Max Planck Institute for Biological Cybernetics, Magnetic Resonance Center, Tübingen, Germany.
Magn Reson Med. 2011 Dec;66(6):1572-81. doi: 10.1002/mrm.22949. Epub 2011 Jun 10.
As field strength increases, the magnetic resonance imaging contrast parameters like relaxation times, magnetization transfer or image phase change, causing variations in contrast and signal-to-noise ratio. To obtain reliable data for these parameters at 16.4 T, high-resolution measurements of the relaxation times T(1), T(2) and T(2)*, as well as of the magnetization transfer ratio and the local frequency in the rat brain were performed. Tissue-specific values were obtained for up to 17 brain structures to assess image contrast. The measured parameters were compared to those found at different field strengths to estimate contrast and signal behavior at increasing field. T(1) values were relatively long with (2272 ± 113) ms in cortex and (2073 ± 97) ms in white matter, but did not show a tendency to converge, leading to an almost linear increase in signal-to-noise ratio and still growing contrast-to-noise ratio. T(2) was short with (25 ± 2) ms in cortex and (20 ± 1) ms in white matter. Magnetization transfer effects increase by around 25% compared to published 4.7 T data, which leads to improved contrast. The image phase, as novel and high-field specific contrast mechanism, is shown to obtain good contrast in deep brain regions with increasing signal-to-noise ratio up to high field strengths.
随着磁场强度的增加，磁共振成像对比参数（如弛豫时间、磁化转移或图像相位变化）会发生变化，从而导致对比度和信噪比的变化。为了在 16.4T 下获得这些参数的可靠数据，对大鼠大脑的弛豫时间 T(1)、T(2)和 T(2)*、磁化转移比以及局部频率进行了高分辨率测量。针对多达 17 种脑结构获得了组织特异性值，以评估图像对比度。将测量的参数与在不同场强下获得的参数进行比较，以估计对比度和信号在增加场强下的行为。T(1)值相对较长，皮质为（2272 ± 113）ms，白质为（2073 ± 97）ms，但没有收敛的趋势，导致信噪比几乎呈线性增加，对比度噪声比仍在增长。T(2)值较短，皮质为（25 ± 2）ms，白质为（20 ± 1）ms。与已发表的 4.7T 数据相比，磁化转移效应增加了约 25%，从而提高了对比度。图像相位作为一种新的、特定于高场的对比机制，在高信噪比下可以在深部脑区获得良好的对比度，直到高场强。
