Estimation of mean and median pO2 values for a composite EPR spectrum

Abstract

Electron paramagnetic resonance (EPR)-based oximetry is capable of quantifying oxygen content in samples. However, for a heterogeneous environment with multiple pO2 values, peak-to-peak linewidth of the composite EPR lineshape does not provide a reliable estimate of the overall pO2 in the sample. The estimate, depending on the heterogeneity, can be severely biased towards narrow components. To address this issue, we suggest a postprocessing method to recover the linewidth histogram which can be used in estimating meaningful parameters, such as the mean and median pO2 values. This information, although not as comprehensive as obtained by EPR spectral-spatial imaging, goes beyond what can be generally achieved with conventional EPR spectroscopy. Substantially shorter acquisition times, in comparison to EPR imaging, may prompt its use in clinically relevant models. For validation, simulation and EPR experiment data are presented.

Electron spin resonance

“…4 Complexities to this method are sometimes encountered, however, and a simple measurement of a peak-to-peak linewidth is not necessarily accurate when the microenvironment is heterogeneous, since the spectrum is composite and can be severely biased toward narrow components. A post-processing procedure is suggested, 5 that can recover the linewidth histogram for a meaningful estimate of the mean and median pO 2 values. Although the information obtained is less comprehensive than that possible from EPR spectral-spatial imaging, the substantially shorter acquisition times may provide an advantage in screening clinical samples.…”

“…Although the information obtained is less comprehensive than that possible from EPR spectral-spatial imaging, the substantially shorter acquisition times may provide an advantage in screening clinical samples. 5 Images may also be obtained [in analogy with magnetic resonance imaging (MRI) at NMR frequencies] using ESR methods, but in contrast to NMR where the magnetically responsive spinning particle (nucleus) is present implicitly, a paramagnetic spin-probe must first be introduced to the subject for ESR imaging. The topic has been reviewed, with particular emphasis on low-frequency spectrometer design, spin-probe development, data acquisition and image-construction for spatial and spectral-spatial imaging and a consideration of the kinds of biological measurements that can indeed be made using such techniques.…”