3T MR Neurography In Lumbosacral Nerves: An Anatomical Study And Clinical Applications

Objective1.To study the anatomy of lumbosacral spinal nerves and branches by dissecting healthy corpse.2.30 healthy volunteers were performed with MRN of lumbosacral spinal nerves by T2-Weighted FRFSE-XL sequence with fat saturation in 3 Tesla high field MR scanner.3D images of normal lumbosacral spinal nerves were reconstructed and compared with the corpse images to explore the value of MRN in displaying of lumbosacral spinal nerves.3.51 patients with lumboscacral nerve correlated diseases were performed with FRFSE-XL-FATSAT MRN.The relationship between spinal nerves and diseases was analyzed by 3D reconstructed images to explore the clinical application of 3 Tesla MRN in lumboscacral nerve correlated diseases.PartⅠ.The anatomical study of 3T MRI in normal lumbosacral spinal nerve1 Materials and Methods1.1 Objects1.1.1 Corpse:2 male corpse fixed by formaldehyde,1 fresh male corpse.1.1.2 Healthy Volunteers:A total of 30 healthy volunteers without lumbosacral disease and back-leg pain symptoms(17 men and 13 women;mean age 25.7 years, range 25-35years) were examined with MRI.1.2 Anatomic methods2 male corpse fixed with formaldehyde:All of the bones,muscles and vessels which surround the lumbosacral spinal nerve were cut off and the whole lumboscacral spinal nerves were liberated carefully.Then anatomical photos were taken as the standard of MRN.1 fresh male corpse:Enough lead oxide was injected into the vessels before dissecting.Then the corpse was dissected as above except keeping the vessels.The specimen of lumboscacral spinal nerves and vessels were fixed on a plastic slab.1.3 Imaging Methods1.3.1 Equipments(1) Specimen:The fresh specimen was scanned with a 16 multi-slice spiral CT scanner(GE Company,Lightspeed 16 CT System).(2)Volunteers:30 volunteers were scanned with a 3 Tesla MR scanner(GE Company,3T Signa EXCITE HD System),with surface phased-array coil(CTL456). AW4.3 workstation was used for image post-procession..1.3.2 Preparation before Scanning(1)Fix the spinal nerve on a plastic slab.(2)Take away any metal materials from volunteers and make sure that all the volunteers keeping calming during examination period.1.3.3Examination methods(1)CT was scanned with 1.25mm thickness,1.375:1 Pitch,altogether 720 images.(2)MRI was performed with supine position,head first.Conventional sagittal(FRFSE-XL sequence,TR/TE/NEX:2000ms/120ms/4;thickness / gap: 4.0mm/1.0mm ) and anxial(FRFSE-XL sequence,TR/TE/NEX:1800ms/120ms/4; thickness / gap:3.5mm/0.5mm ) T2WI Sagittal T1WI(T1-FLAIR sequence, TR/TE/NEX:2700ms/25ms/2;Thick/gap:4.0mm/1.0mm) were obtained.The FOV of sagittal images extended from the superior border of T12 to the inferior border of S1,axial images' FOV contained L3/4,L4/5 and L5/S1 disc.Original MRN images was performed by FRFSE-XL sequence with fat saturation to suppress fat signal(TR/TE/NEX:4000ms/85ms/2,Thick/gap, 1.0mm/0.0mm,totally 42～44 images,acquisition Time:4min17s)(totally 63～88 images and 6min26s～8min35s were needed when examined in sacral spinal nerve).1.4 Image post-processing,observation and data collection1.4.1 Image Post-processing(1)Equipments:Both the CT images of the specimen and the MRN original images of the volunteers were post-processed with AW4.3 workstation.(2)Methods:Specimen's CT images:Reconstructed with VR methods,deleted vessels.Volunteers' MRN images:Reconstructed with MPR,MIP and VR methods, multi-threshold color technique were taken in VR methods,and saved sequential VR images as GIF or AVI type.1.4.2 Image ObservationAll primary images and reconstructed images(two-dimensional and three-dimensional) were observed by two experienced radiologists.(1) The signal,outline,and branches of normal lumbosacral spinal nerves were observed.(2) The displaying ratios of different lumbosacral spinal nerve were evaluated by comparing the MRN images with normal specimen.Which contained the displaying ratios of each segment(T12-L5),femoral nerve,obturator nerve,lumbosacral trunk. 1.4.3 Measurements of volunteers' lumbosacral spinal nerve were as followings:(1)Cross section area of nerve root sheath and ganglion;(2)Length of nerve root sheath and ganglion;(3)Width of nerve root sheath and ganglion;(4)Angle of nerve root sheath.1.5 Statistical analysisAll the Statistical analysis was made using SPSS 13.0 software package.1.5.1 The display ratios of spinal nerves' four segments(range from T12 to L5 spinal nerve),The display ratios of same section at different spinal nerve(range from T12 to L5 spinal nerve),The display ratios of femoral nerve,obturator nerve and lumbosacral trunk were compared with chi square test.The statistically significant difference was set at P＜0.05.1.5.3 The parameters between two sides(with the same section,same number) were compared with Paired-Samples T Test.The statistically significant difference was set at P＜0.05.The parameters among different number(from T12 to LS) were compared with one-way ANOVA,The statistically significant difference was set at P＜0.05.If P＜0.05,parameters were multiple compared with Bonferroni Test.The statistically significant difference was set at P＜0.05.2.Reaults2.1 AnatomyAfter erupting from spinal cord,the anterior and posterior nerve root of lumbosacral plexus extended out vertebral canal through the intervertebral foramina. Then,the posterior nerve root of lumbosacral plexus became much lager than root sheath and formed the ganglion.The spinal nerve divided into two parts after the ganglion: anterior rami and posterior rami,anterior rami was much lager than posterior rami,which was easy to dissect,the latter was hard to dissect.The spinal nerve was increased gradually from T12 to L5,however,reduced gradually from S1 to S5. 2.2 MRN images2.2.1 The normal lumbosacral spinal nerve demonstrated high signal intensity in MRN original images with vertebral body,muscles,and fat low signal intensity. MRN images clearly showed the appearances of spinal nerve root,ganglion and most of the anterior ramus.MPR,MIP and VR images can display the outline of spinal nerve in multi directions.2.2.2 Most of the big branches of T12-L5 spinal nerve could be seen well.The display ratios of T12-L5 nerve root sheath reached 85%～100%.Among them,the display radios of each segment of T12/L1(86.67%,86.67%,85.00%/86.67%,86.67%,83.33%)was lower than that of L2/L3/L4/L5(each segment 100.00%,100.00%,100.00%,100.00%)(P＜0.05);The display ratios of distant posterior segment of L3/L4/L5(100.00%,100.00%,100.00%) were higher than those of T12/L1/L2(0%,0%,41.67%)(P＜0.05).The display ratios of femoral nerve(100.00%),obturator nerve(91.67%) were higher than that of lumbosacral trunk(P＜0.05).No statistical significance(P＞0.05) existed in displaying ratios between femoral nerve and obturator nerve.2.2.3 Measurement of volunteers' lumbosacral spinal nerveNo statistical significance(P＞0.05) existed in parameters between right and left measurements of volunteers' lumbosacral spinal nerve,except the length and width of nerve root sheath.From T12 to L5 most of measured values showed uptrend except the nerve root angle,which showed downtrend from T12 to L5.No statistical significance(P＞0.05) existed among L3,L4 and L5 angle.3.Conclusion3.1 Using 3T FRFSE-XL sequence as MRN method,we can get 2-D MRN original images with high space resolution and high SNR.The signal intensity of spinal nerve is higher than other tissues in the MRN images.The 3D appearance of spinal nerves was clearly demonstrated by reconstructing with multiple methods.3.2 Among all the reconstructing methods,it's easier to different the spinal nerve structure from surrounding tissues with MPR method.VR image is much better than MPR and MIP in demonstrating the difference among spinal nerve,spinal cord,fat, muscles and blood vessels because of using multi-threshold color technique.Spinal nerve VR image can display the three-dimensional structure of spinal nerve more directly.3.3 The display ratios of T12-L5 nerve root sheath,ganglion and proximate anterior rami reached 85%-100%.The displaying ratios of L2～L5 lumbosacral plexus branch is high too(41.6%,100%,100%,100%),The displaying ratios of femoral nerve,obturator nerve, and lumbosacral trunk is 100.00%,91.67%,61.67%respectively.This MRN technique can be used as conventional sequence in 3 Tesla MR Scanner.PartⅡ.The clinical applications of 3T MRI in lumbosacral spinal nerve correlated diseases1.Materals and Methods1.1 Objects51 patients with lumbosacral spinal nerve correlated diseases were examined with MRI.1.2 Methods1.2.1 Equipments:the same as partⅠ.1.2.2 Scanning methods(1)Preparation before scanning:the same as partⅠ.(2)Body position:the same as partⅠ.(3)Conventional images:the same as partⅠ.The scanning range included the whole lesions.(4)MRN images:the same as partⅠ.The scanning range was changed according to the size of lesions.(Images ranged from 42 to 88).1.3 Image Post-processing,Observation and Data Collection1.3.1 Image Post-processing:the same as partⅠ.1.3.2 Image ObservationAll original images and reconstructed images(two-dimensional and three-dimensional) were observed by two experienced radiologists.The value of 3T MRN in diagnosing and displaying of spinal nerve correlated diseases was explored by comparing abnormal changes with normal MRN images.The quality of MRN images were defined as three type,First type:the relationship between spinal nerve and lesions displayed well;Second:unclearly;Third:spinal nerve can't be defined.2.ResultsAmong 51 patients with lumbosacral spinal nerve correlated diseases,First type: 88.24%(45/51);Second:11.76%(6/51);Third:0%(0/51)2.1 26 cases with disc herniation showed disc impression to dural sac,or lateral displacement of nerve root,and partial stenosis of spinal canal.2.2 9 cases with neurogenic tumor showed the growth feature along with the spinal nervous ramification,especially the appearance of tumor extending through the intervertebral foramen.2.3 6 cases with sacral canal cyst clearly showed the appearance of cyst and its relationship with spinal nerve.2.4 3 cases with metastatic tumors not only showed wrapped or pushed nerve roots, but also the outline of tumor.2.5 5 cases of lumbar tuberculosis did not show ganglion and its posterior segment due to the same signals with peri-vertebral abscess,just showed the appearance of nerve root sheath.2.6 2 case of lumbar fracture just showed the compression appearance of nerve root, the signal changes of nerve roots in muscle was hard to define.3.Conclusion3.1 FRFSE-XL MRN images can clearly show the anatomy of lumbosacral nerve and help to detect the pathogencsis and position of the lumbosacral nerve lesions. Together with routine MR images,MRN images can provide direct and additional information for clinical diagnosis of lumbosacral nerve roots diseases.2.2 It can directly display the compression of nerve root and root sheath in MRN images for the patients with disc herniation.For these patients with tumor and cyst, MRN images can display the relationship between spinal nerve and lesions,which is easy to make sure whether the spinal nerve destroyed or surrounded by lesions,and helpful for operators to avoid spinal nerves injured,and then to evaluate the therapeutic effect of operation.2.3 MRN with FRFSE-XL-FATSAT technique can be used as a conventional or supplementary sequence in 3 Tesla MR scanner.And it can supply more direct and integrated two-dimensional or three dimensional images than conventional sequence.