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Assessing Glioma Cell Infiltration Using A Fiber Coherence Index: A DTI Study

Introduction Malignant glioma is one of the most lethal tumors that strikes adults in their prime. Despite advances in diagnosis and treatment, prognosis remains dismal largely due to the infiltrating nature of the tumor cells and the inability to detect these cells using conventional imaging techniques. It has been reported that glioma infiltration occurs preferentially along the white-matter fiber tracts (1). A common site of infiltration is the corpus callosum where glioma can extend across the midline to spread to other locations in the brain. With tumor invasion, the organized structure of a fiber tract can lose its structural integrity and directional coherence, leading to changes in the diffusion properties of water molecules. Diffusion tensor imaging (DTI) is a powerful tool for characterizing tissue diffusion in vivo (2). Recently, several groups employed DTI for the assessment of tumor cell infiltration in glioma patients (3-5). These studies have focused on measuring changes in a scalar diffusion anisotropy index, such as the mean diffusivity, fractional anisotropy (FA), or relative anisotropy (RA). While this approach can be useful in evaluating lowgrade gliomas without peritumoral vasogenic edema (PVE), it often fails on patients with high grade gliomas (WHO grade III and IV) due to the presence of PVE, which can also cause a substantial decrease in diffusion anisotropy. Since the edematous regions are not always infiltrated with tumor, a very high false positive rate occurs when using FA or RA to identify tumor infiltration. In this study, we have used an alternative DTI parameter, regional fiber coherence index (r-FCI), for assessing tumor cell infiltration, and compared its performance with that of FA. Our results suggest that r-FCI is advantageous over FA in delineating white-matter fiber tracts infiltrated by tumor cells in the presence of vasogenic edema.