The Study Of Three-dimensional MR Reconstruction Of Knee Joint

Background and purposeKnee is the most complicated joint of human body, and also a joint which is most prone to injury and pathologic change. Image diagnostics, particularly MRI, places a unique role in the diagnosis of knee lesion. Because of its high resolving power, its multi-direction and multi-parameter imaging on muscle, ligament and cartilage, MRI has been widely used in the diagnosis of knee lesion and joint retrograde affection. But it is not good at displaying some minor structures and lesions. In this study,3D-FSE-CubeT2WI sequence was applied on normal and pathological knee joints, the diagnosis value of 3D-MRI reconstruction of knee joints was explored.Materials and methods10 normal volunteers were chosen as the control group, with 20 knee joints in total.40 cases of knee injury involving 50 knee joints, admitted to our hospital from May,2009 to March 2010, were taken as the injury group.GE sigma HDxt 1.5T superconductive MRI machine and knee joint surface coil were used in MRI examination. Routine MRI examination consisted of T1WI sequence, FSE T2WI sequence, PDWI sequence. The layer width was 4mm, layer distance was 1mm, FOV18×18.Each case was performed an extra axis 3D-FSE-CubeT2WI sequence, volume collection with layer width 0.8mm.Post reconstruction was conducted with GE MRI ADW4.4.Thin-layer axis image taken with FSE-Cube T2WI was collected. Cruciate ligament sagittal MIP,VR reconstruction, articular cavity liquid MIP image, VR image of semilunar plate and transverse ligament curve reconstruction were performed respectively.ACL, PCL 3D-image displayed after sagittal reconstruction of both groups were contrasted with the regularly-scanned sagittal two-dimensional images. The evaluation standard was as follows:GradeⅠ:the whole length of ACL, PCL could be observed in one image. GradeⅡ:ACL alone could be displayed in one image,2 or 3 images were necessary to see the whole length of ACL, PCL. GradeⅢ:ACL, PCL could only be partly observed.ACL, PCL sagittal reconstruction images of the injury group were contrasted with regular sagittal T2WI images.Based on regularly-scanned images and 3D reconstruction T2WI images, two senior radiologists were invited to observe whether there was and how was the injury in cruciate ligaments and semilunar plates and hydrops in joints. Diagnosis reported with double blind method were contrasted. The final result was confirmed by operation or arthroscopy. If not, follow-up survey or the agreement of three senior radiologists would be used for judgment.MR grading of ligament injury:GradeⅠ(normal):figure and signal appeared normal. GradeⅡ(partial laceration):continuous,diameter was broadened or abnormal signal was observed in ligament. GradeⅢ(fragmentation):continuous interruption with or without breaking point retraction was observed. Criteria of articular cavity hydrops:①normal:high signal liquid depth in articular cavity<2mm;②hydrops:high signal liquid depth in articular cavity>2mm;③semilunar plate injury MRI was divided into 3 grades:GradeⅠ:focal signal of the internal marginal zone of meniscus intensified. GradeⅡ:linear high signal was seen in meniscus but not reached articular surface; GradeⅢ:at least one high signal was seen on MRI image of meniscus reaching articular surface.Results1.Anterior Cruciate Ligament1.1 ACL display compared with two methods For control group, ACL sagittal regular MRI scanning indicated:10 GradeⅠ,10 GradeⅡ, no GradeⅢ.3D-FSE-CubeT2WI reconstruction of sagittal ACL indicated that all the 20 cases belonged to Grade I. For injury group, regular MRI scanning indicated that the result of ACL display was:18cases of GradeⅠ,23 of GradeⅡ,9 of GradeⅢ.3D-FSE-CubeT2WI reconstruction indicated:41 cases of GradeⅠ,9 of GradeⅢ.1.2 Comparison of the diagnosis of ACL by the two methodsIn control group, diagnosis by the two methods concluded that 20 cases were all normal GradeⅠ; Of the 50 knee joints of the 40 cases,35 of the joints were clinically diagnosed as ACL injury, accounting for 70%. Diagnosis by regular MRI indicated:9 cases of normal (GradeⅠ),17 cases of partial injury (GradeⅡ),9 cases of fragmentation (GradeⅢ).The result of the diagnosis by 3D-FSE-CubeT2WI indicated:2 case of normal (GradeⅠ),24 cases of partial injury (GradeⅡ),9 cases of fragmentation (GradeⅢ).2.Posterior Cruciate Ligament of Knee2.1 Comparison of the display of PCLIn control group, regular MRI scanning of sagittal PCL indicated:15 cases of GradeⅠ,5 of GradeⅡ, no GradeⅢ.3D-FSE-CubeT2WI of sagittal PCL indicated that all the 20 cases were of GradeⅠ. In injury group, regular MRI scanning of PCL indicated:45 cases of Grade I,4 of GradeⅡ,1 of GradeⅢ.3D-FSE-CubeT2WI of PCL indicated:49 cases of GradeⅡ,1 GradeⅢ. 2.2 Comparison of the diagnosis of both control and injury groupIn control group, both of the two methods indicated that all the 20 cases were normal (GradeⅠ).Of the 50 cases of the injury group,23 of them were diagnosed as PCL injury, accounting for 46%.The diagnosis of PCL by regular MRI was:2 cases of normal,20 cases of partial injury,1 case of fragmentation. The diagnosis of PCL by 3D-FSE-CubeT2WI was:22 cases of partial injury,1 case of fragmentation.3.Comparison of the diagnosis of hydrarthrosis50 knee joints of the 40 cases of injury were all clinically diagnosed as hydrarthrosis. Both regular MRI scanning and 3D-FSE-Cube T2WI imaging diagnosed that there was hydrops in the 50 knee joints.But after reconstruction diagnosis was more specific:15 cases of simple articular cavity hydrops,22 cases of articular cavity hydrops combined with perisynovial bursa hydrops,7 cases were combined with pericruciate ligament hydrops,6 cases were combined with both perisynovial bursa and pericruciate ligament hydrops.4. Comparison of the diagnosis of semilunar palteOf the 70 cases of knee joint semilunar plates,43 of them were clinically diagnosed as normal (GradeⅠ),19 of GradeⅡ,8 of GradeⅢ. Regular MRI diagnosis indicated:43 cases of normal (GradeⅠ),17 of GradeⅡ,10 of GradeⅢ. 3D-FSE-CubeT2WI combined with regular MRI diagnosis indicated:43 cases of normal (GradeⅠ),18 of GradeⅡ,9 of GradeⅢ.5.Display of knee transverse ligamentWith 3D-FSE-CubeT2WI curve reconstruction,70 knee joints were all completely displayed. A new method was provided for the display of tortuous ligament, with which ligament injury could be directly diagnosed.Conclusions1.The display of ACL, PCL was greatly improved by 3D-FSE-CubeT2WI sequence scanning. Morphologic changes of ligament could be observed from any angle.3D VR image became more direct and easier to be accepted clinically. Since volume effect was eliminated, subtle signal change of minor laceration could be observed, missed diagnosis and misdiagnosis were thus reduced. This sequence was still a good solution for cases of suspected ligament injury examined by regular MRI.2.This sequence provided a good platform for the quantitative study of knee joint hydrops. The location of articular cavity hydrops could be 3-dimensionally measured with MRI, and with the development of the technology, it would be possible for the volume of hydrops.3.As to the diagnosis of semilunar plate,3D-FSE-CubeT2WI sequence scanning had high consistency with regular MRI scanning. VR image could be provided and this sequence was also effective for the display of GradeⅢinjury semilunar plate. Because of the limited resolving power, the display of Grade II semilunar plate was not quite satisfactory, signal noise ratio and resolving power have yet to be promoted.4. Thin layer image scanned by 3D-FSE-CubeT2WI was used in this study for the first time. The curve reconstruction of irregular ligament such as knee transverse ligament was performed and the result was good. A new way for the display and diagnosis of ligament with MRI was presented.