Rapid Fetal HASTE MR Imaging

项目摘要 单次激发T2加权（SST 2w）成像是胎儿MRI中最常见的采集序列。其受欢迎程度 它能够提供出色的T2对比度，并在<2 秒尽管有这些优点，但对技术改进的未满足需求使SST 2w高度不足， 开发，并限制收购运行在其潜在速度的一小部分。如此低效的收购 使SST 2w容易受到胎儿运动的影响，需要进行大量的重复扫描，在此期间， 妇女必须忍受在一个封闭的环境中，以不舒服的姿势一动不动。 这些低效的采集不能提供期望的图像质量，并且遭受严重的分辨率损失 在长的读出窗口期间，其引起强信号衰减并且需要积极的部分傅立叶 取样. 我们提出了优化的采集和重建技术，将SST 2w采集速度提高了5倍， 同时提供具有减少的体素模糊的更清晰的图像。为了使这些成为可能，我们将从剪裁开始开始 我们的射频（RF）重新聚焦脉冲，以减少他们的能量沉积显着。这很重要 因为SST 2w采集快速连续地播放大量重聚焦脉冲，这需要长时间的 “冷却”期，以将射频加热保持在安全限值内。该死区时间等于标准的捕获时间 SST 2w增加3 - 4倍。我们将用可变的重聚焦脉冲来代替恒定翻转角的重聚焦脉冲序列。 翻转（vrf）角度方案，在匹配对比度和SNR的同时将能量沉积减少3倍 标准收购。这不仅使我们能够减少未使用的序列时间， 效率，而且还将能量沉积降低到足够低的水平，以允许额外的同时多切片 (SMS)编码. vrf还将允许延长回波时间以减小部分傅立叶因子，从而 减少体素模糊~35%。使用低能量multiPINS脉冲设计进行SMS重新聚焦将使我们 集成3倍短信加速功能。因此，vrf和multiPINS重新聚焦的组合将提供5倍网络 速度超过标准SST 2w，同时保持在射频致热安全水平内。 我们将使用我们的波CAIPI极端控制混叠k空间轨迹，以确保高图像质量， 3-介绍了折叠短信加速。LORAKS相位增强波编码图像重建 约束将更好地补偿部分傅立叶采样并进一步减少模糊。最后，我们将评估 所开发的采集和重建技术提高采集速度的能力， 胎儿SST 2w成像的表观分辨率，同时与标准的对比度和SNR紧密匹配 通过在3T下扫描10名孕妇获得。

Project Summary Single-shot T2-weighted (SST2w) imaging is the most common acquisition sequence in fetal MRI. Its popularity stems from its ability to supply excellent T2 contrast, and encode information from each imaging slice in <2 seconds. Despite these advantages, the unmet need for technical improvements renders SST2w highly under- developed, and constrains the acquisition to run at a fraction of its potential speed. Such inefficient acquisition makes SST2w vulnerable to fetal motion and necessitates a large number of repeat scans, during which pregnant women have to tolerate being inside a confined environment and remain motionless in uncomfortable positions. These inefficient acquisitions fail to provide the desired image quality and suffer from severe resolution loss during the long readout window, which incurs strong signal decay and requires aggressive partial Fourier sampling. We propose optimized acquisition and reconstruction technology to speed up SST2w acquisition by 5-fold, while providing sharper images with reduced voxel blurring. To make these possible, we will begin by tailoring our radiofrequency (RF) refocusing pulses to reduce their energy deposition dramatically. This is important because SST2w acquisition plays a large number of refocusing pulses in rapid succession, which requires a long “cool-off” period to keep RF heating within safety limits. This dead time prolongs the acquisition time of standard SST2w by 3–4-fold. We will replace this train of constant flip angle refocusing pulses with a variable refocusing flip (vrf) angle scheme, which will reduce the energy deposition by 3-fold while matching the contrast and SNR of the standard acquisition. Not only this will allow us to decrease the unused sequence time to improve scan efficiency, but also reduce the energy deposition to low enough levels to permit additional simultaneous multislice (SMS) encoding. vrf will also allow for prolonging the echo time to reduce the partial Fourier factor, thereby decreasing voxel blurring by ~35%. Using low-energy multiPINS pulse design for SMS refocusing will let us incorporate 3-fold SMS acceleration. Combination of vrf and multiPINS refocusing will thus provide a 5-fold net speed up over standard SST2w, while remaining within RF heating safety levels. We will use our wave-CAIPI extreme controlled aliasing k-space trajectory to ensure high image quality when 3-fold SMS acceleration is introduced. Augmenting wave encoded image reconstruction with LORAKS phase- constraint will better compensate partial Fourier sampling and further reduce blurring. Finally, we will evaluate the ability of the developed acquisition and reconstruction technologies to improve the acquisition speed and apparent resolution of fetal SST2w imaging while closely matching the contrast and SNR of the standard acquisition by scanning 10 pregnant women at 3T.