arXiv subjects

Antonio González-López

Publications and source records attributed to Antonio González-López.

4 recordsLinked to original sources

arXiv2025

Secondary spectrum after shieldings in x-ray rooms

Background: Calculating the characteristics of radiation emerging from radiation shielding to determine the level of safety in protected areas has been a widely studied topic in Radiation Protection due to its importance for the protection of the public and professionals. Methods: This work provides spatial distributions of energy spectra of emergent photons after shielding barriers. These distributions are obtained through Monte Carlo simulations using monoenergetic pencil photon beams incident on shielding barriers of different materials and thicknesses. The obtained results are applied to calculate the spectra of transmitted radiation in cases of polyenergetic beams similar to those encountered in clinical practice. Results: The significant contribution of secondary radiation in the radiation found behind shields is demonstrated across a wide range of energies, barrier thicknesses and barrier materials. Conclusion: It is shown that characterizing shields using their response to monoenergetic pencil beams provides a useful tool for characterizing radiation behind shields in a wide range of practical situations.

physics.med-ph↗

arXiv2023

A model for studying the detectability of X-ray images using the representation of images in the primary visual cortex

It is well known that the visual information represented in the simple cells of the primary visual cortex V1 is spatially localized, orientation-sensitive and bandpass-filtered. In addition, the visual information represented is subsampled. On the other hand, the methods used to assess image quality of x-ray systems performing detectability tasks are usually carried out in the spatial or image domain. This study examines the behavior of two observers, IBO and NPW, employed in the evaluation of imaging systems, in a domain that simulates the representation of visual information in V1 to gain a better understanding of the degree of optimization in human observer detectability tasks. The comparison of the two observers is conducted on images of a contrast-detail phantom and is performed in both the spatial and the wavelet domains. Furthermore, the study examines the covariance matrices of the noise. The strong covariance exhibited in the noise among neighboring pixels in the spatial domain results in covariance matrices with relatively high values outside the main diagonal, leading to significant differences between the NPW and IBO observers. In the transformed domain, the band-pass decimated filters have substantially reduced the covariance between neighboring pixels, resulting in the convergence of the detectability indices of both observers. The vast amount of information captured by the retina necessitates an optimization of informational nature. This strategy eliminates low-frequency correlations in the image, after bandpass filtering carried out by simple cells in V1. This loss of information could contribute to the suboptimal performance of the human observer. Interestingly, in V1 the differences between IBO and NPW observers are very small. Therefore, either NPW does not accurately represent the human observer in V1, or the human observer is close to optimal in this domain.

physics.med-ph↗

arXiv2021

High frequency residues: a new set of signals for detectability studies of an X-ray imaging system

A new set of signals for studying detectability of an x-ray imaging system is presented. The results obtained with these signals are intended to complement the NEQ results. The signals are generated from line spread profiles by progressively removing their lower frequency components and the resulting high frequency residues (HFRs) form the set of signals to be used in detectability studies. Detectability indexes for these HFRs are obtained using a non-prewhitening (NPW) observer and a series of edge images are used to obtain the HFRs, the covariance matrices required by the NPW model and the MTF and NPS used in NEQ calculations. The template used in the model is obtained by simulating the processes of blurring and sampling of the edge images. Comparison between detectability indexes for the HFRs and NEQ are carried out for different acquisition techniques using different beam qualities and doses. The relative sensitivity shown by detectability indexes using HFRs is higher than that of NEQ, especially at lower doses. Also, the different observers produce different results at high doses: while the ideal Bayesian observer used by NEQ distinguishes between beam qualities, the NPW used with the HFRs produces no differences between them. Delta functions used in HFR are the opposite of complex exponential functions in terms of their support in the spatial and frequency domains. Since NEQ can be interpreted as detectability of these complex exponential functions, detectability of HFRs is presented as a natural complement to NEQ in the performance assessment of an imaging system.

physics.med-ph↗

arXiv2020

Detectability assessment of an x-ray imaging system using the nodes in a wavelet packet decomposition of a star-bar object

Purpose: Using linear transformation of the data allows studying detectability of an imaging system on a large number of signals. An appropriate transformation will produce a set of signals with different contrast and different frequency contents. In this work both strategies are explored to present a task-based test for the detectability of an x-ray imaging system. Methods: Images of a new star-bar phantom are acquired with different entrance air KERMA and with different beam qualities. Then, after a wavelet packet is applied to both input and output of the system, conventional statistical decision theory is applied to determine detectability on the different images or nodes resulting from the transformation. A non-prewhitening matching filter is applied to the data in the spatial domain, and ROC analysis is carried out in each of the nodes. Results: AUC maps resulting from the analysis present the area under the ROC curve over the whole 2D frequency space for the different doses and beam qualities. Also, AUC curves, obtained by radially averaging the AUC maps allows comparing detectability of the different techniques as a function of the frequency in one only figure. The results obtained show differences between images acquired with different doses for each of the beam qualities analyzed. Conclusions: Combining a star-bar as test object, a wavelet packet as linear transformation, and ROC analysis results in an appropriate task-based test for detectability performance of an imaging system. The test presented in this work allows quantification of system detectability as a function of the 2D frequency interval of the signal to detect. It also allows calculation of detectability differences between different acquisition techniques and beam qualities.

physics.med-ph↗