Department of Neurology, University Hospital Basel, Petersgraben 4, 4031 Basel, Switzerland; Division of Diagnostic and Interventional Neuroradiology, Department of Radiology, University Hospital Basel, Petersgraben 4, 4031 Basel, Switzerland; Medical Image Analysis Center (MIAC), Schanzenstrasse 55, 4031 Basel, Switzerland.
Department of Neurology, University Hospital Basel, Petersgraben 4, 4031 Basel, Switzerland; Division of Diagnostic and Interventional Neuroradiology, Department of Radiology, University Hospital Basel, Petersgraben 4, 4031 Basel, Switzerland; Medical Image Analysis Center (MIAC), Schanzenstrasse 55, 4031 Basel, Switzerland.
Neuroimage. 2015 Mar;108:87-94. doi: 10.1016/j.neuroimage.2014.12.045. Epub 2014 Dec 20.
Different pathological processes like demyelination and axonal loss can alter the magnetisation transfer ratio (MTR) in brain tissue. The standard method to measure this effect is to scan the respective tissue twice, one with and one without a specific saturation pulse. A major drawback of this technique based on spoiled gradient echo (GRE) sequences relates to its long acquisition time due to the saturation pulses. Recently, an alternative concept for MT imaging based on balanced steady state free precession (bSSFP) has been proposed. Modification of the duration of the radiofrequency pulses for imaging allows scanning MT sensitive and non-sensitive images. The steady-state character of bSSFP with high intrinsic signal-to-noise ratio (SNR) allows three-dimensional (3D) whole brain MTR at high spatial resolution within short and thus clinically feasible acquisition times. In the present study, both bSSFP-MT and 2D GRE-MT imaging were used in a cohort of 31 patients with multiple sclerosis (MS) to characterize different normal appearing (NA) and pathological brain structures. Under the constraint of identical SNR and scan time, a 3.4 times higher voxel size could be achieved with bSSFP. This increased resolution allowed a more accurate delineation of the different brain structures, especially of cortex, hippocampus and MS lesions. In a multiple linear regression model, we found an association between MTR of cortical lesions and a clinical measure of disability (r= -0.407, p=0.035) in the bSSFP dataset only. The different relaxation weighting of the base images (T2/T1 in bSSFP, proton density in GRE) had no effects besides a larger spreading of the MTR values of the different NA structures. This was demonstrated by the nearly perfect linearity between the NA matter MTR of both techniques as well as in the absolute MTR differences between NA matter and the respective lesions.
不同的病理过程，如脱髓鞘和轴突丢失，会改变脑组织中的磁化传递率（MTR）。测量这种效应的标准方法是对相应的组织进行两次扫描，一次带有和一次不带有特定的饱和脉冲。基于spoiled gradient echo (GRE) 序列的这种技术的一个主要缺点是由于饱和脉冲，其采集时间较长。最近，基于平衡稳态自由进动（bSSFP）的 MT 成像的替代概念已经提出。通过改变用于成像的射频脉冲的持续时间，可以扫描 MT 敏感和非敏感图像。bSSFP 的稳态特性具有高固有信噪比（SNR），允许在短时间内以高空间分辨率进行三维（3D）全脑 MTR，从而在临床可行的采集时间内完成。在本研究中，使用 bSSFP-MT 和 2D GRE-MT 成像在 31 名多发性硬化症（MS）患者的队列中进行成像，以对不同的正常表现（NA）和病理脑结构进行特征描述。在相同 SNR 和扫描时间的约束下，bSSFP 可实现 3.4 倍的体素尺寸提高。这种分辨率的提高允许更准确地描绘不同的大脑结构，特别是皮质、海马体和 MS 病变。在多元线性回归模型中，我们仅在 bSSFP 数据集发现皮质病变的 MTR 与临床残疾评估指标之间存在关联（r= -0.407，p=0.035）。基础图像的不同弛豫加权（bSSFP 中的 T2/T1，GRE 中的质子密度）除了不同 NA 结构的 MTR 值的更大分布之外没有影响。这通过两种技术的 NA 物质 MTR 之间几乎完美的线性关系以及 NA 物质和各自病变之间的绝对 MTR 差异证明。
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