Engelke K, Majumdar S, Genant H K
Osteoporosis Research Group, University of California at San Francisco 94143.
Magn Reson Med. 1994 Apr;31(4):380-7. doi: 10.1002/mrm.1910310406.
Phantom studies were conducted to investigate the impact of trabecular structure on the T2' signal measured by MRI. For a separation of density from structural effects, several phantoms were built. They consisted of parallel polyethylene strings arranged in a variety of different patterns to simulate a) a constant uniform trabecular distribution with increasing trabecular thickness and b) different structures with identical overall trabecular density. An asymmetric spin echo sequence was used to determine the apparent relaxation time T2'. Changes in T2' are induced by susceptibility differences between the polyethylene strings simulating trabeculae and Gd-DTPA doped saline simulating bone marrow. The results showed an increasing T2' decay rate with a) decreasing spacing while the string density was constant and b) with increasing string density while the string arrangement was constant. The results demonstrate that the T2' signal is affected not only by density but also by spatial distribution. However, the results also indicate that a separation of the two effects is not possible from a T2' measurement alone, but that e.g., a matching CT slice that would provide purely density information is additionally needed. Theoretical simulations confirmed these results.
进行了体模研究，以调查小梁结构对MRI测量的T2'信号的影响。为了将密度与结构效应分离，构建了几个体模。它们由平行的聚乙烯线组成，以各种不同的模式排列，以模拟a）小梁厚度增加时恒定均匀的小梁分布，以及b）具有相同总体小梁密度的不同结构。使用非对称自旋回波序列来确定表观弛豫时间T2'。T2'的变化是由模拟小梁的聚乙烯线和模拟骨髓的钆-二乙三胺五乙酸（Gd-DTPA）掺杂盐水之间的磁化率差异引起的。结果表明，a）当线密度恒定时，间距减小，T2'衰减率增加；b）当线排列恒定时，线密度增加，T2'衰减率增加。结果表明，T2'信号不仅受密度影响，还受空间分布影响。然而，结果还表明，仅通过T2'测量无法分离这两种效应，而是还需要例如提供纯密度信息的匹配CT切片。理论模拟证实了这些结果。
