Application Of MR Diffusion Tensor Imaging And Diffusion Tensor Tractography In Gliomas

Gliomas are common original tumors, which account for 35-55% of all intracranial tumors. Most gliomas are of high malignancy. High-grade gliomas are more invasive and with bad prognosis. Conventional MR imaging is a useful method to diagnose gliomas before operation, demonstrating the basic information of the tumor. However, there are certain limitations of conventional MR imaging in evaluating malignancy and invasion of gliomas or showing correlation of the white matter tract and gliomas nearby. Recently, with rapid development of magnetic technology, many researchers focus on diffusion tensor imaging (DTI), an important new complement method for conventional MR imaging, which can evaluate the proton's diffusion and show fiber tracts alive.We reviewed related reports and studied 31patients with low-grade(gradeⅠandⅡ) and high-grade (gradeⅢandⅣ) gliomas respectively. The purpose of this article was to evaluate the malignancy and invasion of gliomas preoperatively by DTI, and to study the relationship between gliomas and fiber tracts by DTT. This could help to decide on a surgical approach and on the extent of resection of gliomas without damaging important fiber tracts. Methods:A total of 31 patients with gradeⅠtoⅣgliomas underwent conventional MR imaging (T1WI,T2WI and Dark-fluid)and diffusion tensor imaging, using SEIMENS 1.5T AVANTO super conduct magnetic resonance imager. Convent- ional MR imaging(T1WI,T2WI and Dark-fluid)were performed with spin echo and turbo spin echo sequence (slice thickness: 4mm; slice interval: 0.4mm; FOV: 230mm×230mm;T1WI:TR/TE=400/7.8ms;T2WITR/TE= 3250/ 99ms; Dark-fluid: TR/TE= 9000/109ms, TI= 2500ms).Diffusion tensor imaging was performed with a single shot, spin echo, echo-planar, diffusion-weighted pulse sequence(12 different motion probing gradient directions, TR/TE= 4600/88ms, b=0s/ mm2 and b=1000s/mm2,slice thickness: 4mm,slice interval:0.4mm, FOV: 230mm×230mm,6 number of excitation,scanning time:6min5s,429 images).We used LEONARDO workstation to write FA map and DEC map. On FA map,3 ROIs ,including solid portion of glioma, edema area and the edge of edema, and the contralateral normal brain regions were chosen. A statistic analysis was given after calculating the average FA value and relative FA of different ROI. Diffusion tensor tractography was reconstructed by"seed method".Results:Some different manifestations on conventional MR images between low-grade gliomas and high-grade gliomas were observed: low-grade gliomas were well defined, with even signals, slight mass effect and a slight edema and the enhancement of low-grade gliomas were slight or nothing; high-grade gliomas, on the other hand, showed undefined, with complicated signals, strong edema, marked mass effect and significant enhancement. On FA images, all giomas and edema showed very low signals. The mean FA value of all gliomas'ROIs was significant lower than that of normal brain. A decreasing tendency of mean FA value could be observed as follow: solid portion lowest, followed by edema area and edge of edema, both in low -grade and high-grade gliomas. The mean rFA value of high-grade gliomas was significant lower(P<0.05) than that of low-grade gliomas ,in solid portion, edema area and edge of edema. White matter fibers could be well distinguished by different color on DEC images. Low-grade gliomas mainly showed that fiber tracts were vague and with complicated and very dark colors within gliomas ; deformed and a little bit fatter than the other side, with abnormal and dark color in edema; slightly compressed with normal, bright color beyond edema. High- grade gliomas showed much more complicated alteration ,in all ROIs, than that of low grade gliomas, especially fibers within gliomas which appeared extrem- ely vague and dark in color.Four kinds of manifestation were illustrated on DTT: deviation, rarefa- ction, destruction and discontinuation. For fiber tracts of low-grade gliomas,3 of 15cases showed deviation; the other 12 cases showed slight rarefaction. For fiber tracts of high-grade gliomas,13 of 16 cases showed strong destruction and partly discontinuation;2cases showed termination or interruption;1 case mainly showed deviation and part of fiber tracts showed destruction.Conclusion:1. DTI is a helpful method, demonstrating notable alteration of anisot- rophic diffusion of gliomas and showing the correlation of the white matter tract and nearby tumor directly;2. rFA contributes positively to study malignancy and invasion of high- grade gliomas;3. DEC images can provide more useful fiber information of gliomas than FA images alone, and we can gain much more complete information about fiber tracts by combining FA images with DEC images and DTT;4. DTT is useful for preoperative investigation, especially when assisting surgical planning, e.g. deciding on a surgical approach and the extent of rese- ction of gliomas without damaging important fiber tracts nearby, and also helpful to evaluate prognosis by comparing preoperative tractography with that of postoperation.