Abstract： Objective To study the diagnostic value of MR coronal iterative decomposition of water and fat with echo asymmetry and least-squares estimation(IDEAL) water imaging in the far later lumbar disc herniation(FLLDH).Methods A retrospective analysis of pre-operative routine CT axial imaging and MPR post-processing,conventional MR axial plane,sagittal plane and IDEAL imaging was performed in 10 patients with pathologically FLLDH.The above images were observed to find whether it could clearly show the spatial relationship outline of the nucleus pulposus and the nerve root,including the number of affected nerve root(1 or 2),and the compressed part(dorsal root ganglion,postganglionic nerve root or preganglionic nerve root),and the morphological changes of the compressed nerve root(distortion,thinning,enlargement),and were compared with surgical results.Results Surgery showed 2 cases with extra-intervertebral foramen herniation,2 cases with intra-intervertebral foramen herniation,6 cases with mixed herniation.Nine cases involved 1 nerve root,and 1 case involved 2 nerve roots.The conventional CT axial plane could roughly show the local relationship between nucleus pulposus and the nerve root.On conventional CT axial plane,9 cases were diagnosed correctly but 1 case of herniation of extra-intervertebral foramen shifting cephalic to the lower vertebral level was missed.Seven cases of the compressed nerve root were identified with difficulty,2 cases showed obliteration of the fat space and displacement of the nerve root.The spatial relationship of the nucleus pulposus and the nerve root was more visualized by CT MPR images than conventional CT images,but the image was less clear and it could not display the full view.Ten cases on CT MPR images were diagnosed correctly.Nine cases involved 1 nerve root,and 1 case involved 2 nerve roots,the image finding was obliteration of the fat space.Eight cases involved distortion of the compressed nerve root,3 cases involved thinning of the compressed nerve root,1 case involved thickening of the nerve root,6 cases were with no change or no confirmed diagnosis.MR regular scans could roughly show the local relationship of the nucleus pulposus and the nerve root and it is superior to the conventional CT axial scanning.On the conventional axial plane,7 cases of the compressed nerve root were identified with difficulty,3 cases showed obliteration of the fat space and displacement of the compressed nerve root.On the sagittal plane through the intervertebral foramen:5 cases of mixed herniation and 2 cases herniation of intra-intervertebral foramen showed intervertebral disc into the intervertebral foramen,with displacement or annihilation of the compressed nerve root.Two cases of extra-intervertebral foramen herniation were without positive findings.On MR coronal IDEAL water imaging,it could clearly and accurately show the spatial relationship of the nucleus pulposus and the nerve root.It is superior to the conventional CT axial image,CT MPR image and the conventional MR scanning.Ten cases were diagnosed correctly.Four cases were identified as compressed DRG,5 cases were identified as compressed postganglionic nerve root,1 case was identified with compressed L4 postganglionic nerve root and compressed L5 preganglionic nerve root.Ten cases were all identified with distortion of the compressed nerve root,6 cases were identified with the compressed thinning nerve root,and 2 cases with the compressed thickening nerve root.The other nerve roots were not compressed.Conclusion MR coronal IDEAL water imaging is a good tool to show the spatial relationship of nucleus pulposus and the nerve root in FLLDH patients,and it possesses diagnostic value.