尺骨远端次级骨化中心X线与MRI下出现时间的对比研究

Comparison of emergence time of the secondary ossification center of distal ulna under MRI and X-ray

目的:探讨儿童尺骨远端次级骨化中心在MRI与X线下出现的时间以及形态的差异。方法:57名健康男孩志愿者,按年龄分成5个组,从5岁组到9岁组。每组分别用1.5T超导型磁共振机采用FLASH2d梯度回波加脂肪抑制序列行右腕关节扫描及CR射片。观察尺骨远端在MRI及X线片上的不同表现。结果:尺骨远端骺软骨在MRI下呈高信号表现,外形近似于成熟的尺骨远端,骺软骨在X线下不显影;尺骨远端次级骨化中心最早在MRI下表现为一条低信号带,位于高信号表现的骺软骨中,平行于干骺端,此信号带在X线下不能显影;尺骨远端次级骨化中心出现后在MRI下呈粟粒状的低信号表现,位置靠近干骺端,并非骺软骨中央,骨化中心与干骺端呈两种信号强度,X线下骨化中心表现一粟粒状影。结论:尺骨远端次级骨化中心在MRI下的出现时间较X线下早,最早在MRI下表现为一条低信号的临时钙化带。

Objective： To explore emerging time and morphologic features of the secondary ossification center of distal ulna under MRI and compare the result with that of X-ray. Methods： 57 healthy boy volunteers were studied using 1.5 Tesla ultraconduct magnetic resonance and CR. These cases were divided into 5 groups according to their ages, from 5 years old group to 9 years old group. Every case was scanned right wrist joint by MRI with FLASH2D＋FS gradient echo added fat-suppression sequence, and then examined by CR. Results of MRI and X-ray images were compared and analyzed. Results： Epiphyseal cartilage showed strong signal in MR image, with the shape of mature distal part of ulna, however it was unvisible in X-ray images. Before the appearance of the secondary ossification center of distal ulna, a weak signal zone appeared in the cartilage of epiphysis under MRI, which parallelled with metaphysis and was not visible under X-ray. After the emergence of it, a millet-like weak signal appeared in epiphysial cartilage under MR, which neared to metaphysis along longitudinal axis of distal ulna, not in the center of epiphysial cartilage. Two regions of differing signal zone could be defined between the secondary center of ossification and metaphysis. This center could also be visible under X-ray. Conclusions： The secondary ossification center of distal ulna could be visible earlier in MR image than X-ray image, which shows a weak zone of provisional calcification in MR images.