Diffusion imaging of brain tumors

• Published in: NMR in biomedicine Vol. 23; no. 7; pp. 849 - 864
• Main Authors: Maier, Stephan E., Sun, Yanping, Mulkern, Robert V.
• Format: Journal Article
• Language: English
• Published: Chichester, UK John Wiley & Sons, Ltd 01.08.2010
• Subjects: Animals; anisotropy; biexponential; Brain - anatomy & histology; Brain - pathology; Brain Neoplasms - diagnosis; Brain Neoplasms - pathology; brain tumor; Brain tumors; Data processing; diffusion; Diffusion coefficient; Diffusion Magnetic Resonance Imaging - methods; Dislocation; Drugs; Edema; gray matter; Humans; Image Interpretation, Computer-Assisted - methods; kurtosis; Magnetic resonance imaging; Membrane structure; Mobility; N.M.R; Neuroimaging; Probes; spatial discrimination; stretched exponential; Substantia alba; Therapeutic applications; white matter
• ISSN: 0952-3480; 1099-1492; 1099-1492
• DOI: 10.1002/nbm.1544

MRI offers a tremendous armamentarium of different methods that can be employed in brain tumor characterization. MR diffusion imaging has become a widely accepted method to probe for the presence of fluid pools and molecular tissue water mobility. For most clinical applications of diffusion imaging, it is assumed that the diffusion signal vs diffusion weighting factor b decays monoexponentially. Within this framework, the measurement of a single diffusion coefficient in brain tumors permits an approximate categorization of tumor type and, for some tumors, definitive diagnosis. In most brain tumors, when compared with normal brain tissue, the diffusion coefficient is elevated. The presence of peritumoral edema, which also exhibits an elevated diffusion coefficient, often precludes the delineation of the tumor on the basis of diffusion information alone. Serially obtained diffusion data are useful to document and even predict the cellular response to drug or radiation therapy. Diffusion measurements in tissues over an extended range of b factors have clearly shown that the monoparametric description of the MR diffusion signal decay is incomplete. Very high diffusion weighting on clinical systems requires substantial compromise in spatial resolution. However, after suitable analysis, superior separation of malignant brain tumors, peritumoral edema and normal brain tissue can be achieved. These findings are also discussed in the light of tissue‐specific differences in membrane structure and the restrictions exerted by membranes on diffusion. Finally, measurement of the directional dependence of diffusion permits the assessment of white matter integrity and dislocation. Such information, particularly in conjunction with advanced post‐processing, is considered to be immensely useful for therapy planning. Diffusion imaging, which permits monoexponential analysis and provides directional diffusion information, is performed routinely in brain tumor patients. More advanced methods require improvement in acquisition speed and spatial resolution to gain clinical acceptance. Copyright © 2010 John Wiley & Sons, Ltd. In most brain tumors, when compared with normal brain tissue, water diffusion measured with conventional diffusion MRI is elevated. The presence of peritumoral edema, which also exhibits an elevated diffusion coefficient, often precludes the delineation of the tumor on the basis of this diffusion information alone. MR diffusion measurements performed over an extended range of diffusion weighting, however, permit the superior separation of malignant brain tumors, peritumoral edema and normal brain tissue.