A thorough investigation of biomimetic polydopamine (PDA) by Electron Paramagnetic Resonance (EPR) is shown. In addition, temperature dependent spectroscopic EPR data are presented in the range 3.8-300 K. Small discrepancies in magnetic susceptibility behavior are observed between previously reported melanin samples. These variations were attributed to thermally acitivated processes. More importantly, EPR spatial-spatial 2D imaging of polydopamine radicals on a phantom is presented for the first time. In consequence, a new possible application of polydopamine as EPR imagining marker is addressed.

A linear magnetic field scan driver was developed to provide a rapidly scanning magnetic field for use in electron paramagnetic resonance (EPR) spectroscopy. The driver consists of two parts: a digitally synthesized ramp waveform generator and a power amplifier to drive the magnetic field coils. Additionally, the driver provides a trigger signal to a data collection digitizer that is synchronized to the ramp waveform. The driver can also drive an arbitrary current waveform supplied from an external source. The waveform generator is computer controlled through a serial data interface. Additional functions are controlled by the user from the driver front panel. The frequency and amplitude of the waveform are each separately controlled with 12-bit resolution (one part in 4,096). Several versions of the driver have been built with different frequency and amplitude ranges. Frequencies range from 500 to 20,000 Hz. Field sweep amplitudes range up to 80 G pp . This article also gives a brief description of the field coils that are driven by the driver.

In rapid scan EPR the changing magnetic field creates a background signal with components at the scan frequency and its harmonics. The amplitude of the background signal increases with scan width and is more significant for weak EPR signals such as are obtained in the presence of magnetic field gradients. A procedure for distinguishing this background from the EPR signal is proposed, mathematically described, and tested for various experimental conditions.

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A new algorithm for EPR imaging oximetry is described and tested with experimental data for the case of one spatial and one spectral dimension. A single species with variable linewidth is assumed. Instead of creating a 2D image, two one-dimensional profiles are reconstructed: the concentration of the radical and the corresponding oxygen concentration, which reduces the dimensionality of the problem. The algorithm (i) seeks to minimize the discrepancy between experimental data and projections calculated from the profiles and (ii) uses Tikhonov regularization to constrain the smoothness of the results. This approach controllably smoothes profiles rather than the data, while preserving sharp features.

The imaging of the biodistribution and pharmacokinetics is critical in understanding the complexity of drug delivery mechanisms, the status of the disease, and the monitoring of the treatment progress. The imaging techniques, such as magnetic resonance imaging, computed tomography, and positron emission tomography, are suitable for clinical applications. However, with regards to the biodistribution and pharmacokinetics, their availability is often limited due to the requirements of ionizing radiation or high magnetic fields, low spatial and temporal resolution (applicable for animals), and high maintenance costs. Electron paramagnetic resonance (EPR) imaging is a technique that allows for the minimal invasive mapping of unique parameters, such as the oxygen concentration, the redox state, the thiol concentration, or the pH level, in vivo. In this work, a high temporal resolution 3D EPR imaging technique was used for assessing the trityl spin probe pharmacokinetics in mice. The results demonstrate the preliminary outcomes in the application of EPR imaging for the comparison of the trityl spin probe pharmacokinetics between that of a healthy mouse and a tumor-bearing mouse. This study will stimulate further investigation into the use of imaging strategies, such as EPR imaging, to analyze pharmacokinetics.

To be able to perform a two-dimensional study of free radical distribution by the continuous-wave electron paramagnetic resonance method in the X-band, special coils producing a magnetic gradient of 8 G/mm have been designed and construeted. The EPR spectra recorded for this gradient were subjected to the procedure of deconvolution in order to elieit information on the concentration of the radical distribution. The data obtained were used as the souree file of the program reconstructing the image. The reconstruction was based on the iterative simultaneous algebraic reeonstruction teehnique (Andersen A.H., Kak A.C.: Ultrason. lmag. 6, 81-94, 1984). The quality of the generated images depends on the angle of the sample axis to the gradient direction set by a goniometer and on the deconvolution procedures applied. The first tests on artificially generated phantoms indicated a dependence of the obtained images on the magnetic field gradients apptied. The determined spatial distribution of radicals has confirmed their uniform distribution in the sample. The preliminary tests were performed for diphenyl-picrylhydrazyl. Having proved the reliability of the method, analogous measurements were also performed for plyphenylene sulphide PPS-V1 and indicated a homogeneous distribution of radicals in the whole volume of the sample. The images obtained confirmed the uniforro distribution of the radicals.

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