![]() ![]() In particular, changes and thermal drift over time meant that the two different datasets suffered from different misalignment artifacts that negatively affected their usability for constraining the DCM. ![]() Analysis on this data was only possible after extensive use of in-house software ~ Mayo et al., 2007 ! to correct for misalignment. This creates difficul- ties because the two or more micro-CT datasets being used as DCM constraints must be aligned very accurately in three dimensions. In this case the two datasets suffered from misalignment artifacts, both within each dataset and between the two datasets. first attempts to collect data for analysis using this system were made by collecting each dataset one after the other, changing targets in between. The ionization chamber was centered in the x-ray beam at 72 cm from the focal spot with a source-to-image-distance of 120 cm. Methods: A Radcal (Monrovia, Ca) AccuPro dosimeter with a 10×6-6 calibrated ionization chamber was used to measure air kerma for radiographic x-ray exposures made on a Siemens (Erlangen, Germany) Artis ZeeGo fluoroscope operated in the service mode. Purpose: The purpose of this investigation is to quantify various first half-value-layers (HVLs), second HVLs and homogeneity coefficients (HCs) for a state-of-the-art fluoroscope utilizing spectral (copper) filtration. Similarly to other versions of TASMIP, the estimation of spectra is very simple, involving only the evaluation of polynomial expressions. Conclusions: A new version of the TASMIP model for the estimation of x-ray spectra in microfocus x-ray sources has been developed and validated experimentally. The validation of the model against real acquired data showed errors in exposure and attenuation in line with those reported for other models for radiology or mammography. To match the experimentally measured exposure data the combined dataset required to apply a negative filtration of about 0.21 mm Al and an anode roughness of 0.003 mm W. Results: Inherent filtration for the radiology spectra from TASMIP was found to be equivalent to 1.68 mm Al, as compared to spectra obtained from the mammography model. The model was validated by comparing estimated and experimental exposure and attenuation data for different attenuating materials and x-ray beam peak energy values, using two different x-ray tubes. Afterwards, the authors built a unified spectra dataset by combining both models and, finally, they estimated the parameters of the new version of TASMIP for microfocus sources by calibrating against experimental exposure data from a microfocus x-ray source. First, the authors estimated the inherent filtration included in the radiology model by comparing the shape of the spectra with spectra from the mammography model. Methods: The authors used the radiology and mammography versions of an existing empirical model as the basis of the microfocus model. For this reason the authors propose in this work a new model for the simulation of microfocus spectra based on existing models for mammography and radiology, modified more » to compensate for the effects of inherent filtration and energy range. However, most of these models cannot be used directly for modeling microfocus x-ray sources due to differences in inherent filtration, energy range and/or anode material. There is a variety of publicly available tools for estimation of x-ray spectra in radiology and mammography. Purpose: The availability of accurate and simple models for the estimation of x-ray spectra is of great importance for system simulation, optimization, or inclusion of photon energy information into data processing. Results: The Lambert W model was validated for modeling attenuation versus attenuator thickness with respect to the data more » collected in this study (R, In addition to validating the Lambert W model, we also assessed the performance of two-point Lambert W interpolation compared to traditional methods for estimating the HVL and QVL. Nonlinear regression was used to find the best-fit curve of the proposed Lambert W model to each measured transmission versus attenuator thickness data set. Exposure measurements were acquired under narrow-beam geometry using standard methods, including the appropriate ionization chamber, for each radiographic system. To validate this model, transmission of diagnostic energy x-ray beams was measured over a wide range of attenuator thicknesses. Methods: An empirical model, which uses the Lambert W function and represents a generalized Lambert-Beer law, was developed. Purpose: The purpose of this study was to develop and validate a mathematical model to describe narrow-beam attenuation of kilovoltage x-ray beams for the intended applications of half-value layer (HVL) and quarter-value layer (QVL) estimations, patient organ shielding, and computer modeling. ![]()
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