Fast Whole-Brain Direct Myelin Magnetic Resonance Imaging

 描述（由申请人提供）：使用MRI对人脑中髓磷脂结构的体内测量对于广泛的科学和临床神经成像应用是重要的，所述应用包括脑发育和神经系统疾病，例如多发性硬化、阿尔茨海默病和肌萎缩性侧索硬化。使用MRI对髓磷脂进行直接成像是困难的，因为髓磷脂质子的极短T2导致信号在可以获取之前衰减到零。因此，在常规临床MRI方案中，使用使用与脂质-蛋白质双层结构中的髓磷脂相互作用的水质子间接测量髓磷脂结构的方法。这些方法包括扩散加权成像，磁化转移和多指数拟合。这些间接测量方法有时在区分来自髓鞘水的信号以及来自细胞内和细胞外水的信号方面可能是模糊的。最近的研究显示了使用超短回波时间（< 50 µs）的直接髓鞘MRI（DM-MRI）的前景。DM-MRI对比度是使用反转脉冲来抑制来自长T2物质（例如水和脂肪）的信号、用于超短回波采集的半脉冲激励和径向读出以及在两个不同回波处采集的数据的减法来产生的，以产生具有高形态对比度的髓磷脂图像。DM-MRI的缺点是扫描时间长（128 x 128切片约5分钟），这是由于反转和径向采集的空闲时间以及非笛卡尔径向采集的重建时间长。这些缺点使得DM-MRI无法常规用于全脑临床和科学扫描。拟议的工作将使用同步多切片（SMS）并行成像方法，以显着提高DM-MRI的成像速度。将使用功率无关射频（RF）脉冲方法同时反转多个切片，然后使用多切片半RF脉冲同时激发。相位循环将应用于每条径向线，以控制混叠，实现稳健的SMS重建。为了减少重建的时间和复杂性，数据驱动的重建和矢量化网格的方法，充分利用现代CPU的并行处理能力提出。最终的结果将是一种全脑DM-MRI方法，扫描时间约为5分钟，这将适用于常规MRI扫描仪的临床和研究方案。

 DESCRIPTION (provided by applicant): In vivo measurement of the myelin structure in the human brain using MRI is significant for a wide variety of scientific and clinical neuroimaging applications including brain development and neurological diseases such as multiple sclerosis, Alzheimer's diseases, and amyotrophic lateral sclerosis. Direct imaging of myelin using MRI is difficult because the extremely short T2 of myelin protons causes the signal to decay to zero before it can be acquired. Therefore, in routine clinical MRI protocols, methods that indirectly measure myelin structure using water protons that interact with the myelin in the lipid-protein bilayer structure are used. These methods include diffusion-weighted imaging, magnetization transfer and multi-exponential fitting. These indirect measurement methods sometimes can be ambiguous in distinguishing signal from the myelin water and that from the intracellular and extracellular water. Recent studies show the prospect of direct myelin MRI (DM-MRI) using ultra-short echo times (< 50 µs). The DM-MRI contrast is generated using an inversion pulse to suppress signal from long T2 species such as water and fat, half-pulse excitations and radial readouts for the ultra-short echo acquisition, and subtraction of data acquired at two different echoes to produce a myelin image with high morphological contrast. The drawbacks of DM-MRI are the long scan time (~5 min for a 128x128 slice) due to the idling time in inversion and the radial acquisition and long reconstruction time from the non-Cartesian radial acquisition. These drawbacks prohibit DM-MRI from being used routinely for whole brain clinical and scientific scans. The proposed work will use simultaneous multi-slice (SMS) parallel imaging methods to significantly increase the imaging speed of DM-MRI. Multiple slices will be simultaneously inverted using a power independent radio frequency (RF) pulse method and then simultaneously excited using a multi-slice half RF pulse. Phase cycling will be applied to each radial line to control aliasing for a robust SMS reconstruction. To reduce the time and complexity of the reconstruction, a data-driven reconstruction and a vectorized gridding method that fully uses the parallel processing power of modern CPUs are proposed. The final result will be a whole brain DM-MRI method with a scan time of approximately five minutes that will be practical for clinical and research protocols on conventional MRI scanners.