Correlating MALDI-IMS and MRI diffusion measurements in the C6 rat glioma tumor model

Abstract

The processes of tumor growth and treatment response are associated with the upregulation of numerous proteins [1, 2], yet current clinical imaging methods of cancer characterization monitor only gross morphology [3, 4]. This study combines in vivo diffusion weighted magnetic resonance imaging (MRI) with matrix-assisted laser desorption ionization (MALDI) analysis of healthy and tumorous ex vivo specimens in order to examine the proteomic influences on the apparent diffusion coefficient provided by MRI. Spatial co-registration of MALDI and ADC datasets enables examination of the statistical correlations between the two metrics [5] in the hopes of elucidating the proteomic signatures that give rise to particular ADC values. ADC and MALDI data were acquired for two rats, one control and one in which a C6 glioma model of brain cancer was implanted. Principal component analysis was conducted to determine the degree of spatial correlation between the ADC and protein measurements. It was found that ADC and MALDI data correlated significantly (p-value of 0.05) in 44.0% of 114 regions of interest (ROIs) in the two rats. Protein profiles were identified which correlated with statistically similar ADCs in selected ROIs for each rat. The results of this study are consistent with the theory that protein expression in both healthy and tumorous rat brain tissue is a molecular-level source of contrast in diffusion-weighted MRI.