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Emerging Imaging, Affordable Imaging

Fetal vascular ultrasound assessment to identify growth restriction and reduce stillbirth

Project ID: 2020_025

1st supervisor: Jordi Alastruey, King’s College London
2nd supervisor: Kirsten Christensen-Jeffries, King’s College London
Clinical champion: Marietta Charakida, King’s College London
Additional supervisors: Peter Charlton, King’s College London and Mengxing Tang, Imperial College London

Aim of the PhD Project:

  • Develop a methodology which will enable fetal aortic elastic properties to be calculated from an ultrasound scan;
  • Develop new ultrasound protocols and signal and image processing techniques for both current clinical imaging systems and state-of-the-art ultrasound imaging.
  • Investigate whether aortic elasticity measured by this methodology differentiates growth-restricted from normal fetuses.

Project description/background:

There are over 3,000 stillbirths per year in the UK, many of which are associated with fetal growth restriction (FGR). Stillbirth affects about 1 in 200 pregnancies and is the leading cause of perinatal death. In 2016, the Lancet’s “Ending Preventable Stillbirth Series” indicated that stillbirth rates in England and Wales are the highest in Western Europe and have changed little in the past 20 years.1,2 A recent UK study identified FGR, defined as a customised birthweight below the 10th percentile, as the single largest contributor to stillbirth rates, being responsible for about 43% of stillbirths.3

One of the most promising approaches to reduce stillbirths is early diagnosis of FGR. It has been shown that the high mortality rates of FGR are mainly due to lack of recognition of the condition rather than inability to manage it.4 Preventive strategies mostly focus on altering socio-economic parameters, such as improved access to care, or improving maternal wellbeing prior to pregnancy, such as reduced maternal obesity rates.1 However, these strategies are difficult to implement in the mobile, older and more obese pregnant populations of current Western societies. Therefore, a method to accurately screen for FGR to diagnose it early is required.

The main screening tool for FGR during pregnancy is fetal ultrasound (US) scanning, which can be used to measure fetal biometry (dimensions) from which fetal weight can be estimated, and fetal blood flow from which fetal adaptation to hypoxia can be assessed. However, despite these measurements, the sensitivity in detecting FGR remains <40%.5 Therefore, a more sensitive ultrasonographic marker is needed, compared to the traditional fetal biometry and blood flow Doppler examination, in order to identify those fetuses in the third-trimester scan who are at risk of FGR in the next few weeks.

Assessment of fetal vasculature is emerging as a novel area of research with potential to provide information about fetal cardiovascular adaptations in response to maternal stimuli at a much earlier stage than can be detected by blood flow Doppler examinations in the uterine, middle cerebral, and umbilical arteries. It is now possible to assess fetal aortic properties using advanced US-based techniques, which may have utility in FGR screening. Data suggest that growth restricted fetuses have increased aortic stiffness,6,7 however to date there is no methodology which can be used in clinical practice to assess vascular elasticity during pregnancy.

In this study, we aim to develop advanced US and pulse wave analysis techniques to estimate fetal vascular properties. This will include investigating the use of raw radio-frequency (RF) US data, as well as state-of-the-art ultrafast US imaging 8, providing higher temporal resolution across the full field-of-view. We will assess whether aortic elasticity measured by these new techniques differentiates growth-restricted from normal fetuses. If our development is successful, this will provide a novel way to improve detection of FGR and reduce stillbirth rates. It is hoped that the methodology could be implemented in US scanners through our collaboration with Canon Medical Systems.

The project requires a student with a background in engineering/physics/mathematics who knows or is unafraid to learn programming. Some knowledge of medical imaging and physiology would be an advantage.

References:

1. Flenady V, Wojcieszek AM, Middleton P, Ellwood D, Erwich JJ, Coory M et al. Stillbirths: recall to action in high-income countries. Lancet 2016; 387(10019):691–702.
2. Gardosi J, Kady S, McGeown P, Francis A, Tonks A. Classification of stillbirth by relevant condition at death (ReCoDe): population based cohort study. BMJ 2005; 331:1113e7
3. Gardosi J, Giddings S, Buller S, Southam M, Williams M. Preventing stillbirths through improved antenatal recognition of pregnancies at risk due to fetal growth restriction. Public Health 2014; 128:698–702.
4. Lindqvist PG, Molin J. Does antenatal identification of small-for-gestational age fetuses significantly improve their outcome? Ultrasound Obstet Gynecol 2005; 25:258–64.
5. Roma E, Arnau A, Berdala R, Bergos C, Montesinos J, Figueras F. Ultrasound screening for fetal growth restriction at 36 vs 32 weeks’ gestation: a randomized trial (ROUTE). Ultrasound in Obstetrics & Gynecology 2015; 46(4):391–7.
6. Miyashita S, Murotsuki J, Muromoto J, et al. Measurement of internal diameter changes and pulse wave velocity in fetal descending aorta using the ultrasonic phased-tracking method in normal and growth-restricted fetuses. Ultrasound in Medicine & Biology 2015; 41(5):1311–9.
7. Struijk PC, Migchels H, Mathews JV, et al. Fetal aortic distensibility, compliance and pulse pressure assessment during the second half of pregnancy. Ultrasound in Medicine & Biology 2013; 39(11):1966–75.
8. Tanter M, Fink M. Ultrafast imaging in biomedical ultrasound. IEEE Trans Ultrason Ferroelectr Freq Control. 2014; 61(1):102-119

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