Critical oxygen tension in rat brain: a combined 31 P-NMR and EPR oximetry study

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.

Section: Introductionmentioning

confidence: 99%

A parametric approach to spectral–spatial EPR imaging

Som

Potter

Ahmad

et al. 2007

“…Imaging was performed on an L-band (1.2 GHz) EPRI system with a volume resonator with a diameter of 12.6 mm and a useable height of 12 mm. Spectrometer settings were: incident power, 4 mW; scan time per projection, 5.24 s; field of view, 25×25 mm 2 ; gradient strengths, 3.5 and 6 G/cm; modulation amplitudes, 220, 120, 40, 20, 10 mG (with the corresponding measured SNR of 200, 100, 27,16,8). Since spectral shape varies with the modulation amplitude, a separate spectral shape was observed for each modulation amplitude.…”

Section: Epri Experimentsmentioning

confidence: 99%

“…It has a distinct advantage in many medical applications [3][4][5] where it can be used for the direct measurement of both endogenous and introduced free radicals. In the past few years, the potential applications of EPRI to studies of living biological systems have been recognized [6][7][8][9]. Despite all the progress made in the last two decades, the acquisition of high quality images of biological samples has been limited by several technical factors including resolution, sensitivity, and speed of data acquisition [10,11].…”

Section: Introductionmentioning

confidence: 99%

Enhanced resolution for EPR imaging by two-step deblurring

Ahmad

Clymer

Vikram

et al. 2007

The broad spectrum of spin probes used for electron paramagnetic resonance imaging (EPRI) result in poor spatial resolution of the reconstructed images. Conventional deconvolution procedures can enhance the resolution to some extent but obtaining high resolution EPR images is still a challenge. In this work, we have implemented and analyzed the performance of a postacquisition deblurring technique to enhance the spatial resolution of the EPR images. The technique consists of two steps; noniterative deconvolution followed by iterative deconvolution of the acquired projections which are then projected back using filtered backprojection (FBP) to reconstruct a high resolution image. Further, we have proposed an analogous technique for the iterative reconstruction algorithms such as multiplicative simultaneous iterative reconstruction technique (MSIRT) which can be a method of choice for many applications. The performance of the suggested deblurring approach is evaluated using computer simulations and EPRI experiments. Results suggest that the proposed procedure is superior to the standard FBP and standard iterative reconstruction algorithms in terms of meansquare-error (MSE), spatial resolution, and visual judgment. Although the procedure is described for 2D imaging, it can be readily extended to 3D imaging.

“…(4) can be approximated numerically by selecting a suitable distribution of sampling points. (6) where w i the weight associated with the ith projection, and its value depends on the data distribution. The error of approximation depends on the number of projections (N) and the distribution of the projections.…”

Section: Theorymentioning

confidence: 99%

“…Due to its ability for direct detection and characterization of both endogenous and introduced free radicals, EPRI has a distinct advantage in many biological applications [2][3][4][5][6][7]. However, the long acquisition time, especially for 4D spectral-spatial imaging, can be a bottle-neck for many in vivo biological applications.…”

Section: Introductionmentioning

confidence: 99%

Uniform distribution of projection data for improved reconstruction quality of 4D EPR imaging

Ahmad¹,

Vikram²,

Clymer³

et al. 2007

In continuous wave (CW) electron paramagnetic resonance imaging (EPRI), high quality of reconstruction in a limited acquisition time is a high priority. It has been shown for the case of 3D EPRI, that a uniform distribution of the projection data generally enhances reconstruction quality. In this work, we have suggested two data acquisition techniques for which the gradient orientations are more evenly distributed over the 4D acquisition space as compared to the existing methods. The first sampling technique is based on equal solid angle partitioning of 4D space, while the second technique is based on Fekete points estimation in 4D to generate a more uniform distribution of data. After acquisition, filtered backprojection (FBP) is applied to carryout the reconstruction in a single stage. The single-stage reconstruction improves the spatial resolution by eliminating the necessity of data interpolation in multi-stage reconstructions. For the proposed data distributions, the simulations and experimental results indicate a higher fidelity to the true object configuration. Using the uniform distribution, we expect about 50% reduction in the acquisition time over the traditional method of equal linear angle acquisition.