Radiation dose and image quality in K‐edge subtraction computed tomography of lung in vivo

K‐edge subtraction computed tomography (KES‐CT) allows simultaneous imaging of both structural features and regional distribution of contrast elements inside an organ. Using this technique, regional lung ventilation and blood volume distributions can be measured experimentally in vivo. In order for this imaging technology to be applicable in humans, it is crucial to minimize exposure to ionizing radiation with little compromise in image quality. The goal of this study was to assess the changes in signal‐to‐noise ratio (SNR) of KES‐CT lung images as a function of radiation dose. The experiments were performed in anesthetized and ventilated rabbits using inhaled xenon gas in O₂ at two concentrations: 20% and 70%. Radiation dose, defined as air kerma (K_a), was measured free‐in‐air and in a 16 cm polymethyl methacrylate phantom with a cylindrical ionization chamber. The dose free‐in‐air was varied from 2.7 mGy to 8.0 Gy. SNR in the images of xenon in air spaces was above the Rose criterion (SNR > 5) when K_a was over 400 mGy with 20% xenon, and over 40 mGy with 70% xenon. Although in human thorax attenuation is higher, based on these findings it is estimated that, by optimizing the imaging sequence and reconstruction algorithms, the radiation dose could be further reduced to clinically acceptable levels.     

Performance comparison of OSLD (Al2O3:C) and TLD (LiF:Mg,Cu,P) in accreditation proficiency testing

The U.S. Navy uses a dosimetric system, which employs the LiF:Mg,Cu,P thermoluminescence dosimeters (TLDs), developed and produced by Thermo Fisher Scientific. Every two years, the Naval Dosimetry Center (NDC) performs proficiency testing to maintain its national accreditation. Since 2007, the U.S. Navy has also tested InLight Basic - OSLN Optically Stimulated Luminescence Al₂O₃:C dosimeters (OSLD) manufactured by Landauer. In 2011 and 2013, the Naval Dosimetry Center performed proficiency testing for both systems. Here we present a comparison of the performance of TLDs (LiF:Mg,Cu,P) and OSLDs (Al₂O₃:C) in five categories of proficiency testing. The testing included irradiation with photons, neutrons, beta particles and selected mixtures of these radiations. All irradiations were performed at the Pacific Northwest National Laboratory (PNNL). The delivered doses were not reported to the NDC. The official comparison of delivered and reported doses was conducted by PNNL in terms of dose bias and its standard deviation for each category of accreditation. In total, the NDC reported to the PNNL doses for 147 dosimeters of each type (TLD and OSLD). Both NDC tested dosimetric systems have passed established limits. The comparison of OSLD and TLD system performance in each category is discussed. Advantages and disadvantages of both systems are analyzed.     

MCNP simulations of a glass display used in a mobile phone as an accident dosimeter

It has been demonstrated that glass display of mobile phones can be used as a device for accident dosimetry. Published studies concentrated on the experimental investigation of parts of the glass display. In the work presented here, the experimental results are compared with results of radiation transport calculations using the Monte Carlo code MCNP5.An experimental setup of an irradiation of an extracted glass display is simulated. The simulation is then extended to a simulation of a modern day mobile phone consisting of all major parts. Simulations are performed for various irradiation conditions and different geometric and material properties.The results of the simulation show a good agreement with the experiments for an extracted glass sample as well as for an actual modern mobile phone. The glass display is exposed to radiation in various angular and energy distributions. Simulated results were compared to experimentally determined results. The effects of the irradiation condition on the photon energy dependence were investigated and variations in the material constants of the display glass composition were discussed. This work affirms the usability of a mobile phone as a versatile and flexible accident radiation detector.     

Algorithm Analysis on MMW Dosimetry for the Cell Monolayer Cultered in Petri Dish with the FDTD Method

Four algorithms are developed to help the dosimetry study for experiments on millimeter-wave (MMW) biological effects on cells in vitro with the finite-difference time-domain (FDTD) method. Their performances in evaluating the MMW irradiation dose are displayed and compared, including the induced current density and the specific absorption rate (SAR), that are distributed over the cell monolayer cultured in Petri dish. With the discussion on individual characteristics of the algorithms, the conclusion is reached that an appropriate algorithm is essential in providing accurate data on the MMW irradiation dose by way of numerical calculation, which should be considered carefully in related experiments.     

AlanineESR Dosimetry system for routine use in radiation processing

A new alanine-polystyrene (PS) dosimeter prepared with simplified molding procedure and an automatic desk-top dose-reader of alanine dosimeter were developed for the purpose of routine use. Combination of these two allows us to apply a reliable alanine/ESR dosimetry system to routine dosimetric process control in industrial gamma radiation processing.     

Current and charge collector as e beam energy and dose meter for industrial use

Many parameters of interest for characterizing a high power processing electron beam in air can be measured using a charge density detector system.

A rugged detector head placed in or moved through an electron beam may be used to measure the effective beam energy, current density within the beam and charge delivered to the product plane.

The liquid cooled detector may also be used to calibrate routine dosimeter for electron beam use over the full range of doses and dose rates currently used for industrial purposes.

Further uses for the detector as an accelerator control sensor element are also discussed.     

Optoelectronic reader for CET dosimeter, a radiation accident chemical dosimetry system

The use of chlorobenzene–ethanol–trimethylpentane solution (CET) in radiation dosimetry is based on radiolytic formation of hydrochloric acid which protonates a pH indicator, thymolsulphonphthalein. The high molar absorptivity of its red form at 552 nm is responsible for a high sensitivity of the system: doses in the range 0.2–15 Gy can be measured. Together with a visual colour comparator it has formed a personnel dosimetry system suitable for accident and civil defense use.

A newly constructed optoelectronic reader with two two-colour light emitting diodes (550 and 690 nm) as light sources and a silicone photocell as a detector uses the differential absorbance at these two wavelengths as the response. The response is a direct function of dose and can be recorded and processed electronically.     

The operational benefits of integrated PC control of gamma irradiation plants

Compared with the traditional PLC control systems used on many gamma irradiation plants, the semi-intelligent decision making capabilities of a fully integrated PC control system can bring many benefits to the plant operator.

The authors will describe how plant operation is fully automatic with the PC control providing all the input-output data required to run the plant efficiently and safely. Detailed product tracking, with live on-screen data, can be incorporated to give both plant operator and product manufacturer complete confidence in the irradiation process. Advanced features such as on-line diagnostics and mechanical part failure prediction are also described.

Also available is automated dosimetry, reducing the opportunity for human error, whilst at the same time saving on staff costs and providing highly professional dose validation reports and comprehensive routine dosimetry documentation.

The benefits of PURIDEC's PC control system are not only available with its new plants. The system can be supplied as an upgrade to plants of all ages and design giving the current operator all the benefits described in the paper.     

TL and OSL dosimetric properties of Opal gemstone for gamma radiation dosimetry

In this work, the response of the natural material Opal was studied in relation to its thermoluminescence (TL) and optically stimulated luminescence (OSL), after exposure to the gamma radiation of a ⁶⁰Co source. The structure of the powdered Opal was verified using the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. The material, in its stone form, was turned into powder and mixed to Teflon (also in powder) in three different concentrations, and then pellets were manufactured. The aim of this work was to evaluate the response of these pellets in high-doses of gamma radiation beams, and to observe their possible application as dosimeters, using the TL and OSL techniques. The dosimetric properties of the samples were analyzed by means of different tests, as: TL emission curves and OSL signal decay curves, reproducibility of TL and OSL response, minimum detectable dose, TL and OSL dose–response curves (5 Gy–10 kGy), and fading. The results obtained in this work, for the TL and OSL phenomena, demonstrated that the pellets of Opal + Teflon present an adequate performance e possibility of use as dosimeters in beams of high-dose gamma radiation.     

Energy response of the TL detectors based on YAlO3:Mn crystals

This study demonstrates the energy response of thermoluminescent (TL) detectors based on YAlO₃:Mn crystals. Experimental results of the relative sensitivity of YAlO₃:Mn²⁺ detectors to various kinds of photon radiation (from ⁶⁰Со, ¹³¹Cs, ¹⁹²Ir, and ¹³⁷Cs isotopes; X-ray from 220 kVp; and photon radiation from a linear accelerator (LINAC) at 5, 10, and 15 MV) agree with the theoretical energy response from Monte Carlo simulation. In addition to YAlO₃ (YAP), energy response was calculated for other yttrium-containing oxides such as Y₂O₃, Y₃Al₅O₁₂ (YAG), and Y₄Al₂O₉ (YAM). A possibility of filtering (modification) of the energy response of high atomic number (Z) materials by the metallic filters was shown.