Sadanand Siddharth, Stobbe Rob, van Mieghem Tim, Shinar Shiri, Krishnan Pradeep, Miller Elka, Stanisz Greg, Sussman Dafna
Maternal Fetal Imaging Laboratory (MFI Lab), Institute for Biomedical Engineering, Science and Technology (iBEST), Departments of Biomedical Physics & Engineering, Toronto Metropolitan University, Toronto, ON, Canada.
Peter S. Allen MR Research Centre, Biomedical Engineering Department, University of Alberta, Edmonton, AB, Canada.
Front Pediatr. 2025 May 9;13:1443387. doi: 10.3389/fped.2025.1443387. eCollection 2025.
Magnetic resonance imaging (MRI) is commonly used as a tool for confirming a fetal brain abnormality suspected on ultrasound. Common clinical MRI sequences typically only reveal changes in the brain once there are gross abnormalities. Detection of more minute changes in brain tissue microstructure could permit earlier detection of complications, allowing for potentially more timely, effective interventions. Tissue microstructure corresponding to neuronal development can be captured before the appearance of broad anatomical changes using more advanced imaging, such as magnetization transfer (MT) MRI. This study aimed to investigate the feasibility of an MT MRI pulse sequence developed by the researcher, yarnball (YB) MT, for fetal brain imaging.
A yarnball (YB) readout trajectory was used to accelerate imaging and increase sensitivity. A multiband saturation pulse was implemented to increase MT specificity from saturation transfer (ST) confounds. MT-weighted images were derived from three-point magnetization transfer ratio asymmetry (MTR) to reduce acquisition time to within a breath hold. Sensitivity and specificity were evaluated on agar phantoms with varied MT and ST confound concentrations. Pilot imaging was done with singleton third trimester gestations complicated with mild ventriculomegaly recruited from Mount Sinai Hospital.
YB MT covers a 350 mm 3D field of view (FoV) within a 13 s breath hold and a 28 s acquisition. The sequence demonstrated a limit of quantification (LOQ) of agar of 0.62% w/w and no dependence on glucose in agar phantoms with glucose ST confound. Pilot imaging of third trimester pregnancies with mild ventriculomegaly with the sequence revealed MT contrast in the fetal brain that was spatially consistent with the development of white matter at this gestational age. All participants reported the sequence and the breath hold to be tolerable.
The developed YB MT pulse sequence is sensitive to fetal physiological MT signal is tolerable to participants, and does not demonstrate sensitivity to ST confounds in phantom imaging. While the breath hold was reported to be tolerable, motion artefacts and spiral trajectory blurring affected subjects' imaging. Ongoing work, including online reconstruction, expedited trajectories, and improvements in the signal-to-noise ratio should address these challenges. This proof of principle is a step towards the clinical translation of gestational metabolic imaging, such as MT imaging of fetal myelin, for the early detection of gestational complications.
磁共振成像（MRI）通常用作确认超声怀疑的胎儿脑异常的工具。常见的临床MRI序列通常只有在出现明显异常时才会显示脑部变化。检测脑组织微观结构中更细微的变化可以更早地发现并发症，从而可能进行更及时、有效的干预。使用更先进的成像技术，如磁化传递（MT）MRI，可以在广泛的解剖学变化出现之前捕捉与神经元发育相对应的组织微观结构。本研究旨在探讨研究人员开发的一种MT MRI脉冲序列——纱球（YB）MT用于胎儿脑成像的可行性。
采用纱球（YB）读出轨迹来加速成像并提高灵敏度。实施多波段饱和脉冲以提高MT特异性，减少饱和转移（ST）混淆。MT加权图像由三点磁化传递率不对称（MTR）得出，以将采集时间缩短至一次屏气内。在具有不同MT和ST混淆浓度的琼脂模型上评估灵敏度和特异性。对从西奈山医院招募的患有轻度脑室扩大的单胎妊娠晚期孕妇进行了初步成像。
YB MT在13秒屏气和28秒采集时间内覆盖350 mm的三维视野（FoV）。该序列在琼脂模型中显示出0.62% w/w的定量限，并且在存在葡萄糖ST混淆的琼脂模型中不依赖于葡萄糖。使用该序列对患有轻度脑室扩大的妊娠晚期孕妇进行的初步成像显示，胎儿脑中的MT对比度在空间上与该孕周白质的发育一致。所有参与者都报告该序列和屏气是可以耐受的。
所开发的YB MT脉冲序列对胎儿生理MT信号敏感，参与者可耐受，并且在模型成像中对ST混淆不敏感。虽然报告称屏气是可以耐受的，但运动伪影和螺旋轨迹模糊影响了受试者的成像。正在进行的工作，包括在线重建、加速轨迹以及提高信噪比，应能应对这些挑战。这一原理验证是朝着将妊娠代谢成像（如胎儿髓磷脂的MT成像）临床转化以早期发现妊娠并发症迈出的一步。
