Diffusion Tensor Imaging Of Facial Nerve:An Exploratory Study

Besides fine and tortuous,there are many variations in facial nerve branches and distribution.Various artifacts of conventional DTI is serious.For the parotid segement of the facial nerve,blood vessels,parotid ducts and lymph nodes around the facial nerve.For the temperal segement of the facial nerve,the facial nerve is surrounded by bone almost in the whole process.DTI-RESOLVE can significantly reduce magnetic sensitive artifacts and flow artifacts,especially for salivary gland near the body surface.In this study,the DTI-RESOLVE sequence was used to image the facial nerve in the parotid gland and temporal bone.The group level analysis of common space and ROI was used for to explore the distribution pattern of facial nerve in parotid gland,and the pathogenesis of facial nerve with peripheral facial paralysis.1.The distribution of parotid segments of healthy facial nerves with diffusion tensor Imaging[Objective]The present study aimed to determine whether an extracranial segment of the facial nerve could be delineated using diffusion tensor imaging(DTI)tractography.[Methods]A total of 16 volunteers with healthy facial nerves received high-definition 3D-T1WI-1 mm and high-definition DTI scanning in a 3T-MR imaging system.The SPM-old norm method was used in the present study,which enabled the 16 volunteers to have their 3D-T1WI-1 mm to be matched with MNI152_T1₀.5 mm,and establish horizontal T1 WI standard templates of 0.5-mm layer thick groups containing parotid glands.The common interest region with a diameter of 10 mm was calculated via fslmaths,and this was placed in the facial nerve stem in the foramen.Track Vis and its Diffusion Toolkit software were used for the facial nerve tracing of the 0.5-mm thin-layer DTI data to obtain the DTI-tractography images of the extracranial segment of facial nerves of the 16 volunteers in the standard space distribution at the group level,and the fractional anisotropy(FA)and mean diffusivity(MD)values of the extracranial segment of the facial nerve.Then,a statistical analysis was conducted.A binary mask was applied for all images to obtain the distribution of the extracranial segments of the facial nerve.[Results]Tthere was no statistical difference in FA and MD values of the extracranial segment of facial nerves on both sides in healthy subjects.[Conclusion] Although the facial nerve distribution of the horizontal tracing group level in the present study had a certain error,this basically met the extracranial facial nerve distribution mode of the anatomical study.Large sample facial nerve scanning could perhaps reduce the error,and allow for more accurate evaluation of the extracranial segment of facial nerve distribution.2.The healthy facial nerves in temporal bone with diffusion tensor Imaging[Objective] The present study aimed to determine whether a temporal segment of the facial nerve could be delineated using diffusion tensor imaging(DTI)tractography.To describe the distribution of the facial nerve in the temporal bone.[Methods] 18 healthy volunteers of facial nerve were scanned with three-dimensional T1 weighted structure image and diffusion tensor imaging(DTI)on 3T-MR.The scanning method is as same as that in the first part.The standard spatial image of 0.5mm3 voxel MNI152?T1?0.5mm was interpolated to the size of 0.4mm3,then the group level MNI152?T1?0.4mm image was obtained.The group level common region of interest(ROI)was made on the mastoid segment of the facial nerve on both sides of the group level MNI-T1-0.4mm image.The DTI data of all volunteers were eddy current corrected.With the aid of affine transformation and non-linear registration of T1 structure image and mni152-T1-0.4mm image,the T1 structure images and DTI datas of 0.4mm3 voxel MNI space were obtained.Using FSL,DTK and trackvis toolkits,DTI datas of temporal segment of the facial nerve were calculated and DTI nerve fibers were traced.The average and maximum distribution probability maps of the facial nerve in the temporal bone segment were calculated.The FA,MD,ad and RD of the facial nerve in the temporal bone segment were extracted.DTI indexes of the temporal segment of the facial nerve on both sides were statistically analyzed.[Results] There was no significant difference in FA,MD,AD and RD between the two sides of the temporal segment of the facial nerve in healthy people.The distribution of the facial nerve of the temporal bone segment was basically in accordance with the anatomic research results on the distribution of the facial nerve of the temporal segment of the facial nerve.[Conclusion] DTI can be used as a new MR imaging method to study the temporal segment of the facial nerve.Group level analysis can be performed in common space and common region of interest(ROI).3.The peripheral facial paralysis study with diffusion tensor imaging[Objective] The present study aimed todescribe the temporal segment of the facial nerve in patients with peripheral facial paralysis using diffusion tensor imaging(DTI).To explore the possibility of using DTI sequence to evaluate peripheral facial paralysis.[Methods] The patients with peripheral facial paralysis received three-dimensional T1 structure and DTI scan on 3.0T-MR.The 0.5mm3 standard spatial image of mni152-T1-0.5mm was interpolated to the size of 0.4mm3,and the group level image of mni152-T1-0.4mm was obtained.The group level common region of interest(ROI)was made on the mastoid segment of the facial nerve on both sides of the group level MNI-T1-0.4mm image.The DTI data of all volunteers were eddy current corrected.With the aid of affine transformation and non-linear registration of T1 structure image and mni152-T1-0.4mm image,the T1 structure images and DTI datas of 0.4mm3 voxel MNI space were obtained.Using FSL,DTK and trackvis toolkits,DTI datas of temporal segment of the facial nerve were calculated and DTI nerve fibers were traced.The DTI indexes of temporal segment of the facial nerve were extracted from the maximum distribution probability map,including FA,MD,ad and RD.DTI indexes aforementioned in affected side,healthy side and both sides of healthy person were analyzed statistically.[Results] On the temporal segment of the facial nerve with peripheral facial paralysis,the FA of the affected side decreased,the MD and RD increased,which was statistically different from that of the healthy side;while the AD was no statistical difference with healthy side.The RD value of the facial nerve in the affected side was also statistically different from that in the healthy people,while the other DTI indexes were not statistically different.[Conclusion] The decrease of FA and the increase of MD and RD showed that the diffusion of water molecules around the facial nerve increased,which indicated that the integrity of facial nerve was decreased.The AD on the affected side was not statistically different from that on the healthy side,which indicates that there is no significant damage on the axon of the affected side.Therefore,this study speculated that the increase of RD was the main reason for the decrease of FA,and the injury of myelin sheath of facial nerve resulted in facial dysfunction.