Functional Magnetic Resonance Imaging In Brain Tumors: Research And Clinical Value

Brain rumors are of high morbidity. Furthermore, because of the specially involved region, they are characterized by high mutilation and fatality rate. The target that neurosurgeons have pursued up to now is to resect the tumor to the greatest degree and to protect nerve function utmostly. At the same time, how to delineate the tumor margin accurately and describe cortical function area or white matter fiber tracts adjacent to tumors precisely is the major mission that neuroradiologists have faced.With the development of functional MRI, such as perfusion weighted imaging(PWI),diffusion weighted imaging(DWI),diffusion tensor imaging (DTI),blood oxygenation level dependent functional MRI (BOLD-fMRI) and magnetic resonance spectroscopy(MRS), neuroimaging of brain tumors has evolved from a purely anatomy-based discipline to one that incorporates morphologic abnormality with physiologic alterations in extracellular compartment kinetics, cellular metabolism, and hemodynamics. Functional MRI has become a new tool of diagnosis, guiding surgery, monitoring therapy response, and predicting prognosis of patients with brain tumor. In this paper, We have investigated the application of PWI, BOLD-fMRI and DTI in brain tumor.The first partObjective: To investigate astrocytoma invasion and to delineate the tumor margin more precisely through PWI, with combination of pathophysiological characteristic in peritumoral area.Methods: 45 patients with histologically verified astrocytoma and classified gradeⅠ,Ⅱ,Ⅲ,Ⅳwere examined through PWI preoperatively followed by conventional MRI. The PWI original data were reestablished to get a color map of rCBV. The maximum rCBV ratio in tumor solid portion,immediate peritumoral area and distant peritumoral area were calculated for each lesion in rCBV map by using contralateral normal white matter as reference. The pathology specimens were obtained in tumor solid portion and peritumoral area. The immunohistochemical technique was used to detect microvascular density (MVD) of tumor solid portion and peritumoral area with CD34 related antigen monoclonal antibody. The HE staining of peritumoral area was used to assess tumor invasion. The correlation tests were used to determine the strength of the relationship between The maximum rCBV ratio and MVD in the solid portion. The difference of MVD in peritumoral area and the maximum rCBV ratio in immediate peritumoral area was detected between invasional and non- invasional astrocytoma.Results: The maximum rCBV ratio in the solid portion correlated well with MVD in the solid portion among astrocytomas (γ=0.714, P=0.001). Significant difference of the maximum rCBV ratio in the solid portion was found between invasional and non- invasional astrocytoma (P=0.001). There were significant difference of the maximum rCBV ratio in immediate peritumoral area (P=0.007) and MVD in peritumoral area (P=0.014) between invasional and non-invasional astrocytoma. In invasional astrocytoma, significant difference of the maximum rCBV ratio was found between in immediate peritumoral area and in distant peritumoral area (P=0.004).Conclusion: PWI is feasible for evaluation of astrocytomas angiogenesis. The assessment of astrocytomas invasion through PWI is based on the pathophysiological fact that there was significant difference of MVD in peritumoral area between invasional and non-invasional astrocytoma. The maximum rCBV ratio in immediate peritumoral area can be applied to evaluate astrocytomas invasion, and be helpful to delineate the tumor margin more precisely.The second partObjective: To explore affection of tumors near the central sulcus on motor cortex through BOLD-fMRI, and to evaluate the operation effect with guidance of BOLD-fMRI. We also want to determine whether BOLD-fMRI can be applied preoperatively to assess the risk of a new motor deficit after surgery.Methods: 57 patients with tumor adjacent to the central sulcus were enrolled in the study as fMRI group. Preoperative BOLD-fMRI technique in each patient were performed. An activation scan was achieved by using a motor task paradigm, which consisted of finger-to-thumb touching in a repeating pattern. All the scanning data were transformed to a Matlab platform, and BOLD-fMRI map were synthesized with SPM2 software. The distance from the tumor to primary motor cortex (M1) were measured. The M1 volume from the ipsilateral, contralateral and the percentage difference in the M1 volumes between the both lateral hemispheres were calculated. With guidance of BOLD-fMRI map, all patients from fMRI group were operated. As control group, 45 patients with tumor in the same position were made a routine MRI examination without BOLD-fMRI before surgery.Results: Morphologic changes of M1 area from ipsilateral were observed. The average distance from the tumor to M1 area was 12.5±5.6 mm. Patients from fMRI group were divided into four groups based on tumor type and distance from M1 area: (1) extra-axial, far, (6 cases); (2) extra-axial, near, (10 cases); (3) intra-axial, far (19 cases); and (4) intra-axial, near (22 cases). In group 3, The difference between M1 volume from the ipsilateral (Vi) and the one from contralateral(Vc) was significant statistically(P=0.003). In group 4, The difference between Vi and Vc was significant statistically too(P=0.026). There were significant difference of percentage difference in the M1 volumes (D) between intraaxial and extra-axia group. The difference of D value between group 3 and group 4 was significant statistically(P=0.039). There was significant difference of tumor resection ratio between fMRI group and control group(P=0.046), however, there was no difference of postoperatively changes of muscle power between both groups. In fMRI group, there were difference of postoperatively changes of muscle power among four groups, and 80% (8/10) patients suffering from postoperative motor deficits belonged to group 4.Conclusion: The affection to motor cortex for vicinal brain tumors depends mainly on the distance between lesion and ipsilateral M1 and whether the lesion is located intra-axis or extra-axis. BOLD-fMRI can be helpful to resect lesions near motor cortex to greatest degree, and to preserve motor function area utmostly, which increases the precision and accuracy of surgery. The application of BOLD fMRI in pre-operation plays an guiding role in making surgery plans. BOLD-fMRI can be applied preoperatively to assess the risk of a new motor deficit after surgery.The third partObjective: To explore the DTI features of normal white matter, and to value application of DTI and DTT in brain tumor for the sake of protection of involving white matter tracts .Methods: A total of 30 healthy adults and 32 patients with brain tumor were examined by DTI. All data were transformed to Leonardo workstation, and processed with DTI software. The fractional anisotropy (FA) value of different brain tissues of healthy adults was measured, and the FA value of tumor solid area,peritumoral and opposite mirror area were calculated. Based on diffuiosn value of each pixel, the three-dimensional diffusion tensor tractography (DTT) map could be obtained to observe tumor's influence to white matter fiber tract. Operation project was determined with reference to DTT map.Results: The FA value of different normal brain tissue was diverse. The white matter fiber tract could be observed clearly on three-dimensional DTT map. The difference of FA value among tumor solid area,peritumoral and opposite mirror area in intra-axial tumor was significant statistically(P <0. 01). There was no difference of FA value between peritumoral and opposite mirror area in extra-axial tumor. The tumor's influence to near white matter fiber tract could be observed on DTT map. In 32 patients with brain tumor, DTT map clearly demonstrated 14 white matter fiber tracts near tumor were not involved by tumor, 11 were close to tumor and displaced, 7 were invaded and disrupted by tumor. Gross total resection was achieved in 26 patients, while neurological deterioration was seen in only 4 patients.Conclusion: The FA map of DTI offered the optimal visualization of white matter fiber tracts. DTI were valuable in presenting the topographical character of involved white matter tracts and relationship with the margins of neighboring rumors. DTI should be of great value in the surgical planning as well as protection of involving white matter tracts .