Overmodulation of projections as signal‐to‐noise enhancement method in EPR imaging

Abstract

A study concerning the image quality in electron paramagnetic resonance imaging in two-dimensional spatial experiments is presented. The aim of the measurements was to improve the signal-to-noise ratio (SNR) of the projections and the reconstructed image by applying modulation amplitude higher than the radical electron paramagnetic resonance linewidth. Data were gathered by applying four constant modulation amplitudes, where one was below 1/3 (Amod = 0.04 mT) of the radical linewidth (ΔBpp = 0.14 mT). Three other modulation amplitude values were used in this experiment, leading to undermodulated (Amod < 1/3 ΔBpp), partially overmodulated (Amod ~ 1/3 ΔBpp) and fully overmodulated (Amod > > 1/3 ΔBpp) projections. The advantages of an applied overmodulation condition were demonstrated in the study performed on a phantom containing four shapes of 1.25 mM water solution of 2, 2, 6, 6-tetramethyl-1-piperidinyloxyl. It was shown that even when the overmodulated reference spectrum was used in the deconvolution procedure, as well as the projection itself, the phantom shapes reconstructed as images directly correspond to those obtained in undermodulation conditions. It was shown that the best SNR of the reconstructed images is expected for the modulation amplitude close to 1/3 of the projection linewidth, which is defined as the distance from the first maximum to the last minimum of the gradient-broadened spectrum. For higher modulation amplitude, the SNR of the reconstructed image is decreased, even if the SNR of the measured projection is increased.

Natural Compounds in Liposomal Nanoformulations of Potential Clinical Application in Glioblastoma

“…The dynamic measurements can be performed and acquire spectra even every 1 ms, if necessary the in vivo experiment as described in [ 52 ]. Moreover, such a solution enables the analysis of the over-modulated signal with the use of multiharmonic analysis, which additionally improves the S/N ratio [ 53 , 54 ]. In addition, chemical reactions take place better in larger volumes under more realistic conditions.…”

Adaptive Modulation Amplitude in 2D Spectral-Spatial EPR Imaging

“…To obtain high spatial resolution in EPRI experiments large magnetic field gradient needs to be applied, which unfortunately causes signal broadening with simultaneous * corresponding author; e-mail: t.czechowski@novilet.eu amplitude decrease. Multiple attempts were made to increase the signal to noise ratio (SNR), which resulted in increasing the measurement speed [9,10], adjusting the detection method [1,11,12] and spectral-spatial imaging technique [13]. To overcome low SNR the amplitude of modulation higher than the 1/3 of the linewidth (referred to as an overmodulation) has been proposed.…”