Development and Characterization of NMR and MRI Methods for Assessment of Tumor Oxygen Consumption

Abstract

A common feature of invasive cancers is that they have an upregulation of glucose metabolism and reduced oxygen utilization. The overall goal of this research was to develop a 17Oxygen MRI method to access this aberrant tumor metabolism using a T1ρ weighted pulse sequence on a Bruker NMR Spectrometer. An assessment of the reliability of this pulse sequence for quantifying the ratio of concentrations of H217O (necessary for measuring the metabolic rate in vivo) water in 4 pairs of phantoms was preformed. Specifically, we varied the pH and concentration of Gadopentetic acid (Gd-DTPA) (which modulated T1 and T2 profiles) in 4 different combinations to mimic conditions in the tumor microeviorment. We then used the signal decay data collected at a low and high spin lock power and inserted this data into an eqaution. This equation was then used to compute the ratio of concentration between an enriched and unenriched phantom in each of the 4 pairs.

The two -frequency method was able to quantify [H217O] successfully in the phantoms without Gd-DTPA using the fitted signal data but failed to yield the correct result for the raw data. Thus, to further evaluate these approaches we need employ studies at clinical field strengths. Nevertheless, our results suggest that the quantification of H217O is insensitive to pH but sensitive to changes in T1 and T2.