The Study On The Influence Of The Numbers Of Diffusion Gradients-encoding Directions In Diffusion Tensor Imaging On Normal White Matter

Objective:To study the influence of the numbers of Diffusion Gradients-encoding Directions (DGDs) on the variation of FA and ADC from the different time to scan repeated;on Fractional anisotropy(FA),Apparent Diffusion Coefficient(ADC) and signal-to-noise ratio(SNR);on the displaying ability about fibers of different courser, different size and complicated course with DTI and DTT. To discuss the more optimal number of DGDs, so that it can be increased on the reliability of measurements and application value on clinic works.Methods:The DTI and DTT were performed on 30 healthy younger volunteers with four different DGDs,the number of DGDs was 20,30,64,and 256 separately.FA and ADC from the different time to scan repeated were measured and the variation were compared. FA, ADC and SNR from the genu and spenium of corpus callosum, middle peduncle of cerebellum,internal capsule, the pericallosal parietal and frontal lobe, thalamus, lentiform nucleus, and head of caudate nucleus with the numbers of DGDs were measured and compared. The numbers of fiber bundle and lengthes from the callosum,middle peduncle of cerebellum,the pericallosal frontal lobe, and corticospinal tract on different courser were measured and compared. All of above were compared on two conditions,one was identical acquisition time, the other was identical number of exciation(NEX).Statistical analysis was obtained.Results:1.the difference of the variation of FA,ADC from the white matter among the DGDs groups on three times were no statistically significient(p>0.05).2.When acquisition time or NEX was identical,the difference of SNR, FA and ADC from the white matter among the DGDs groups (DGDs=20,30,64,256) were no statistically significient(p>0.05).3.When NEX was identical,the difference of FA,ADC from the genu and spenium of corpus callosum,middle peduncle of cerebellum,internal capsule, the pericallosal parietal and frontal lobe among the DGDs groups were no statistically significient(p>0.05).but the difference of FA,ADC from thalamus, lentiform nucleus,and head of caudate nucleus among the DGDs groups were statistically significient(p<0.05);the value of the above parameters was compared each other, the difference between the direction of 20 and 30 was no statistically significient(p>0.05),the difference between the direction of 64 and 256 was no statistically significient(p>0.05),the difference between the direction of 20 or 30 and 64 or 256 was statistically significient(p<0.05).When acquisition time was identical, the difference of SNR, FA and ADC from the white matter among the DGDs groups (DGDs=20(NEX=3),30(NEX=2),64(NEX=1))were no statistically significient(p >0.05).4. When NEX was identical,the difference of the numbers of fiber bundle and lengthes from the callosum,middle peduncle of cerebellum,the pericallosal frontal lobe, and corticospinal tract on different courser among the DGDs groups (DGDs=20,30,64,256) were statistically significient(p<0.05).the value of the above parameters was compared each other, the difference between the direction of 20 and 30,30 and 64,64and 256 was statistically significient(p<0.05),the direction of 30> the direction of 20, the direction of 64>the direction of 30,the direction of 256> the direction of 64.When acquisition time was identical,the difference of the numbers of fiber bundle and lengthes from the four fiber bundles on different courser among the DGDs groups (DGDs=20(NEX=3),30(NEX=2),64(NEX=1))were no statistically significient(p>0.05).Conclusion:1.The reproducibility of tensor information from DGDs on20 and above 20 directions was better.2.Because the noise level of DGDs on20 and above 20 directions didn't increase, the effect of the numbers of DGDs to SNR could be neglected.3.DTI with 64 directions could express to give consideration to two or more things on anisotropy, the displaying ability of fiber tracts and diffusion ability, increased the application value on clinic works.4.Along with the increasing of the numbers of DGDs, the displaying ability of the fiber tracts in different courser different size and complicated course could be increased with DTI.In addition, selecting the numbers of DGDs, should be accord with patient's conditionsto so as improve the DTI in clinical practice...