Low energy photon attenuation measurements of hydrophilic materials for tissue equivalent phantoms

The object of the study was to measure the linear attenuation coefficients of hydrophilic materials with the aim of investigating their suitability as tissue equivalent materials. Hydrophilic materials are used in the ophthalmic industry for the manufacture of soft contact lenses. Hydrophilic materials have the trade name "Biogel" and are commonly known as hydrogels. Two types of hydrophilic material were tested, ED4C (72% water uptake by weight) and EDIS (60% water uptake by weight). The measurements were obtained using gamma-ray photons of energy 59.5 keV, and x-ray photons of energies 44.23 and 17.44 keV. Measurements were made for material types ED4C and EDIS in both the dry and fully hydrated state. Measurements were also made on powdered samples of ED4C at different hydration levels using a photon energy of 17.44 keV and powdered samples of EDIS at different hydration levels using a photon energy of 59.5 keV. The precision of the measurements was approx. 1%. It was found that material ED4C has linear attenuation coefficients that closely match those of the calculated values for soft tissue across the range of energies used.