Accelerated dynamic EPR imaging using fast acquisition and compressive recovery

Abstract

Electron paramagnetic resonance (EPR) allows quantitative imaging of tissue redox status, which provides important information about ischemic syndromes, cancer and other pathologies. For continuous wave EPR imaging, however, poor signal-to-noise ratio and low acquisition efficiency limit its ability to image dynamic processes in vivo including tissue redox, where conditions can change rapidly. Here, we present a data acquisition and processing framework that couples fast acquisition with compressive sensing-inspired image recovery to enable EPR-based redox imaging with high spatial and temporal resolutions. The fast acquisition (FA) allows collecting more, albeit noisier, projections in a given scan time. The composite regularization based processing method, called spatio-temporal adaptive recovery (STAR), not only exploits sparsity in multiple representations of the spatio-temporal image but also adaptively adjusts the regularization strength for each representation based on its inherent level of the sparsity. As a result, STAR adjusts to the disparity in the level of sparsity across multiple representations, without introducing any tuning parameter. Our simulation and phantom imaging studies indicate that a combination of fast acquisition and STAR (FASTAR) enables high-fidelity recovery of volumetric image series, with each volumetric image employing less than 10 s of scan. In addition to image fidelity, the time constants derived from FASTAR also match closely to the ground truth even when a small number of projections are used for recovery. This development will enhance the capability of EPR to study fast dynamic processes that cannot be investigated using existing EPR imaging techniques.

Development of a fast‐scan EPR imaging system for highly accelerated free radical imaging

“…Even with an air core magnet, implementation of an additional large fast‐sweep coil powered by a separate power supply is also associated with certain technical difficulties, including the need for the use of sophisticated field‐driving current amplifiers, stabilization of the current in the main field circuitry to overcome distortions caused by coupling with the sweep field, and the need for proper timing of data acquisition with the magnetic field. Recent developments in fast‐field‐scanning CW‐EPR reduced the acquisition time of single‐EPR projection to tens of milliseconds …”

“…Recent developments in fast-field-scanning CW-EPR reduced the acquisition time of single-EPR projection to tens of milliseconds. 18,23,44,[47][48][49] The short times required for fast-scan sweep of the magnetic field also determine the rate of data transfer, which is needed to acquire the given projection. Thus, fast-scan projection acquisition requires major acceleration of the acquisition data transfer, and of the control waveform data from the control computer to acquisition electronics.…”

“…The magnetic field B 0 is generated by a water‐cooled spherical solenoid resistive magnet, with an axial opening of 29 cm in diameter, capable of generating a magnetic field up to 0.12 T (Figure ). The design was originally reported by Hoult et al and later adapted for EPR experiments . The magnet is constructed on 2 aluminum‐cast hemispherical formers.…”

“…The design was originally reported by Hoult et al 16 and later adapted for EPR experiments. 17,18 The magnet is constructed on 2 aluminum-cast hemispherical formers. The magnet provides homogeneity of better than 3 ppm over a spherical volume of 10 cm.…”

Molecular Probes for Evaluation of Oxidative Stress by In Vivo EPR Spectroscopy and Imaging: State-of-the-Art and Limitations

“…However, recent advances in EPR technology suggest that this technological lock will soon be removed. Pulsed EPR [18], rapid-scan EPR [19], and fast field scanning CW EPR associated with improved image reconstruction procedures [20][21][22] considerably reduce the acquisition time (tridimensional EPR images with a submillimetric resolution are obtained in one or two minutes). Secondly, available molecular probes are extremely limited in number, they have a poor biostability, and their lack of specificity makes the interpretation of observations difficult.…”