Preliminary Study Of Diffusion Tensor Imaging And Fiber Tractography In Normal Brain And Diffuse Gliomas At 3T MRI

Purpose To evaluate the application of a new parallel imaging technique-array spatial sensitivity encoding technique ( ASSET ) in 3T MR diffusion tensor imaging.Materials and Methods On 3T GE Signa Excite MR scanner, DTI of the special testing MR phantom was scanned. DTI was performed by using an 8-channel phase array coil with and without ASSET, respectively, and by using a standard quadrature head coil without ASSET. On the intermediate slice of each sequence, a 50mm~2 round ROI was placed in the center and in the half-radial anterior, posterior, left, right, left-anterior, right-anterior, left-posterior, right-posterior to the center, respectively. The signal intensity value in above-mentioned ROIs and the transverse/ longitudinal diameter ratio were measured.Results The signal intensity of the image with 8-channel phase array coil was significantly higher than that with standard quadrature head coil (P<0.001) and the image homogeneity of the former was better than that of the latter. The geometrical distortion was least in the DTI image with 8-channel phase array coil and ASSET.Conclusion DTI image quality with 8-channel phase array coil and ASSET was much higher than that with standard quadrature head coil.Purpose To obtain the diffusion tensor imaging and the fiber tractography of the normal human brain, to quantitatively assess intrinsic characteristics of water molecule diffusion, and to provide a reference for future studies.Materials and Methods On 3T GE Signa Excite MR scanner, DTI scans were performed in 20 healthy volunteers with ASSET-SE-EPI sequences. Mean diffusivity (MD) values, fractional anisotropy (FA) values, and relative anisotropy (RA) values were measured in the genu of corpus callosum, splenium of corpus callosum, bilateral anterior limbs, genu, and posterior limbs of internal capsules, bilateral external capsules, bilateral frontal and occipital white matter, bilateral caudate nucleus head, putamens, and thalami, respectively. The values were analyzed by using SPSS 11.5 statistical analysis software. Three dimensional fiber tractography was performed with FuncTool software.Results There was no significant difference of MD values, FA values, and RA values between left and right hemisphere and between sexes. The difference of MD value between the white matter tracts and the deep gray nuclei was not statistically significant, but the FA and RA value of the white matter tracts was significantly higher than those of the deep gray nuclei. The anisotropy showed significant difference among different white matter tracts and among deep gray nuclei. Among white matter tracts, FA and RA value was highest in the corpus callosum, secondly in the genu and the posterior limb of internal capsule, the third in the anterior limb of internal capsule, the frontal and occipital lobe, and lowest in the external capsule. Among deep gray nuclei, the FA and RA value was highest in the thalamus, secondly in the caudate nucleus head, and lowest in the putamen. On directionally encoded color map, the different fiber tracts and their directions could be distinguished by different colors. Fiber tractography could show the track and connection of the fiber tracts three dimensionally.Conclusion DTI could show the microstructure of the white matter fiber tract, analyze the characteristics of water molecule diffusion quantitatively, and distinguish different fiber tracts. The directionally encoded color map and the fiber tractography could show the direction and the connection of the fiber tracts clearly. DTI supplies a new functional imaging technique for the research on neuro-functional anatomy and neurologic disease.Purpose To evaluate the effect of ASSET - DTI and the fiber tractography on the diagnosis and grading of diffuse gliomas, and to display the relationship between the tumor and surrounding structures.Materials and Methods On 3T GE Signa Excite MR scanner, DTI scans were performed in 37 patients with diffuse gliomas (WHO grade: grade II16 cases, grade III 11 cases, and grade IV 10 cases ) by using ASSET-SE-EPI sequence. MD values and FA values were measured in the tumor, at the peritumoral edema, normal-appearing white matter (NWM) region on T2WI surrounding the tumor and edema, distant normal-appearing white matter region on T2WI ipsilateral to the tumor, and the corresponding region on contralateral side, respectively. The values were analyzed by using SPSS 11.5 statistical analysis software. Three dimensional fiber tractography of peritumoral fiber tracts was performed with FuncTool software.Results MD value in the tumor, at the peritumoral edema, and NWM was significantly higher than those of contralateral region (P<0.01), while FA value was significantly lower (PO.01). The intratumoral FA value of grade II was significantly lower than those of grade III and IV (Pn-,,,=0.024;Pn,v=0.030). The intratumoral and peritumoral edematous MD value of grade II was higher than those of grade III and IV, but the difference was not significant (P>0.05). MD and FA values between tumor and peritumoral edema showed no difference in all tumors (P>0.05). The fiber tractography showed that the main influence of grade II gliomas to adjacent white matter tracts was displacement, but infiltration and destruction were also revealed. The destruction of fiber tracts could be seen in all edema regions around grade III gliomas, and invasion or even destruction of fiber tracts could be seen in some NWM regions. The destruction of fiber tracts was clearly demonstrated in both edema region andNWM region around grade IV gliomas.Conclusion Infiltration and destruction of the peritumoral white matter tracts can be seen in diffuse gliomas with various grades, reflecting the characteristic infiltrative growth pattern of diffuse gliomas. MD and FA value could be used to distinguish glioma from normal brain structure. FA value could be used to distinguish low-grade glioma from high-grade glioma. The directionally encoded color map and the three-dimensional fiber tractography could show the relationship between tumor and adjacent white matter tracts clearly and intuitively.