Cardiac MRI of the fetal heart using a novel triggering method: Initial results in an animal model

Abstract

Purpose: To investigate MRI of the fetal heart by way of a novel triggering method with the use of an MR-compatible cardiotocography (CTG) in an animal model. Materials and Methods:Fetal cardiac MRI was performed on four pregnant ewes on a 1.5 Tesla (T) MR system. A CTG was rendered MR compatible and its signal was used for the triggering of the fetal heart to perform cardiac cine MRI of the fetal heart with maternal freebreathing with cine steady-state free precession. The left ventricular volume and function were measured from the short-axis (view). The image quality of anatomical structures was assessed.Results: All cardiac valves and the foramen ovale could be visualized. Myocardial contraction was depicted in cine sequences. The average blood volume at the end systole was 1.7 mL (SD 6 0.12). The average volume at the end diastole was 4.6 mL (6 0.4); thus the average stroke volumes of the left ventricle were 2.87 mL (6 0.31) with ejection fractions of 60.53% (6 4.17). Conclusion:The newly developed MR compatible CTG could be used as a tool for cardiac triggering method of the fetal heart. This novel device might help fetal cardiac MRI technology in the future. THE RAPID DEVELOPMENT of cardiac MR imaging in the past few years has enabled many different investigations, for example investigations into coronary arteries and myocardial infarctions. In practice, twodimensional (2D) CINE steady-state free precession (SSFP) imaging is the most reliable and frequently used technique for left ventricular (LV) function assessment. To assess the LV function correctly, speed as well as synchronization of data acquisition with the cardiac cycle are required, so that artifacts due to cardiac motion and flow constraints that dictate the viable window for data acquisition are avoided. To avoid the artifacts caused by cardiac motion, it is customary that either finger pulse oximetry or electrocardiography (ECG) triggering/gating techniques are used so that data acquisition can be synchronized with the cardiac cycle.Although the use of MR imaging during pregnancy is limited to the second and third trimester, its diagnostic value has been increasing in recent years. In the field of fetal MR imaging, the evaluation of the fetal heart is one of the greatest challenges. Nowadays, the gold standard in fetal cardiac imaging is the use of ultrasound (US), because it can be obtained during the entire pregnancy; it is easy to use and thus more practicable. Both the measurement of the cardiac volume and the evaluation of volumetric changes with US are possible, and the technology has been improving. Because cardiac chambers do not lend themselves to geometric assumptions, it has always been difficult to calculate their dimensions, even though studies have shown that 3D US has a better reproducibility than 2D (1-4). To be able to do so, it is necessary to trace the volume of the cardiac chambers manually, due to the appearance of various US specific artifacts, such as speckles and acoustic shadowing, which appear when traced automaticall...

Reference Ranges of Blood Flow in the Major Vessels of the Normal Human Fetal Circulation at Term by Phase-Contrast Magnetic Resonance Imaging

“…3 Briefly, the fetal weight was calculated using segmentation of a 3-dimensional steady-state free precession acquisition of the whole fetus to measure the fetal volume (Mimics; Materialise Group, Leuven, Belgium). The weight was derived from the volume using the previously published conversion: fetal weight (g)=fetal volume (mL)×1.03+120.…”

“…Potential approaches to achieving triggered fetal cardiac imaging include self-gating and cardiotocographic gating, which have both recently been shown to be feasible in fetal lambs, with the latter used to make PC-MRI measurements. [2][3][4] Metric-optimized gating (MOG) is a retrospective technique that acquires temporally oversampled data and then iteratively sorts the data using hypothetical ECG trigger times until artifact in the associated images is minimized. 5,6 PC-MRI with MOG has been shown to be feasible in the late-gestation human fetus and validated using an in vivo simulation of fetal vessels.…”

IRM fœtale : une révolution en route

“…Des innovations sont en cours, comme le maté riel cardiofetal dé dié [41] et les instruments amagné tiques. Le monitoring d'accouchements sous IRM, peut être envisagé permettant de suivre toutes les é tapes « en image », pré venant certaines pathologies dystociques [42].…”

An exploration of the potential utility of fetal cardiovascular MRI as an adjunct to fetal echocardiography

“…The fetal heart is extremely small, with a total length of between 2 and 4 cm depending on gestational age, and beats with high heart rates of up to 160 beats per minute . Electrocardiographic ‘gating’, a means of improving spatiotemporal resolution, is not yet practicable in the fetus, although several non‐invasive methods are under investigation . Unpredictable three‐dimensional fetal motion, maternal bulk motion and fetal and maternal breathing movements present additional difficulties, with no additional benefit from attempted fetal sedation …”