Tian Ye, Detterich Jon, Pruetz Jay D, Yagiz Ecrin, Wood John C, Nayak Krishna S
Ming Hsieh Department of Electrical and Computer Engineering, University of Southern California, Los Angeles, California, USA.
Children's Hospital Los Angeles, Los Angeles, California, USA.
J Cardiovasc Magn Reson. 2024 Dec 3;27(1):101130. doi: 10.1016/j.jocmr.2024.101130.
Contemporary 0.55T magnetic resonance imaging (MRI) is promising for fetal MRI, due to the larger bore, reduced safety concerns, lower acoustic noise, and improved fast imaging capability. In this work, we explore improved fetal cardiovascular magnetic resonance (CMR) without relying on any synchronizing devices, prospective, or retrospective gating, to determine the feasibility of real-time MRI evaluation of fetal cardiac function as well as cardiac and great vessel anatomies by using spiral balanced steady-state free precession (bSSFP) at 0.55T.
A real-time spiral bSSFP pulse sequence for fetal CMR was implemented and optimized on a 0.55T whole-body MRI. Fetal CMR was prospectively performed between May 2022 and August 2023. The protocol included (1) real-time images at standard cardiac views, for 10-20 s/view and 40-43.6 ms/frame and (2) 4-9 stacks of slices at standard cardiac views that each cover the whole heart, with 15-30 slices/stack, and 2-5 s/slice, at 320-349 ms/frame. Images were evaluated by a fetal cardiologist. Quantitative measurements of cardiothoracic area ratio and cardiac axis were compared with previous reports. Diagnostic accuracy was compared against postnatal echocardiographic findings.
Twenty-nine participants were enrolled for 32 CMR exams, with mean maternal age 33.6 ± 5.8 years (range 22-44 years) and mean gestational age 32.8 ± 3.9 weeks (range 23-38 weeks). The proposed sequence enabled evaluation of the fetal heart in <30 min in all cases (average 22 min). Real-time MRI allowed easy adjustment of scan plan, automatic whole-heart volumetric sweeping, and flexible choice of reconstruction temporal resolution. For key cardiac anatomic features, 60% (315/527) were delineated well. Mean cardiothoracic area ratio and cardiac axis were 0.27 ± 0.04 and 45.8 ± 7.8 degrees. Diagnostic agreement with postnatal echocardiographic findings was 84% (26/31).
A spiral real-time bSSFP pulse sequence at 0.55T can provide both low-framerate and high-framerate fetal heart images without relying on maternal breath-hold, specialized gating devices, or cardiac gating. The low-framerate images offer high diagnostic quality structural evaluations of the fetal heart, while the high-framerate images capture fetal heart motion and may enable functional assessments.
当代0.55T磁共振成像（MRI）在胎儿MRI方面颇具前景，这得益于其更大的孔径、更低的安全隐患、更低的噪音以及更强的快速成像能力。在本研究中，我们探索在不依赖任何同步设备、前瞻性或回顾性门控的情况下改进胎儿心血管磁共振成像（CMR），以确定使用0.55T螺旋平衡稳态自由进动（bSSFP）序列对胎儿心功能以及心脏和大血管解剖结构进行实时MRI评估的可行性。
在一台0.55T全身MRI上实现并优化了用于胎儿CMR的实时螺旋bSSFP脉冲序列。于2022年5月至2023年8月前瞻性地开展胎儿CMR检查。方案包括：（1）在标准心脏视图下采集实时图像，每视图采集10 - 20秒，帧时40 - 43.6毫秒；（2）在标准心脏视图下采集4 - 9层切片，每层覆盖整个心脏，每层15 - 30片，每片采集2 - 5秒，帧时320 - 349毫秒。由一位胎儿心脏病专家对图像进行评估。将心胸面积比和心脏轴的定量测量结果与既往报告进行比较。将诊断准确性与产后超声心动图检查结果进行比较。
29名参与者接受了32次CMR检查，母亲平均年龄33.6±5.8岁（范围22 - 44岁），平均孕周32.8±3.9周（范围23 - 38周）。所提出的序列在所有病例中均能在<30分钟内（平均22分钟）完成对胎儿心脏的评估。实时MRI便于调整扫描方案、自动进行全心容积扫描以及灵活选择重建时间分辨率。对于关键心脏解剖特征，60%（315/527）显示良好。平均心胸面积比和心脏轴分别为0.27±0.04和45.8±7.8度。与产后超声心动图检查结果的诊断一致性为84%（26/31）。
0.55T螺旋实时bSSFP脉冲序列无需依赖母亲屏气、特殊门控设备或心脏门控，即可提供低帧率和高帧率的胎儿心脏图像。低帧率图像可对胎儿心脏进行高质量的结构评估，而高帧率图像可捕捉胎儿心脏运动并可能实现功能评估。
