Jang Hyungseok, Carl Michael, Ma Yajun, Searleman Adam C, Jerban Saeed, Chang Eric Y, Corey-Bloom Jody, Du Jiang
Department of Radiology, University of California San Diego, San Diego, CA, USA.
GE Healthcare, San Diego, CA, USA.
Quant Imaging Med Surg. 2020 May;10(5):895-906. doi: 10.21037/qims.2020.04.13.
Myelin alteration is closely associated with neurological diseases such as multiple sclerosis (MS). Unfortunately, due to myelin's extremely short T2* (~0.3 ms or shorter at 3T), it cannot be directly imaged with conventional MR imaging techniques. Recently, ultrashort echo time (UTE) imaging-based methods have been proposed for direct imaging of myelin. In this study, we explore the feasibility and efficacy of inversion recovery prepared zero echo time (IR-ZTE) imaging for direct volumetric imaging of myelin in white matter of the brain .
In the proposed method, an adiabatic IR preparation pulse is used to suppress long T2 white matter signal, followed by dual echo ZTE imaging where the remaining long T2 components, including gray matter, are suppressed by dual echo subtraction. In the implementation of ZTE, the sampling strategy introduced in Water- and Fat-Suppressed Proton Projection MRI (WASPI) was incorporated to acquire the k-space data missing due to the radiofrequency (RF) transmit/receiver switching time. The IR-ZTE sequence was implemented on a 3T clinical MR system and evaluated using a myelin phantom composed of six different myelin concentrations (0% to 20%), a cadaveric human brain, four healthy volunteers, and seven MS patients.
In the myelin phantom experiment, the ZTE signal intensity showed high linearity to the myelin concentrations (R=0.98). In the and experiments, the IR-ZTE sequence provided high contrast volumetric imaging of myelin in human brains. The IR-ZTE sequence was able to detect demyelinated foci lesions in all MS patients.
Adiabatic IR prepared dual echo ZTE imaging allows for direct, volumetric imaging of myelin in white matter of the brain .
髓鞘改变与诸如多发性硬化症（MS）等神经系统疾病密切相关。不幸的是，由于髓鞘的T2*极短（在3T时约为0.3毫秒或更短），它无法用传统的磁共振成像技术直接成像。最近，基于超短回波时间（UTE）成像的方法已被提出用于髓鞘的直接成像。在本研究中，我们探讨了反转恢复准备零回波时间（IR-ZTE）成像用于大脑白质中髓鞘直接容积成像的可行性和有效性。
在所提出的方法中，使用绝热IR准备脉冲来抑制长T2白质信号，随后进行双回波ZTE成像，其中包括灰质在内的剩余长T2成分通过双回波减法被抑制。在ZTE的实施过程中，纳入了水脂抑制质子投影MRI（WASPI）中引入的采样策略，以获取由于射频（RF）发射/接收切换时间而缺失的k空间数据。IR-ZTE序列在3T临床磁共振系统上实施，并使用由六种不同髓鞘浓度（0%至20%）组成的髓鞘模型、一具人类尸体脑、四名健康志愿者和七名MS患者进行评估。
在髓鞘模型实验中，ZTE信号强度与髓鞘浓度显示出高度线性关系（R = 0.98）。在人体脑实验中，IR-ZTE序列提供了髓鞘的高对比度容积成像。IR-ZTE序列能够在所有MS患者中检测到脱髓鞘病灶。
绝热IR准备的双回波ZTE成像允许对大脑白质中的髓鞘进行直接的容积成像。
