Toward functional imaging of the placenta

Thesis

In obstetrics, the application of computer-based image analysis to provide deeper insight into pathology in early pregnancy is highly desirable but underdeveloped. One such pathology, fetal growth restriction (FGR) is a leading cause of mortality and morbidity in pregnancy. FGR affects approximately 3-10% of pregnancies in the western world leading to increased risk of stillbirth and health problems in later life. Morphometric or functional measurement of the placenta in pregnancy in utero may aid diagnosis of this pathology as the interface between placenta and mother is the site where the pathology manifests itself. Detection of growth restriction is yet to be resolved as poor, unreliable biochemical and image-based biomarkers have made it hard to detect and manage these pregnancies effectively.

By the provision and development of tools for quantification of the placenta by three dimensional (3D) ultrasound (US) using image segmentation and mesh processing, this thesis aims to better facilitate clinical investigation of this major problem in obstetric healthcare.

In a first contribution, 3D placental volume measurement using 3D US is used to classify the difference between normal and FGR pregnancies. Volume was estimated using the semi-automated random walker (RW) algorithm. The repeatability and reliability of the method was tested between three observers and showed the new method to be equivalent to manual segmentation. In a study of 143 women performed by our clinical partners, significantly smaller placental volume was found in pregnancies defined as small-for-gestational age (SGA).

Expanding on volumetry, the utero-placental interface (UPI) is the location where the pathology that leads to FGR occurs. Manual manipulation of the volume is requiredtovisualisetheinterface, soweinvestigatedapplyinga“meshflattening” process to convert the contorted UPI into a disc to provide a standardised way to view the interface between acquistions and subjects.

Finally, an existing, two dimensional (2D) Doppler standardisation technique was extended into 3D to provide standardisation of values of Doppler vascularity. This technique was then applied to measure the vascularity of volumes of interest relative to the interface between placenta and mother. This test was then applied clinically in 143 women and found that the vascularity of the small-for-gestational age (SGA) pregnancies was significantly smaller than that of the population who produced appropriately sized babies. These three tools each provide augmentation of our understanding of placental health and function in pregnancy. From measuring the gross volume to estimating the blood flow we show the potential clinical application for image analysis performed on 3D power Doppler (PD) ultrasound volumes.

Authors: Stevenson, G; Gordon Stevenson

• Publication date: 2014
• DOI: 10.5287/ora-6rkad9xjy
• Type of award: DPhil
• Level of award: Doctoral
• Awarding institution: University of Oxford
• Language: English
• Keywords: placenta; obstetrics; volumetric; 3D; ultrasound; analysis; Doppler
• Subjects: Medical Engineering; Engineering; Engineering & allied sciences; Obstetrics; Biomedical engineering