Mosher T J, Smith H, Dardzinski B J, Schmithorst V J, Smith M B
Department of Radiology-MC H066, Center for Nuclear Magnetic Resonance Research, M108 NMR Building, M.S. Hershey Medical Center, Pennsylvania State University College of Medicine, Hershey, PA 17033, USA.
AJR Am J Roentgenol. 2001 Sep;177(3):665-9. doi: 10.2214/ajr.177.3.1770665.
The purpose of this study was to perform a quantitative evaluation of the effect of static magnetic field orientation on cartilage transverse (T2) relaxation time in the intact living joint and to determine the magnitude of the magic angle effect on in vivo femoral cartilage.
Quantitative T2 maps of the femoral-tibial joint were obtained in eight asymptomatic male volunteers using a 3-T magnet. Cartilage T2 profiles (T2 vs normalized distance from subchondral bone) were evaluated as a function of orientation of the radial zone of cartilage with the applied static magnetic field (B(0)).
At a normalized distance of 0.3 from bone, cartilage T2 is 8.6% longer in cartilage oriented 55 degrees to B(0) compared with cartilage oriented parallel with B(0). Greater orientation variation is observed in more superficial cartilage. At a normalized distance of 0.6, cartilage T2 is 18.3% longer. The greatest orientation effect is observed near the articular surface where T2 is 29.1% longer at 55 degrees.
The effect of orientation on cartilage T2 is substantially less than that predicted from prior ex vivo studies. The greatest variation in cartilage T2 is observed in the superficial 20% of cartilage. Given the small orientation effect, it is unlikely that the "magic angle effect" accounts for regional differences in cartilage signal intensity observed in clinical imaging. We hypothesize that regional differences in the degree of cartilage compression are primarily responsible for the observed regional differences in cartilage T2.
本研究旨在对完整活关节中静磁场方向对软骨横向（T2）弛豫时间的影响进行定量评估，并确定体内股骨软骨的魔角效应大小。
使用3-T磁体对8名无症状男性志愿者的股胫关节进行定量T2成像。根据软骨径向区域与外加静磁场（B(0)）的方向关系，评估软骨T2分布曲线（T2与距软骨下骨的归一化距离）。
在距骨归一化距离为0.3处，与平行于B(0)方向的软骨相比，与B(0)成55度角方向的软骨T2长8.6%。在更表层的软骨中观察到更大的方向变化。在归一化距离为0.6处，软骨T2长18.3%。在关节表面附近观察到最大的方向效应，此处55度角方向的T2长29.1%。
方向对软骨T2的影响远小于先前离体研究预测的结果。在软骨表层20%区域观察到软骨T2的最大变化。鉴于方向效应较小，“魔角效应”不太可能是临床成像中观察到的软骨信号强度区域差异的原因。我们推测，软骨压缩程度的区域差异是观察到的软骨T2区域差异的主要原因。
