Advancements of high-resolution diffusion tensor imaging of brain / 中国介入影像与治疗学

Diffusion tensor imaging (DTI) is an imaging method that can be used to describe changes of tissue structure through the diffusion of water molecules in living tissue. Fiber tracking based on DTI can display the anatomic structure of cerebral nerve fibers noninvasively and clearly, which is of great value for diagnosis and treatment of brain diseases. However, due to the Gaussian hypothesis of the diffusion tensor model, it is difficult to indicate fiber directions in fiber crossing region. A high-resolution DTI method was proposed to estimate the direction distribution of multiple fibers. The research advancements of fiber tracking based on high-resolution DTI were reviewed in this article.

Structural magnetic resonance imaging and diffusion tensor imaging study on white matter in left-and right-handed adults / 中华行为医学与脑科学杂志

Objective To explore the differences of macrostructural and microstructural and their correlations in brain white matter (WM) between left-and right-handed adults.Methods Structural magnetic resonance imaging (sMRI) and diffusion tensor imaging (DTI) were performed on twenty-three left-handed (LH) and thirty-two right-handed (RH) healthy subjects.The WM volume,fractional anisotropy (FA) and mean diffusivity (MD) were mearsured and compared between the two groups by using the voxel-based morphometry (VBM) and voxel-based analysis (VBA) methods.Results (1) LH adults showed lower WM volume than RH adults in bilateral splenium of corpus callosum (SC) (Left:x=-15,y=-57,z =13.5,t=-5.160;Right:x=18,y=-42,z=12,t=-3.654;P＜0.001).Compared with the RH adults,the FA values in WM of the left postcentral gyrus (PoCG) (x =-24,y =-46,z =54) and the above left insula (INS) (x =-36,y =-12,z =20) increased (P＜ 0.001),as well as the average FA values,the average length and number of streamlines in WM tracts increased (P＜0.05) in LH adults.Compared with the RH adults,the MD values in the right HIP (x=24,y=-34,z=-2) decreased(P＜0.001),as well as the average MD values decreased,and the average length in WM tracts increased (P＜0.05) in LH adults.(2)There was positive correlation between FA and the volume of right splenium of corpus callosum in LH and RH adults (LH:r=0.716,RH:r=0.471,P＜0.05).There was negative correlation between FA and MD in the left PoCG (LH:r=-0.769,RH:r=-0.841),left INS (LH:r=-0.775,RH:r=-0.744) and right HIP (LH:r=-0.842,RH:r=-0.742) in LH and RH adults (all P＜0.05).Conclusion There are differences in both macrostructure and microstructure of white matter in several brain regions and WM tracts between left-handed and right-handed people,and correlations between these measures were also observed.

Effect of Increasing Diffusion Gradient Direction Number on Diffusion Tensor Imaging Fiber Tracking in the Human Brain

OBJECTIVE: To assess the effects of varying the number of diffusion gradient directions (NDGDs) on diffusion tensor fiber tracking (FT) in human brain white matter using tract characteristics. MATERIALS AND METHODS: Twelve normal volunteers underwent diffusion tensor imaging (DTI) scanning with NDGDs of 6, 11, 15, 21, and 31 orientations. Three fiber tract groups, including the splenium of the corpus callosum (CC), the entire CC, and the full brain tract, were reconstructed by deterministic DTI-FT. Tract architecture was first qualitatively evaluated by visual observation. Six quantitative tract characteristics, including the number of fibers (NF), average length (AL), fractional anisotropy (FA), relative anisotropy (RA), mean diffusivity (MD), and volume ratio (VR) were measured for the splenium of the CC at the tract branch level, for the entire CC at tract level, and for the full brain tract at the whole brain level. Visual results and those of NF, AL, FA, RA, MD, and VR were compared among the five different NDGDs. RESULTS: The DTI-FT with NDGD of 11, 15, 21, and 31 orientations gave better tracking results compared with NDGD of 6 after the visual evaluation. NF, FA, RA, MD, and VR values with NDGD of six were significantly greater (smallest p = 0.001 to largest p = 0.042) than those with four other NDGDs (11, 15, 21, or 31 orientations), whereas AL measured with NDGD of six was significantly smaller (smallest p = 0.001 to largest p = 0.041) than with four other NDGDs (11, 15, 21, or 31 orientations). No significant differences were observed in the results among the four NDGD groups of 11, 15, 21, and 31 directions (smallest p = 0.059 to largest p = 1.000). CONCLUSION: The main fiber tracts were detected with NDGD of six orientations; however, the use of larger NDGD (> or = 11 orientations) could provide improved tract characteristics at the expense of longer scanning time.

Diffusion Tensor Imaging Study on Cervical Spinal Cord Injury without Radiographic Abnormality / 中国康复理论与实践

Objective To apply MR diffusion tensor imaging (DTI) to quantitatively analyze cervical spinal cord injury without radio-graphic abnormality (CSCIWORA). Methods 15 patients with CSCIWORA and 20 healthy controls were scanned with MRI of convention-al scans and DTI. The fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured. Results FA and ADC of the pa-tients were (0.475±0.109) and (1.438±0.252)×10-3 mm2/s, respectively. Whereas, they were (0.604±0.096) and (1.371±0.280)×10-3 mm2/s in the controls. Compared with the controls, the FA was less (P<0.05) in the patients, but the ADC was not significantly different (P=0.267). The fiber tracking (FT) showed the abnormality of white matter fiber tracts of cervical spinal cord in the patients. Conclusion DTI can de-tect the CSCIWORA, and FT can directly display the injuries of white matter fiber tracts of cervical spinal cord, which provide more infor-mation to evaluate the clinical severity of CSCIWORA.

Diffusion Tensor Imaging Study on Cervical Spinal Cord Injury without Radiographic Abnormality / 中国康复理论与实践

@#Objective To apply MR diffusion tensor imaging (DTI) to quantitatively analyze cervical spinal cord injury without radiographic abnormality (CSCIWORA). Methods 15 patients with CSCIWORA and 20 healthy controls were scanned with MRI of conventional scans and DTI. The fractional anisotropy (FA) and apparent diffusion coefficient (ADC) were measured. Results FA and ADC of the patients were (0.475±0.109) and (1.438±0.252)×10-3 mm2/s, respectively. Whereas, they were (0.604±0.096) and (1.371±0.280)×10-3 mm2/s in the controls. Compared with the controls, the FA was less (P<0.05) in the patients, but the ADC was not significantly different (P=0.267). The fiber tracking (FT) showed the abnormality of white matter fiber tracts of cervical spinal cord in the patients. Conclusion DTI can detect the CSCIWORA, and FT can directly display the injuries of white matter fiber tracts of cervical spinal cord, which provide more information to evaluate the clinical severity of CSCIWORA.

Initial study of the degeneration of lumbar intervertebral discs by magnetic resonance diffusion tensor imaging / 中华放射学杂志

Objective To evaluate the earlier changes of degeneration discs in vivo using magnetic resonance diffusion tensor imaging (DTI).Methods From September 2010 to March 2011,88 consecutive outpatients [age 16-63 years,mean age (37 ± 13) years] were enrolled in this study.The excluded criteria were as follows: spinal deformity,spinal tumors and post-operation of spine.The mean diffusion (MD) and fractional anisotropy (FA) values on DTI images of 428 intervertebral discs which without susceptibility artifacts were measured.Fiber track (FT) images of annulus of intervertebral discs were analyzed.MD and FA were also measured on FT.The quartile and median were used to record the nonnormal distribution dates.The Chi-square test statistic was applied by SPSS1 1.0 software package.Results Annulus fibrosis type had closely related to the Pfirrmann grading.Three types were divided based on FT charts of degenerated intervertebral disc.Intact type was noted in 135 discs,Pfirrmann Ⅱ level has a high percentage(92 discs,68.15％) in this type; Scrambled type was noted in 195 discs,Pfirrmann Ⅲ and Ⅳ level were accounted for 63.07％ (123 discs) ; Conglomerate type was noted in 98 discs,the Pfirrmann Ⅳ and Ⅴ level were accounted for 83.68％ (82 discs) (Mantel-Haenszel test,x2 =183.90,P ＜ 0.01).Different annulus types had different MD and FA values.The median(range)of FA of complete,messy and clumps type fibrous ring were 0.32 (0.29-4.35),0.35 (0.33-0.38),0.54 (0.46-0.62).The corresponding median(range)of MD were 12.40(11.50-13.20) x 10-10,11.10(9.92-12.00) × 10-10,6.30(5.03-7.72) × 10-10 mm2/s.Scrambled annulus fibers had lower MD values and higher FA values,which had significant difference (x2 =219.74,243.88,P ＜0.01).Conclusions DTI is a non-invasive method to assess intervertebral disc structural changes in vivo.MD and FA values are helpful to evaluate the intervertebral disc degeneration.

Anisotropy Measurement and Fiber Tracking of the White Matter by Using Diffusion Tensor MR Imaging: Influence of the Number of Diffusion-Sensitizing Gradient Direction

PURPOSE: Recent development of diffusion tensor imaging enables the evaluation of the microstructural characteristics of the brain white matter. However, optimal imaging parameters for diffusion tensor imaging, particularly concerning the number of diffusion gradient direction, have not been studied thoroughly yet. The purpose of this study was to evaluate the influence of the number of diffusion gradient direction on the fiber tracking of the white matter. MATERIALS AND METHODS: 13 healthy volunteers (ten men and three women, mean age 30 years, age range 23-37 years) were included in this study. Diffusion tensor imaging was performed with different numbers of diffusion gradient direction as 6, 15, and 32, keeping the other imaging parameters constant. The imaging field ranged from 1 cm below the pons to 2-3 cm above the lateral ventricle, parallel to the anterior commissure-posterior commissure line. FA (fractional anisotropy) maps were created via image post-processing, and then FA and its standard deviation were calculated in the genu and the splenium of the corpus callosum on each of FA maps. Fiber tracking of the corticospinal tract in the brain was performed and the number of the reconstructed fibers of the tract was measured. FA, standard deviation of FA and the number of the reconstructed fibers were compared statistically between the different diffusion gradient directions. RESULTS: FA is not statistically significantly different between the different diffusion gradient directions. By increasing the number of diffusion gradient direction, standard deviation of FA decreased significantly, and the number of the reconstructed fibers increased significantly. CONCLUSION: The higher number of diffusion gradient direction provided better quality of fiber tracking.