Optimizing neuromelanin contrast in the substantia nigra and locus coeruleus using a magnetization transfer contrast prepared 3D gradient recalled echo sequence
Optimizing neuromelanin contrast in the substantia nigra and locus coeruleus using a magnetization transfer contrast prepared 3D gradient recalled echo sequence
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DOI：
10.1016/j.neuroimage.2020.116935
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发表时间：
2020-09-01
期刊：
影响因子：
5.7
通讯作者：
Haacke, E. Mark
中科院分区：
文献类型：
--
作者：
Liu, Yu;Li, Junchen;Haacke, E. Mark
黑质（SN）和蓝斑（LC）中的神经黑色素（NM）损失正在使用磁化传递对比（MTC）磁共振成像作为帕金森病（PD）的成像生物标志物进行研究。MTC脉冲以抑制具有高大分子含量的组织的方式操作，从而突出LC和SN中NM的存在。MTC脉冲还导致组织的有效T1减小。过去，3D梯度回波（GRE）序列通常使用单个翻转角（FA）运行，以便在尝试可视化NM时突出T1缩短效应。我们认为，NM将是最好的看到与低FA（相对于恩斯特角），因为NM具有较高的水含量相对于周围组织。因此，本文的目标是使用3D GRE MTC策略性采集梯度回波（STAGE）成像方法优化SN和LC中的NM对比度（作为翻转角的函数）。为了实现这一点，短重复时间（62 ms），收集了14名健康志愿者（年龄范围24 - 43岁，平均值+/-SD = 34.8 +/-6.0岁，6名男性）在7个不同翻转角（范围从5度到40度）下的3D GRE成像数据。通过测量这些结构与周围组织之间的对比度噪声比，我们发现显示最佳NM对比度的FA对于SN为15度-20度，对于LC为20度-25度。使用仅具有两个翻转角（15度和30度）的STAGE成像，不仅可以量化T1和质子密度等组织特性，还可以在任意FA处生成合成MTC图像。这些合成图像使得可以针对LC或SN中可能发生的作为年龄或疾病的函数的组织性质的任何变化来优化对比度。总之，实际上，在标准临床成像设置中，可以在大约7分钟内收集两种FA的两次扫描，以评价LC和SN中NM的信号强度和体积。
Neuromelanin (NM) loss in the substantia nigra (SN) and locus coeruleus (LC) is being investigated as an imaging biomarker for Parkinson's disease (PD) using magnetization transfer contrast (MTC) magnetic resonance imaging. The MTC pulse operates in a way to suppress tissue with high macromolecular content thereby highlighting the presence of NM in the LC and the SN. The MTC pulse also leads to a reduction in the effective T1 of the tissue. In the past, a 3D gradient echo (GRE) sequence has usually been run with a single flip angle (FA) generally to highlight the T1 shortening effect when trying to visualize NM. We contend that the NM will be best seen with a low FA (relative to the Ernst angle) because the NM has high water content relative to the surrounding tissues. Therefore, the goal of this paper was to optimize the NM contrast in the SN and LC as a function of flip angle using a 3D GRE MTC strategically acquired gradient echo (STAGE) imaging approach. In order to accomplish this, short repeat time (62 ms), 3D GRE imaging data were collected for 7 different flip angles ranging from 5 degrees to 40 degrees for 14 healthy volunteers (age range 24-43 years, mean +/- SD = 34.8 +/- 6.0 years, 6 males). By measuring the contrast-to-noise ratio between these structures and the surrounding tissues, we found that the FA showing the best NM contrast was 15 degrees -20 degrees for the SN and 20 degrees -25 degrees for the LC. Using STAGE imaging with just two flip angles (15 degrees and 30 degrees) made it possible to quantify not only tissue properties such as T1 and proton density but also to generate synthetic MTC images at an arbitrary FA. These synthetic images make it possible to optimize the contrast for any changes in tissue property that might occur in the LC or SN as a function of age or disease. In conclusion, practically, two scans could be collected in roughly 7 min each for both FAs in a standard clinical imaging setting to evaluate the signal intensity and volume of the NM in the LC and SN.