Electron Paramagnetic Resonance Oxygen Images Correlate Spatially and Quantitatively with Oxylite Oxygen Measurements

Abstract

Tumor oxygenation predicts cancer therapy response and malignant phenotype. This has spawned a number of oxymetries. Comparison of different oxymetries is crucial for the validation and understanding of these techniques. Electron paramagnetic resonance (EPR) imaging is a novel technique for providing quantitative high-resolution images of tumor and tissue oxygenation. This work compares sequences of tumor pO 2 values from EPR oxygen images with sequences of oxygen measurements made along a track with an Oxylite oxygen probe. Four-dimensional (three spatial and one spectral) EPR oxygen images used spectroscopic imaging techniques to measure the width of a spectral line in each image voxel from a trityl spin probe (OX063, Amersham Health R&D) in the tissues and tumor of mice after spin probe injection. A simple calibration allows direct, quantitative translation of each line width to an oxygen concentration. These four-dimensional EPR images, obtained in 45 minutes from FSa fibrosarcomas grown in the legs of C3H mice, have a spatial resolution of f1mm and oxygen resolution of f3 Torr. The position of the Oxylite track was measured within a 2-mm accuracy using a custom stereotactic positioning device. A total of nine images that involve 17 tracks were obtained. Of these, most showed good correlation between the Oxylite measured pO 2 and a track located in the tumor within the uncertainties of the Oxylite localizability. The correlation was good both in terms of spatial distribution pattern and pO 2 magnitude. The strong correlation of the two modalities corroborates EPR imaging as a useful tool for the study of tumor oxygenation.

Effect of Cholesterol on Distribution of Stable, Hydrophobic Perchlorotriphenylmethyl Triethylester Radical Incorporated in Lecithin Liposomal Membranes

“…26) The unusual behavior of PTM-TE is probably attributable to Cl · · · Cl and p· · · p interactions between aromatic rings of neighboring radicals. 15) Aggregate formations of the derivatives of perchlorotriphenylmethyl radical have been observed in dichloromethane/toluene (1 : 1 v/v) and explained by the above interactions, which had always been observed in crystal structures of the radical derivatives. 27) The molecular shape of PTM-TE may also contribute to the phase separation.…”

“…13) Therefore, they have been injected intravenously into experimental animals, and in vivo oxygen maps have been imaged with OMRI 14) and ESR imaging. 15) Furthermore, water-soluble trityl radicals were also utilized as probes of superoxide generation 12) and pH 16) for ESR spectroscopy and its imaging. In contrast to hydrophilic trityl radicals, only a few reports have described the application of hydrophobic ones.…”

Object dependent sweep width reduction with spectral–spatial EPR imaging

“…1d describes the reduction of sweep width when the spatial FOV is larger than the ROI. This leads to the following definition of sweep width as (6) where k = ΔL′/ΔL, and ΔB = cΔL. This value of ΔB SW is clearly smaller than the previous definition.…”

“…(1) and Eq. (6). Both the conventional method and the reduced-sweep method required maximum gradient of 30 mT/m.…”

“…Useful information concerning local fluid environment is reported in the EPR spectra. One can design a variety of spin probes to be sensitive to specific aspects of physiology including temperature, pH, microviscosity, tissue oxygenation, and a distribution of exogenous paramagnetic species [1][2][3][4][5][6]. For an application of EPRI to in vivo physiology it is important to complete data acquisition in minimum time.…”