Department of Biomedical Engineering, Ulsan National Institute of Science and Technology, Ulsan, South Korea.
Korea Basic Science Institute, Ochang, South Korea.
Magn Reson Med. 2018 Nov;80(5):1949-1961. doi: 10.1002/mrm.27202. Epub 2018 Apr 15.
To evaluate the robustness of MR transverse relaxation times of trabecular bone from spin-echo and gradient-echo acquisitions at multiple spatial resolutions of 7 T.
The effects of MRI resolutions to T and T2* of trabecular bone were numerically evaluated by Monte Carlo simulations. T , T2*, and trabecular structural indices from multislice multi-echo and UTE acquisitions were measured in defatted human distal femoral condyles on a 7 T scanner. Reference structural indices were extracted from high-resolution microcomputed tomography images. For bovine knee trabecular samples with intact bone marrow, T and T2* were measured by degrading spatial resolutions on a 7 T system.
In the defatted trabecular experiment, both T and T2* values showed strong ( |r| > 0.80) correlations with trabecular spacing and number, at a high spatial resolution of 125 µm . The correlations for MR image-segmentation-derived structural indices were significantly degraded ( |r| < 0.50) at spatial resolutions of 250 and 500 µm . The correlations for T2* rapidly dropped ( |r| < 0.50) at a spatial resolution of 500 µm , whereas those for T remained consistently high ( |r| > 0.85). In the bovine trabecular experiments with intact marrow, low-resolution (approximately 1 mm , 2 minutes) T values did not shorten ( |r| > 0.95 with respect to approximately 0.4 mm , 11 minutes) and maintained consistent correlations ( |r| > 0.70) with respect to trabecular spacing (turbo spin echo, 22.5 minutes).
T measurements of trabeculae at 7 T are robust with degrading spatial resolution and may be preferable in assessing trabecular spacing index with reduced scan time, when high-resolution 3D micro-MRI is difficult to obtain.
评估 7T 多空间分辨率下自旋回波和梯度回波采集的小梁骨横向弛豫时间的稳健性。
通过蒙特卡罗模拟数值评估 MRI 分辨率对小梁骨 T 和 T2的影响。在 7T 扫描仪上，对脱脂人远端股骨髁多切片多回波和 UTE 采集的 T 、 T2和小梁结构指数进行测量。参考结构指数从高分辨率微计算机断层扫描图像中提取。对于骨髓完整的牛膝关节小梁样本，通过在 7T 系统上降低空间分辨率来测量 T 和 T2*。
在脱脂小梁实验中，T 和 T2值与小梁间距和数量均具有很强的相关性（|r|>0.80），在 125μm 的高空间分辨率下。在 250 和 500μm 的空间分辨率下，MR 图像分割衍生结构指数的相关性显著降低（|r|<0.50）。在 500μm 的空间分辨率下，T2的相关性迅速下降（|r|<0.50），而 T 的相关性则保持较高（|r|>0.85）。在骨髓完整的牛小梁实验中，低分辨率（约 1mm，2 分钟）T 值没有缩短（相对于约 0.4mm，11 分钟的|r|>0.95），并且与小梁间距保持一致的相关性（|r|>0.70）（涡轮自旋回波，22.5 分钟）。
7T 小梁骨 T 值的测量在空间分辨率降低时具有稳健性，并且当难以获得高分辨率 3D 微 MRI 时，通过减少扫描时间评估小梁间距指数可能是优选的。
