Pulsed Electron Spin Resonance Ex Situ Probe for Tooth Biodosimetry

An electron spin resonance (ESR) probe that includes a static field source and a microwave resonator for the measurement of paramagnetic defects in tooth enamel is presented. Such defects are known to be a good marker for quantifying the amount of ionizing radiation dose absorbed in the tooth. The probe can measure the tooth when it is positioned just above its outer surface, i.e., in ex situ geometry. It is operated in pulsed mode at a frequency of ~6.2 GHz that corresponds to the magnitude of the static magnetic field of its permanent magnet. A detailed design of the probe is provided, together with its specifications in terms of measurement volume and signal-to-noise-ratio for a typical sample. Experimental results that verify its sensitivity and capability to measure gamma-irradiated teeth are provided. The current minimal detected signal by the probe corresponds to a radiation dose of ~4 Gy.     

Electron Spin Resonance Imaging Probes and a Sample Holder for Thin and Long One-Dimensional Samples

Most electron spin resonance (ESR) experiments involve the use of samples that can be easily placed in millimeter-size tubes and measured efficiently in conventional resonators. However, in some cases, the samples must remain intact, due to which conventional commercial resonators may not be suitable to measure them. Here, we describe a set of three resonators, which can be combined and incorporated as part of a 1-D continuous wave ESR imaging probe to measure and image very thin (~50–500 μm) and very long (~10–30 mm) objects. The dielectric resonators we employ make it possible to greatly enhance spin sensitivity per unit of length––compared to the use of a rectangular ESR cavity, at ~9.3 GHz. In addition, a special sample holder was developed to facilitate the handling and measurement of such thin and long delicate objects, which in our case are the Arabidopsis roots. A detailed design of the resonators, imaging probe, and the sample holder is provided, along with experimental results for the resonator properties, its spin sensitivity, and imaging capability.     

A Miniature Electron Spin Resonance Probehead for Transcutaneous Oxygen Monitoring

Oxygen concentration in the skin is an important clinical indicator for monitoring pathological conditions such as chronic wounds, skin cancer, and peripheral vascular disease. Currently, the only clinically approved method for acquiring these oxygen levels is based on electrochemical measurements that employ Clarke-type electrodes attached to the skin. This technique has many drawbacks and limitations, making it unattractive for standard medical practice and care. Electron spin resonance (ESR), which can obtain the oxygen concentration through measurements of the spin–spin relaxation time (T ₂) of paramagnetic species interacting with molecular oxygen, provides a possible alternative. However, a traditional ESR setup requires a large homogenous static magnetic field source with limited gap between the poles and complicated equipment, making it unattractive for clinical use. Here, we present a new design for a miniature ESR probehead, which is comprised of a specially designed permanent magnet and a small microwave resonator. The small size of the probehead (36 mm diameter cylinder with a height of 24 mm) enables transcutaneous measurements from virtually any part of the skin. Compared to the electrochemical method, this ESR-based approach may provide faster and more accurate readings of oxygen concentration in the skin, making it highly attractive for future clinical use.