Radiology and Biomedical Imaging, University of California San Francisco, San Francisco, California, USA.
Department of Brain and Behavioral Sciences, University of Pavia, Pavia, Italy.
Magn Reson Med. 2024 Aug;92(2):702-714. doi: 10.1002/mrm.30093. Epub 2024 Mar 25.
This study aimed to develop a new high-resolution MRI sequence for the imaging of the ultra-short transverse relaxation time (uT) components in the brain, while simultaneously providing proton density (PD) contrast for reference and quantification.
The sequence combines low flip angle balanced SSFP (bSSFP) and UTE techniques, together with a 3D dual-echo rosette k-space trajectory for readout.
The expected image contrast was evaluated by simulations. A study cohort of six healthy volunteers and eight multiple sclerosis (MS) patients was recruited to test the proposed sequence. Subtraction between two TEs was performed to extract uT signals. In addition, conventional longitudinal relaxation time (T) weighted, T-weighted, and PD-weighted MRI sequences were also acquired for comparison.
Typical PD-contrast was found in the second TE images, while uT signals were selectively captured in the first TE images. The subtraction images presented signals primarily originating from uT components, but only if the first TE is short enough. Lesions in the MS subjects showed hyperintense signals in the second TE images but were hypointense signals in the subtraction images. The lesions had significantly lower signal intensity in subtraction images than normal white matter (WM), which indicated a reduction of uT components likely associated with myelin.
3D isotropic sub-millimeter (0.94 mm) spatial resolution images were acquired with the novel bSSFP UTE sequence within 3 min. It provided easy extraction of uT signals and PD-contrast for reference within a single acquisition.
本研究旨在开发一种新的高分辨率 MRI 序列，用于对脑中超短横向弛豫时间（uT）成分进行成像，同时提供质子密度（PD）对比以供参考和定量。
该序列结合了低翻转角平衡稳态进动快速成像（bSSFP）和 UTE 技术，以及用于读取的 3D 双回波蔷薇形 K 空间轨迹。
通过模拟评估预期的图像对比度。招募了六名健康志愿者和八名多发性硬化症（MS）患者的研究队列来测试所提出的序列。通过减去两个 TE 来提取 uT 信号。此外，还采集了常规的纵向弛豫时间（T）加权、T 加权和 PD 加权 MRI 序列进行比较。
在第二个 TE 图像中发现了典型的 PD 对比度，而 uT 信号则选择性地在第一个 TE 图像中被捕获。在减去 TE 之后，图像呈现出主要来自 uT 成分的信号，但前提是第一个 TE 足够短。MS 患者的病变在第二个 TE 图像中显示出高信号，但在减去 TE 的图像中则显示出低信号。病变在减去 TE 的图像中的信号强度明显低于正常白质（WM），这表明与髓鞘相关的 uT 成分减少。
使用新的 bSSFP UTE 序列在 3 分钟内获得了具有 3D 各向同性亚毫米（0.94mm）空间分辨率的图像。它提供了易于提取 uT 信号和 PD 对比以供参考的单一采集。
