Majumdar S, Genant H K
Department of Radiology, University of California, San Francisco 94143.
J Magn Reson Imaging. 1992 Mar-Apr;2(2):209-19. doi: 10.1002/jmri.1880020215.
Magnetic field inhomogeneities due to differences in susceptibility between trabecular bone and bone marrow result in a reduction in T2*. The authors previously quantified the relationship between the relaxation rate enhancement per unit change in bone density, delta R2*, using dried, excised vertebral bodies immersed in saline. In the present study, they investigated the precision and reproducibility of such measurements in vitro and found that the short-term precision ranges from 2% to 11%, while the long-term precision error, which may be governed by the placement of the region of interest, can vary up to 50%. A chemical shift-selective asymmetric spin-echo sequence was used to assess T2* changes in the saturated fat component of bone marrow in vivo. It was shown that the marrow fat relaxation rate increases as the surrounding trabecular bone density increases and that the delta R2* of the marrow fat component was 0.20 sec-1/mg/cm3. The results also indicate that the distribution of T2* varies with image resolution. Both in vitro and in vivo, characteristics of the relaxation time distribution such as the mean, standard deviation, and skewness decrease as image resolution decreases, the degree of variation depending on the density of the surrounding trabecular network.
由于小梁骨和骨髓之间的磁化率差异导致的磁场不均匀性会使T2降低。作者之前使用浸泡在盐水中的干燥、切除椎体，量化了骨密度每单位变化时的弛豫率增强（delta R2）之间的关系。在本研究中，他们调查了此类测量在体外的精度和可重复性，发现短期精度范围为2%至11%，而长期精度误差（可能受感兴趣区域的放置影响）最多可变化50%。使用化学位移选择性不对称自旋回波序列在体内评估骨髓饱和脂肪成分中的T2变化。结果表明，随着周围小梁骨密度增加，骨髓脂肪弛豫率升高，骨髓脂肪成分的delta R2为0.20秒-1/毫克/立方厘米。结果还表明，T2*的分布随图像分辨率而变化。在体外和体内，随着图像分辨率降低，弛豫时间分布的特征（如均值、标准差和偏度）都会减小，变化程度取决于周围小梁网络的密度。
