Electron paramagnetic resonance in human fingernails: the sponge model implication

Area of Science:

• Biophysics
• Dosimetry
• Materials Science

Background:

• Electron paramagnetic resonance (EPR) fingernail dosimetry is hindered by non-radiation signals (mechanically induced signal [MIS] and background signal [BKS]) that overlap the radiation-induced signal (RIS).
• These interfering signals make accurate dose measurements below 5 Gy extremely difficult.
• Fingernail tissue's mechanical properties, including its sponge-like behavior and water absorption, are crucial for understanding these signals.

Purpose of the Study:

• To investigate the nature of the mechanically induced signal (MIS) and background signal (BKS) in fingernail dosimetry.
• To develop methods for isolating and distinguishing these non-radiation signals from the radiation-induced signal (RIS).
• To establish a foundation for accurate in vivo EPR dosimetry using fingernails.

Main Methods:

• Development and implementation of three distinct methods for isolating MIS and BKS.
• Modeling fingernail tissue as a deformed sponge to understand mechanical stress absorption.
• Investigating the effect of water soaking on signal components and measuring fingernail porosity.

Main Results:

• Fingernail tissue deformation, analogous to a sponge, explains MIS and BKS as responses to elastic and plastic stresses.
• Soaking fingernail samples in water for 10 minutes effectively eliminates the MIS without significantly altering the RIS.
• Pre-soaked (unstressed) fingernails exhibit distinct dosimetric properties compared to stressed samples, including higher signal stability and less intense non-radiation components.

Conclusions:

• The study proposes a new interpretation of mechanical deformation in fingernails, enabling differentiation between MIS and RIS.
• Water soaking is identified as a practical method to remove interfering mechanical signals, paving the way for improved EPR dosimetry.
• Findings support the potential for accurate in vivo EPR dosimetry using pre-soaked fingernails, overcoming limitations of previous methods.