A pilot study of fMRI and fiber tracking to monitor effects of irradiation on brain tumour patients

Purpose: A pilot study to develop objective quantitative measures of brain function using fMRI and fiber tracking (DTI), in order to indicate whether fMRI/DTI can visualize changes in brain function following radiation treatment and to gain insight into the degree of cerebral plasticity induced by the lesion itself and/or the treatment. Methods: Four patients with a brain tumour having had cranial radiotherapy within the last 2-5 years were included (1 meningioma, 3 low grade glioma). All tumours were located supratentorially in the frontal lobes. Patients were scanned with a 3.0 T MRI scanner (Siemens Allegra head scanner). The imaging protocol included a localizer, high resolution anatomical images (3D MPRAGE (T1) and 3D spin echo (T2) sequences), rapid dynamic imaging while the patient performed a task (fMRI) and diffusion tensor imaging (DTI). The N-BACK test (working memory test including spatial and language testing) was chosen as neuro-psychological task reflecting neuro-cognitive functions located near and around the tumour. The fMRI data were analyzed using an automated computerized brain mapping technique (Brainvoyager). Among the specifically active areas of working memory those closest to the tumour were selected and the activity of cortical areas around them evaluated. Tractography was operated on the diffusion tensor images to locate fibers around the tumour using 3D Slicer. The images were registered to diagnostic scans. The activation maps and fiber tracts were fused to the diagnostic scans according to the transformations computed with the registration process. Results: Results have already been completed for 2 patients. For these patients, the pre-irradiation scans did not show significant tissue deformation showing that rigid registration was sufficient for these cases (non-rigid registration is not needed in such cases). For the post-irradiation fMRI the memory function within the irradiated area and around the tumor could be demonstrated: e.g. in one patient an activation in the auditory cortex and in the prefrontal cortex have been observed. The DTI analysis showed that the symmetry of the fibers was disrupted around the tumour. Further results of integrated imaging of DTI, fMRI and radiotherapy planning will be shown. Conclusion: This study has shown the feasibility to image memory function by fMRI and fiber tracking in irradiated brain tissue. Whether those functions are in the normal range needs to be examined by future longitudinal studies and by comparison with a control group. Methods of quantification need to be defined, however, this is a first step to develop objective and quantitative measures of brain function using combined fMRI and DTI in order to understand the effects of irradiation on functionally important areas and minimize them.