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Objective: through the use of a different number of diffusion gradient encoding direction (Diffusion Gradients-encoding Directions, DGDs) diffusion tensor imaging study of the same gradient direction repeatedly scan the degree of variation of FA and ADC values ??in different time periods, and validate its repeatability; research DGDs various parts of anisotropy differences in white matter FA values ??ADC value and SNR; the different number DGDs diffusion tensor imaging on a different course, different sizes and running complex fiber bundles display capability. Explore the more optimized diffusion tensor imaging DGDs, to increase the reliability of the white matter measurements to improve the value of clinical work. Methods: 30 young healthy volunteers different number DGDs (20,30,64,256), diffusion tensor imaging, computing, FA map, ADC map, Trace and white matter fiber tracts tracer imaging. Measuring FA values ??in different time periods repeat scan, ADC values; measuring different number DGDs in the corpus callosum, knee, cerebellar peduncle, internal capsule, corpus beside the frontal lobe, occipital lobe, thalamus, putamen, tail like nuclear head FA values, ADC value and SNR values; measuring frontal lobe in the corpus callosum, the corticospinal tract, cerebellar peduncle, corpus next four different white matter fiber tracts running fiber bundle number and length. FA and ADC value variation of repeated scans of the same gradient direction at different time periods; in both cases the same excitation frequency and acquisition time different number DGDs on various parts of the white matter in the FA values ??ADC value and SNR differences; different walking line white matter fiber tracts in the differences of the number and length of the fiber bundle, and for statistical analysis. Results: (1) repeated scanning of the three time periods of the same gradient direction different parts of the white matter FA values ??and the coefficient of variation of the ADC value in the group between the three time periods compared the differences were not statistically significance (p gt; 0.05 ). (2) in the excitation frequency and acquisition time the same two cases, the various parts of the white matter of the SNR, in between different number DGDs group, comparing the differences were not statistically significant (p gt; 0.05). (3) the same number of excitations, the corpus callosum, knee, small cerebellar peduncle, internal capsule, corpus next to the frontal lobe, occipital lobe of the various parts of the FA values ??and ADC values ??DGDs = 20,30,64,256 group In comparison, the difference was not statistically significant (p gt; 0.05). Thalamus, putamen, caudate nucleus head these parts FA and ADC values ??20,30,64,256 direction group comparison, the difference was statistically significant (p lt; 0.05); pairwise comparison, 20 direction 30 direction difference was not statistically significant (p gt; 0.05), the difference was not statistically significant (p gt; 0.05) 64 direction and the direction of 256 20 directions, 30 direction 64 direction, 256 The direction of the difference was statistically significant (p lt; 0.05). Same acquisition time, the ministries of FA values ??and ADC values ??of the white matter DGDs = 20 (NEX = 3), 30 (NEX = 2), 64 (NEX = 1) between the two groups, the differences were not statistically significant (p gt; 0.05). (4) the same number of excitations, calculate the corpus callosum, the corticospinal tract, corpus next to the frontal lobe and cerebellar peduncle the number and length of the fiber bundle, compare DGDs = 20,30,64,256 groups, and the differences were statistically significant (p gt; 0.05). Between 20 direction 30 direction of the difference was statistically significant (p lt; 0.05), 30 directions gt; 20 directions; 30 direction 64 direction of the difference was statistically significance (p lt; 0.05) 64 direction gt; 30 directions; 64 direction 256 direction difference was statistically significant (p lt; 0.05), 256 direction gt; 64 directions. In the same acquisition time, four fiber bundle of fiber bundle number and length of the DGDs = 20 (NEX = 3) .30 (NEX = 2) .64 (NEX = 1) between the two groups, the differences were not statistically significant (p gt; 0.05). Conclusion: (1) 20 and the above gradient-encoding direction of the obtained information of the tensor repeatability better. (2) the noise level of 20 and above the DTI gradient encoding direction of the original image is not increased to the gradient encoding direction of 20 and above the impact on SNR can be ignored. (3) direction of 64 to be able to compare both the expression of the degree of anisotropy of white matter fiber, diffusion capacity and the fiber bundle display capabilities, improved guiding value for clinical application. (4) With the the DGDs number increased, DTI can improve the display capabilities of different walk the line, the different size and complex fiber bundles traveling. In addition, in clinical use can be selected according to the patient conditions diffusion gradient encoding direction, to improve the success rate of the DTI examination.
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