Roseli Künzel

X-ray spectroscopy in mammography with a silicon PIN photodiode with application to the measurement of tube voltage

In this work a silicon PIN photodiode was employed in mammographic x-ray spectroscopy under clinical and nonclinical conditions. Measurements have been performed at a constant potential tungsten anode tube, adapted in this work with molybdenum filters to produce a beam like that used in mammography, and at a clinical equipment with a molybdenum anode tube by using an additional aluminum filtration. The corrected x-ray spectra were in full agreement with those generated by theoretical models published in the literature and agree well with those measured with a CdZnTe detector for tube voltages less than 30 kV. The half value layer and the relative exposure values calculated from the corrected silicon PIN photodiode spectra were in agreement with those measured with an ionization chamber. These results indicate that a silicon PIN photodiode are very suitable for mammographic x-ray spectroscopy. As an application, the voltage (kV) applied to mammographic x-ray equipment has been measured through the evaluation of the spectra high energy cut off. Uncertainties evaluated for the voltage values calculated from the measured spectra are less than 0.13% for voltages in the range 20-35 kV. The low uncertainties associated with the obtained results in this work point out that the method employed can be accurately used for calibration of noninvasive mammographic kVp meters.

X-ray transmission through nanostructured and microstructured CuO materials.

This study presents a comparison of the X-ray transmission through microsized and nanosized materials. For this purpose CuO nanoparticles, with 13.4 nm average grain size, and CuO microparticles, with a mean particle size of 56 μm, were incorporated separately to beeswax in a concentration of 5%. Results show that the transmission through the above material plates with microsized and nanosized CuO was almost the same for X-ray beams generated at 60 and 102 kV tube voltages. However, for the radiation beams generated at 26 and 30 kV tube voltages the X-rays are more attenuated by the nanostructured CuO plates by a factor of at least 14%. Results suggest that the difference in the low energy range may be due to the higher number of particles/gram in the plates designed with CuO nanoparticles and due to the grain size effect on the X-ray transmission.

Effects of the particle sizes and concentrations on the X-ray absorption by CuO compounds

This work presents a study on the effects of the particle size, material concentration and radiation energy on the X-ray absorption. CuO nanoparticles and microparticles were incorporated separately into a polymeric resin in concentrations of 5%, 10% and 30% relative to the resin mass. X-ray absorption by these materials was analyzed with a CdTe detector. The X-ray absorption is higher for the nanostructured material compared to the microstructured one for low energy X-ray beams for all CuO concentrations.

Ambient dose equivalent and effective dose from scattered x-ray spectra in mammography for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations

In this study, scattered x-ray distributions were produced by irradiating a tissue equivalent phantom under clinical mammographic conditions by using Mo/Mo, Mo/Rh and W/Rh anode/filter combinations, for 25 and 30 kV tube voltages. Energy spectra of the scattered x-rays have been measured with a Cd(0.9)Zn(0.1)Te (CZT) detector for scattering angles between 30 degrees and 165 degrees . Measurement and correction processes have been evaluated through the comparison between the values of the half-value layer (HVL) and air kerma calculated from the corrected spectra and measured with an ionization chamber in a nonclinical x-ray system with a W/Mo anode/filter combination. The shape of the corrected x-ray spectra measured in the nonclinical system was also compared with those calculated using semi-empirical models published in the literature. Scattered x-ray spectra measured in the clinical x-ray system have been characterized through the calculation of HVL and mean photon energy. Values of the air kerma, ambient dose equivalent and effective dose have been evaluated through the corrected x-ray spectra. Mean conversion coefficients relating the air kerma to the ambient dose equivalent and to the effective dose from the scattered beams for Mo/Mo, Mo/Rh and W/Rh anode/filter combinations were also evaluated. Results show that for the scattered radiation beams the ambient dose equivalent provides an overestimate of the effective dose by a factor of about 5 in the mammography energy range. These results can be used in the control of the dose limits around a clinical unit and in the calculation of more realistic protective shielding barriers in mammography.

X-ray spectroscopy applied to the study of the radiation transmission through nanomaterials

In this study, we compare the energy absorbed by nanostructured and microstructured materials as a function of the x-ray beam energy and material concentration. For this purpose, we used CuO microparticles, with a mean particle size of about 56 μm, and nanoparticles with size in the range 10 – 100 nm. These particles were separately incorporated into a polymeric resin in proportions of 5% and 30% relative to the resin mass. Plates with about 5x5 cm² in area and uniform thickness were produced for each material. The x-ray generator was a Philips, model MG 450, with a tungsten anode tube. Measurements were performed for beams generated at 25, 40 and 100 kV tube voltages. Data were registered with an Amptek XR-100T-CdTe detector. Results show that nanostructured materials absorb more radiation than the microstructured ones for both material concentrations in the resin. For example, for a 5% particle concentration and material thickness of (6.0±0.2) mm, the difference between air kerma values is about 16% for 25 kV, 8% for 40 kV and about 2% for 100 kV.

Ambient Dose Equivalent, Effective Dose and Mean Sv/Gy Conversion Coefficients from Scattered X-Ray Spectra in Mammography

In this study, scattered X-ray distributions were produced by irradiating a tissue equivalent phantom under clinical mammography conditions by using Mo/Mo, Mo/Rh and W/Rh anode/filter combinations, for 25 and 30 kV tube voltages. Energy spectra of the scattered X-rays have been measured with a Cd0.9Zn0.1Te (CZT) detector for scattering angles between 30° and 165°. Experimental spectra have been corrected by a stripping procedure and then compared with calculated ones produced by semi-empirical models. In order to validate the adopted spectroscopic procedure, the values of HVL and air kerma calculated through the measured spectra were compared with those measured with an ionization chamber at the same experimental set-up at a non-clinical constant potential equipment with a tungsten anode and molybdenum filtration. Values of air kerma, ambient dose equivalent and effective dose have been evaluated through the X-ray spectra obtained in a clinical mammography unit. Mean conversion coefficients relating air kerma to ambient dose equivalent and effective dose from the scattered beams for all anode/filter combinations were evaluated. The mean conversion coefficient values from air kerma to ambient dose equivalent are between 0.21 and 0.54 Sv/Gy whereas the coefficients from air kerma to effective dose are between 0.036 and 0.11 Sv/Gy for the scattered radiation in the mammography energy range. Results show that for the scattered radiation beams the ambient dose equivalent gives an overestimate of the effective dose by a factor of about 5 in the mammography energy range. These results can be used in the control of the dose limits around a clinical unit and in the calculation of more realistic protective shielding barriers in mammography.