Fast Whole-Brain Direct Myelin Magnetic Resonance Imaging

 描述（由申请人提供）：使用 MRI 对人脑髓磷脂结构进行体内测量对于各种科学和临床神经成像应用具有重要意义，包括大脑发育和神经系统疾病，如多发性硬化症、阿尔茨海默病和肌萎缩侧索硬化症。使用 MRI 直接对髓磷脂进行成像很困难，因为髓磷脂质子的 T2 极短，导致信号在获取之前衰减到零。因此，在常规临床 MRI 方案中，使用利用与脂蛋白双层结构中的髓磷脂相互作用的水质子来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磷脂水的信号以及来自细胞内和细胞外水的信号方面可能不明确。最近的研究显示了使用超短回波时间（< 50 µs）的直接髓磷脂 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、半脉冲激励和用于超短回波采集的径向读数以及在两个不同回波处获取的数据相减以产生具有高形态对比度的髓磷脂图像而生成的。 DM-MRI 的缺点是扫描时间长（128x128 切片约 5 分钟），这是由于反演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造成的。这些缺点使得 DM-MRI 无法常规用于全脑临床和科学扫描。所提出的工作将使用同时多切片（SMS）并行成像方法来显着提高 DM-MRI 的成像速度。将使用与功率无关的射频 (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，从而实现稳健的 SMS 重建。为了减少重建的时间和复杂性，提出了一种数据驱动的重建和充分利用现代CPU并行处理能力的矢量化网格方法。最终结果将是扫描时间约为五分钟的全脑 DM-MRI 方法，这对于传统 MRI 扫描仪的临床和研究方案来说是实用的。

 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.