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

Abstract

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.

Development and testing of a CW-EPR apparatus for imaging of short-lifetime nitroxyl radicals in mouse head

“…CW-EPR imaging is a practical solution to the visualization of free radical molecules that have a short relaxation time in animal subjects, and several methods are available to reduce the acquisition time of EPR imaging for small rodents: (i) pulsed EPR method [21][22][23][24], (ii) rapid-scan EPR method [25][26][27][28], (iii) EPR imaging using spinning magnetic field gradients [29,30], and (iv) uniform distribution of projections [12][13][14][15]. While pulsed EPR imaging has been intensively developed for animal imaging over the past decade, it is limited to free radical species that have a longer relaxation time, on the order of microseconds.…”

“…Image-reconstruction based on one-step FBP with a uniform distribution of projections has been reported elsewhere [12][13][14][15]. In image-reconstruction, we used a Hamming filter to suppress noise in a process of deconvolution.…”

“…Recently, Samouilov et al reported in vivo 3D EPR imaging at 1.2 GHz for live mice with an acquisition rate of 1.3 s/projection in the context of EPR/NMR co-registration imaging [11]. In addition to a fast-scan approach, the concept of the uniform distribution of projections is useful for further reducing the acquisition time of a data set of 3D projections [12][13][14][15]. Although there has been significant progress in EPR instrumentation as described above, 3D EPR imaging of short-lifetime nitroxyl radicals, such as TEMPOL, in living animals has not yet been demonstrated.…”

EPR oximetry in three spatial dimensions using sparse spin distribution

“…The average data collection time for the six datasets was 8.8 min/dataset considering a 1.53 G/s scan rate. At the same scan rate considering a spectral window of 12 times the maximum HWHM, the data collection time is 6 h 31 min for 512 projections generated using 4D uniform distribution of points over a hypersphere [52]. The acquisition time reduction is more than 40:1.…”

“…The projection angles were generated using 4D uniform distribution of points over a hypersphere [52]. 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.…”