Fetal 3D cardiovascular cine image acquisition using radial sampling and compressed sensing

Factors influencing image quality in fetal cardiovascular magnetic resonance cine imaging using Doppler ultrasound gating: A multicenter study

BACKGROUND

Fetal cine cardiovascularmagnetic resonance (CMR) is an emerging technique for evaluating the fetal heart in conditions such as congenital heart disease, but limited evidence on factors affecting image quality restricts its clinical potential. This study investigated key determinants of image quality in a multicenter cohort.

METHODS

This study analyzed fetal CMR scans from April 2021 to July 2023 at three centers (University Hospital Bonn, Children's Hospital Colorado, Phoenix Children's Hospital). Cine image quality was assessed using a 5-point Likert scale (1=non-diagnostic to 5=excellent) across three criteria as follows: contour sharpness, blood-to-structure contrast, and artifacts. Overall image quality scores were calculated by the average of all criteria. Apparent signal-to-noise (aSNR) and contrast-to-noise ratios (aCNR) were measured. Nine parameters were evaluated for their impact on image quality, namely: gestational age, body mass index (BMI), fetal motion, patient positioning, gating signal stability, breathing technique, field strength, slice thickness, and flip angle. Comparisons were conducted using the Mann-Whitney U test.

RESULTS

A total of 98 scans were analyzed. Higher overall image quality, aSNR, and aCNR were observed in participants with BMI <30 kg/m², gestational age ≥32 weeks, low fetal motion severity, and stable gating signals (e.g., overall image quality for BMI <30 kg/m² vs ≥30 kg/m²: 4.4±0.7 vs. 4.1±0.7, p<0.001). Supine positioning resulted in better overall image quality compared to the left lateral position (4.5±0.5 vs. 4.2±0.8, p=0.001). Breath-holds provided similar overall image quality but improved contour sharpness and reduced artifacts compared to free breathing (5 [4,5] vs. 4 [4,5], p=0.042; and 4 [3-5] vs. 4 [3-5], p=0.014, respectively). At 1.5T field strength, higher contrast and fewer artifacts were observed compared to 3T (5 [4,5] vs. 5 [4,5], p=0.041; and 4 [4,5] vs. 4 [3-5], p=0.010, respectively). Slice thickness showed no significant impact on image quality.

CONCLUSION

Various factors (e.g. BMI) influence fetal cardiac cine MRI image quality. Understanding these factors may help achieving reliable examinations and better exploit the potential of fetal cardiac MRI in clinical routine.

The New Frontiers of Fetal Imaging: MRI Insights into Cardiovascular and Thoracic Structures

Fetal magnetic resonance imaging (fMRI) represents a second-line imaging modality that provides multiparametric and multiplanar views that are crucial for confirming diagnoses, detecting associated pathologies, and resolving inconclusive ultrasound findings. The introduction of high-field magnets and new imaging sequences has expanded MRI's role in pregnancy management. Recent innovations in ECG-gating techniques have revolutionized the prenatal evaluation of congenital heart disease by synchronizing imaging with the fetal heartbeat, thus addressing traditional challenges in cardiac imaging. Fetal cardiac MRI (fCMR) is particularly valuable for assessing congenital heart diseases, especially when ultrasound is limited by poor imaging conditions. fCMR allows for detailed anatomical and functional evaluation of the heart and great vessels and is also useful for diagnosing additional anomalies and analyzing blood flow patterns, which can aid in understanding abnormal fetal brain growth and placental perfusion. This review emphasizes fMRI's potential in evaluating cardiac and thoracic structures, including various gating techniques like metric optimized gating, self-gating, and Doppler ultrasound gating. The review also covers the use of static and cine images for structural and functional assessments and discusses advanced techniques like 4D-flow MRI and T1 or T2 mapping for comprehensive flow quantification and tissue characterization.

Reference Values for Fetal Cardiac Dimensions, Volumes, Ventricular Function and Left Ventricular Longitudinal Strain Using Doppler Ultrasound Gated Cardiac Magnetic Resonance Imaging in Healthy Third Trimester Fetuses

BACKGROUND

Recent advances in hardware and software permit the use of cardiac MRI of late gestation fetuses, however there is a paucity of MRI-based reference values.

PURPOSE

To provide initial data on fetal cardiac MRI-derived cardiac dimensions, volumes, ventricular function, and left ventricular longitudinal strain in healthy developing fetuses >30 weeks gestational age.

STUDY TYPE

Prospective.

POPULATION

Twenty-five third trimester (34 ± 1 weeks, range of 32-37 weeks gestation) women with healthy developing fetuses.

FIELD STRENGTH/SEQUENCE

Studies were performed at 1.5 T and 3 T. Cardiac synchronization was achieved with a Doppler ultrasound device. The protocol included T2 single shot turbo spin echo stacks for fetal weight and ultrasound probe positioning, and multiplanar multi-slice cine balanced steady state free precession gradient echo sequences.

ASSESSMENT

Primary analyses were performed by a single observer. Weight indexed right ventricular (RV) and left ventricular (LV) volumes and function were calculated from short axis (SAX) stacks. Cardiac dimensions were calculated from the four-chamber and SAX stacks. Single plane LV longitudinal strain was calculated from the four-chamber stack. Interobserver variability was assessed in 10 participants. Cardiac MRI values were compared against available published normative fetal echocardiogram data using z-scores.

STATISTICAL TESTS

Mean and SDs were calculated for baseline maternal/fetal demographics, cardiac dimensions, volumes, ventricular function, and left ventricular longitudinal strain. Bland-Altman and intraclass correlation coefficient analysis was performed to test interobserver variability.

RESULTS

The mean gestational age was 34 ± 1.4 weeks. The mean RV and LV end diastolic volumes were 3.1 ± 0.6 mL/kg and 2.4 ± 0.5 mL/kg respectively. The mean RV cardiac output was 198 ± 49 mL/min/kg while the mean LV cardiac output was 173 ± 43 mL/min/kg.

DATA CONCLUSION

This paper reports initial reference values obtained by cardiac MRI in healthy developing third trimester fetuses. MRI generally resulted in slightly larger indexed values (by z-score) compared to reports in literature using fetal echocardiography.

EVIDENCE LEVEL

1 TECHNICAL EFFICACY: Stage 2.

Fetal Cardiac MRI Using Doppler US Gating: Emerging Technology and Clinical Implications

Fetal cardiac MRI using Doppler US gating is an emerging technique to support prenatal diagnosis of congenital heart disease and other cardiovascular abnormalities. Analogous to postnatal electrocardiographically gated cardiac MRI, this technique enables directly gated MRI of the fetal heart throughout the cardiac cycle, allowing for immediate data reconstruction and review of image quality. This review outlines the technical principles and challenges of cardiac MRI with Doppler US gating, such as loss of gating signal due to fetal movement. A practical workflow of patient preparation for the use of Doppler US-gated fetal cardiac MRI in clinical routine is provided. Currently applied MRI sequences (ie, cine or four-dimensional flow imaging), with special consideration of technical adaptations to the fetal heart, are summarized. The authors provide a literature review on the clinical benefits of Doppler US-gated fetal cardiac MRI for gaining additional diagnostic information on cardiovascular malformations and fetal hemodynamics. Finally, future perspectives of Doppler US-gated fetal cardiac MRI and further technical developments to reduce acquisition times and eliminate sources of artifacts are discussed. Keywords: MR Fetal, Ultrasound Doppler, Cardiac, Heart, Congenital, Obstetrics, Fetus Supplemental material is available for this article. © RSNA, 2024.