A microwave resonator for limiting depth sensitivity for electron paramagnetic resonance spectroscopy of surfaces

EPR biodosimetry: challenges and opportunities

This paper briefly examines electron paramagnetic resonance (EPR) techniques to measure dose from exposure to external radiation, assessing their current status, potential future uses and the challenges impacting their progress. We conclude the uses and potential value of different EPR techniques depend on the number of victims and whether they characterize short- or long-term risks from exposure. For large populations, EPR biodosimetry based on in vivo measurements or using co-located inanimate objects offer the greatest promise for assessing acute, life-threatening risk and the magnitude and extent of such risk. To assess long-term risk, ex vivo EPR methods using concentrated enamel from exfoliated teeth are most impactful. For small groups, ex vivo EPR biodosimetry based on available samples of teeth, nails and/or bones are most useful. The most important challenges are common to all approaches: improve the technique's technical capabilities and advance recognition by planning groups of the relative strengths EPR techniques offer for each population size. The most useful applications are likely to be for triage and medical guidance in large events and for radiation epidemiology to evaluate long-term risks.

Benefits and challenges of in vivo EPR nail biodosimetry in a second tier of medical triage in response to a large radiation event

Following large-scale radiation events, an overwhelming number of people will potentially need mitigators or treatment for radiation-induced injuries. This necessitates having methods to triage people based on their dose and its likely distribution, so life-saving treatment is directed only to people who can benefit from such care. Using estimates of victims following an improvised nuclear device striking a major city, we illustrate a two-tier approach to triage. At the second tier, after first removing most who would not benefit from care, biodosimetry should provide accurate dose estimates and determine whether the dose was heterogeneous. We illustrate the value of using in vivo electron paramagnetic resonance nail biodosimetry to rapidly assess dose and determine its heterogeneity using independent measurements of nails from the hands and feet. Having previously established its feasibility, we review the benefits and challenges of potential improvements of this method that would make it particularly suitable for tier 2 triage. Improvements, guided by a user-centered approach to design and development, include expanding its capability to make simultaneous, independent measurements and improving its precision and universality.

The design of X-band EPR cavity with narrow detection aperture for in vivo fingernail dosimetry after accidental exposure to ionizing radiation

For the purpose of assessing the radiation dose of the victims involved in the nuclear emergency or radiation accident, a new type of X-band EPR resonant cavity for in vivo fingernail EPR dosimetry was designed and a homemade EPR spectrometer for in vivo fingernail detection was constructed. The microwave resonant mode of the cavity was rectangular TE101, and there was a narrow aperture for fingernail detection opened on the cavity’s wall at the position of high detection sensitivity. The DPPH dot sample and the fingernail samples were measured based on the in vivo fingernail EPR spectrometer. The measurements of the DPPH dot sample verified the preliminary functional applicable of the EPR spectrometer and illustrated the microwave power and modulation response features. The fingernails after irradiation by gamma-ray were measured and the radiation-induced signal was acquired. The results indicated that the cavity and the in vivo EPR dosimeter instrument was able to detect the radiation-induced signal in irradiated fingernail, and preliminarily verified the basic function of the instrument and its potential for emergency dose estimate after a radiation accident.

Scientific and Logistical Considerations When Screening for Radiation Risks by Using Biodosimetry Based on Biological Effects of Radiation Rather than Dose: The Need for Prior Measurements of Homogeneity and Distribution of Dose

An effective medical response to a large-scale radiation event requires prompt and effective initial triage so that appropriate care can be provided to individuals with significant risk for severe acute radiation injury. Arguably, it would be advantageous to use injury rather than radiation dose for the initial assessment; i.e., use bioassays of biological damage. Such assays would be based on changes in intrinsic biological response elements; e.g., up- or down-regulation of genes, proteins, metabolites, blood cell counts, chromosomal aberrations, micronuclei, micro-RNA, cytokines, or transcriptomes. Using a framework to evaluate the feasibility of biodosimetry for triaging up to a million people in less than a week following a major radiation event, Part 1 analyzes the logistical feasibility and clinical needs for ensuring that biomarkers of organ-specific injury could be effectively used in this context. We conclude that the decision to use biomarkers of organ-specific injury would greatly benefit by first having independent knowledge of whether the person's exposure was heterogeneous and, if so, what was the dose distribution (to determine which organs were exposed to high doses). In Part 2, we describe how these two essential needs for prior information (heterogeneity and dose distribution) could be obtained by using in vivo nail dosimetry. This novel physical biodosimetry method can also meet the needs for initial triage, providing non-invasive, point-of-care measurements made by non-experts with immediate dose estimates for four separate anatomical sites. Additionally, it uniquely provides immediate information as to whether the exposure was homogeneous and, if not, it can estimate the dose distribution. We conclude that combining the capability of methods such as in vivo EPR nail dosimetry with bioassays to predict organ-specific damage would allow effective use of medical resources to save lives.

Developments in Biodosimetry Methods for Triage With a Focus on X-band Electron Paramagnetic Resonance In Vivo Fingernail Dosimetry

Instrumentation and application methodologies for rapidly and accurately estimating individual ionizing radiation dose are needed for on-site triage in a radiological/nuclear event. One such methodology is an in vivo X-band, electron paramagnetic resonance, physically based dosimetry method to directly measure the radiation-induced signal in fingernails. The primary components under development are key instrument features, such as resonators with unique geometries that allow for large sampling volumes but limit radiation-induced signal measurements to the nail plate, and methodological approaches for addressing interfering signals in the nail and for calibrating dose from radiation-induced signal measurements. One resonator development highlighted here is a surface resonator array designed to reduce signal detection losses due to the soft tissues underlying the nail plate. Several surface resonator array geometries, along with ergonomic features to stabilize fingernail placement, have been tested in tissue-equivalent nail models and in vivo nail measurements of healthy volunteers using simulated radiation-induced signals in their fingernails. These studies demonstrated radiation-induced signal detection sensitivities and quantitation limits approaching the clinically relevant range of ≤ 10 Gy. Studies of the capabilities of the current instrument suggest that a reduction in the variability in radiation-induced signal measurements can be obtained with refinements to the surface resonator array and ergonomic features of the human interface to the instrument. Additional studies are required before the quantitative limits of the assay can be determined for triage decisions in a field application of dosimetry. These include expanded in vivo nail studies and associated ex vivo nail studies to provide informed approaches to accommodate for a potential interfering native signal in the nails when calculating the radiation-induced signal from the nail plate spectral measurements and to provide a method for calibrating dose estimates from the radiation-induced signal measurements based on quantifying experiments in patients undergoing total-body irradiation or total-skin electron therapy.

On the Possibility of Miniature Diamond-Based Magnetometers Using Waveguide Geometries

We propose the use of a diamond waveguide structure to enhance the sensitivity of magnetometers relying on the detection of the spin state of nitrogen-vacancy ensembles in diamond by infrared optical absorption. An optical waveguide structure allows for enhanced optical path-lengths avoiding the use of optical cavities and complicated setups. The presented design for diamond-based magnetometers enables miniaturization while maintaining high sensitivity and forms the basis for magnetic field sensors applicable in biomedical, industrial and space-related applications.

Autobiography of James S. Hyde

The papers, book chapters, reviews, and patents by James S. Hyde in the bibliography of this document have been separated into EPR and MRI sections, and within each section by topics. Within each topic, publications are listed chronologically. A brief summary is provided for each patent listed. A few publications and patents that do not fit this schema have been omitted. This list of publications is preceded by a scientific autobiography that focuses on selected topics that are judged to have been of most scientific importance. References to many of the publications and patents in the bibliography are made in the autobiography.

Using Stable Free Radicals to Obtain Unique and Clinically Useful Data In Vivo in Human Subjects

This paper attempts to: (1) provide a critical overview of the challenges and opportunities to extend electron paramagnetic resonance (EPR) into practical applications in human subjects, based on EPR measurements made in vivo; (2) summarize the clinical applications of EPR for improving treatments in cancer, wound healing and diabetic care, emphasizing EPR's unique capability to measure tissue oxygen repeatedly and with particular sensitivity to hypoxia and (3) summarize the capabilities of in vivo EPR to measure radiation dose for triage and medical guidance after a large-scale radiation exposure. The conclusion is that while still at a relatively early stage of its development and availability, clinical applications of EPR already have demonstrated significant value and the field is likely to grow in both the extent of its applications and its impact on significant problems.

Dielectric-Backed Aperture Resonators for X-Band in vivo EPR Nail Dosimetry

A new resonator for X-band in vivo EPR nail dosimetry, the dielectric-backed aperture resonator (DAR), is developed based on rectangular TE₁₀₂ geometry. This novel geometry for surface spectroscopy improves at least a factor of 20 compared to a traditional non-backed aperture resonator. Such an increase in EPR sensitivity is achieved by using a non-resonant dielectric slab, placed on the aperture inside the cavity. The dielectric slab provides an increased magnetic field at the aperture and sample, while minimizing sensitive aperture resonance conditions. This work also introduces a DAR semi-spherical (SS)-TE₀₁₁ geometry. The SS-TE₀₁₁ geometry is attractive due to having twice the incident magnetic field at the aperture for a fixed input power. It has been shown that DAR provides sufficient sensitivity to make biologically relevant measurements both in vitro and in vivo Although in vivo tests have shown some effects of physiological motions that suggest the necessity of a more robust finger holder, equivalent dosimetry sensitivity of approximately 1.4 Gy has been demonstrated.