The Studies Of Peripheral Nerves Morphology In The Region Of Upper Limb Based On MR Diffusion Tensor Imaging With Multiple Post-Processing Methods

Part1: Three-dimensional display of peripheral nerves in the wristregion based on the MR diffusion tensor imaging scan and maximumintensity projection post-processingObjectives: To achieve3-dimensional (3D) display of peripheral nerves in the wristregion by using maximum intensity projection (MIP) post-processing methods toreconstruct raw images acquired by a diffusion tensor imaging (DTI) scan, and to comparethe diffusion values and3D nerve imaging quality between scan schemes with differentnumbers of diffusion directions.Materials and Methods: MR images were acquired by using a Signa HDxt3.0T MRIscanner with an8-channal wrist coil. We performed DTI scans in6(DTI6) and25(DTI25)diffusion directions on20wrists of10healthy young volunteers. The MIP post-processingmethods employed2types of DTI raw images:1) single-direction and2) T2-weighted trace.The fractional anisotropy (FA) and apparent diffusion coefficient (ADC) values of themedian and ulnar nerves were measured at multiple testing sites. The FA and ADC valuesof median nerves were measured at the level of the distal radioulnar joint, pisiform bone,and hamate bone (marked as M1, M2, and M3). The FA and ADC values of ulnar nerveswere measured at the level of the distal radioulnar joint and pisiform bone (marked as U1and U2). Then they were compared between DTI6and DTI25. Two radiologists usedcustom evaluation scales to evaluate the volunteers’3D nerve imaging qualityindependently in a random order. In addition,6wrists of5patients with carpal tunnelsyndrome,6wrists of6patients with nerve lacerations, and1patient with neurofibroma ofthe median nerve were tested by the same methods.Results: In both DTI6and DTI25, nerves in the wrist region could be displayedclearly by the2MIP post-processing methods. The FA and ADC values were not significantly different between DTI6and DTI25, except for the FA value of the ulnar nerveat the level of pisiform bone (p=0.03). As to the imaging quality of each MIPpost-processing method, there were no significant differences between DTI6and DTI25.The imaging quality of single-direction MIP post-processing was better than that fromT2-weighted traces (p <0.01) because of the higher nerve signal intensity. For theneuropathy, morphological changes of nerve can be observed intuitively by usingsingle-direction MIP reconstruction. For the nerve lacerations, the observed changes ofmorphology and signal intensity of the distal portion met the process of neuralregeneration.Conclusions: Three-dimensional displays of peripheral nerves in the wrist can beachieved by MIP post-processing for single-direction images and T2-weighted trace imagesfor both DTI6and DTI25. The FA and ADC values of the median nerves can be accuratelymeasured by using DTI6data. Adopting6-direction DTI scan and MIP post-processing isan efficient method for evaluating peripheral nerves. Part2: Volume-rendering3D display of the peripheral nervein the wrist region based on2post-processing methods forMR diffusion tensor imagingObjectives: To achieve3D display of the peripheral nerve in the wrist region basedon2post-processing methods for MR diffusion tensor imaging (DTI) data (volumerendering [VR] reconstruction for single-direction images and subtraction ofunidirectionally encoded images for suppression of heavily isotropic objects [SUSHI]), andto compare these methods in the aspect of imaging quality, noise level, and degree ofnoise-removing difficulty.Materials and Methods: MR images were acquired with a Signa HDxt3.0T MRIscanner by using an8-channal wrist coil.We performed DTI scans in6(DTI6) and25(DTI25) encoding diffusion directions on20wrists of10healthy young volunteers,6wrists of5patients with carpal tunnel syndrome, and6wrists of6patients with nervelaceration in the wrist region. We used VR to reconstruct2kinds of images:(1) single-direction (anterior-posterior [AP] direction) and (2) SUSHI (AP direction withsubtraction of the superior-inferior [SI] direction). Two radiologists used custom evaluationscales to evaluate the volunteers’3D nerve imaging quality, noise level, and degree ofnoise-removing difficulty independently in a random order.Results: In both DTI6and DTI25, VR reconstruction for single-direction showed thenerves clearly, but with obvious noise. In DTI25, VR reconstruction for SUSHI showed thenerves clearly, with excellent nerve signal intensity. There was no significant differencebetween single-direction and SUSHI nerve imaging quality for the median nerve. In DTI6,some ulnar nerve signal intensity was lost (7/20) after SUSHI post-processing, resulting ina significant difference between single-direction and SUSHI nerve imaging quality scores.The majority of noise was removed after SUSHI post-processing and the remnant noisebecame loose, was no longer connected with nerves, and could be removed more easily.For followed-up nerve laceration cases, regenerated nerves inside of the scars can beobserved clearly by VR reconstruction for SUSHI.Conclusions: VR reconstruction for single-direction and SUSHI based on DTI25rawdata provides excellent3D displays of the peripheral nerves in the wrist region. SUSHIpost-processing is a useful denoising tool because it automatically reduces the majority ofisotropic object noise, and is very suitable of observing the status of regenerated nervesinside of the scars. Part3. Stereoscopic Display of the Peripheral Nerve in the elbow regionBased on MR Diffusion Tensor Imaging With Multiple Post-ProcessingMethods and its ApplicationObjectives: To obtain a stereoscopic display of the peripheral nerves in the elbowregion based on a magnetic resonance (MR) diffusion tensor imaging (DTI) data usingthree post-processing methods: volume rendering (VR), maximum intensity projection(MIP), and fiber tractography, to evaluate the difference and correlation of them, and toexplore the application of the single-direction VR/MIP reconstruction. Materials and Methods: The MR images were acquired with a Siemens MagenetomVerio3.0T MRI scanner (Siemens Healthcare; Erlangen, Germany) using a4-channal flexcoil (Flex small4; Siemens). Twenty-four elbows of12healthy young volunteers wereapplied in20encoding diffusion direction MR DTI scan. Images belonging to asingle-direction (anterior–posterior direction, perpendicular to the nerve) were subjected toVR and MIP reconstruction. All raw DTI data were transferred to the Siemens MRworkstation for fiber tractography post-processing. Imaging qualities of fiber tractographyand VR/MIP were evaluated by two observers independently based on a custom evaluationscale. For each nerve, scores of VR/MIP reconstruction of the single-direction and fibertracking were compared using Friedman test. Intraclass correlation coefficient (ICC)analysis was used to compare the correlation of the imaging quality scores for each nerveamong VR/MIP and fiber tractography. Inter-and intraobserver agreements for evaluationscores were calculated by using the Kappa statistic. In order to test the accuracy ofdepiction for the neuropathy by using these methods,1patient with cubital tunnelsyndrome and1patient with ulnar nerve entrapment (underwent ulnar nerve repair andsubmuscular anterior transposition10years ago) were recruited for the DTI scan withmultiple post-processing (using GE Signa HDxt3.0T magnetic resonance scanner and theknee coil; the scanning parameters and post-processing method were similar with the firsttwo parts of the studies)Results: Stereoscopic displays of the nerves were obtained in all24elbows by VR,MIP, and fiber tractography post-processing methods. The VR/MIP post-processingmethods were easier to perform compared to fiber tractography. For each nerve, there wasno significant difference among the scores of fiber tracking and VR/MIP reconstruction forsingle-direction. The imaging quality scores of fiber tractography and VR/MIP weresignificantly correlated based on intraclass correlation coefficient (ICC) analysis (ICCranged0.709-0.901), which suggested that the scores based on the fiber tractography andVR/MIP for the same sample were consistent. Inter-and intraobserver agreements weregood to excellent. For the cubital tunnel syndrome case, morphological changes such as theulnar nerve in the cubital tunnel became flat due to entrapment can be observed intuitivelyby stereoscopic VR/MIP images. For the ulnar nerve anterior transposition and entrapmentcase, the ulnar nerve entrapment occured in the submuscular segment, and the nervebecame thin with obvious angle formation. Conclusions: Stereoscopic displays of the peripheral nerve in the elbow region can beachieved by using VR, MIP and fiber tracking post-processing methods based on raw DTIimages. VR and MIP reconstruction could be used as preview tools before fiber tracking todetermine whether the raw images are satisfactory. The overall morphology of thepathological nerves can be observed more intuitively by single-direction VR/MIPreconstruction than the conventional2D image.