Department of Radiology, University of California, San Diego, USA.
Department of Radiology, University of California, San Diego, USA; Department of Radiology, China-Japan Friendship Hospital, Beijing, China.
Neuroimage. 2014 Feb 15;87:32-41. doi: 10.1016/j.neuroimage.2013.10.053. Epub 2013 Nov 2.
White matter of the brain contains a majority of long T2 components as well as a minority of short T2 components. These are not detectable using clinical magnetic resonance imaging (MRI) sequences with conventional echo times (TEs). In this study we used ultrashort echo time (UTE) sequences to investigate the ultrashort T2 components in white matter of the brain and quantify their T2s and relative proton densities (RPDs) (relative to water with a proton density of 100%) using a clinical whole body 3T scanner. An adiabatic inversion recovery prepared dual echo UTE (IR-dUTE) sequence was used for morphological imaging of the ultrashort T2 components in white matter. IR-dUTE acquisitions at a constant TR of 1000 ms and a series of TIs were performed to determine the optimal TI which corresponded to the minimum signal to noise ratio (SNR) in white matter of the brain on the second echo image. T2s of the ultrashort T2 components were quantified using mono-exponential decay fitting of the IR-dUTE signal at a series of TEs. RPD was quantified by comparing IR-dUTE signal of the ultrashort T2 components with that of a rubber phantom. Nine healthy volunteers were studied. The IR-dUTE sequence provided excellent image contrast for the ultrashort T2 components in white matter of the brain with a mean signal to noise ratio of 18.7 ± 3.7 and a contrast to noise ratio of 14.6 ± 2.4 between the ultrashort T2 white matter and gray matter in a 4.4 min scan time with a nominal voxel size of 1.25 × 1.25 × 5.0mm(3). On average a T2* value of 0.42 ± 0.08 ms and a RPD of 4.05 ± 0.88% were demonstrated for the ultrashort T2 components in white matter of the brain of healthy volunteers at 3T.
脑白质含有大多数长 T2 成分和少数短 T2 成分。这些成分在常规回波时间 (TE) 的临床磁共振成像 (MRI) 序列中无法检测到。在这项研究中，我们使用超短回波时间 (UTE) 序列来研究脑白质中的超短 T2 成分，并使用临床全身 3T 扫描仪定量测量它们的 T2和相对质子密度 (RPD)（相对于质子密度为 100%的水）。使用绝热反转恢复双回波 UTE (IR-dUTE) 序列对白质中的超短 T2 成分进行形态成像。在恒定的 TR 为 1000ms 和一系列 TI 的条件下进行 IR-dUTE 采集，以确定与脑白质中第二回波图像上的最小信噪比 (SNR) 相对应的最佳 TI。通过在一系列 TE 下对 IR-dUTE 信号进行单指数衰减拟合来定量测量超短 T2 成分的 T2。通过比较超短 T2 成分的 IR-dUTE 信号与橡胶仿体的信号来定量测量 RPD。对 9 名健康志愿者进行了研究。IR-dUTE 序列为脑白质中的超短 T2 成分提供了极好的图像对比度，在 4.4 分钟的扫描时间内，平均信噪比为 18.7 ± 3.7，超短 T2 白质与灰质之间的对比噪声比为 14.6 ± 2.4，标称体素大小为 1.25×1.25×5.0mm(3)。在 3T 下，健康志愿者脑白质中的超短 T2 成分的平均 T2*值为 0.42 ± 0.08ms，RPD 为 4.05 ± 0.88%。
