1346866 - Real-time fetal cardiac MRI at 0.55T enables assessment of ventricular function and heart and great vessel anatomy

Accurate fetal assessment of congenital heart disease is important for both proper diagnosis and prognosis, to provide parental counseling and postnatal planning. Fetal cardiac MRI (CMR) is standard of care for static anatomic assessment but to date, is limited regarding cardiac evaluation. We believe fetal CMR can be useful when ultrasound imaging is suboptimal or limited. New whole-body 0.55T systems can provide superior fetal CMR image quality and patient experience, because of the larger bore sizes (70-80cm), lower acoustic noise, and lower specific absorption rate. In this study, we demonstrate the feasibility of real-time fetal CMR at 0.55T, which does not require any breath-hold or gating, to provide evaluation of fetal cardiac function and anatomy.



Methods:

Experiments: Imaging was performed on a whole-body 0.55T system (prototype MAGNETOM Aera, Siemens Healthineers)^[1] and real-time interactive scanning platform (RTHawk, HeartVista)^[2]. Five volunteers with healthy pregnancies (maternal age 32-39 years, gestational age 25-34 weeks) were enrolled after providing written informed consent, and the study was approved by our Institutional Review Board.

Data Acquisition: Fetal CMR was performed using a real-time 2D spiral bSSFP sequence with golden angle increment. Scan parameters: flip angle 90^o; in-plane resolution 1.5 or 1.7 mm²; TR/TE 5.32/0.71 ms; FOV 24cm; slice thickness 4mm. We acquired 10-20 s recordings of key cardiac views (4-chamber, short-axis, and long-axis). In 4 subjects, we acquired volumes of 20-40 mm thickness, by running an automated sequential multi-slice “real-time sweep”, where imaging was performed for 2-5 s per slice, then shifted by 1-2 mm, until the entire volume was covered.

Reconstruction: We performed spatiotemporally constrained reconstruction^[3] with parameters selected by two board certified cardiologists. Images were reconstructed at 40 and 320 ms/frame to visualize cardiac dynamics and cardiovascular anatomy, respectively. Slice-to-volume registration (SVR)^[4] was performed on the 320ms/frame reconstructions.

Results:

In all 5 subjects, real-time movies at 40ms/frame captured cardiac motion in multiple cardiac views, without using any retrospective gating. The 4 chambers and their motion were clearly depicted. Two representative subjects are shown in Figure 1.

In all 4 subjects with volumetric coverage, reconstruction at 320ms/frame was adequate to assess normal cardiac anatomy and great artery relationships. Figure 2 shows one representative subject. Specifically, we could visualize the great vessels crossing, no significant ventricular septal defects, and the pulmonary arteries arising properly. Figure 3 shows SVR results, where additional details are revealed which increased diagnostic confidence.

Conclusion:

We have demonstrated a real-time CMR at 0.55T for fetal heart assessment that does not relay on any gating, providing both high-temporal resolution images for functional evaluation and volumetric images for structural evaluation.