Electron paramagnetic resonance in human fingernails: the sponge model implication

Abstract

The most significant problem of electron paramagnetic resonance (EPR) fingernail dosimetry is the presence of two signals of non-radiation origin that overlap the radiation-induced signal (RIS), making it almost impossible to perform dose measurements below 5 Gy. Historically, these two non-radiation components were named mechanically induced signal (MIS) and background signal (BKS). In order to investigate them in detail, three different methods of MIS and BKS mutual isolation have been developed and implemented. After applying these methods, it is shown here that fingernail tissue, after cut, can be modeled as a deformed sponge, where the MIS and BKS are associated with the stress from elastic and plastic deformations, respectively. A sponge has a unique mechanism of mechanical stress absorption, which is necessary for fingernails in order to perform its everyday function of protecting the fingertips from hits and trauma. Like a sponge, fingernails are also known to be an effective water absorber. When a sponge is saturated with water, it tends to restore to its original shape, and when it loses water, it becomes deformed again. The same happens to fingernail tissue. It is proposed that the MIS and BKS signals of mechanical origin be named MIS1 and MIS2 for MISs 1 and 2, respectively. Our suggested interpretation of the mechanical deformation in fingernails gives also a way to distinguish between the MIS and RIS. The results obtained show that the MIS in irradiated fingernails can be almost completely eliminated without a significant change to the RIS by soaking the sample for 10 min in water. The proposed method to measure porosity (the fraction of void space in spongy material) of the fingernails gave values of 0.46-0.48 for three of the studied samples. Existing results of fingernail dosimetry have been obtained on mechanically stressed samples and are not related to the "real" in vivo dosimetric properties of fingernails. A preliminary study of these properties of pre-soaked (unstressed) fingernails has demonstrated their significant difference from fingernails stressed by cut. They show a higher stability signal, a less intensive non-radiation component, and a nonlinear dose dependence. The findings in this study set the stage for understanding fingernail EPR dosimetry and doing in vivo measurements in the future.

Comparison of Continuous Wave and Rapid Scan X-band Electron Paramagnetic Resonance of Irradiated Clipped Fingernails

“…The CW results are in full agreement with previously published ones (Figure 2 in reference (6) ) and indicate that only background and radiation-induced components are present in the spectra. The lineshapes are similar for the three dose levels.…”

“…A notable, non-radiation signal is the so-called mechanically induced signal, MIS, which is caused by the stress imposed on the fingernail during clipping. A fast and simple procedure of sample preparation that drastically reduces the impact of mechanical stress on dose measurements in fingernails has been developed (6) . It consists of a brief (10-15 min) soaking of fingernails in water followed by drying.…”

“…1-2 mm × 2-3 mm. As recommended in reference (6) , to eliminate (or significantly reduce) the mechanical stress caused by cutting, all collected fingernail clippings were soaked in distilled water for 10 min and dried on paper towels for 10 min. A pooled set of the treated fingernail clippings was split into three samples, one sample was kept unirradiated as a control and two other samples were irradiated using a calibrated 137 Cs source to 5 and 10 Gy.…”

“…There is renewed interest in quantitation of these electron paramagnetic resonance (EPR) signals because of their potential utility for measuring radiation dose, especially for medical triage in situations where there is a need to determine whether large numbers of people were exposed to medically significant doses of radiation (3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13) . Fingernail dosimetry has been applied to three cases of accidental radiation exposure (14) .…”

EPR measurements of fingernails in Q-band

“…Significant progress in the development of electron paramagnetic resonance (EPR) dosimetry in fingernails has been achieved in recent years (see Reyes et al, 2008Reyes et al, , 2009Romanyukha et al, 2007bRomanyukha et al, , 2010Trompier et al, 2007Trompier et al, , 2009. Chemically, fingernails are mainly composed of alpha keratin, a protein made of three alpha helical peptide chains, twisted in a left-handed coil that is strengthened by disulfide bridges from adjacent cystein groups.…”