Imaging the Short-Term Memory by fMRI and Fiber Tracking for the Study of Effects of Irradiation in Brain Tumor Patients. A Feasibility Study

Purpose/Objective(s): To measure brain function by fMRI and fiber tracking (DTI), in order to indicate whether fMRI/DTI can visualize changes in brain function following radiation treatment.Materials/Methods: Five patients irradiated for a brain tumor were included. An MRI (3.0 T, Siemens Allegra head scanner) with high resolution anatomical images and 3D spin echo, rapid dynamic imaging for fMRI and DTI were performed. The working memory was tested by the N-BACK test reflecting neuro-cognitive functions. The fMRI data were analyzed using an automated computerized brain mapping technique (Brainvoyager QX). Among the active areas of working memory those closest to the tumor were selected and the activity of cortical areas around them evaluated. The activation maps and fiber tracts were fused to the diagnostic scans according to the transformations computed with the registration process. Tractography was operated on the diffusion tensor images to locate fibers next to the fMRI activation spots and next to the tumor using 3D Slicer. A matched control group of healthy subjects is being scanned in order to evaluate the method used (N-BACK test, DTI).Results: For the post-irradiation fMRI the working-memory function within the irradiated area and around the tumor could be demonstrated; out of 5 scanned patients, only 2 were able to perform the working-memory test with a minimum accuracy of 80%. fMRI activation spots could be found within the irradiated area and around the tumor. Evaluation of fiber tracking only possible in a descriptive manner: the symmetry of the fibers was disrupted around the tumor. The 3 patients irradiated to a high dose (60 Gy) could either not perform the test or performed badly. In the run of this feasibility study, many unexpected difficulties needed to be overcome in order to fuse all different datasets (functional information, radiotherapy dose, volumes etc), and distorted data. Results of matched data of healthy controls and validity of the method will be shown.Conclusions:We could demonstrate the feasibility to image memory function by fMRI and fiber tracking in irradiated brain tissue. 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. Future studies are needed to show whether memory imaging is a valid tool to evaluate function and influence of irradiation.

• [Handle]http://hdl.handle.net/2078.1/82088
• [DOI]https://doi.org/10.1016/j.ijrobp.2009.07.552