Placental Imaging Techniques

Background: This study is a proof-of-concept, case-control exploration of quantitative ultrasound (QUS) and ultrafast power Doppler imaging (uPDI) imaging techniques, applied to the placenta to evaluate health of the placenta, blood flow visualized by colored doppler imaging in patients with and without FGR. Investigators will utilize the Verasonics Vantage 256 research ultrasound machine (Verasonics, Inc, Kirkland, WA) for this study, which is not FDA approved/experimental, along with a standard-of-care Phillips ultrasound machine which is FDA approved.

Use of QUS gained interest within the 1980s to evaluate the health of a range of tissues, from myocardial [heart muscle], to artery plaques, to breast masses, to bone density. More recently, there has been great interest in QUS for evaluation of fetal tissue health, including fetal liver and lung tissue, as well as placental tissue to gauge both gestational age as well as placental health. QUS imaging creates a number of values including an attenuation coefficient estimate (ACE), specified in decibels (dB) which is a measurement of the ultrasound waves' absorption and scattering as they move through human tissue. QUS also generates other values including a frequency-dependent attenuation value. These numerical estimates of absorption and scattering along with others provided by QUS are believed to change within the placenta with increased gestational age due to increasing deposition of collagen and fibrin, two types of connective fibers. Measures of absorption, scattering, and related tissue properties may also be altered in unhealthy versus healthy placental tissue. Thus, QUS is believed to have the potential to inform the clinician about placental health which may be affected by uteroplacental insufficiency predisposing to fetal growth restriction. Researchers will also investigate power Doppler imaging (uPDI), a newer ultrasound modality that uses an ultra-high frame rate and clutter filtering to increase the Doppler imaging sensitivity. Traditional Doppler ultrasound displays color onto the normally greyscale ultrasound where blood flow is seen by the machine. However, traditional ultrasound with Doppler has difficulty in detecting blood flow within smaller vessels, such as the smallest spiral arteries of the placenta which provide nutrient and gas exchange to the fetus. It is believed uPDI may be able to better visualize these small vessels and other small areas of slow blood flow or pooled blood within the placenta, providing more direct evaluation of placental tissue perfusion and health.

Procedure: Ultrasounds will be performed every 3 weeks until delivery for both cohorts following informed consent. The first ultrasound will take place within 1 week of enrollment to allow for the sonographer to be scheduled. Ultrasounds will be performed by trained MFM sonographers. Ultrasounds will take place within the Maternal Fetal Medicine suite of Carilion Clinic [102 Highland Ave, Roanoke, VA], in clinical exam rooms with dimmable lights and calming music to reduce patient stress. Upon entering the exam room, IRB-approved study team members and/or sonographers will introduce themselves by name and capacity, then ask the name and date of birth of the subject to verify subject identity against the research enrollment log and EMR. The purpose for the visit will be reiterated and the subject's wish to continue to participate in the research will be verified to ensure continued consent. Any questions the subject has will be answered to the subject's satisfaction. An agenda for the encounter will be set by the IRB-approved study team member or sonographer, so the patient knows what to generally expect and how long the visit will take. The subject will be seated in a reclined position and asked to raise the bottom portion of their shirt, while the sonographer drapes the patient according to standard clinical procedure. Ultrasound gel will be applied to the subject's abdomen and the sonographer will then begin the ultrasound using the machine's transducer [part held in sonographer's hand].

To begin, an ultrasound using a standard-of-care, Philips ultrasound machine will be used to first verify continued fetal viability and perform a basic anatomical survey to ensure continued eligibility for the subject's given cohort [either Case [FGR-positive] or Control [FGR-negative]]. These Philips ultrasound machines are located in each of the standard MFM exam rooms. Following this, the sonographer will transition to the research ultrasound machine for the rest of the visit.

Participants will have research ultrasounds performed of their placentas using a Verasonics Vantage 256 system (a popular research ultrasound platform used for human imaging under IRB approval). The gestational age of the fetus, estimated fetal weight in grams, and growth/weight percentile measurements for that gestational age will be recorded during the research visits. The placenta will be scanned at a central, peripheral, and 'mid-disc' region to acquire QUS and uPDI images with the Verasonics research ultrasound as well. Three measurements will be acquired at these locations. The Verasonics machine will be programmed to project B-mode (brightness mode) images for the sonographer at the time of the research ultrasound for confirmation of correct placental location. These B- or brightness mode images will project a 2-dimensional, greyscale image of the placenta (or fetus) to the sonographer to orient him/her to the location they are scanning and find the placenta. The machine will be programmed to display thermal index (TI) and mechanical index (MI) during all exams, which are derived estimates of the heat and pressure created by ultrasound waves' energy. These are displayed for safety and kept within International Society of Ultrasound of Obstetrics and Gynecology (ISUOG) guidelines. The Verasonics machine will be programmed with a "hard stop" not to exceed these limits. The energy exposure from Ultrasound has no known cumulative effect. Following the ultrasound procedure, the subject will be cleaned of ultrasound gel with a cloth and drapes removed. The subjects will be told of any changes noticed since the last visit to the growth or health of their baby or placenta. Incidental findings obtained during the research ultrasound will be shared with the subject's routine clinical provider and the patient by IRB-approved and qualified physicians on the research team. The PI will advise the participant's routine clinical provider that all results obtained with the research ultrasound should be validated using an FDA Approved ultrasound and standard of care ultrasound techniques.

Following all research ultrasound procedures during the visit, subjects will be given an opportunity to ask any further questions they wish and receive answers to their satisfaction. Printouts of their baby from the standard-of-care ultrasound machine will be provided to subjects. Subjects will then be led back out of the MFM suite to the front desk where they will be scheduled for their next research visit.

Participants will not be under the primary care of the research physicians. The research physicians will not be involved in decisions regarding the timing, method, or procedures used to terminate a pregnancy or determining the viability of a neonate.

Analysis: Researchers will evaluate QUS and uPDI images of the placentas. Researchers will evaluate which QUS parameters are most strongly associated with FGR diagnosis by comparing them to numbers obtained by QUS in normal estimated fetal growth pregnancies. Researchers will examine uPDI images in FGR pregnancies versus those obtained from normal growth weight pregnancies.

Secondary analysis: Researchers will perform multimodal analysis to determine whether these ultrasound modalities can distinguish between pregnancies with: A.) confirmed diseases deriving from a placental origin; B.) abnormal umbilical artery assessments, severe FGR, preeclampsia and stillbirth; C.) no complications.