Vascular Phenotyping of Brain Tumors with MR Microscopy (μMRI)

Arvind P. Pathak¹, Jiangyang Zhang¹, Melina Jones²

The angiogenic phenotype of brain tumors is a critical determinant of their pathophysiology, efficacy of therapy and image contrast in MRI. While histological techniques such as optical microscopy are excellent for imaging microvasculature at the "cellular" scale, they suffer from limited coverage, and 3D blood vessel geometry once destroyed by sectioning requires complex reconstruction. In contrast, in vivo MRI with its sub-millimeter resolution has proved useful for obtaining angiogenic biomarkers such as blood volume and vessel size index at the "systemic" scale. Noninvasive techniques that enable characterization of the angiogenic phenotype at spatial resolutions intermediate to the "cellular" and "systemic" are scarce. Here we describe a new method for characterizing the angiogenic phenotype of a brain tumor model using magnetic resonance microscopy (μMRI), which in combination with different kinds of MR contrast can provide a wealth of information on the brain tumor microenvironment inaccessible by other imaging methods. The high-resolution 3D images of the vasculature generated by μMRI enabled us to characterize morphological differences between the angio-architecture of the contralateral brain and that of the tumor using fractal analysis.