high-resolution 3D reconstruction from 2D MRI slices to allow for improved visibility of structures for future clinical use2 . The use of Image Quality metrics provides quantitative evaluation of the SRR images and allows comparisons to be drawn between the original 2D images and the SRR. These metrics are tested for statistical significance, providing an objective assessment of the SRR images

Micro-CT and histological investigation of the spatial pattern of feto-placental vascular density

Introduction: There are considerable variations in villous morphology within a normal placenta. However, whether there is a reproducible spatial pattern of variation in villous vascular density is not known. Micro-CT provides three-dimensional volume imaging with spatial resolution down to the micrometer scale. In this study, we applied Micro-CT and histological analysis to investigate the degree of heterogeneity of vascularisation within the placenta. Method: Ten term placentas were collected at elective caesarean section, perfused with contrast agent and imaged whole with Micro-CT. Eight full depth tissue blocks were then taken from each placenta and imaged. Sections were taken for histological analysis. Data was analysed to investigate vascular fill, and vascular density in relation to location from cord insertion to placental edge at each scale. Results: Whole placental imaging revealed no spatially consistent difference in villous vessel density within the main placental tissue, although there was a great degree of heterogeneity. Both block imaging and histological analysis found a large degree of heterogeneity of vascular density within placentas, but no strong correlation between villous vascular density and block location (rs = 0.066, p = 0.7 block imaging, rs = 0.06, p = 0.6 histological analysis). Discussion: This work presents a novel method for imaging the human placenta vascular tree using multiscale Micro-CT imaging. It demonstrates that there is a large degree of variation in vascular density throughout normal term human placentas. The three-dimensional data created by this technique could be used, with more advanced computer analysis, to further investigate the structure of the vascular tree

Photoacoustic imaging of the human placental vasculature

Minimally invasive fetal interventions require accurate imaging from inside the uterine cavity. Twin‐to‐twin transfusion syndrome (TTTS), a condition considered in this study, occurs from abnormal vascular anastomoses in the placenta that allow blood to flow unevenly between the fetuses. Currently, TTTS is treated fetoscopically by identifying the anastomosing vessels, and then performing laser photocoagulation. However, white light fetoscopy provides limited visibility of placental vasculature, which can lead to missed anastomoses or incomplete photocoagulation. Photoacoustic (PA) imaging is an alternative imaging method that provides contrast for hemoglobin, and in this study, two PA systems were used to visualize chorionic (fetal) superficial and subsurface vasculature in human placentas. The first system comprised an optical parametric oscillator for PA excitation and a 2D Fabry‐Pérot cavity ultrasound sensor; the second, light emitting diode arrays and a 1D clinical linear‐array ultrasound imaging probe. Volumetric photoacoustic images were acquired from ex vivo normal term and TTTS‐treated placentas. It was shown that superficial and subsurface branching blood vessels could be visualized to depths of approximately 7 mm, and that ablated tissue yielded negative image contrast. This study demonstrated the strong potential of PA imaging to guide minimally invasive fetal therapies

An automated localization, segmentation and reconstruction framework for fetal brain MRI

Reconstructing a high-resolution (HR) volume from motion-corrupted and sparsely acquired stacks plays an increasing role in fetal brain Magnetic Resonance Imaging (MRI) studies. Existing reconstruction methods are time-consuming and often require user interaction to localize and extract the brain from several stacks of 2D slices. In this paper, we propose a fully automatic framework for fetal brain reconstruction that consists of three stages: (1) brain localization based on a coarse segmentation of a down-sampled input image by a Convolutional Neural Network (CNN), (2) fine segmentation by a second CNN trained with a multi-scale loss function, and (3) novel, single-parameter outlier-robust super-resolution reconstruction (SRR) for HR visualization in the standard anatomical space. We validate our framework with images from fetuses with variable degrees of ventriculomegaly associated with spina bifida. Experiments show that each step of our proposed pipeline outperforms state-of-the-art methods in both segmentation and reconstruction comparisons. Overall, we report automatic SRR reconstructions that compare favorably with those obtained by manual, labor-intensive brain segmentations. This potentially unlocks the use of automatic fetal brain reconstruction studies in clinical practice

Placenta Imaging Workshop 2018 report: Multiscale and multimodal approaches

The Centre for Medical Image Computing (CMIC) at University College London (UCL) hosted a two-day workshop on placenta imaging on April 12th and 13th 2018. The workshop consisted of 10 invited talks, 3 contributed talks, a poster session, a public interaction session and a panel discussion about the future direction of placental imaging. With approximately 50 placental researchers in attendance, the workshop was a platform for engineers, clinicians and medical experts in the field to network and exchange ideas. Attendees had the chance to explore over 20 posters with subjects ranging from the movement of blood within the placenta to the efficient segmentation of fetal MRI using deep learning tools. UCL public engagement specialists also presented a poster, encouraging attendees to learn more about how to engage patients and the public with their research, creating spaces for mutual learning and dialogue

MRI Measurement of Placental Perfusion and Oxygen Saturation in Early Onset Fetal Growth Restriction

Objective We hypothesized that a multi‐compartment MRI technique that is sensitive to fetal blood oxygenation would identify changes in placental blood volume and fetal blood oxygenation in pregnancies complicated by early‐onset Fetal Growth Restriction (FGR). Design Case‐Control study. Setting London, UK. Population Women with uncomplicated pregnancies (estimated fetal weight, EFW>10th centile for gestational age, GA and normal maternal and fetal Doppler ultrasound, n=12) or early‐onset FGR (EFW<3rd centile with or without abnormal Doppler US<32 weeks GA, n=12) were studied. Methods All women underwent MRI examination. Using a multi‐compartment MRI technique, we quantified fetal and maternal blood volume and feto‐placental blood oxygenation. Main Outcome Measures Disease severity was stratified according to Doppler pulsatility index and the relationship to the MRI parameters investigated, including the influence of gestational age at scan. Results The FGR group (mean GA:27+5wks, range:24+2 to 33+6wks) had a significantly lower estimated fetal weight compared to the control group (mean GA:29+1wks) (‐705g 95%CI=(‐353, ‐1057g)). MR‐derived feto‐placental oxygen saturation was higher in controls compared to FGR (75 (±9.6)% vs 56 (±16.2)%, p=0.02, 95%CI=(7.8‐30.3)%). Feto‐placental oxygen saturation estimation correlated strongly with gestational age at scan in controls (r=‐0.83) Conclusion Using a novel multimodal MRI protocol we demonstrated reduced feto‐placental blood oxygen saturation in pregnancies complicated by early‐onset FGR. The degree of abnormality correlated with disease severity defined by ultrasound Doppler findings. Gestational age dependent changes in oxygen saturation were also present in normal pregnancies

Placental MRI Predicts Fetal Oxygenation and Growth Rates in Sheep and Human Pregnancy

Magnetic resonance imaging (MRI) assessment of fetal blood oxygen saturation (SO(2)) can transform the clinical management of high‐risk pregnancies affected by fetal growth restriction (FGR). Here, a novel MRI method assesses the feasibility of identifying normally grown and FGR fetuses in sheep and is then applied to humans. MRI scans are performed in pregnant ewes at 110 and 140 days (term = 150d) gestation and in pregnant women at 28(+3) ± 2(+5) weeks to measure feto‐placental SO(2). Birth weight is collected and, in sheep, fetal blood SO(2) is measured with a blood gas analyzer (BGA). Fetal arterial SO(2) measured by BGA predicts fetal birth weight in sheep and distinguishes between fetuses that are normally grown, small for gestational age, and FGR. MRI feto‐placental SO(2) in late gestation is related to fetal blood SO(2) measured by BGA and body weight. In sheep, MRI feto‐placental SO(2) in mid‐gestation is related to fetal SO(2) later in gestation. MRI feto‐placental SO(2) distinguishes between normally grown and FGR fetuses, as well as distinguishing FGR fetuses with and without normal Doppler in humans. Thus, a multi‐compartment placental MRI model detects low placental SO(2) and distinguishes between small hypoxemic fetuses and normally grown fetuses