ABSTRACT
Objective:To propose a method of image similarity measurement based on structure information and intuitionistic fuzzy set and measure the similarity between CT image and CBCT image of radiotherapy plan positioning, aiming to objectively measure the setup errors.Methods:A total of four pre-registration images of a nasopharyngeal carcinoma patient on the cross-sectional and sagittal planes and a pelvic tumor patient on the cross-sectional and coronal planes were randomly selected. Five methods were used to quantify the setup errors, including correlation coefficient, mean square error, image joint entropy, mutual information and similarity measure method.Results:All five methods could describe the deviation to a certain extent. Compared with other methods, the similarity measure method showed a stronger upward trend with the increase of errors. After normalization, the results of five types of error increase on the cross-sectional plane of the nasopharyngeal carcinoma patient were 0.553, 0.683, 1.055, 1.995, 5.151, and 1.171, 1.618, 1.962, 1.790, 3.572 on the sagittal plane, respectively. The results of other methods were between 0 and 2 after normalization, and the results of different errors of the same method slightly changed. In addition, the method was more sensitive to the soft tissue errors.Conclusions:The image similarity measurement method based on structure information and intuitionistic fuzzy set is more consistent with human eye perception than the existing evaluation methods. The errors between bone markers and soft tissues can be objectively quantified to certain extent. The soft tissue deviation reflected by the setup errors is of significance for individualized precision radiotherapy.
ABSTRACT
A acuidade visual e a função de sensibilidade ao contraste são medidas clássicas utilizadas para avaliar a capacidade do sistema visual humano. Estas duas funções são os principais indicadores dos aspectos críticos da percepção e do processamento visual da forma ou do detalhe espacial. O objetivo principal deste trabalho é levantar e discutir alguns aspectos teóricos e experimentais básicos relacionados à acuidade visual e à função de sensibilidade ao contraste. A acuidade visual estima a habilidade do sistema visual para discriminar detalhes espaciais, enquanto a função de sensibilidade ao contraste estima a percepção de qualquer padrão em função de sua freqüência espacial.
This work discusses some important aspects about visual acuity, VA, and contrast sensitivity function, CSF. The VA and the CSF are classical functions or measurements used to appreciate the capacity of the human visual system on perception and on visual processing of form or spatial detail. One of the goals of this paper is to discuss important theoretical and experimental aspects related to VA and CSF that are the principal indicators of perception and visual processing of form in humans. Visual acuity estimates the ability of the visual system to resolve spatial details, whereas CSF estimates the perception of any pattern in function of the spatial frequency.