Brain Tumors: Clinical Applications of Functional Magnetic Resonance Imaging and Diffusion Tensor Imaging

Abstract

One of the most exciting methodologies in the clinical neurosciences evolving toward the end of the twentieth century was functional magnetic resonance imaging (fMRI). Whereas MRI is used to produce structural images of subjects’ brain the functional component allows an in vivo measurement of brain activity. fMRI has provided new insights into human cognitive functions. Till now it was mainly used for basic scientific questions and has provided foundations for at least five large-scale neurocognitive networks identified in the human brain, namely for spatial attention, language, memory-emotion, executive function, and face and object recognition. In addition, white matter tractography based on diffusion tensor imaging (DTI) has become a well-accepted noninvasive tool for exploring the white matter architecture of the human brain in vivo. These two MR techniques are complementary in describing functional and anatomical components of grey and white matters. Furthermore, fMRI is useful to define the seed regions for DTI, because large interindividual anatomical variations make it difficult to define tracking seed areas based reliably on macroanatomical landmarks. An accurate definition of seed regions for the reconstruction of a specific neuronal pathway becomes even more challenging in patients suffering from space occupying brain lesions due to the displacement of the tissue and the distortion of anatomical landmarks around the lesion. Therefore, fMRI and DTI play a growing role in clinical neuroimaging with increasing applications in neurosurgical planning using neuronavigation. By means of neuronavigational devices both modalities can intuitively be used during surgical procedures. The goal of tumor surgery is to optimize the extent of resection, while minimizing the risk of a permanent neurological deficit. Because the tumor may infiltrate eloquent areas and because of major intersubject anatomical and functional variability, cortical functional organization, subcortical connectivity and brain plasticity can be studied at an individual scale. Presurgical functional neuroimaging and tractography can show the relationships between eloquent regions and the tumor, and consequently the cortical and subcortical structures essential for brain functions can be identified and preserved. In addition, post-operative control and longitudinal neuroimaging studies are important to study adaptive changes in network behaviour and to monitor the effects of brain plasticity.