High resolution MR imaging of the fetal heart with cardiac triggering: a feasibility study in the sheep fetus

Abstract

The aim of this study was to perform fetal cardiac magnetic resonance imaging (MRI) with triggering of the fetal heart beat in utero in a sheep model. All experimental protocols were reviewed and the usage of ewes and fetuses was approved by the local animal protection authorities. Images of the hearts of six pregnant ewes were obtained by using a 1.5-T MR system (Philips Medical Systems, Best, Netherlands). The fetuses were chronically instrumented with a carotid catheter to measure the fetal heart frequency for the cardiac triggering. Pulse wave triggered, breath-hold cine-MRI with steady-state free precession (SSFP) was achieved in short axis, two-, four- and three-chamber views. The left ventricular volume and thus the function were measured from the short axis. The fetal heart frequencies ranged between 130 and 160 bpm. The mitral, tricuspid, aortic, and pulmonary valves could be clearly observed. The foramen ovale could be visualized. Myocardial contraction was shown in cine sequences. The average blood volume at the end systole was 3.4 + or - 0.2 ml (+ or - SD). The average volume at end diastole was 5.2 + or - 0.2 ml; thus the stroke volumes of the left ventricle in the systole were between 1.7 and 1.9 ml with ejection fractions of 38.6% and 39%, respectively. The pulse wave triggered cardiac MRI of the fetal heart allowed evaluation of anatomical structures and functional information. This feasibility study demonstrates the applicability of MRI for future evaluation of fetuses with complex congenital heart defects, once a noninvasive method has been developed to perform fetal cardiac triggering.

Diagnosis and Treatment of Fetal Cardiac Disease

“…288,289 The development of these more sophisticated sequences, with improved temporal resolution, has enhanced the ability of MRI to evaluate fetal cardiac structure despite fetal motion and rapid fetal heart rates. 290,292 However, although these advanced sequences can generate highly useful information without true gating, this singleshot imaging approach has limited spatial resolution. 287 Highresolution, gated fetal cardiac MRI has been performed in chronically instrumented sheep with the use of cine steadystate sequences.…”

“…287,292 Although the clinical utility of the technology has not been well established and although it currently is used mostly as a research tool, fetal cardiac MRI is reasonable to perform in the evaluation of certain forms of fetal cardiovascular disease, including heterotaxy and systemic venous anomalies, and in the assessment of associated extracardiac malformations.…”

“…In summary, with increasingly sophisticated MRI technology, faster imaging sequences, improvements in resolution, and innovative gating algorithms, fetal cardiac MRI has the potential to complement ultrasound imaging in the evaluation of fetal visceroatrial situs, 288,290,294 cardiac structure, 286,[288][289][290][291][292] and cardiac function. 287,292 Although the clinical utility of the technology has not been well established and although it currently is used mostly as a research tool, fetal cardiac MRI is reasonable to perform in the evaluation of certain forms of fetal cardiovascular disease, including heterotaxy and systemic venous anomalies, and in the assessment of associated extracardiac malformations.…”

“…287 Highresolution, gated fetal cardiac MRI has been performed in chronically instrumented sheep with the use of cine steadystate sequences. 292 The ongoing development of additional algorithms, including metric-optimized gating, 293 may help to establish a clinical role for gated fetal cardiac MRI, but at present, its use mostly lies in the research arena.…”

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

“…Theoretically, the capability to visualize anomalies of both the heart and the great vessels would be of great importance in the field of prenatal diagnostics, but it is not yet feasible to achieve this with current MRI technology. In a previous study, pulse wave triggered cardiac MRI was performed (8) in sheep fetuses in utero, but due to the invasiveness of this approach, this method cannot be applied to human fetuses. A newer approach of cardiac imaging is the so-called self-gating technique of the heart, which does not require any kind of external cardiac triggering.…”