High-Field MR Center, Department of Biomedical Imaging and Image-Guided Therapy, Medical University of Vienna, Austria.
Siemens Healthcare GmbH, Erlangen, Germany.
Invest Radiol. 2019 Jan;54(1):48-54. doi: 10.1097/RLI.0000000000000508.
The aim of this study was to assess and compare the overall performance, reliability, variability, as well as the accuracy of diffusion tensor imaging (DTI) and fiber tracking metrics, for the muscles of the calf at 3 T and 7 T.
Ten volunteers (5 males; mean age, 29.1 ± 4.7 years), with no history of muscle disease, were examined twice at 3 T and 7 T, using a stimulated-echo acquisition mode DTI sequence. Signal-to-noise ratio (SNR) and DTI metrics (track numbers [trn], length [trl], volume [trv], fractional anisotropy [FA], mean [MD], axial [AD], and radial diffusivity [RD]) of the whole-calf muscles, the tibialis anterior, the gastrocnemius medialis, the gastrocnemius lateralis, and the soleus were collected. The Student t test was used to compare SNR and DTI metrics obtained at 3 T and 7 T. The coefficients of variation and the intraclass correlation coefficients were derived to assess the variability and the reliability of the DTI measurements at 3 T and 7 T. To further assess the accuracy of the measurements, the absolute difference was computed for each DTI metric at 3 T and 7 T and then compared (Student t test). The applied level of significance for all the statistical analyses was P < 0.05.
As expected, the SNR was higher at 7 T than at 3 T (+111%; P < 0.001). At 7 T, the tracked fibers of the whole calf muscles, the gastrocnemii, and the soleus were more numerous (trn +5.5%, +3.1%, +8.5%, and +15.1%, respectively), longer (trl +13.1%, +18.8%, +19.3%, and +33.3%, respectively), and showed a greater volume (trv +12.1%, +12.2%, +14.7%, and +15.7%, respectively) than at 3 T (P < 0.05 each). The soleus demonstrated higher FA (+14.3%), lower MD (-1.7%), AD (-1.9%), and RD (-2%) at 7 T than at 3 T (P < 0.05 each), whereas the other muscles showed more heterogeneous results. The coefficients of variation were good (ie, <10%) for all DTI metrics at both 3 T and 7 T. The intraclass correlation coefficient was excellent (>0.750) at 7 T and 3 T for several DTI metrics, such as the trn of the gastrocnemii and the soleus, the trv of the gastrocnemii, the FA of the whole-calf muscles, gastrocnemius medialis, tibialis anterior, and soleus, and the RD of all investigated muscles (ie, whole-calf muscles, gastrocnemii, tibialis anterior, and soleus). There were no significant differences between the 2 consecutive measurements with each device, except for the trn of the whole-calf muscles and the FA of the gastrocnemius lateralis (higher mean absolute difference at 3 T and 7 T, respectively; P < 0.05 each).
Despite the numerous challenges associated with DTI of the muscles, both 3 T and 7 T demonstrated reliable and precise results.
本研究旨在评估和比较 3T 和 7T 下弥散张量成像（DTI）和纤维追踪指标在评估小腿肌肉整体表现、可靠性、变异性和准确性方面的性能。
10 名志愿者（5 名男性；平均年龄 29.1±4.7 岁），无肌肉疾病史，分别在 3T 和 7T 下使用受激回波采集模式 DTI 序列进行两次检查。收集全小腿肌肉、胫骨前肌、腓肠肌内侧、腓肠肌外侧和比目鱼肌的信噪比（SNR）和 DTI 指标（轨迹数量[trn]、长度[trl]、体积[trv]、各向异性分数[FA]、平均弥散度[MD]、轴向弥散度[AD]和径向弥散度[RD]）。采用 Student t 检验比较 3T 和 7T 获得的 SNR 和 DTI 指标。得出变异系数和组内相关系数，以评估 3T 和 7T 下 DTI 测量的变异性和可靠性。为了进一步评估测量的准确性，计算了 3T 和 7T 每个 DTI 指标的绝对差异，然后进行比较（Student t 检验）。所有统计分析的应用显著性水平均为 P<0.05。
正如预期的那样，7T 时的 SNR 比 3T 时高（+111%；P<0.001）。在 7T 时，全小腿肌肉、腓肠肌和比目鱼肌的追踪纤维数量（trn 增加了+5.5%、+3.1%、+8.5%和+15.1%）、长度（trl 增加了+13.1%、+18.8%、+19.3%和+33.3%）和体积（trv 增加了+12.1%、+12.2%、+14.7%和+15.7%）都多于 3T（P<0.05 每个）。与 3T 相比，7T 时比目鱼肌的 FA（+14.3%）更高，MD（-1.7%）更低，AD（-1.9%）和 RD（-2%）更低（P<0.05 每个），而其他肌肉的结果则更为复杂。3T 和 7T 时，所有 DTI 指标的变异系数都很好（即，<10%）。7T 和 3T 时，几个 DTI 指标的组内相关系数都很好（>0.750），例如腓肠肌和比目鱼肌的 trn、腓肠肌的 trv、全小腿肌肉的 FA、腓肠肌内侧、胫骨前肌和比目鱼肌，以及所有研究肌肉的 RD（即全小腿肌肉、腓肠肌、胫骨前肌和比目鱼肌）。除了全小腿肌肉的 trn 和腓肠肌外侧的 FA（分别在 3T 和 7T 时的平均绝对差异更高，P<0.05 每个）外，两种设备的两次连续测量之间没有显著差异。
尽管 DTI 存在许多与肌肉相关的挑战，但 3T 和 7T 都显示出可靠和精确的结果。
