A parametric approach to spectral–spatial EPR imaging

Abstract

Continuous wave electron paramagnetic resonance imaging for in vivo mapping of spin distribution and spectral shape requires rapid data acquisition. A spectral-spatial imaging technique is presented that provides an order of magnitude reduction in acquisition time, compared to iterative tomographic reprojection. The proposed approach assumes that spectral shapes in the sample are wellapproximated by members from a parametric family of functions. A model is developed for the spectra measured with magnetic field modulation. Parameters defining the spin distribution and spectral shapes are then determined directly from the measurements using maximum a posteriori probability estimation. The approach does not suffer approximation error from limited sweep width of the main magnetic field and explicitly incorporates the variability in signal-to-noise ratio versus strength of magnetic field gradient. The processing technique is experimentally demonstrated on a one-dimensional phantom containing a nitroxide spin label with constant g-factor. Using an L-band EPR spectrometer, spectral shapes and spin distribution are accurately recovered from two projections and a spectral window which is comparable to the maximum linewidth of the sample.

EPR oximetry in three spatial dimensions using sparse spin distribution

“…), object geometry, and collection angles. Sensitivity of the estimated values can be predicted using the Cramèr-Rao (CR) lower bound [41]. Further, the CR bound analysis informs the choice of projection angles and the trade-off between more angles and higher SNR per angle.…”

“…Following previous 4D spectral-spatial developments [30], we describe the acquired spectra in terms of the Radon transform of a spectral-spatial object, assuming a small amplitude Zeeman modulation and lock-in detection of the absorption first harmonic. Our 4D forward model is an extension of the 2D model described in [41].…”

“…For each set of angles a random initialization of projection angles was used so that projection angles corresponding to the final uniform distributions were different for each set. Since the information content of a low gradient projection is small [41], the permissible spectral angle range was selected to be 30-81.47°. The upper limit is a hardware constraint on maximum gradient strength.…”

Nitroxide Spin-Labelling and Its Role in Elucidating Cuproprotein Structure and Function

“…This leads to a lack of temporal sensitivity which can mask important biological events. Recent technological advances have reduced acquisition times for spectral-spatial imaging thereby making the technique attractive for biologically rapid events and even for low signal-to-noise probes [67][68][69][70].…”

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

“…2 and 3 are true and estimated histograms for 2 of the 50 runs considered. Also, note that the error variance for an estimated histogram will be higher for components with larger linewidths [20] because of their lower SNR. This effect is observed in (Fig.…”