Institute for Diagnostic and Interventional Radiology, University Hospital of Zurich.
Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric University Hospital, University of Zurich, Zurich.
Invest Radiol. 2019 Mar;54(3):160-168. doi: 10.1097/RLI.0000000000000523.
The aim of this study was to evaluate the efficiency and performance of different fat suppression techniques for clinical 7 T knee magnetic resonance imaging including the slice-selective gradient reversal (SSGR) technique.
This article is an ethical board-approved prospective study with written informed consent from 8 volunteers (mean, 31 ± 4 years). It included fat phantom and knee magnetic resonance imaging at 3 T (Magnetom Skyra; Siemens Healthcare) and at 7 T (Achieva, Philips Healthcare). At 3 T, an axial proton density-weighted turbo spin echo sequence with spectral adiabatic inversion recovery (SPAIR) was acquired. At 7 T, a series of 5 proton density-weighted turbo spin echo sequences was acquired: (a) without fat suppression, (b) with spectral presaturation with inversion recovery (SPIR), (c) with SPAIR, (d) with SSGR, and (e) with the combination of SSGR + SPIR. Additional noise scans allowed pixelwise calculation of signal-to-noise ratio and contrast-to-noise ratio maps. Quantitative data at 7 T were compared with each other but not to 3 T. Two independent radiologists evaluated overall image quality, homogeneity and grade of fat suppression, and the delineation between 2 adjacent structures. Results were compared using Wilcoxon signed rank and paired sample t tests.
Relative signal-to-noise ratios of fat demonstrated that the SPIR technique reduced the fat signal to 45% ± 5.4%; SPAIR, 18% ± 1.2%; SSGR, 14% ± 1.1%; and SSGR + SPIR, 11% ± 0.3%. Contrast-to-noise ratio showed superior contrast between muscle-fat (P < 0.001) and fluid-fat (P ≤ 0.001) for SSGR and SSGR + SPIR. The radiologists rated the overall image quality higher at 7 T than 3 T. The homogeneity and grade of fat suppression as well as the delineation between 2 different (adjacent) structures were rated best for SSGR + SPIR.
At 7 T, fat saturation for clinical knee imaging using SSGR and the combination of SSGR + SPIR was superior compared with standard methods based on spectrally selective radiofrequency pulses.
本研究旨在评估不同的脂肪抑制技术在临床 7T 膝关节磁共振成像中的效率和性能，包括选择性梯度反转（SSGR）技术。
本研究为伦理委员会批准的前瞻性研究，8 名志愿者（平均年龄 31±4 岁）签署了书面知情同意书。研究包括脂肪体模和膝关节磁共振成像，分别在 3T（Magnetom Skyra；西门子医疗）和 7T（Achieva，飞利浦医疗）上进行。在 3T 上，采集了轴位质子密度加权涡轮自旋回波序列，采用谱反转恢复（SPAIR）。在 7T 上，采集了一系列 5 个质子密度加权涡轮自旋回波序列：（a）无脂肪抑制，（b）频谱预饱和反转恢复（SPIR），（c）SPAIR，（d）SSGR，（e）SSGR+SPIR。额外的噪声扫描允许逐像素计算信噪比和对比噪声比图。7T 的定量数据相互比较，但不与 3T 比较。两名独立的放射科医生评估了整体图像质量、均匀性和脂肪抑制程度，以及两个相邻结构之间的界限。结果采用 Wilcoxon 符号秩和配对样本 t 检验进行比较。
脂肪的相对信噪比显示，SPIR 技术将脂肪信号降低至 45%±5.4%；SPAIR 降低至 18%±1.2%；SSGR 降低至 14%±1.1%；SSGR+SPIR 降低至 11%±0.3%。对比噪声比显示 SSGR 和 SSGR+SPIR 具有更好的肌肉-脂肪（P<0.001）和液体-脂肪（P≤0.001）对比度。放射科医生认为 7T 的整体图像质量高于 3T。SSGR+SPIR 的均匀性和脂肪抑制程度以及两个不同（相邻）结构之间的界限评分最高。
在 7T 下，与基于谱选择性射频脉冲的标准方法相比，使用 SSGR 和 SSGR+SPIR 的临床膝关节成像的脂肪饱和技术更优。
