Human Fetal Blood Flow Quantification with Magnetic Resonance Imaging and Motion Compensation

Summary

Here we present a protocol for measuring fetal blood flow rapidly with MRI and retrospectively performing motion correction and cardiac gating.

Abstract

Magnetic resonance imaging (MRI) is an important tool for the clinical assessment of cardiovascular morphology and heart function. It is also the recognized standard-of-care for blood flow quantification based on phase contrast MRI. While such measurement of blood flow has been possible in adults for decades, methods to extend this capability to fetal blood flow have only recently been developed.

Fetal blood flow quantification in major vessels is important for monitoring fetal pathologies such as congenital heart disease (CHD) and fetal growth restriction (FGR). CHD causes alterations in the cardiac structure and vasculature that change the course of blood in the fetus. In FGR, the path of blood flow is altered through the dilation of shunts such that the oxygenated blood supply to the brain is increased. Blood flow quantification enables assessment of the severity of the fetal pathology, which in turn allows for suitable in utero patient management and planning for postnatal care.

The primary challenges of applying phase contrast MRI to the human fetus include small blood vessel size, high fetal heart rate, potential MRI data corruption due to maternal respiration, unpredictable fetal movements, and lack of conventional cardiac gating methods to synchronize data acquisition. Here, we describe recent technical developments from our lab that have enabled the quantification of fetal blood flow using phase contrast MRI, including advances in accelerated imaging, motion compensation, and cardiac gating.

Introduction

Comprehensive assessment of the fetal circulation is necessary for monitoring fetal pathologies such as fetal growth restriction (FGR) and congenital heart disease (CHD)^1,2,3. In utero, patient management and planning for postnatal care depend on the severity of the fetal pathology^4,5,6,7. Feasibility of fetal blood flow quantification with MRI and its applications in assessing fetal pathologies have recently been demonstrated³

Protocol

All MRI scans were performed with informed consent from volunteers as part of a study approved by our institutional research ethics board.

NOTE: The methods described below have been used on a 3T MRI system. The acquisition is performed using a radial phase contrast MRI sequence. This sequence was prepared by modifying the readout trajectory (to achieve a stellate pattern) of the manufacturer's Cartesian phase contrast MRI. The sequence and sample protocols are available upon request through our C²P exchange platform. All reconstructions in this work were performed on a standard desktop computer with the following specificati....

Results

In general, phase MRI examinations of flow target six major fetal vessels: the descending aorta, ascending aorta, main pulmonary artery, ductus arteriosus, superior vena cava, and umbilical vein. These vessels are of interest to the clinician as they are often implicated in CHD and FGR, influencing the distribution of blood throughout the fetus⁹. A typical scan duration with the radial phase contrast MRI is 17 s per vessel such that the scans are short while also allowing time for enough data acqu.......

Discussion

This method enables the non-invasive measurement of blood flow in human fetal great vessels and allows for retrospective motion correction and cardiac gating by making use of iterative reconstruction techniques. Fetal blood flow quantification has been performed with MRI in the past^1,3,8,9. These studies had a prospective approach to mitigate motion corruption w.......

Materials

Name	Company	Catalog Number	Comments
elastix	Image Sciences Institute, University Medical Center Utrecht		Image registration software
Geforce GTX 960	Nvidia	04G-P4-3967-KR
gpuNUFFT	CAI²R		Non-uniform fast Fourier transform
MAGNETOM Prisma	Siemens	10849583
MATLAB	MathWorks
Radial Phase Contrast MRI sequence			Trajectory modification of manufacturer's Cartesian Phase Contrast sequence
Segment	Medvisio		Data analysis
VENGEANCE	Corsair	LPX DDR4-2666