Presurgical Evaluation Of The Brain Tumor In Language Related Areas With Functional MRI

Part I :Preliminary study of the functional language area on functional MRIPurpose: To investigate the word association paradigm for activating the language areas of interest in the brain on blood oxygen level dependent functional magnetic resonance imaging (BOLD-fMRI) and to determine effectiveness as a clinical tool in the preoperative evaluation of patients with intracranial tumors.Materials and Methods: A non-vocal paradigm for activation of the language areas was developed and validated on 10 Chinese right-handed volunteers (7 female, 3 male, average age 29-year-old). The complete scanning protocol included T1 weighted FSE reference images, T2* weighted echo planar imaging (EPI) and 3D fast spoiled gradient echo images acquired by BrainWave RealTime (RT) on a 3.0T magnet (GE Signa Excite^? HD_X). The final paradigm involved visual presentation of familiar Chinese characters (frequency of use > 1000/day) followed by visual interrogation requiring the subject to make choices by pressing right or left thumb buttons. The choices involved word associations based upon meaning with variable tonal interference. Each stimulus session interpolated with rest lasted for 20 seconds. Activation maps were analyzed using AFNI software to discriminate areas of consistent activation by the paradigm from background activation and to superimpose the activation maps onto higher resolution T1 weighted anatomic images. We calculated functional language laterality index (LI) by taking out the inferior frontal gyrus, inferior parietal lobe and superior and middle temporal lobe.Results: Several initial iterations of the paradigm failed to produce useful activation maps and required modification of the protocol to reduce the complexity of language tasks, eliminate verbalization and implement head immobilization to reduce corruption of data from involuntary head movements.For the final protocol, all volunteers performed the study successfully. Language areas visible on activation maps for this word association paradigm included: left inferior frontal gyrus(BA44,45), lateral dorsal side of frontal lobe(BA8,9), bilateral superior posterior temporal gyrus(BA21,22), bilateral superior parietal lobe(BA39,40), left anterior insular(BA13), bilateral medial frontal lobe(SMA, BA6), bilateral precental motor cortex(BA6), bilateral occipital cortex (BA17,18,19)and bilateral superior cerebellum. Although all 10 volunteers were right-handed, 9 volunteers showed greater activation on the left with LI > 0.10. Only one volunteer had a LI = -0.237, indicating the right side is the language dominant hemisphere.Conclusion: A word association paradigm utilizing frequently used nouns with variable tonal interference is easy to perform and consistently activates the language neuro-network compromised by frontal, parietal, temporal and occipital lobes. The activation maps show lateralization and relationship to anatomic structuresPart II:Diffusion tensor tractography of frontal lobe white matter fibersPurpose: To establish visualization methods of the main white matter fibers in the frontal lobe by using diffusion tensor tractography (DTT) and to investigate the correlation with known anatomy.Materials and Methods: Single shot echo planar diffusion tensor imaging on a 3.0T magnet (GE Signa Excite? HDx) in 25 directions was performed in 10 healthy volunteers. By selecting appropriate regions of interest and setting fractional anisotropy (FA) threshold, angle threshold and step size, white matter fibers in the frontal lobe were visualized by finding the pathways of high diffusivity (corresponding to Brownian motion along the course of axons) using Volume-one1.5 and diffusion TENSOR Visualizer 1.5 (dTV)software. Finally the coherence between reconstructed white matter fibers and known anatomy of those was observed.Results:, Three dimentional architecture of the white matter fibers in the frontal lobe on DTT, which include (i) arcuate fasciculus, (ii) inferior fronto-occipital fasciculus, (iii) uncinate fasciculus, (iv) corpus callosum and (v) anterior thalamic radiation, could be visualized by using diffusion tensor tractography. Results correlated with known anatomy.Conclusion: Results of frontal lobe white matter tractography in healthy volunteers were highly consistent with known anatomy. This method is a promising way for studying fiber connectivity in the human brain and may allow evaluation of neural fiber distortion or destruction by tumor.Part III:Presurgical evaluation of tumor in language related areas with functional MRI and diffusion tensor tractographyPurpose: To explore the anatomic relationship of forntal lobe tumors related with the language areas and white matter on BOLD-fMRI and DTT as a clinical tool for guiding tumor resections that spare language function.Materials and Methods: Six patients with left frontal lobe tumors (4 gliomas, 1 germinoma, 1 intra-axial cavernoma) close to Brocca and Wernicke language areas were studied. BOLD and DTI were performed on a 3.0T magnet (GE Signa Excite^? HD_X), BOLD using the word association paradigm developed in Part I and DTT technique developed in PartII. Language activation maps and fiber tracts were superimposed upon high resolution T1 weighted anatomic images of the brain for displaying the relationship between tumor, language functional areas and white matter tracts. For imaging processing, BOLD analysis was performed with AFNI and fiber-tracking with the software of Volume-one1.56 and diffusion TENSOR Visualizer 1.5 (dTV).Results: In 6 patients the relationship of Brocca's area and precentral motor area to the frontal lobe tumor was identified allowing pre-operative neurosurgical planning to minimize language and motor disruption. Diffusion tensor images were corrupted by motion in one patient but successfully demonstrate the impact of tumor on white matter tracts in 5 patients. Fractional anisotropy images, showed disruption of the left arcuate fasciculus in one patient, deviation/deformation in 2 cases and unaffected by tumor in the remaining two cases. Post-operatively, no patients showed recurrence and no patients showed deterioration of language function, though 1 patient who had mild aphasia pre-operation did not improve.Conclusion: The combination of fMRI and DTI is helpful for identifying the relationship of brain tumors to language cortex and white matter fibers for planning surgical resections that spare language function.