From the Stanford University School of Medicine (R.J.).
Departments of Radiology (E.T., A.M.L., V.T., M.I.).
AJNR Am J Neuroradiol. 2020 Jul;41(7):1256-1262. doi: 10.3174/ajnr.A6616. Epub 2020 Jun 25.
Conventional single-shot FSE commonly used for fast MRI may be suboptimal for brain evaluation due to poor image contrast, SNR, or image blurring. We investigated the clinical performance of variable refocusing flip angle single-shot FSE, a variation of single-shot FSE with lower radiofrequency energy deposition and potentially faster acquisition time, as an alternative approach to fast brain MR imaging.
We retrospectively compared half-Fourier single-shot FSE with half- and full-Fourier variable refocusing flip angle single-shot FSE in 30 children. Three readers reviewed images for motion artifacts, image sharpness at the brain-fluid interface, and image sharpness/tissue contrast at gray-white differentiation on a modified 5-point Likert scale. Two readers also evaluated full-Fourier variable refocusing flip angle single-shot FSE against T2-FSE for brain lesion detectability in 38 children.
Variable refocusing flip angle single-shot FSE sequences showed more motion artifacts (< .001). Variable refocusing flip angle single-shot FSE sequences scored higher regarding image sharpness at brain-fluid interfaces (< .001) and gray-white differentiation (< .001). Acquisition times for half- and full-Fourier variable refocusing flip angle single-shot FSE were faster than for single-shot FSE (< .001) with a 53% and 47% reduction, respectively. Intermodality agreement between full-Fourier variable refocusing flip angle single-shot FSE and T2-FSE findings was near-perfect (κ = 0.90, κ = 0.95), with an 8% discordance rate for ground truth lesion detection.
Variable refocusing flip angle single-shot FSE achieved 2× faster scan times than single-shot FSE with improved image sharpness at brain-fluid interfaces and gray-white differentiation. Such improvements are likely attributed to a combination of improved contrast, spatial resolution, SNR, and reduced T2-decay associated with blurring. While variable refocusing flip angle single-shot FSE may be a useful alternative to single-shot FSE and, potentially, T2-FSE when faster scan times are desired, motion artifacts were more common in variable refocusing flip angle single-shot FSE, and, thus, they remain an important consideration before clinical implementation.
传统的单次激发 FSE 常用于快速 MRI，但由于图像对比度、SNR 或图像模糊较差，可能并不适合脑评估。我们研究了可变重聚焦翻转角单次激发 FSE 的临床性能，这是单次激发 FSE 的一种变体，具有更低的射频能量沉积和潜在更快的采集时间，是快速脑 MRI 的替代方法。
我们回顾性比较了半傅里叶单次激发 FSE 与半傅里叶和全傅里叶可变重聚焦翻转角单次激发 FSE 在 30 例儿童中的应用。三位读者使用改良的 5 分 Likert 量表评估运动伪影、脑-脑脊液界面的图像锐利度以及灰白质区分的图像锐利度/组织对比度。两位读者还评估了全傅里叶可变重聚焦翻转角单次激发 FSE 在 38 例儿童中的脑病变检测能力与 T2-FSE 的比较。
可变重聚焦翻转角单次激发 FSE 序列显示更多的运动伪影（<0.001）。可变重聚焦翻转角单次激发 FSE 序列在脑-脑脊液界面的图像锐利度（<0.001）和灰白质区分（<0.001）方面得分更高。半傅里叶和全傅里叶可变重聚焦翻转角单次激发 FSE 的采集时间均快于单次激发 FSE（<0.001），分别减少了 53%和 47%。全傅里叶可变重聚焦翻转角单次激发 FSE 与 T2-FSE 检查结果的模态间一致性近乎完美（κ=0.90，κ=0.95），真实病变检测的差异率为 8%。
可变重聚焦翻转角单次激发 FSE 实现了比单次激发 FSE 快 2 倍的扫描时间，同时改善了脑-脑脊液界面和灰白质区分的图像锐利度。这些改进可能归因于对比度、空间分辨率、SNR 的提高以及与模糊相关的 T2 衰减的降低。虽然可变重聚焦翻转角单次激发 FSE 可能是单次激发 FSE 的有用替代方法，并且在需要更快扫描时间时可能是 T2-FSE 的替代方法，但可变重聚焦翻转角单次激发 FSE 中的运动伪影更为常见，因此在临床实施之前，这仍然是一个重要的考虑因素。
